The Design Of High Speed Sigma-Delta Modulator

Over sampling techniques based on sigma-delta AD converter is widely used in the mixed-signal circuits. Compared with other AD converters, sigma-delta AD converter has several advantages, including not sensitivities to noise, small quantization noise, high resolution, and good linearity and so on. Now sigma-delta is the one of most significant technology in the AD converter domain.This paper made a deeply analysis about the basic principle of the two order sigma-delta modulator. Based on this analysis, turn out one which has 14bits resolution, 8MHz sampling frequency and 256 over sampling ratio. The first part in this paper introduces the background of this topic and my major work. The basic principle of sigma-delta modulator is introduced in the second part. The third part is talked about noise contributions. It turns out the requirements of the circuit blocks from a reasonable noise budget. The details include the minimal sampling and integrating capacitor, DC gain of the open loop amplifier, the dominate pole of the closed loop amplifier, how to design comparator and switch, and so on. In the fourth part, it's talked about the structure and simulation of the circuit blocks, including the implementation and simulation results of the amplifier, comparator, bandgap, switch, non overlap two-phase clock. The fifth part is mainly about how to use this modulator and conclusion. The simulation of this modulator is based on CSMC 0.6 processand it can be used in high performance DSP-Based motor controller which need resolution less than 14 bits, sampling frequency less than 8MHz.