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Telephone Circuit Description and Troubleshooting
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5
®
Training Manual
Digital Cordless Telephone
Circuit Description and Troubleshooting Course: TE-04
Table of Contents
Introduction
Why Spread Spectrum?
1
1
Telephone Hook ON/OFF
On/OFF Hook
19
19
Features
Cordless Features Answering Machine Features
2
2 2
Incoming Telephone Line Amplifier TX Signal Processing
IC701 Codec IC751 ASIC Troubleshooting
23 25
25 27 29
Narrow Band vs. Spread Spectrum
Analog (Narrow Band) Digital (Narrow Band) Digital (Spread Spectrum)
3
3 3 3
RF Unit
Transmitter TDD (Time Division Duplex) Receiver
31
31 33 35
Overall Block
Base Handset
7
7 7
RX Signal Processing
IC751 ASIC IC701 Codec
37
37 39
Matching Handset to Base
Matching
9
9
Charging
Charge Problems
11
11
Outgoing Telephone Line Amp
Circuit Description
41
41
Link Establishment
Heartbeat Link Establishment Protocol Master/Slave Operation (TDD)
13
13 14 14
Telephone Company Services
Call Waiting Caller ID (Type 1 ON Hook) Call Waiting ID(Type 2 OFF Hook) Voice Messaging
43
43 43 43 43
Cordless Telephone Block (Base) Line Input and Ring Detect
Line Input Ring Detect
15 17
17 17
Caller ID Data Format
FSK (Frequency Shift Keying) Data Timing
45
45 45
Data Packet Type Formats
45 47
Call Waiting ID Format
Data Timing
49
49
Loopback Tests RF Test Other Base Test Modes Audio System Tests Record and Playback Tests
70 72 74 75 76
Caller ID On Hook Amplifier
Circuit Description
51
51
Service Bulletin No. 165
77
Caller ID Data Demodulation
Input FSK Demodulator
53
53 53
Answering Machine Block (Base)
Switching and AGC DSP Board IC201 TAD
55
55 55 55
TAM Switching
Mic Recording Incoming Line Signals DSP Analog Out
57
57 57 57
AGC
Switch
59
59
DSP Interface Cordless Telephone Block (Handset) Test Modes
Handset Loopback Tests RF Test Base (Radio Block Test Modes)
61 63 65
65 66 67 69
1
Introduction
Purpose of Course
This course will introduce you to Spread Spectrum technology using the cordless phone model SPP-A967 as the example. We will cover the circuits, as well as testing, troubleshooting procedures and applicable use of a spectrum analyzer. In addition, we will discuss the new features of these phones, especially in areas that involve new telephone company services such as Caller ID and Voice Messaging. We will also describe the circuits and functions of the answering machine section. There will be emphasis on known problems from past models and on customer education/expectation issues.
One major problem remained due to the fact that so many devices are using the 900 MHz spectrum. All of these systems transmitted using narrow bandwidth. This made it easy for them to be jammed or interfered with. This means that if two neighboring homes have cordless phones that are trying to operate on the same channel, the quality of the audio may be severely degraded or the phones could be rendered completely useless. The new Sony 900 MHz Digital Cordless Telephones and Cordless Telephone Answering Machines use a technology new to consumer electronics called Spread Spectrum to overcome the problems mentioned previously. This technology has been used by the military for years due to its excellent anti-jamming capability (interference rejection) and privacy features. The primary advantage of a spread spectrum communication system is its ability to reject interference whether it is from another cordless phone or some other source. It also adds a privacy feature because the transmitter and receiver are synced by a certain code. The signal can also be output using higher power because the power density is low due to the signal being spread. The fundamental concept of the spread spectrum system is to spread the digital source signal with a digital code sequence, noise-like in nature, called a pseudo random noise (PN) code. Through this spreading technique, the original narrow-band digital signal is made to appear as a wide band of noise. The receiver must know the PN code used by the transmitter in order to properly recover the transmitted signal. The receiver will also only recover data from the areas of the spectrum that the PN code specifies. Other receivers on the same channel will not be capable of recovering the transmitted message without the correct PN code.
Why Spread Spectrum?
The trend towards higher quality telephones has been continuing for the past several years. The introduction of the 900 MHz analog telephones was a leap forward. They allowed for greater range and interference rejection due to the use of the 900 MHz spectrum. However, these telephones still suffered from a relatively limited range and lack of security. Someone with the right equipment could easily listen to your phone calls since the audio was being transmitted over the air. Cordless telephones continued to move forward with the introduction of the digital 900 MHz products. These systems offered better security. Since the transmitted information was digital, more specialized equipment would be needed to intercept it. They also offered the benefits of the 900 MHz spectrum
Cordless Telephone Type Conventional 46/49 MHz 900 MHz Analog 900 MHz Digital 900 MHz Spread Spectrum
Privacy No No Yes Yes
Relative Range Average Good Good Excellent
Features
Cordless Features
High Power Digital Spread Spectrum - Provides superior range and interference reduction. The 900MHz band has lower potential for interference because it is less crowded than a conventional 46-49MHz band. Digital Spread Spectrum technology provides up to ten times more power output than analog 900MHz systems. This allows you to can carry your cordless phone further and continue your conversation over a greater range. JOG DIAL - One-finger access to directory dialing numbers and Caller ID memories. Simply push the button and jog up and down to find the entry you are looking for; push the button again to dial the number. You should note that some areas require you to use the full ten-digit number even if you are in the same area code. When this is the case the user can set the area code to 111 so that the full ten-digit number will be left when using Caller ID. 50-Number Directory Dialing - Provides quick access to a broad range of frequently dialed numbers. For easy reference, each phone number can be identified by the person's name. Digital Privacy - Uses sophisticated digital speech encoding between the handset and base unit to ensure privacy. This ID code matches the handset and base. Auto Channel Hopping - Automatically scans all available channels and selects the clearest one for your call. If any interference is encountered during your call, the phone automatically hops to the channel that offers the clearest reception. This is one of the biggest customer education issues. When the customer gets close to out of range the phone begins to automatically changes channels. This causes the customer to hear clicks in the earpiece of the handset. The customer needs to be told this is normal if they are close to the out of range area. Caller ID with CALL WAITING - Allows you to screen the phone number and name of an incoming second call while continuing your call (requires specific Caller ID on Call Waiting service from phone service provider).
Memory Match Ringing - Sounds a distinctive ring if an incoming call matches one of your three one-touch dial numbers (requires Caller ID service from phone service provider). 6-Hour Talk Time and 10-Day Standby - These are maximum times under optimal conditions. Battery life is a combination of many factors and cannot be measured exactly. 3-Number One-Touch Dialing There are three buttons on the phone which can contain stored numbers that will be dialed when pressed. 1-Way Paging - Sends a beep to the handset so you can summon someone or locate a missing handset by pressing the handset locator button.
Answering Machine Features
Tapeless, All Digital Message Storage - Records both your greeting and incoming messages on IC chips. There are no moving parts so reliability is improved. Up to 20-minute message capacity for ICM and OGM. Voice-Guided Operation - Uses built-in voice prompts to take you through initial set-up and operation. Voice Time/Day Stamp - Records the time/day after each message. 3 Message Boxes - Allows incoming messages to be stored in three separate "message boxes" so that each person using the machine can access their messages directly. Announce-Only Mode - Answers calls without taking messages. Multi-Function LCD Display - Functions as a digital message counter, message length indicator, mailbox indicator, etc. Audible Message Indicator - Beeps when messages have been received (switchable ON/OFF). Flash Memory - Protects your recorded messages in the event of a power outage without the need for battery backup. Remote Access Allows messages to be retrieved remotely using any Touchtone phone.
2
3
Narrow Band vs. Spread Spectrum
Overview
In this section we will describe how narrow band and spread spectrum work and their differences. We will also look at why spread spectrum technology is the answer to much of the channel crowding problems that exist today.
pear as noise. The PN code in Sony SS telephones is twelve times the data rate. This is referred to as the chip rate. The bits in the PN code are called chips because they are non-information bearing. This multiplied signal is applied to a differential encoder and then to the BPSK modulator to be transmitted. Binary Phase Shift Keying (BPSK) is a type of phase modulation. Phase modulation changes the phase of the carrier dependent on the amplitude of the incoming signal. Since the input in this case is digital, there are only two possible phases that will be produced. When the digital signal, which consists of a series of highs and lows, is applied to the BPSK circuit, it produces a signal that contains the carrier phase shifting between 0 and 180 degrees. A low is represented by no phase change while a high is represented by a 180-degree phase shift. In the sequence below, a low is input initially so there is no phase change until the signal changes to a high. When a high is input, the output signal's phase is shifted 180 degrees from the original. Then the signal changes back to a low, causing the output phase to return to no phase change state.
Digital Signal
Analog (Narrow Band)
Cordless telephones that operate in the 46/49 MHz range all use analog transmission. This means that the intelligence signal used to modulate the carrier is analog. These analog signals were FM modulated with the carrier RF. This type of modulation produced a signal with a narrow bandwidth that was quite susceptible to noise on a channel. If there were interference at that channel frequency from another cordless phone or other source, this would cause static at the receiver. If the problem was very severe, there may be no reception at all. The range of this type of signal is limited because the S/N ratio must be high.
Digital (Narrow Band)
First, we must understand that there is really no such thing as a digital RF transmission. What is meant by a digital system in this case is the fact that the original audio (intelligence) is digitized before it is modulated. This digital signal is then transmitted using a FM modulated carrier. This kind of transmission is superior to analog, but it does have the same problems with interference and range since its bandwidth is narrow. The bandwidth is still narrow because it is dependent on the data rate. The higher the data rate the wider the bandwidth of the transmitted signal.
BPSK Signal
0
0
1
1
0
BPSK (Binary Phase Shift Keying)
Digital (Spread Spectrum)
In the Sony spread spectrum system the original or baseband data is differentially encoded. Then it is multiplied with a PN code (pseudo-random noise code) to increase the data rate. A pseudo random noise sequence is a string of non-information bearing data that appears to have a random quality. In actuality the pattern is chosen because it looks random but is not. This means that when modulated, the PN code will ap-
NARROW BAND SIGNAL NOISE
SPREAD SPECTRUM SIGNAL
AMPLITUDE
NOISE FLOOR
FREQUENCY
NOT TO SCALE
BANDWIDTH COMPARISON
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4
5
Even though a single frequency is modulated by the data, the information is contained in the rate of phase change. This means that the information is spread throughout the entire bandwidth in the sidebands. This entire process is called Differential Binary Phase Shift Keying (DBPSK) since the signal is differentially encoded and then BPSK modulated. The output is a spread signal that appears to be noise. The signal is spread because the data rate was multiplied by 12 by the PN code. This signal can be received even though it is in the noise region. This is because the receiver must apply the same PN code to the BPSK demodulated signal. Only a receiver with the same PN code can receive the desired signal and this increases security and range. There will also be a tremendous increase in interference rejection. If there is a large amount of noise in the same area as the signal, it does not effect the signal. When the signal is de-spread by the PN code, the desired signal becomes a narrow band signal and the undesired or noise signal will spread and be discarded by the next stage of the receiver.
Interference Spectral density Signal Spectral density Signal
~ Processing
Gain Interference
Frequency
Frequency
De-spreading Results
NARROW BAND SIGNAL NOISE
SPREAD SPECTRUM SIGNAL
AMPLITUDE
NOISE FLOOR
FREQUENCY
NOT TO SCALE
BANDWIDTH COMPARISON
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7
Overall Block
Overview
The SPP-A967 consists of two separate pieces, the handset and the base. These pieces work in conjunction to provide cordless telephone operations and are mated together by the matching circuit. The matching circuit in the base assigns a code to the handset so that the handset and base can communicate. It is possible to have more than one handset matched with the same base. However, handsets are not sold separately. The base unit also contains a telephone answering machine (TAM) and a battery charging circuit.
sponsible for transmitting and receiving any information necessary between the handset and base. IC751 ASIC also is responsible for changing the ID code used by the handset and base to communicate.
TAM Block
The TAM block contains the circuitry for the telephone answering machine. This block processes the audio that is sent to and from the line during TAM operations. The circuitry includes the switching, AGC and DSP board. This block stores the OGM and converts it to audio to be output on the line. It converts this audio from the line and stores these ICMs in a flash memory. The OGM and ICM will not be lost if power is disconnected.
Base
The base unit consists of five main blocks. They are the telephone line, Caller ID On Hook amplifier, charging and matching, cordless and TAM blocks.
Matching and Charging
There are three terminals on both the handset and the base. When the handset is placed on the base, these terminals match up. The two outer terminals are for charging. The load placed on the base by the handset activates the charge circuit, which operates continuously when the handset is on the base. The charge LED should always be lit at this time. Matching also occurs when the handset is placed on the base. When charging is detected, a signal is sent through the ART terminal from the handset to the base. The handset acknowledges this data through its transmitter. The base receives this signal and repeats the process.
Telephone Line Block
The telephone line block interfaces with the telephone line to deliver full duplex conversation. It contains ring detect, ON/OFF Hook and Incoming and Outgoing telephone line amplifiers. This block interacts with the cordless and TAM blocks so that any signals that need to go to or from the telephone line are processed.
Handset
Cordless Block
The cordless block in the handset is identical to the one used in the base. The same ICs and RF Unit are used. This block interacts with the speaker and mic instead of the telephone line. The ASIC in the handset controls all of its key functions.
Caller ID On Hook Amplifier
The Caller ID On Hook amplifier is used to input Caller ID signals to the Caller ID demodulator located in the Cordless block. This is necessary because when the phone is ON hook and not active, a path is needed to deliver this data. The easiest solution to this problem was to add a circuit connected directly to the line. This circuit amplifies the CID signal and inputs it to the cordless block for demodulation.
Matching and Charging
The handset charge circuit is the circuit between the charge terminals and the battery. The matching circuit detects charge to notify the ASIC in the handset that ART (Asynchronous Receive/Transmit) data is coming. The rest of the matching circuit delivers the ART data to the ASIC.
Cordless Block
The cordless block contains any circuits between the incoming and outgoing telephone line amplifiers and the antenna. This includes the Codec (Coder/Decoder), the ASIC (Application Specific IC) and the RF Unit. It also contains an FSK Demodulator used for Caller ID. This block is re-
CALLER ID ON HOOK AMP CORDLESS BLOCK TELEPHONE LINE TELEPHONE LINE BLOCK CORDLESS BLOCK KEYPAD AND DISPLAY
SPEAKER
KEYPAD AND DISPLAY
TAM BLOCK
MIC
CHARGE CONTROL SPEAKER MATCHING AND CHARGING MIC
+
ART
+
ART
BASE
-
-
MATCHING AND CHARGING
HANDSET
SPP A967 OVERALL BLOCK
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Matching Handset to Base
Overview
This section deals with communication between the handset and the base. We will discuss how the base and handset are matched by using the information stored in the EEPROM. The handset and base can communicate only when the EEPROM information is matched.
BASE STATION
HANDSET
(PARK) (PARK DETECT) SYSTEM PARAMETERS VIA WIRE (PARK DETECT)
A-FRAME SYSTEM ID CONFIRMED VIA RF
Matching
The base and handset need to be matched. This means that data from the base must be written to the handset and stored. This data contains information on the ID code (Scrambling) and the PN Code (Spreading). This information needs to be the same in the handset and the base in order for communication to occur. This data is contained in the A Frame and is transmitted each time the handset and base are activated before lock up occurs. If this signal is not verified, no communication is possible. When the handset is initially placed on the base for charging, the ID information is sent from the base to the handset. IC751 ASIC is alerted via the charge detect input at pin 62. This input is called ParkP. When the handset is placed on the base, it is referred to as parking. There are three contacts on the base and handset. They are the positive (+) charge terminals, the negative (-) charge terminals and ART. When the park input is detected, IC751/34 ARTO outputs data. This data goes through a level shifting circuit, which consists of Q952 and associated components. It is then sent through the ART contact on the base and enters the handset through its ART terminal. IC501 in the handset is waiting for data because IC501/62 ParkP is LOW. This is LOW because Q301 senses when the handset is placed on the base. The ART terminal is the middle contact on the handset and the base. When the handset receives the ART data, it is sent through a level shifter and applied to IC501/33 ARTI. When this data is recognized, an acknowledgement of receipt of this data is sent by transmitting the data back to the base via RF. When the base receives the acknowledge signal, the process is repeated. The base and handset are now matched.
A-FRAME VIA WIRE SYSTEM ID CONFIRMED
A-FRAME VIA RF
BASE - HANDSET MATCHING
Troubleshooting
Any problems with matching will cause the handset and base not to communicate. Problems in this area are related to failure of the base receive or handset transmit sections or by problems with the contacts or the charge circuit. These types of failures are typically caused by the contacts on the handset or the base becoming dirty or corroded. This causes a charge not to be detected or the data not to be sent properly. Troubleshooting consists of checking to see which of the three possible areas is not working. Visual inspection of the charge contacts is usually all that is required to determine if there is a contact problem. If the charge light does not come on, you may have a problem with the charge or charge detect circuits. If the charge light comes on, you need to determine if the handset transmitter and base receiver are functioning properly. This can be done by using the transmit and receive test that will be discussed later. A quick way to determine if the problem lies in the handset or the base is to try the handset on the bad unit with a known good base. This is possible because any handset can be matched with any base. It is also possible to have more than one handset matched to the same base.
BASE KEY BOARD +5V 9V R302 R528 CHARGE CONTROL Q407, Q401,Q402,Q406 Q503 D505
B+
QUICK IC201 CHG TAD 57 SB867116 CHARGE DET. 61
D302 CHARGE
IC501 ASIC M7004-11 33 ARTI
TX DATA
RF UNIT RFU501
R421 Q403 R427 L603 R431
R527 R529
PARKP 62 R303 B+
62 PARKP IC751 ARTO 34 ASIC M7004-11 51,52,53,54 RECEIVE DATA D303 RF UNIT RFU901 BASE MAIN BD. R760 R954 R955 D301 + Q952 L604 ART ART
D305 R301 Q301 R302 C307
D302
D304
C301
D306
BPT24
HANDSET MAIN BD.
MATCHING
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Charging
Charging
The charge circuit is somewhat different from previous Sony cordless telephones. The SPP-A967 uses a charge system that allows the handset to be charged whether it is put on to the base face up or face down. This is possible because the charge terminals on the handset are no longer tied to ground. Instead they are input to a bridge rectifier circuit consisting of D301, D302, D303 and D304. This allows the current to flow to the battery correctly no matter which way the handset is placed on the base. When the handset is placed on the base, the battery places a load across the charge circuit and Q401 turns ON. This activates the charge detect circuit. When the charge detect circuit is activated, Q402 conducts which causes Q403 to turn ON. When Q403 turns ON, three things occur: ! ! D302 Charge LED is turned ON; A LOW is placed on IC751/62 ParkP which will start the matching process; and ! IC201/61 goes LOW which causes IC201/57 Quick CHG to output a voltage level that causes Q407 to conduct. When Q407 conducts, it turns Q406 ON fully. This causes the charge current to flow through the B-E junction of Q406 and R423 instead of through R405. There will be more charge current available since R423 and Q406 are in parallel with R405. The charge current will be kept constant because 1.2 volts will be maintained across the charge resistor R423 or R405 and the B-E junction of Q401. The charge circuit is always active no matter how long the handset should remain on the base. This is indicated by the fact that the charge LED never goes OFF when the handset is ON the base.
Charge Problems
Dirty contacts or the battery usually causes charge problems. Charge contacts should be cleaned regularly by the customer. If the problem is due to dirty charge contacts, it should be an easy repair. Charge contacts can be cleaned using a solvent and a cotton swab. In some cases it may be necessary to replace the contacts if you are not able to remove the dirt or corrosion that has built up. Keep in mind that if the charge LED is not coming ON, the unit will also not be able to match the handset and base. This would mean that the customer could be complaining about no lock up and actually have a charge or contact problem. Bad batteries are probably the most common failure in cordless telephones. When using NiCad batteries, the user should allow the battery to be fully discharged before charging it. They are susceptible to the memory effect if not discharged fully before charging. The memory effect will decrease the life of the battery. To properly test the life of a Ni-Cad battery, you must use a cycle charger. The cycle charger starts by completely discharging the battery. It then charges the battery fully and discharges it. It monitors how long it takes to fully discharge the battery and then converts the time in to milli amps per hour (mAh). The battery is determined in to be in good condition if the mAh reading is 80% of the mAh value written on the battery. For instance, a 1000 mAh rated battery must read at least 800 mAh on the cycle charger to be considered good. This cycle should be repeated at least three times. This repetition can actually reverse the memory effect in some instances.
B+9V
+5V
Q406
R424
BASE KEY BOARD
R302 D302 CHARGE
HANDSET +
L603
R405 10 W
R423 6.8 W Q401
R425 IC201 TAD SB867116 57 QUICK CHG 51 DET CHG.
Q407 ART TO L604 MATCHING D402 R407 B+ 9V
R404
D403
R406 Q402 BASE MAIN BD R421 Q403 R431 TO IC751/62 ASIC PARK P
CHARGING
15TE04 1167
8 4 99
12
13
Link Establishment
Overview
During the Ringer ON (Standby) mode, the handset periodically sends a "heartbeat" signal to the base unit. This is necessary to ensure that the channel selected is free from noise should a call come in or if the user makes a call. If there is an incoming or outgoing call, the handset and base need to establish a link. This is done using the link establishment protocol. Transmission and reception are then continued using the TDD (Time Division Duplex) method.
10 SEC HEART-BEAT 1 SEC 1 SEC HEART-BEAT
Heartbeat
When the handset is in the Ringer ON mode, it wakes up intermittently to listen for a signal from the base. This is done to lengthen battery life. This means that once every second for 10 ms the receiver section is turned ON to listen for an incoming signal from the base. Once every 10 seconds the transmitter of the handset also comes ON to transmit A Frame data to the base. This is called the heartbeat. The heartbeat consists of 2ms of transmission and 2ms of reception by the handset. The heartbeat transmission lasts for approx. 2ms. It is followed by an acknowledgement of the A Frame reception from the base. This acknowledgement also lasts for 2ms. If the base does not receive the A Frame from the handset or the handset does not receive the acknowledge signal from the base, then there is a link error. When a link error occurs a channel change is made until the heartbeat is established again. If the heartbeat is not established, the system will act as if it is in the Ringer OFF mode. In the Ringer OFF mode the handset is in sleep mode. There will be no intermittent reception or heartbeat established. Therefore the handset will not ring because it cannot receive the ring signal from the base. Pressing the Talk or Jog Dial buttons can awaken the handset. You may notice it may take slightly longer to establish a link between handset and base in this mode. This is because you are not guaranteed a clear channel if there is no heartbeat system in place.
10 MSEC RX RX RX RX RX RX
1 SEC 2 MSEC 2 MSEC 10 MSEC
RX
TX RX
RX
HEART-BEAT
HANDSET HEART-BEAT
Link Establishment Protocol
In order to use the cordless phone, a link needs to be established between the handset and the base. This is done when the initiating party (handset or base) sends A Frame data that includes a request for a link. The party that initiates this is called the master. This data is received by the receiving party (handset or base) and transmitted back to the master as an acknowledgement. The receiving party is called the slave. Once this acknowledge signal is sent, a link is established and voice communication (V Frame) can begin.
MASTER SLAVE
Master/Slave Operation (TDD)
The SPP-A967 uses a system called TDD (Time Division Duplex). As we saw earlier, this allows transmission and reception on the same channel. Since our information is digital, it can be stored and read out in a controlled fashion. This means that the handset and base receive and transmit at intervals, unlike analog phones that use two different channels to communicate. This means that a master/slave type operation is used to control data flow between the handset and the base unit. This is used because one unit needs to control the time periods for receive and transmit operations to avoid data collisions. The one that controls the timing is called the master while the other is called the slave. In this system, either the handset or base can be the master. The one that initiates the link is automatically made the master. That means if the base receives a ring signal through the phone line, it will contact the handset to establish a link and become master of TDD operations. If the user initiates a call by pressing the Talk button on the handset, then the handset becomes the master. The drawing below shows the timing chart for communications. Each TX and RX interval is approximately 2ms in length.
MASTER TIME SLOT A MASTER TX TX RX V TX RX
A-FRAME SYSTEM ID CONFIRMED SYSTEM ID CONFIRMED A-FRAME
V-FRAME
V-FRAME
V-FRAME
A'
V-FRAME
V
MASTER RX A SLAVE RX A' SLAVE TX V V
TRIP DELAY
LINK ESTABLISHMENT PROTOCOL
LINK ESTABLISHMENT TIMING CHART
14
15
Cordless Telephone Block (Base)
Overview
The cordless telephone block is responsible for all communication to and from the handset. The handset contains a cordless telephone block that does the inverse of the one in the base. When the base is transmitting, the handset is receiving and vice versa. This is merely a two-way spread spectrum radio system.
IC150 FSK Demodulator
IC150 FSK Demodulator demodulates incoming FSK data for both types of Caller ID. The data output from this IC is input to IC751 ASIC. There are a number of control lines that aid the ASIC in receiving this data. The ASIC places the caller ID data into the regular data stream to be transmitted to the handset. When the handset receives this data, it displays the correct characters on its LCD.
IC751 ASIC
When transmitting, IC751 ASIC contains the scrambler, differential encoder and spreading blocks in the TX signal path. These blocks prepare the PCM digital signal to be transmitted. The ASIC is also responsible for producing data for commands. Examples are ring detect data to alert the handset of an incoming call and Caller ID data since this is displayed on the handset. Regardless of the type of data, it must go through the scrambler, differential encoder and spreading blocks. During receive, IC751 ASIC performs the reverse operations on the data so that it can be sent to IC701 Codec to be D/A converted. IC751 ASIC also controls the data stored in IC951 EEPROM as well as controlling the dial mode switch.
Telephone Line Block
The telephone line block sends ring detect to IC751 ASIC. IC751 ASIC sends hook control and mute control signals to the telephone line block. The telephone line block sends ring detect, external off hook detect and line detect to the answering machine block. The telephone line block also contains the incoming and outgoing line amplifiers. These circuits deliver line audio to and from the answering machine and to IC701 Codec. The incoming telephone line amplifier also delivers Caller ID signals to IC150 FSK Demodulator
IC701 Codec
On the transmit side, IC701 Codec converts the audio and DTMF tones present on the line to a PCM digital signal that will be processed by the ASIC before being transmitted. During reception, IC701 Codec receives the audio data from IC751 ASIC and D/A converts it to an audio signal. This audio signal is output to the telephone line block.
RF Unit
The RF Unit modulates the carrier with TX data from IC751 ASIC. It amplifies the modulated carrier and transmits it to the handset. The RF Unit also receives transmitted signals from the handset and demodulates them so a signal can be reconstructed by IC751 ASIC.
DIAL MODE SWITCH RING DETECT EXOFHK LINE DETECT TO ANSWERING MACHINE BLOCK HOOK CONTROL RING DETECT MUTE CONTROL EEPROM IC951 ARTO TO ANSWERING MACHINE BLOCK CHARGE DETECT FROM ANSWERING MACHINE BLOCK INCOMING MJ101 LINE JACK TELEPHONE LINE BLOCK OUTGOING RX RX C ID ON HOOK AMP CONTROL CODEC IC701 TX
CONTROL
ASIC IC751 TX RF UNIT RFU901
CALLER ID
FSK DEMOD IC150
TO ANSWERING MACHINE BLOCK FROM ANSWERING MACHINE BLOCK
CORDLESS TELEPHONE BLOCK (BASE)
4TE04 8 3 99
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Line Input and Ring Detect
Overview
Here we will discuss the line input and the circuits that are connected to it. The ring detect circuit will also be covered.
Ring Detect
The central office sends out a ring signal to let the receiving caller know that they have an incoming call. This ring signal is a 40 to 90 VAC 20 Hz signal applied across the phone line. It is applied through D103 and D102, which are zener diodes. These zener diodes clip the top and bottom of the ring signal by 5.6 volts, for a total of 11.2 volts reduction. C105 blocks any DC that may be on the line. R103 is the current limiting resistor. It drops any voltage between what remains of the ring voltage and the voltage dropped by the LED inside PH101 and D104. The LED is only on during the positive cycle of the ring. When the LED in PH101 emits light to the base of the internal phototransistor, this turns the phototransistor ON, placing 0 volts at the collector. This 0 volts causes Q103, which is normally ON, to turn OFF. This causes a HIGH to be present at Q103/C. This voltage is input to IC751/81 GPIOB6. IC751 ASIC detects this voltage level and outputs data to the transmit section to alert the handset of the incoming call. If the handset is in the Ringer ON mode, it will ring. The base does not ring on this unit. The LOW at PH101/C also causes Q109 to conduct B-E. This causes the voltage at Q109/E to be LOW. IC201/27 Ring Det detects this voltage. IC201 TAD is the TAM controller; therefore the answering machine section of the unit knows when and how many times the phone has rung. No Ring Ring 5V 0V PH101/C 5V .6V Q109/E 4.3V 0V Q109/B 0V 0V Q109/C
Q103/E Q103/B 0V .6V 0V 0V
Line Input
The purpose of the circuit is to input the signals from the central office of the telephone company into the base of the SPP-A967. These signals pass through the line input circuit which consists of MJ101, F101, SG1, L101, L102 and C101. MJ101 is a modular jack that contains two contacts and accepts the RJ-11 plug that is connected to the phone jack. F101 is a fuse that will open if the line current is above 500ma. SG1 is a spark gap that will short in the event of a sudden voltage surge. Lightening strikes are the most common cause of these surges. L101, L102 and C101 are used to suppress noise and small spikes from interfering with phone or answering machine operations. The output of this circuit feeds three other circuits. They are: ! Telephone Line All voice functions are routed through this circuit. It is responsible for closing the loop between the phone tip and ring when the telephone goes OFF hook. In addition, Caller ID OFF hook signals are routed through this circuit. Caller ID ON Hook When the telephone is ON Hook or not in use, a different path is needed to deliver Caller ID signals. Ring Detect Is used to detect an incoming ring signal. This is necessary for both the TAM and cordless sections of the SPP-A967 for obvious reasons.
! !
0V 5V Q103/C See Line Detect and Ring Detect test on page 75 of this book.
TO CALLER ID ON HK AF AMP C107 & C108
TO TELEPHONE LINE BRIDGE D111,D112,D113,D114 MJ101 2 SG1 1 F101 L101
RD5.6ESB2
L102 C101 D103 D102 R103 C105
PH101 PS2501-ILA
B+5V R104
B+5V R147 R146 TO IC201/27 TAD/RING DET L ON RING
D105 MTZJ-T
77-6.8
Q109 B+ R111 R110 Q103 R112
TO IC751/81 ASIC/GPIOB6 H ON RING
LINE INPUT AND RING DETECT
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19
Telephone Hook ON/OFF
Overview
When a ring signal is received, the SPP-A967 can pick up the line by using the cordless telephone section or the answering machine section. When the line is picked up, the loop between the telephone company central office and the telephone is closed. This allows audio and data information to flow to and from the phone line. In addition, the answering machine section of the SPP-A967 needs to know if another phone on the line has been picked up. This is so the answering machine is disabled if someone on another phone extension picks up the line.
Cordless OFF Hook Operation
When the phone rings, either the user or the answering machine picks up the line. If the user presses Talk on the handset, data is sent via RF from the handset to the base to pick up the line. This signal is eventually received by IC751 ASIC in the base. IC751/37 GPIOB7 outputs a HIGH when this data is received, which is applied to Q101/B causing it to turn ON. When Q101 turns ON, its collector goes LOW causing the internal LED in PH103 to emit light. This light is received at the base of the internal phototransistor of PH103. This turns the transistor ON and allows the line current to flow through its E-C junction. This is called seizing or grabbing the line. When this occurs, sufficient current flows through Q105 CE to cause the central office to sense the line is OFF hook and dial tone is sent. This signal is then coupled by T101 to the incoming telephone line amplifier.
ON/OFF Hook
Bridge
Th incoming phone line is passed through the line input circuit to the hook ON/OFF circuit and is applied across a bridge rectifier consisting of D111 to D114. This bridge rectifier serves two purposes. The first is to convert the ring signal to a DC voltage so that it can be blocked by C178. The second is to maintain the polarity of the line. The battery voltage from the phone line is passed to this point. When the phone is ON hook (not active), there will be approximately 48 VDC at this point relative to the phone line ground. The phone line ground is found at the anodes of D112 and D114. However, the most convenient point to attach a probe or clip to is the anode of D115.
Dial Tone 50mv 5 ms
Answering Machine OFF Hook Operation
When the Answer Mode is set to ON and the phone rings the correct number of times as set by the ringer select switch, IC201 TAD will answer. This is done by IC201/3 going HIGH, which turns Q108 ON. When Q108 is turned ON, current will flow through PH103's internal LED, causing the internal phototransistor of PH103 to conduct and close the line.
FROM TEL LINE INPUT L102 & L101
D114 C117
C116 D113 C178 R101 22 PH103 PS2533-1 HOOK ON/ OFF R121 R120 D115 Q105 R119 C121 C120 C122 PH102 PS2501-ILA EXTERNAL OFF HOOK DETECT TO IC201/20 TAD/EXT OFF HK. R102 R118 R117 R125 T101 TO & FROM AUDIO CIRCUIT C123
D112 C118 D111 C119 Q108
R148 FROM IC201/3 TAD/DP PHONE LINE GND. B+5V
Q107 FROM IC751/37 ASIC/ GPIOB7 Q106 R115 Q101 R105 C109 R149 TO IC201/28 TAD/LINE DETECT R123 R122 C181
PHONE LINE GND.
COLD GND.
TELEPHONE HOOK ON/OFF
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21 External Off Hook Detection
When the line is OFF hook because the answering machine is answering a call, IC201/20 EXT OFF HK is monitored to determine if another extension in the house is picked up. This is necessary so the answering machine does not continue answering a call if the call is answered on another extension. This line is low when the telephone is OFF hook because of the operation of Q106, Q107 and PH102. When the line is OFF hook there will be approximately 3.8 VDC at the junction of R120 and C120. This voltage will vary depending on the loop length between the central office and the telephone, how many telephones are on the line, and how much current they draw when idle. This 3.8 volts causes current to flow through Q107 B-E junction and R123 to phone line ground, causing .6 volts to be present at Q106/B. This voltage causes Q106 to be forward biased, causing the internal LED of PH102 to light. This turns the internal phototransistor of PH102 ON and places a LOW at IC201/20 Ext OFF Hook Detect. When another extension is picked up, there is a drop in the line voltage. During testing, the phone line used dropped the voltage at the junction of R120 and C120 from 3.8 to 2.5 volts. This causes a temporary loss of forward bias to Q107. When Q107 turns OFF, Q106 will also turn OFF. This causes the internal LED of PH102 to turn OFF which will cause the internal phototransistor of PH102 to turn OFF. This alerts IC201 TAD that another line extension has been picked up. When IC201/20 Ext OFF Hook Detect goes HIGH during answering machine operation, IC201 should cease the answering machine function. You should note that the input to IC201/20 Ext OFF Hook Detect would only go HIGH for a period of around four seconds. This is due to C121.
Acts of God
Many problems in this area are related to lightening strikes. Any sign of burnt or discolored components can usually identify this type of problem. In addition, resistance measurements of the bridge diodes R101, D115, Q105 and T101 should be taken if you suspect lightning or surge damage. Other problems can be divided into two groups: no line seizing or low/no audio.
No Line Seizure
The first thing to check if the line is not being seized is whether the internal phototransistor is operating. Short the internal phototransistor of PH103 C-E. This should cause the line to be seized. If the line is not seized by shorting these points, the problem is not with PH103 or the OFF hook circuit. If shorting the C-E junction of PH103 seizes the line, check the voltage across the internal LED of PH103. This voltage is normally around 1.2 volts. If this voltage is not around 1.2 volts, troubleshoot the path from IC751/37 to Q101 to determine where the problem lies. If the voltage across the internal LED of PH103 is normal, then replace PH103. If PH103 is operating normally by closing when Talk is pressed on the handset, something in the path from PH103 to Q105 may be open. One point of interest is that if R101 is open and you are using the BK1045B line emulator, the line emulator will click continuously as if the hook switch was constantly being opened and closed. However, if you are using a regular phone line, it will appear as if the hook switch has not been closed.
Low or No Audio
Low audio problems are usually the result of components being damaged by surges or lightning. You can isolate these problems by unloading circuits that are not necessary to audio operation. This would include removing R120, R119 and D115. Remove these components one at a time to determine where the problem lies. In addition to providing protection, the Q105 circuit provides stabilization to the line impedance. If there are open or shorted components in that circuit, there will be no or low audio.
Troubleshooting
Troubleshooting this circuit can be difficult. The first thing to keep in mind is that the ground for most of these circuits is a line or phone line ground. In this case, phone line ground means not earth ground. You will not be able to troubleshoot this circuit if you are using earth ground. The easiest place to connect to phone line ground is D115/A. Another issue with grounding is to be sure that your oscilloscope or phone line emulator is isolated from ground. You will encounter problems if these two pieces of test equipment share the same ground.
FROM TEL LINE INPUT L102 & L101
D114 C117
C116 D113 C178 R101 22 PH103 PS2533-1 HOOK ON/ OFF R121 R120 D115 Q105 R119 C121 C120 C122 PH102 PS2501-ILA EXTERNAL OFF HOOK DETECT TO IC201/20 TAD/EXT OFF HK. R102 R118 R117 R125 T101 TO & FROM AUDIO CIRCUIT C123
D112 C118 D111 C119 Q108
R148 FROM IC201/3 TAD/DP PHONE LINE GND. B+5V
Q107 FROM IC751/37 ASIC/ GPIOB7 Q106 R115 Q101 R105 C109 R149 TO IC201/28 TAD/LINE DETECT R123 R122 C181
PHONE LINE GND.
COLD GND.
TELEPHONE HOOK ON/OFF
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23
Incoming Telephone Line Amplifier
Overview
We know that the audio that is passed through the hook switch circuit travels in two directions; to and from the central office. The line circuits we covered earlier have both incoming and outgoing audio. Beginning with this section, we will cover where the incoming and outgoing audio paths split and will continue to follow the incoming audio path. The incoming audio path will be referred to later as TX (transmit path) since it will either be transmitted by the cordless telephone section or input to the TAM section. The outgoing audio will be referred to as RX since it will be received from the handset or TAM sections before exiting via the phone line.
The signal is passed through C111, R126 and R127. Part of this signal is sent through R129 and other components to the OUTGOING telephone amplifier. This circuit functions as a sidetone attenuation circuit and feeds the outgoing signal back to the outgoing telephone amplifier. This signal is out of phase with the amplifier input signal and will produce a cancellation effect. If this circuit is open and the handset is placed face down while in the Talk mode, a loud squeal will be heard because the excessive sidetone will cause feedback. This may be dependent on the volume setting of the handset. Under normal conditions the handset should not squeal when placed face down. The signal at R127 is also input to IC101/2. IC101 is an operational amplifier used to amplify the TX signal. The signal is amplified and output at IC101/1. It passes through R191 and is split there. One line goes to the answering machine section and the other to the cordless section. We will follow the cordless path.
Incoming Telephone Line Amplifier
The audio is coupled from the ON/OFF hook circuit to the line amplifier by T101. A transformer is used for isolation since these two circuits use different ground. The audio is passed through C124. After this you will notice that the outgoing telephone line amplifier output is also present. This is because both audio paths share the hook circuit. You will notice in the waveform below that the dial tone signal looks noisier than normal. This is because noise is being input on this line by the outgoing telephone amplifier.
R191/156 Junction 50mv 5 ms
The signal is split again after R156. One line is sent to the FSK Demodulator for OFF hook Caller ID. The other line will be passed through C137, R133, C139 and L701 and sent to IC701 Codec. Q171 is a mute transistor that will be activated by a LOW from IC751/95 NVCLK. This pin will go LOW when the phone is dialing to prevent it from interfering with the DTMF signals. SB165 refers to a problem with Q171. Follow the bulletin's instructions to repair.
C124/111 Junction 50mv 5 ms
B+5V FROM Q102/C & , Q104/C OUTGOING TEL LINE AMP TO IC301/2 SWITCH INPUT (TAM)
R132
TO IC150/2 FSK DEMOD/IN C137
C198 C191 3 FROM ON/OFF HOOK CIRCUIT T101 C124 R126 C111 C177 C192 C193 C199 R128 R127 C133 2 R135 + IC101 1/2 1 R191 R156 R308
R133 R137
C139 L701
TO IC701/13 CODEC LINE IN C706
C135
R129
FROM OUTGOING TEL LINE AMP FROM IC751/95 ASIC/NVCLK "L" DURING DIALING
C197 R190
C131 C194 R175 Q171
INCOMING TELEPHONE LINE AMPLIFIER
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25
TX Signal Processing
Overview
Now that the audio signal has passed through the telephone section of the SPP-A967 base unit, we need to prepare it to be transmitted. The audio will be input to the IC701 Codec. IC701 Codec converts the analog audio signal to a PCM digital signal. This data is also placed in packets before being sent to IC751 ASIC. This signal is known as the baseband signal. IC751 ASIC processes the baseband signal in three stages. They are the Scrambler, Differential Encoder and Spreading blocks. This signal is then sent to RFU901 RF Unit to be BPSK modulated and transmitted. The combination of the Differential Encoder and BPSK, which takes place in the RF Unit, is called Differential Binary Phase Shift Keying. This process is called either DBPSK or DPSK. . We will use the term DBPSK. This system uses a sine wave carrier that is phase modulated by the differentially encoded baseband data to produce the transmit signal. DBPSK is used because it simplifies design by using a non-coherent receiver. Non coherent in this case means that the receiver and transmitter are not phase-matched or synchronized to each other. The receiver demodulates the signal based on the phase of the previous incoming signal. In other words, only phase changes are detected, not the absolute phase of the signal. See Base Loopback tests on pages 69 and 70 to aid in troubleshooting.
IC701/13 50 mv 5 ms
IC701/30 2 V 5 ms
IC701/20 2 V .1 ms
IC701 Codec
The incoming audio or FSK signal is input to IC701/13 Line IN. Inside IC701 Codec, the audio will be applied through a switch to the Modulator and filter. This switch is always closed. The signal is then applied to a Modulator and Filter circuit, which converts the analog to digital. This block also places the data into packets using the timing signals from the Control Register block. The Control Register distributes timing signals from IC751 ASIC to control operations in IC701 Codec. The TX data is now read into and out of a 16-bit register and exits at IC701/30 DataO. This signal is now called baseband data.
IC701/21 2 V .400 us
IC701/26 1 V .4 us
FROM Q103/C RING DETECT
81 IC701 CODEC 10497-15 CONTROL REGISTER FRAME ICLK MCLK RESET B 20 21 26 25 R902 R915 27 R914 32 R913 28 26 FRAME CDCICLK CDCMCLK RESET B
RING DET
RAM
CPU
ROM
13 FROM L701 TELEPHONE LINE AMP (TX)
LINE IN
LINE AMP
MODULATOR AND FILTER
16-BIT REGISTER
Data 0 30
CDCDATAI
24 IC751 ASIC M7004-11
DATA STEERING
SCRAMBLER
DIFF ENCODER
SPREADING
49 TO RFU901
TXDATA
TX SIGNAL PROCESSING
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27
IC751 ASIC
IC751 ASIC contains the scrambler, differential encoder and spreading blocks in the TX signal path. These blocks prepare the PCM digital signal to be transmitted. The ASIC is also responsible for producing data for commands. Examples are ring detect data to alert the handset of an incoming call and Caller ID data since this is displayed on the handset. Regardless of the type of data, it must go through the scrambler, differential encoder and spreading blocks.
The reason a differential encoder is used is because when this type of data is BPSK modulated, the receiver does not have to be phase synced to the transmitter. This is called non-coherent reception.
Spreading
The function of the spreader block is to combine the baseband data with the PN code. The data rate of the PN code is 12 times higher than the baseband data. The factor by which the PN code data rate is greater than the baseband data is called the chip rate. Each bit in the PN code is also referred to as a chip. They are called chips because they are non-information bearing. Remember that the greater the data rate, the wider the bandwidth of a transmitted signal. The PN code converts the original low rate digital signal into a higher rate digital signal. Every bit in the baseband data is Exclusive ORed with a predefined twelve-bit PN code sequence to form a higher rate spread signal. When modulated, this data will appear to be noise due to the nature of the PN code.
Data Steering
The data steering circuit mixes the instruction data into the audio data stream. This is necessary since all data must go through the scrambler, differential encoder and spreading circuits.
Scrambler
The scrambler block is an encoder that is used to vary the data with an ID. This means the scramble block receives an ID code from the internal RAM of the ASIC. This code sets up a series of logic operations that are dependent on the code. If the code is changed, the sequence of logic operations changes. This ID code is used to ensure that the same or similar Sony phones can be used in close proximity to each other without picking up each other's line. An example would be if you and your neighbor have the same model phone, your handset couldn't communicate with their base because the ID code is different. Consequently, you could not pick up their phone line and make calls that would appear on their bill.
ONE BIT BASEBAND SIGNAL PN CODE 12 CHIPS
Differential Encoder
The differential encoder is used to encode the data so that all zeroes are represented by a change in state. This is performed by applying the output of a XOR gate, delayed by one bit period, and inputting it through a logic network to the other input of the XOR gate. The output of the input data stream and the output of the encoder are shown below.
Input data Output data 0 0 1 0 0 1 0 0 1 0 0 1 0 0 0 1
ONE CHIP SPREAD SIGNAL
SPREADING
FROM Q103/C RING DETECT
81 IC701 CODEC 10497-15 CONTROL REGISTER FRAME ICLK MCLK RESET B 20 21 26 25 R902 R915 27 R914 32 R913 28 26 FRAME CDCICLK CDCMCLK RESET B
RING DET
RAM
CPU
ROM
13 FROM L701 TELEPHONE LINE AMP (TX)
LINE IN
LINE AMP
MODULATOR AND FILTER
16-BIT REGISTER
Data 0 30
CDCDATAI
24 IC751 ASIC M7004-11
DATA STEERING
SCRAMBLER
DIFF ENCODER
SPREADING
49 TO RFU901
TXDATA
TX SIGNAL PROCESSING
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29
The data rate of the baseband signal is 80 kbps. The data rate of the spread data is 960 kbps. Note that this is twelve times greater than the baseband signal and the chip rate is twelve. The bandwidth occupied by the pseudo random noise modulated data will be twelve times wider than the original modulated packet bandwidth. The signal is then output at IC751/49 TX Data. The waveforms below show this output with the scope set at two different timebases. The first shows the actual data and the second shows that there are gaps between bursts of data. These bursts occur every 2ms. This is because the system uses TDD, which means that the RF Unit switches between transmit and receive modes. To use the extender cable you must first remove the main board from the Lower Cabinet Assembly. There is also one screw on this side of the board that holds the RF unit in place. Once the board is removed you will notice that RFU901 RF Unit is attached to the Main Board by a shield. The shield must be unsoldered as shown in the picture below.
Unsolder to remove RF Unit
IC751/49 .2 V 5 us
IC751/49 .2 V 2 ms
RF Unit Shields
Troubleshooting
Troubleshooting the TX signal-processing path can be difficult since IC701 Codec and IC751 ASIC are located underneath RFU901 RF Unit. In order to get to the pins of the IC, you must use an extender cable. The part number for the cable is T-998-606-59.
Once the shield is unsoldered you can remove RFU901 RF Unit from the Main board. The extender can then be connected between the RF Unit and the Main board as shown in the picture below.
IC751
IC701
RF Unit Extended
RF Unit Extender
With the RF Unit extended you now have access to IC701 Codec and IC751 ASIC. From there you can trace the signal path shown in the TX Signal Processing diagram. You may also want to resolder the ICs if the complaint is related to intermittent transmission of data.
FROM Q103/C RING DETECT
81 IC701 CODEC 10497-15 CONTROL REGISTER FRAME ICLK MCLK RESET B 20 21 26 25 R902 R915 27 R914 32 R913 28 26 FRAME CDCICLK CDCMCLK RESET B
RING DET
RAM
CPU
ROM
13 FROM L701 TELEPHONE LINE AMP (TX)
LINE IN
LINE AMP
MODULATOR AND FILTER
16-BIT REGISTER
Data 0 30
CDCDATAI
24 IC751 ASIC M7004-11
DATA STEERING
SCRAMBLER
DIFF ENCODER
SPREADING
49 TO RFU901
TXDATA
TX SIGNAL PROCESSING
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31
RF Unit
Overview
This section will discuss the operation of the RF Unit. Since the RF Unit is a replaceable block, we will concentrate on the connections to the RF Unit at CN901 and CN902. Explanations of the operation of the RF unit will be given to aid in troubleshooting. All troubleshooting in this area is limited to the RF Unit connectors. The picture below shows you the connectors Remove screw to and the position of pin 1 on each of them.
CN902 CN901 remove RF Unit
A frequency synthesizer is a precision PLL circuit that uses divide by circuits to produce a series of frequencies in small steps throughout a certain range. The range in the case of 900 MHz SS telephones would be from 902 MHz to 928 MHz. The discrete steps in this frequency range are the channel carrier frequencies shown in the table. These frequencies are allocated by the FCC for cordless telephones using spread spectrum technology. They are given channel numbers 1 through 20, just like the frequencies in the 46/49 MHz cordless telephones.
Channel Number 1 2 3 4 5 6 7 8 9 10 Channel Center Frequency (MHz) 903.6 904.8 906.0 907.2 908.4 909.6 910.8 912.0 913.2 914.4 Channel Number 11 12 13 14 15 16 17 18 19 20 Channel Center Frequency (MHz) 915.6 916.8 918.0 919.2 920.4 921.6 922.8 924.0 925.2 926.4
RF Unit
The operation of the RF Unit can be broken down into two main categories: transmitter and receiver.
Transmitter
The RF unit will be responsible for modulating the transmit data that is input to it by IC751 ASIC. The RF Unit develops a carrier using the frequency synthesizer output and then modulates the data. Different power levels will be used depending on the distance between the handset and the base.
The frequency synthesizer is enabled by IC751/75 SYNEN. The frequency synthesizer in the base is always enabled. Consequently there will always be 5 volts present at CN902/15 SYNEN. The synthesizer in RFU901 receives a master clock signal from IC751/66 SYNTH5MCLK. This 9.60 MHz signal is used as a reference for creating the output frequency. If this frequency is offset, there will be a corresponding offset in the TX output frequency. This can be corrected by replacing X752. The synthesizer requires data clock and strobe inputs from IC751 ASIC in order to operate. These signals are required to control the divide by circuits. These signals will show activity when the phone is not in use (Standby) and during channel changes when the phone is in use.
Frequency Synthesizer
A frequency synthesizer is used to develop a precision carrier, which will be modulated by the input data. The synthesizer will also develop a frequency for removing the data from the carrier.
CN901 VBAT (FOR RX) RXIP RXIN RXQP ANT901 (ANTENNA) 1 6 5 4 B+ 51 RXIP 52 RXIN 53 RXQP 54 RXQN 43 44 CN902 VBAT (FOR TX) VBAT (FOR PLL) TX DATA RFU901 RF UNIT Q751 TXPWR0 4 Q750,751 TX POWER ATTENUATOR TXPWR1 5 2 10 7 R754 R750 49 TX DATA IC751 ASIC M7004-11 85 80 TXPWR0 TXPWR1 B+ LNAATN RXEN
RXQN 3 LNAATN RXEN 8 7
AGC 2
60 AGC
Q750
TXEN 6 TXRXSW 3 SYNDATA 12 SYNCLK 11 SYNSTB 13 SYNEN 15 REFOSC 14
79
TXEN
82 TXRXSEL 65 SYNDATA 71 SYNCLK 72 SYNSTB 75 SYNEN 66 SYNTH5MCLK 97 XTAL1 X752 98 XTAL0
RF UNIT
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33 Modulation and Power Control
The carrier created using the synthesizer is used to BPSK modulate the data from IC751/49 TX Data. This data is input to the RF Unit at CN902/ 7. BPSK changes the phase of the carrier depending on whether the data input is a one or a zero. This is a suppressed carrier system so the carrier frequency will not be seen on the spectrum analyzer. The level of the data is also changed depending on how close the receiver and the transmitter are to each other. This is done using the outputs from IC751/85 TXPWR0 and IC751/80 TXPWR1. These outputs control two level control transistors, which are used to switch in different resistors between the TX Data line and ground. Changing the data level in this way reduces the amount of phase change in the RF signal transmitted by the unit. The TXPWR0 and TXPWR1 lines are also input to the RF Unit to control the amount of power output by the transmitter.
Location TXPWR0 TXPWR1 Power Out Distance CN902/4 CN902/5 --------------------Low Power Low High 1mW Below 1m Mid Power High Low 10mW 1-5m High Power Low Low 100mW Above 5m
The previous table shows the logic states, power output levels and the approximate distances when switching occurs. The distances will vary greatly dependent on the environmental conditions. If the antenna is disconnected from either unit, handset or base, the output will always be at the highest level.
TDD (Time Division Duplex)
Since this cordless phone uses TDD, the transmitter and receiver alternate using the carrier frequency. This is done using the TXRXSW line. This line is output from IC751/82 to CN902/3 and switches the receiver and transmitter ON and OFF alternately. A LOW on this line means the receiver is ON, while a HIGH means the transmitter is ON. In addition, there is also a TXEN line that turns the transmitter ON and OFF. This line is output from IC751/79 to CN902/6. Both of these lines show a 250 Hz square wave when the phone is in operation because the transmitter and receiver alternate every 2ms. Troubleshooting the transmitter section will be discussed in the test mode section of the course. The tests on pages 72, 73 and 74 can be used to check the transmitter section.
CN901 VBAT (FOR RX) RXIP RXIN RXQP ANT901 (ANTENNA) 1 6 5 4 B+ 51 RXIP 52 RXIN 53 RXQP 54 RXQN 43 44 CN902 VBAT (FOR TX) VBAT (FOR PLL) TX DATA RFU901 RF UNIT Q751 TXPWR0 4 Q750,751 TX POWER ATTENUATOR TXPWR1 5 2 10 7 R754 R750 49 TX DATA IC751 ASIC M7004-11 85 80 TXPWR0 TXPWR1 B+ LNAATN RXEN
RXQN 3 LNAATN RXEN 8 7
AGC 2
60 AGC
Q750
TXEN 6 TXRXSW 3 SYNDATA 12 SYNCLK 11 SYNSTB 13 SYNEN 15 REFOSC 14
79
TXEN
82 TXRXSEL 65 SYNDATA 71 SYNCLK 72 SYNSTB 75 SYNEN 66 SYNTH5MCLK 97 XTAL1 X752 98 XTAL0
RF UNIT
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35
Receiver
The receiver is enabled when the transmitter is disabled. The TXRXSW lines discussed earlier and the RXEN line, which is connected between CN901/7 and IC751/44, control this. The receiver section has four outputs: RXIP, RXIN, RXQP and RXQN. In order to understand why the receiver section has four outputs, we must take a look at what occurs in the RF Unit. The receiver receives the signal from the T/R section. This section is a duplexer, which is controlled by the TXRXSW discussed earlier. This signal is then applied to the Low Noise Amplifier (LNA). The LNA amplifies the low-level input signal so that it can be processed. The LNA has an input called LNAATN at CN901/8. This signal controls the gain of the LNA. If IC751 ASIC determines that the received signal is too noisy, it will increase the gain of the LNA by setting IC751/43 LOW.
This signal is split in two and applied to two mixers. The first mixer combines the RF with the output of the synthesizer. This produces an output called I. The I output is applied to an amplifier that outputs complementary signals IP and IN for I Positive and I Negative. The second RF signal is applied to a mixer with the output of the synthesizer phase shifted by 90 degrees. This signal is called Q and will lag behind the I signal by 90 degrees. The Q signal is applied to an amplifier, which outputs complementary signals called QP and QN. These signals are applied to IC751 ASIC and the probability detector will form one data stream from them. The gain of the I and Q amplifiers is determined by the AGC line that is connected to CN901/2 from IC751/60. This AGC signal is derived by the ASIC from the condition of the incoming signal. Troubleshooting the receiver will be covered in the test mode section. The L3 Loopback test described in page 70 can help check the RX signal. The RX Sensitivity check in page 74 can be used to test the quality of reception.
SYNTH OUTPUT
TXRXSEL LNA T/R
IP IN 900 Shift
AGC
LNAATN
QP QN
RECEIVER
CN901 VBAT (FOR RX) RXIP RXIN RXQP ANT901 (ANTENNA) 1 6 5 4 B+ 51 RXIP 52 RXIN 53 RXQP 54 RXQN 43 44 CN902 VBAT (FOR TX) VBAT (FOR PLL) TX DATA RFU901 RF UNIT Q751 TXPWR0 4 Q750,751 TX POWER ATTENUATOR TXPWR1 5 2 10 7 R754 R750 49 TX DATA IC751 ASIC M7004-11 85 80 TXPWR0 TXPWR1 B+ LNAATN RXEN
RXQN 3 LNAATN RXEN 8 7
AGC 2
60 AGC
Q750
TXEN 6 TXRXSW 3 SYNDATA 12 SYNCLK 11 SYNSTB 13 SYNEN 15 REFOSC 14
79
TXEN
82 TXRXSEL 65 SYNDATA 71 SYNCLK 72 SYNSTB 75 SYNEN 66 SYNTH5MCLK 97 XTAL1 X752 98 XTAL0
RF UNIT
21TE04 1168
6 9 99
36
37
RX Signal Processing
IC751 ASIC
Probability Detector
The probability detector extracts the original transmitted data stream from the four outputs of the RF amp. There will be only one data stream output from this block. This system is proprietary to the chipset manufacturer and will not be discussed further. The I and Q inputs to IC751 ASIC should look like the signal shown below:
PN CODE
12 CHIPS
ONE CHIP SPREAD SIGNAL BASEBAND SIGNAL
ONE BIT
DE-SPREADING
The diagram below illustrates the result of despreading in a DSSS system. If we think of the frequency spectrum of our spread signal versus a narrow band noise signal, we can see that after despreading occurs that the desired signal has been shifted to a narrow band signal. The noise will have been shifted to a wide band signal. Since the amplitude of the noise and desired signal are now reversed, it is easy to distinguish the desired signal. This occurs because the PN code used by the receiver is the same as the transmitter. The desired signal is recovered and the noise signal is spread and has less affect on the desired signal. The area between the new noise floor and the desired signal is called processing gain. It is one of the key factors in the design of spread spectrum systems. The higher the chip rate, the higher the processing gain. This means the wider you spread the signal, the less susceptible it is to narrow band noise.
Interference Spectral density Signal Spectral density Interference Signal
I and Q inputs .1V 2ms
De-spreader
Since the receiver knows the PN Code used by the transmitter, it is able