| With the rapid development of large-scale digital integrated circuits,the advantages of data processing in the digital domain become more and more obvious,and analog-to-digital converters emerge as the times require.As a channel from analog domain to digital domain,the research of analog-to-digital converter(ADC)has always been a hotspot in the field of chip research at home and abroad.Sigma-Delta ADC uses noise shaping and digital signal processing technology to replace the complex analog signal processing technology used in Nyquist rate converter.It is widely used in pressure sensing,industrial process control,digital audio and other fields.Firstly,the research background,significance and research status of Sigma-Delta modulator at home and abroad are summarized.Next,the Sigma-Delta modulator is introduced comprehensively.The oversampling technology is explained from the point of quantization noise,and the theoretical basis of noise shaping is deduced from the point of negative feedback.Then,the relationship between the signal-to-noise ratio(SNR)and key parameters of the system(including oversampling ratio and order)is analyzed and deduced.Meanwhile,the performance index of the Sigma-Delta modulator is given.Next,some important non-ideal effects in the switched capacitor circuits are explained in this paper,such as channel charge injection,clock feedthrough,parasitic capacitance of the switch,etc.For operational amplifier,the effects of its offset voltage in the switched capacitor integrator are also strictly deduced.In view of the above non-ideal effects,the dynamic error elimination scheme based on the bottom board sampling technique with delayed switch and chopper stabilization is adopted in this paper.Finally,based on the 0.15μm BiCMOS process,the transistor-level Sigma-Delta modulator circuit with the proposed error elimination scheme is designed and implemented.The schematic diagram is edited with Cadence software,and the transistor-level circuit is simulated by Spectre and Hspice software,and the simulation results are processed with MATLAB software.Simulation results show that the Sigma-Delta modulator circuit designed in this paper has good performance.The integrator will not overload in the rated input range,and the output signal has no error with the theoretical value.When the frequency of the input signal is 9.765625 kHz and the amplitude of the input signal is 150 mV,the SNR of modulator is 81.9 dB.In addition,the second harmonic distortion is-96.0 dB,and the third harmonic distortion is-87.0dB,and the signal to noise and distortion ratio is 81.0 dB,and the effective number of bits is 13 bit,and the input offset voltage is about 0.07 mV. |
