Text preview for : SAN2202.pdf part of Panasonic AN 22023 I need datasheet AN 22023



Back to : SAN2202.pdf | Home

sames

SAN2202 APPLICATION NOTE
SINGLE CHIP "SPEAKERPHONE" WITH 8 - OHM LOUDSPEAKER AMPLIFIER

1 Scope
This application note describes a low-cost add-on circuit for driving an 8-Loudspeaker to get a simple loudhearing ("Speakerphone") Telephone. To possible ways of supplying the amplifier are shown: SAN2202a: SAN2202b: Amplifier supply in shunt transistor path Amplifier supply by power extraction circuit (SAN3020)

It can be added to any SA253x application without interfering with PTT-relevant parameters, like AC-impedance, Sidetone cancellation or DC-mask.

2 Key Features · Low cost additional circuit enables use of loudhearing function · Full duplex "handsfree" operation via handset microphone and loudspeaker (at distances <2m between · · · · · · ·
telephone and user) Can be added to any SA253x- application Enables use of low cost 8 - Loudspeaker High output power with low distortion Entirely powered from the telephone line No influence of loudspeaker amplifier in AC-impedance, sidetone cancellation or DC-mask Loudspeaker volume adjustable by potentiometer Excellent sidetone cancellation of SAS253x circuits enables high loudspeaker volume without howling between handset microphone and loudspeaker

SAN2202

PDS038-SA2531/2-001

Rev. B

21-03-00

SAN2202

TABLE OF CONTENTS

1 SCOPE.............................................................................................................................................................................................................1 2 KEY FEATURES ..............................................................................................................................................................................................1 3 OTHER APPLICABLE DOCUMENTS AND PAPERS ......................................................................................................................................3 4 REVISION STATUS .........................................................................................................................................................................................3 5 GENERAL DESCRIPTION ...............................................................................................................................................................................3 5.1 AMPLIFIER SUPPLY: COMPARISON OF SAN2202A AND SAN2202B: ..............................................................................................................3 6 BLOCK DIAGRAM ...........................................................................................................................................................................................4 6.1 HOW TO AVOID HOWLING .............................................................................................................................................................................4 7 CIRCUIT DESCRIPTION ..................................................................................................................................................................................5 7.1 8 LOUDSPEAKER AMPLIFIER .......................................................................................................................................................................5 7.2 AMPLIFIER SUPPLY IN SHUNT TRANSISTOR PATH ............................................................................................................................................5 7.3 AMPLIFIER SUPPLY BY POWER EXTRACTION CIRCUIT SAN3020 ......................................................................................................................5 8 MEASUREMENT RESULTS & CURVES .........................................................................................................................................................6 8.1 FREQUENCY RESPONSE ..............................................................................................................................................................................6 8.2 MAXIMUM SENDING LEVEL ............................................................................................................................................................................6 8.3 MAXIMUM OUTPUT POWER ...........................................................................................................................................................................6 8.4 ON-RESISTANCE IN PULSE DIALING ...............................................................................................................................................................7 9 APPLICATION SCHEMATIC............................................................................................................................................................................8 10 LIABILITY AND COPYRIGHT STATEMENT ..................................................................................................................................................9

2/9

sames

SAN2202

3 Other applicable documents and papers
1. Data Sheet SA2531/2 Single Chip Telephone 2. Application Note SAN3020: Power extraction for external loads

4 Revision status
SAN2202 Application Note (this document)

5 General description
The amplifier is a simple, low cost add-on circuit to the SA253x single chip telephone family. It is supplied by the line current and amplifies the receive signal, taken from either RO1 or RO2 (Receive outputs), see Fig.1. Compared to more complex "real" handsfree circuits there is no channel switching or anti-larsen circuit implemented, therefore the receive and transmit gains must be lower to avoid howling. However, at short distances between user and telephone (<2m, which is adequate for normal office work) there is even full duplex "handsfree" operation possible, when the handset is placed next to the telephone with the microphone facing to the user. Due to the excellent sidetone cancellation of the SA253x circuits, howling between handset microphone and loudspeaker will only occur, when both are put very close to each other. In normal operation, no howling will occur, even with maximum loudspeaker volume. Due to the unique structure of the SA253x family's line adaption, adding the amplifier has no influence on the important PTT related parameters, like AC-impedance, DC-mask, etc. (see Pt. 5.1 below).

Note: all subsequent component numbering refers to the schematic, shown in Pt. 9

5.1 Amplifier supply: Comparison of SAN2202a and SAN2202b: The following table describes the difference between the two types of amplifier supply: while the simple SAN2202a supply shows slight influence in maximum sending level and "Make"-resistance in pulse dialing , the SAN2202b (3 extra components) supply has no influence in these parameters and has a more stable maximum output driving capability at high line currents (see Fig.4 & 5).

Parameter AC impedance off -hook DC mask Tx-/Rx-gains "Make"-resistance in pulse dialing max. sending level (soft clip level = 4Vpp) max. 8 output power; THD <2% max. 8 output power; THD <3% number of extra components

SAN2202a (Shunt path supply) no influence no influence no influence <230 @ 20mA no influence for ILine <40mA <4Vpp for ILine >40mA (see.Fig.3) 26mW 32mW none

SAN2202b (Power extraction) no influence no influence no influence <160 @20mA no influence ; soft clip level 27mW 34mW 3parts: 1 transistor,1diode,1resistor

3/9

sames

SAN2202

6 Block diagram
Fig. 1 shows the block diagram of the speech paths: the transmitted signal is fed to the line via the 2-4 wire interface and the receive signal coming from line is fed to the Rx amplifier. The same Rx signal passes an attenuator for volume control and is then amplified by the loudspeaker amplifier.

RX Amplfier Handset

TX Amplfier

Transmit path

Z ACr Acoustic feedback Sidetonet 2-4 wire interface Line

LS Amplfier manual volume control

Receive path

Fig. 1: speakerphone block diagram

6.1 how to avoid howling As can be seen on Fig.1, there is an acoustic loop from loudspeaker acoustic feedback (determined by the mechanical distance between loudspeaker and handset microphone Tx amplifier sidetone LS amplifier. Howling will occur, when the total loop gain is 1 ( equal to 0dB) . Therefore the following conditions will have an effect in loop gain:

Parameter:
Transmit gain Sidetone

measure to reduce howling
reduce gain increase sidetone cancellation decrease loudspeaker volume limit bandwidth

Note:
must meet the SLR limits can be done by optimizing the sidetone network, the better the sidetone cancellation, the more gain can be given to the loudspeaker for good performance, a maximum of loudspeaker volume is desirable, therefore this should be the least step howling will occur with the frequency of the highest amplification. Therefore the frequency response curve should be as flat as possible and limited to the speech band ( 300..3400Hz) In normal operation, the distance can be down to a few centimeters, when the handset is put onto or off the cradle. The loop should be adjusted such that in normal speech mode there is no howling at distances >5..10 cm. Additionally, the loudspeaker can be mounted away from the handset microphone position, like on the side or on the rear, if possible.

Loudspeaker volume

Loudspeaker frequency response

acoustic coupling between loudspeaker and handset microphone

increase distance between loudspeaker and handset microphone

4/9

sames

SAN2202

7 Circuit description
7.1 8 loudspeaker amplifier The amplifier is a simple Class-A type amplifier. Gain is set by R6, the bandwidth is imited by CC4 (to avoid howling). Q4 and Q6 should be matched in gain (complementary types). Nearly all the line current will flow through these transistors, independent of the signal output amplitude. The maximum power dissipation of Q4 and Q6 is Ptot = VCE * (ILine - IIC1) where: VCE,Q4 = VBE,Q4+UD2 and VCE,Q6 = VBE,Q6+UD1

VBE(Q4,Q6) 0.7V, VTH(D2,D1) 0.52V. ISA2531/2= typ. 3mA (see data sheet) Power dissipation at Iline =100mA: Ptot = (0.7+0.52) * (0.1-0.003) = 118mW

In order to maintain no interference of the circuit to AC-impedance, DC-mask, maximum sending level, etc..., the 1) amplifiers´ supply voltage VCC must be limited to <2.44V . This is accomplished by VCC = VBE(Q6) + VTH(D1)+ VTH(D2)+VBE(Q4) .

VCC = 0.68V + 0.5V + 0.5V + 0.68V = 2.36V
1)

Critical for SAN2202a configuration, not critical for SAN2202b configuration.

VLI can range between 2.5...6.5V 4.5V ± 2Vpeak(max. sending level), the C-E saturation voltage of Q3 is assumed >60mV To maintain full transmit swing (± 2Vpeak ) VC(Q3) = VCC =(2.5V-60mV) < 2.44V Transistor Q1,R1,R2 and R3 forms an impedance matching circuit to provide better matching between the receive output of the IC and the output amplifier stage. 7.2 Amplifier supply in shunt transistor path This configuration requires no extra components. However, the maximum voltage of VPP must be considered: If VPP rises >2.44V, the maximum transmit level will be slightly distorted at the negative half-wave. Additionally, the "Make"-resistance in pulse dialing will be higher, because with CS being pulled to VSS, VLI cannot be shorted to VBE (as in the standard application AN1500 with the collector of Q3 being connected to VSS). During pulse dialing, VLI will be 2.5V, thus increasing the total "ON"-resistance by
RON = 2.5V - 0.6V = 111( 20mA)....19.6(100mA) I Line - 3mA

7.3 Amplifier supply by power extraction circuit SAN3020 This power extraction can be used to supply any external load by the available line current without affecting the performance of the single chip telephone. A detailed description of this circuit is given in application note SAN3020. "ON"-resistance in pulse dialing (compared to the standard application AN1500) is only increased by 10 (see. Fig. 6).

5/9

sames

SAN2202

8 Measurement results & curves
8.1 Frequency response Fig. 2 shows the frequency response curve of the loudspeaker amplifier. The curve shows the output level on an 8 resistor (solid line) and an 8 loudspeaker (dotted line; PHILIPS AD3371 series 80mm 8 speaker) measured with maximum volume and -10dBm Rx level on line. The peak at 200Hz is a resonant frequency of the specific loudspeaker type.
Gain of the amplifier is set by the resistors R6 and the attenuation of VR1. The bandwidth is adjusted by CC4.

Frequency response of LS-A plifier m
-12 -13 Output level [dBm] 8 Ohm Resistor -14 -15 -16 -17 -18 100 8 Ohm Loudspeaker

1000 f [Hz]

10000

Fig. 2:Frequency response of loudspeaker amplifier (PLine=-10dBm)

8.2 maximum sending level Fig.3 shows the maximum Transmit sending level, measured at LI vs. line current, assuming a total harmonic distortion (THD) of less than 1%. AN2201a (dotted line): At line currents >40mA, VPP will rise up to 2.5V (@ 90mA) and sending level will be slightly distorted before it reaches the soft clip level (± 2Vpeak ) . AN2202b (solid line):There is no influence in maximum sending level, the transmit signal can be up to the soft clip level at line currents of >12mA.

max. sending level @ THD <1%
4,4 4,2 4 3,8 VLI [Vpp] 3,6 3,4 3,2 3 2,8 2,6 15 20 25 30 35 40 45 50 55 60 SAN2202a SAN2202b

Line current [mA]

Fig. 3: maximum sending level vs. line current (@ THD <1%) 8.3 maximum output power Fig.4 and Fig.5 show the maximum output power on an 8 loudspeaker at f=1kHz: the curves indicate the maximum output power with <2% and <3% total harmonic distortion. SAN2202a: The lower output drive capability at higher line currents results from nonlinearities at higher collector currents and mismatch in the complementary transistor types. SAN2202b: Maximum output power is not decreased with higher line currents.

6/9

sames

SAN2202

SAN2202a: LS output power vs. line current
35

LS output power @8 Ohm s

30

25

[mWrms]

20

15

10

5

Pm [m THD<2% ax W], Pm [m THD<3% ax W],

0 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85

line current [mA]

Fig. 4: SAN2202a: maximum output power on 8 loudspeaker vs. line current, f=1kHz
SAN2202b: LS output power vs. line current
35 30 LS output power @8Ohms 25 [mWrms] 20 15 10 5 0 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 line current [mA] Pmax [mW], THD<2% Pmax [mW], THD<3%

Fig. 5: SAN2202b: maximum output power on 8 loudspeaker vs. line current,f=1kHz

8.4 On-resistance in pulse dialing As described in Pt. 7.2 and 7.3, the ONresistance (="Make"-resistance) in both applications is higher than with the standard application, AN1500. However, the ONresistance in pulse dialing is generally low with SA253x - applications, this parameter allows a wide tolerance to meet the PTT specs. Germany's BAPT223 ZV5, for example, allows RON 390 @ ILine >24mA. Fig. 6 shows the ON-resistance ,measured on a-and b-terminals in pulse dialing with the SAN2202 applications compared to the standard application SAN2201. Note: since the measurement is taken at a- and b-terminals, the overall resistance including ON-resistance of line-transistor) will be measured.
On-resistance in pulse dialing
250

200 a-b resistance [Ohms]

AN1500 SAN2202a SAN2202b

150

100

50

0 20 30 40 50 60 70 80 90

line current [mA]

Fig. 6:On-resistance in pulse dialing with SAN2201,SAN2202a and -b

7/9

sames

SAN2202

9 Application schematic
1 2 3 4 5 6 7 8

SAN2202A Amplifier supply in shunt transistor path
A
21

SAN2202B Amplifier supply by power extraction circuit SAN3020
Q5 BC327-40

FCI LS

M1

23

A
vpp

1 27

LI IC1

M2

24

5K1 R7

21

FCI LS

M1

23

1 28

RI

27

6

STB CS CI

SA2531/2

C12 X RO2 AGND RR
3

C11 10u

RO1

2

LI I_96

M2

24

7

12

vin Power to speaker amp
10 8 22

6

STB CS CI

SA2531/2

vpp

CC6 X RO2 AGND RR
3

HS/DP MO MODE LLC VDD

C1 C2 C3 C4 R1 R2 R3 R4 OSC VSS

D3

16 15 14 13 20 19 18 17

Q2 BC327

5

25

7

12

CC8 10u

CC7 10u

B

Q3 BC327

5

C13 10u

25

28

RI

RO1

2

B

vin C1 C2 C3 C4 R1 R2 R3 R4 OSC VSS
16 15 14 13 20 19 18 17

9

11

10 8 22

4

26

HS/DP MO MODE LLC

9

C

11

C

8 Ohm Loudspeaker Amplifier
R1 47K vin VR1 50K Q1 BC337-10 10U CC2 CC1 270nF R4 22K Q6 BC327-40 CC3 100U D1 CC4 47nF
+

VDD
4

vpp CC5 470U

26

The information furnished here by SAMES is believed to be correct and accurate. However, SAMES shall not be held liable to any party for any damages including but not limited to personal injury, property damage, loss of profits, loss of use, interuption of business or indirect, special, incidental or consequential damages, of any kind,

+

R2 47K

R3 1K

R6 5K1

D2

+

Q4 BC337-40 R5 22K

SP1 8 Ohm

in connection with or arising out of the furnishing, performance or use of the technical data. No obligation or liability to any third party shall arise or flow out of SAMES rendering technical or other services.

D

SAMES Telecom
Sch. SAN2202 Pn# Single Chip Telephone Application Circuit Sh 01 of 01 Date : 3rd March 1997 Rev : 1.1

D

1

2

3

4

5

6

7

8

8/9

sames

SAN2202

10 Liability and Copyright Statement
Disclaimer: The information contained in this document is confidential and proprietary to South African Micro-Electronic Systems (Pty) Ltd ("SAMES") and may not be copied or disclosed to a third party, in whole or in part, without the express written consent of SAMES. The information contained herein is current as of the date of publication; however, delivery of this document shall not under any circumstances create any implication that the information contained herein is correct as of any time subsequent to such date. SAMES does not undertake to inform any recipient of this document of any changes in the information contained herein, and SAMES expressly reserves the right to make changes in such information, without notification,even if such changes would render information contained herein inaccurate or incomplete. SAMES makes no representation or warranty that any circuit designed by reference to the information contained herein, will function without errors and as intended by the designer.

South African Micro-Electronic Systems (Pty) Ltd
P O Box 15888, Lynn East, 0039 Republic of South Africa, 33 Eland Street, Koedoespoort Industrial Area, Pretoria, Republic of South Africa

Tel: Fax:

012 333-6021 012 333-3158

Tel: Fax:

Int +27 12 333-6021 Int +27 12 333-3158

Web Site : http://www.sames.co.za

9/9

sames