Design of a Continuous-Time Loop Filter for ΔΣ Modulators with Excess Loop Delay

Abstract

In this paper, we propose a continuous-time (CT) loop filter for minimizing the quantization noise in a Delta-Sigma (ΔΣ) modulator. We use the impulseinvariant transformation to obtain a CT loop filter from a discrete-time (DT) loop filter. We consider a nonideal CT ΔΣ modulator which is affected by the excess loop delay (ELD). The ELD is known to affect the stability and noise shaping performance of the CT ΔΣ modulator. Our objective is to design the CT modulator whose stability is not affected by the presence of ELD. A design example for a lowpass CT ΔΣ modulator based radio frequency (RF) receiver is provided for simulations. We also compare the mean squared error (MSE) performance of our modulator with the conventional design.