An Open-Loop Amplifier Multi-Bit Sigma Delta Modulator

Abstract

A new multi-bit quantizer for sigma delta modulators is proposed. The multi-bit quantizer has multiple single-bit quantizers, and the output of one of the single-bit quantizers is fed back to the input of another single-bit quantizer via a filter. Multi-bit quantization is achieved by averaging the outputs of the single-bit quantizers. Because of this architecture, the multi-bit quantizer realizes multi-bit quantization without external signals such as dithering signals that are needed in conventional architectures. The multi-bit quantizer allows for designing a new open-loop amplifier multi-bit sigma delta modulator. The open-loop amplifier multi-bit sigma delta modulator uses differential pairs for its loop filter instead of closed-loop amplifiers that consume considerable power for high frequency applications. The open-loop amplifier multi-bit sigma delta modulator is designed with a 90nm CMOS process. The achievable SNDR is 43dB with the bandwidth of 80MHz when noises other than quantization noises are not taken into consideration. The sampling frequency is 2.56GHz, and the power consumption of main analog parts is 15mA.