Opamp gain insensitive MASH sigma delta modulator for wide bandwidth applications

Abstract

This work presents a means to enhance the immunity of non-ideal opamp gain effect of the fourth order multistage noise shaped (MASH) sigma-delta modulator (SDM) for wide bandwidth applications. The first stage of the SDM is a low-distortion single-loop second order SDM, while the second stage is a low-distortion interpolative second order SDM with Chebyshev type II filter technique. Theoretically, the conventional MASH SDM is impacted by the nonlinear finite gain of the operational amplifier. This impact may have two main phenomena. First, it leaks the incompletely corrected quantization error to the output. Secondly, the nonlinearity causes the harmonic distortion of the input signal. The proposed architecture can reduce the distortion and the sensitivity of the nonlinear finite opamp gain to improve the performance by using low-distortion technique in the MASH SDM. Furthermore, the lower power budget and simplified digital cancellation logic can be achieved. The experimental results indicate that the dynamic range (DR) can reach 87dB with power dissipation of 65 mW. A test SDM chip for Asymmetric Digital Subscriber Line (ADSL) application is designed and implemented by TSMC 0.25 um 1P5M process.

A low power sigma-delta modulator for dual-mode wide-band receiver

“…According to [5,7,9,10], it can enhance the bandwidth and relieve the specifications of the opamp. The signal transfer function (STF) is unity in the first stage, and the NTF is derived as follows:…”