Hybrid loopfilter sigma-delta modulator with NTF zero compensation

Abstract

A low power second order hybrid loopfilter Sigma-Delta modulator with high resolution is presented. The structure is composed by a first active integrator followed by a switched-capacitor (SC) integrator. This modulator architecture exploits the coefficient scaling property of the active integrator, while the SC integrator is modified to shift its pole from inside the unit circle to z=1 at DC in the z-domain. Poles of the loopfilter are zeroes of the noise transfer function (NTF). As a result the NTF zero is also shifted to z=1. This NTF zero compensation for the SC integrator will result in better in-band noise suppression & improved noise shaping. The second order hybrid sigma-delta modulator with a 4-bit quantizer and an oversampling ratio (OSR) of 32 is simulated in simulink. The modulator can achieve 89dB SNDR with a dynamic range of 91dB.