FPGA implementation of all-digital adaptive delta sigma Modulator with enhanced SQNR and dynamic range

Abstract

This paper presents an efficient technique to enhance the signal to quantization noise ratio (SQNR) and dynamic range of delta-sigma Modulator (ΔΣ) with one bit quantizer, called all-digital adaptive delta sigma modulator. It is divided into two main parts. One is the conventional delta sigma modulator part and another is adaptation part. In adaptation part, a signal which is similar to the input signal, but lower in the range is generated, called an adaptive signal. Now the difference between the input and the adaptive signal is fed to the conventional modulator. We are inserting a limiter in the adaptation part which is absent from previously reported work, so our design works perfectly for any types of signal (square wave, staircase etc). We design 1st order and 2nd order adaptive ΔΣ modulator with modification from previously reported work and insert limiter into that. We also implement two conventional and two adaptive ΔΣ modulator on a Xilinx Virtex-7 Field Programmer Gate Array (FPGA). It was shown that 2nd order adaptive ΔΣ modulator having an average SQNR improvement of 26.492 dB over the 2nd order conventional ΔΣ modulator at over sampling ratios (OSRs) of 512 in an input signal power range from −85 dB to 5 dB. Also 2nd order and 1st order adaptive ΔΣ modulator dynamic range approximately improved 17 dB and 10 dB over the 2nd order and 1st order non adaptive ΔΣ modulator.