High Precision Audio Sigma-Delta ADC Research And Design Of Modulators

With the rapid development of the integrated circuit industry,research on Analog to Digital Converter(ADC)is becoming increasingly in-depth.In nature,the common sound signals,vibration signals,etc.that we can feel are analog quantities.To utilize digital technology for digital processing of analog signals in daily life,an analog-to-digital converter is required.Therefore,research on analog-to-digital converters is becoming increasingly in-depth.It is mainly divided into Nyquist ADC and oversampling ADC.Nyquist ADC refers to the analog-to-digital converter that meets Nyquist criterion sampling.Compared with Nyquist ADC,the main reason why Sigma Delta ADC can achieve high precision is that oversampling and noise shaping technology are used,and the design of modulator is critical when designing its ADC system.Sigma Delta ADC is widely used in high-precision signal processing fields such as healthcare and audio.The thesis compares the characteristics of modulators with other architectures such as first-order modulators,second-order modulators,and higher-order modulators,and designs the structure and related parameters of Sigma-Delta ADC modulators to ensure the implementation of functions and indicators.The modulator structure was systematically modeled using the SIMULINK environment in MATLAB,and the relevant modulator coefficients were optimized.FFT analysis was performed on the output results of the ideal model of the Sigma-Delta modulator,and various non ideal factors were added to determine whether the system indicators were met through the output results of the modulator.Design a transistor level circuit based on the obtained modulator coefficients,observe the output of the circuit,and repeatedly adjust and optimize the modulator coefficients to obtain a feasible modulator structure for the circuit.A high-precision audio Sigma-Delta ADC modulator has been designed,in which the circuit switches use CMOS complementary switches to greatly eliminate the nonlinearity of the switches.At the same time,chopping technology is added to the first stage integrator to reduce the offset and low-frequency l/f noise of the first stage integrator.The modulator structure adopts a second-order multi bit quantization structure.The use of a second-order modulator structure can ensure the stability requirements of the modulator.The modulator design structure adopts the SMIC 0.18um CMOS process,and the circuit level design and simulation of the structure are carried out based on the SMIC 0.18um process.In the frequency range of 20～20kHz,the signal-to-noise ratio reaches 98dB and the effective digits can reach 16 bits.