Design Of A PGA In Sigma-Delta ADC With High Accuracy

Sigma-Delta ADC is a main kind of oversampling Analog-to-Digital Converter with high resolution and low transition rate. Programmable Gain Amplifier (PGA) is used to amplify or attenuate the analog signal to adapt to the various full-scale values of ADC module, so that optimizing the dynamic range of the whole system.In this paper, a precision PGA circuit applied to the I-AADC is designed. The structure of the PGA consists of operational amplifiers, switched-capacitor circuit and some additional circuits. This thesis focuses on the design of operational amplifier of PGA. In this thesis, the gain boost configuration is used to increase the gain of total op-amp, thereby reducing the deviation of PGA; in order to significantly reduces the noise of the input signal and the operational amplifier itself, chopper-stabilization technique is adopted, increased the signal to noise ratio generated by the operational amplifier; rail-to-rail technology effectively improves the performance of the operational amplifier, the bias circuit designed in the op amp reduces power consumption while increasing the output range of the signal, at the same time, the driving ability of the signal is improved, so that the output signal is better to meet input signal requirements of the modulator followed.The magnification is adjusted by turning clock switch in the amplifier, to enable the different gain of 1,2,64 and 128, so that the input signal is automatically adjusted to fit the best input range of A/D converter according to actual requirements before conversion, so as to effectively maintain the conversion accuracy of ADC at a low input.With 0.35 um CMOS process model, Cadence Spectre simulation tools is chosen to simulate the op amp in PGA circuit. The results show that the PGA can meet the requirements of the subsequent modulator on the performance of ±2.5V in input signal range and higher signal to noise ratio.