A $\Sigma \Delta$-FIR-DAC for Multi-Bit $\Sigma \Delta$ Modulators

Abstract

In this paper, a new digital-to-analog converter (DAC) is proposed for multi-bit continuous-time sigma-delta modulators (ΣΔMs). This -finite-impulse-response-DAC (ΣΔ-FIR-DAC) digitally converts the multi-bit output of the quantizer to a 1.5-bit signal at a higher rate and then injects it to the modulator loop filter by using a 1.5-bit DAC. An FIR filter is merged into 1.5-bit DAC to improve the clock jitter insensitivity. Furthermore, a new implementation of ΣΔ-FIR-DAC is presented to reduce the output rate of ΣΔ-FIR-DAC down to the original rate of the modulator. This reduced rate ΣΔ-FIR-DAC (RR-ΣΔ-FIR-DAC) can be used in both continuous-time and discrete-time ΣΔMs. Theoretical analysis supported by simulation results are provided to evaluate the performance, clock jitter immunity and robustness against DAC elements mismatch in the proposed modulators.