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CERN Project ID LHC Doc. Creator Miguel Cerqueira Bastos
CH-1211 Geneva 23 Sub-Proj. ID - EDMS Doc. 1070495
Switzerland Equip. Code - Doc Rev. / Rev. Date 1.0 / 2009-01-25
TE-EPC
Power Converter Group Equipment Description
The LHC DS22 bit ADC
The LHC high precision current measurement chain
The main power converters in LHC require an unprecedented level of accuracy in the control of current to the
superconducting magnets, in the order of ~10-6.
The power converter output current accuracy is mainly determined by the DCCT (Direct Current Current Transducer)
and ADC (Analogue-Digital Converter) employed.
There are three types of ADCs used in the LHC: a 16 bit Delta Sigma and a 16 bit SAR, both included in the power
converters' digital controller electronics (FGC) and, in the case of the main and inner triplet power converters, a 22 bit
delta sigma standalone unit.
Introduction to Delta sigma converters
The ADC employed in the digital regulation loops for the LHC requires high resolution and accurate digitization of low
frequency waveforms. Since the ADC can be one of the major sources of error in the magnet current, along with the
current transducer, its performance largely determines the overall accuracy which can be obtained. The potential of the
Delta-Sigma method to deliver ppm performance determined the choice of this method for the LHC.
The simplified block diagram of a first order Delta sigma ADC is shown in Fig.1.
Fig. 1