Research And Implementation Of A Fourth-Order Low Distortion And High Precision Sigma Delta Modulator

The Sigma-Delta ADC is widely used in high precision electronic scale, industrial process control, medical equipment, instruments and other occasions in need of precision measurement. The advantage of the Sigma-Delta ADC is high precision, but low speed. In some applications of MHz signal bandwidth, such as wireless communication systems, the demand of the high precision ADCs continues to increase. The conventional ADC can not meet the high precision. So, under this demand, improving the speed of the Sigma-Delta ADC has important significance without the sacrifice of precision. To solve the shortcomings of the traditional 4th-order feed-forward Sigma-Delta modulator in power consumption and circuit implementation, a new 4th-order low distortion and high precision Sigma-Delta modulator has been proposed and implemented in circuits level to meet the needs of wireless communication systems and applications in precision and speed. The contents of the paper are as follows:Firstly, it states the modeling and simulation of the Sigma-Delta modulator in system level and uses the MATLAB SIMULINK tool to build it. Adjust the coefficients of the integrators to avoid the overload of the following integrators. Statistics and analysis the output voltage of the every integrator to decide the output swing of the amplifier used in the integrator. Change the timing of the Sigma-Delta modulator based on the conventional Sigma-Delta modulator topology. Without degradation of the performance of the Sigma-Delta modulator, trying to increase the time for the quantizer and feedback DAC to improve the linearity. And it solves the unstable problem of the Sigma-Delta modulator because of the non-linearity of the quantizer and the feedback DAC. In the process of building the model, some non-ideal factors such as white noise of the switch and the flick noise of the OPAMP are considered to prove the feasibility of the model.Secondly, based on the simulation of the MATLAB system model, the circuits of the 4th-order low distortion and high precision Sigma-Delta modulator are implemented. Because the acquirements of OPAMP used in each integrator of the Sigma-Delta modulator are vary, we play a great role in the design of the OPAMP to achieve a good FOM value. A rail to rail and low supply voltage comparator is designed. It has the advantage of no static power consumption and full input swing. Do the trans simulation of the circuits of the Sigma-Delta modulator, and use the MATLAB tool to analysis the simulation results to prove its the performance which are same with the simulation of the model.Finally, based on 0.18 mm 1P6 M CMOS process, the layout of the 4th order low distortion and high precision Sigma Delta modulator design for wireless communication applications is realized. In the layout, some MOS tubes are designed with the principle of cross matching. The area of the modulator layout is 1000 mm *800 mm. The proposed sigma delta modulator is simulated in a 1.8V supply CMOS technology with the sine-wave input of-6-d B amplitude and 347-k Hz frequency by 65536-point FFT analysis and a 87.5-d B SNR had been achieved with 15.2 m W total power consumption under 32-X oversampling ratio at 160 MHz sampling frequency. The simulation results show that it is very suitable for wireless electronic devices.