Research And Implementation Of Multi-rate Digital Filter Based On Sigma-delta Modulator

With the increasing demand for data processing,efficient and flexible digital signal processing systems are favored.In each module of the processing system,data format and processing speed are often set to be optimal to reduce the computational complexity and the amount of data storage.In this way,multi-rate digital signal processing technology has developed rapidly and been widely used in various fields.MEMS digital geophone,the background of this paper,is a sensor system based on Sigma-Delta modulation,which can quantize the vibration signal into a high-precision digital waveform in which obtain the characteristic information of the vibration signal.The process also requires the use of multi-rate signal processing technology.This paper studies and implements a multi-rate digital filter,which is compatible with the multi-sampling rate signal from the previous stage of the system.It solves a problem of the original DSP processing module,that is,the input signal sampling rate is single.It also has an adjustable output rate,so the overall flexibility of the system has been greatly improved.Without changing the original system structure,a multi-rate signal converter is added to match the original processing module.The two form a complete architecture of the multi-rate digital filter.Simulink model simulation verifies that the multi-rate signal converter can convert the multi-sampling rate Sigma-Delta modulated signal to a fixed rate of 128KHz modulated signal without changing the signal bit width and pass-band characteristics.The original input sampling rate can be 16KHz,32KHz,64KHz,256KHz,512KHz and 1024KHz.Then build the HDL model and realize the design as a digital circuit,the pre-simulation verifies that the digital circuit is fully functional.Based on 0.18 μm high-temperature CMOS technology,and through a series of chip back-end design processes,we finally got two ASIC chips,multi-rate signal converter and digital decimation filter with adjustable output rate.We built a test platform and independently verified that the function of each module meets the design expectations.The overall system simulation results show that the system noise floor is below-150dB,and the signal-to-noise ratio reaches 113dB.The multi-rate digital filter designed in this paper can process Sigma-Delta modulated signals at various sampling rates to obtain 24-bits high-precision digital waveforms with adjustable output rates.It can flexibly and efficiently process signals in different applicable scenarios.It can be widely used in various sensor systems based on Sigma-Delta modulation principle.