Research Of Digital Filter In ∑-△A/D Converter

A/D converter is a very important part of digital signal processing,with the development of scientific and technological and the improvement of people requirements,high-precision analog-to-digital converters and signal processing circuit integrated has become a trend.The higher resolution achieved by conventional Nyquist rate A/D converters are limited by the matching precision of components which are high-bit quantizer;so it is hard to achieve high resolution. However a kind ofΣ-AA/D converter with low-bit quantizer and oversampling,takes advantage of increasing speed and high density provided by modern VLSI technology,with digital filtering technology,achieved high accuracy by overcome the traditional Nyquist rate A / D converters on the resolution limit.Σ-ΔA/D converter including modulator and digital filter in two parts.Modulator sampling of the input analog signal with high sampling rate,use low-bit quantizer to quantization the difference value of sampling.Then the digital filter decimating the data flow code after quantization,achieve high resolution digital signals.In the realization of digital decimating filter,a multistage taken to reduce the signal frequency and filtering noise of outside base-band.Multistage can reduce the order of the filter,largely decrease operational and the complexity of the structure of the circuit.According to the characteristics of decimate filter,first-class uses of a comb filter to down-eight times,some of half-band filters used to down-two times behind it.Because the first-class filter has a certain level lower,a FIR filter can used to amplitude compensation at last-class.Simulation design comb filter and half-band filters under Matlab first,then use FPGA of Cyclone chip made in ALTERA implementation with VHDL language and QUARTUSⅡsoftware.By using bit-cut to further improve the use of resources when realizing comb filter,in the filtering effect of the guarantee and improve the efficiency of the hardware about twenty nine percent.By using transpose parallel multiplier structure to·largely improve speed when realizing half-band filters, multiplication can complete in a clock period,then obtain filtering output by pipeline adder.