A cascaded CT ΣΔ modulator with NTF zero and simple mismatch tuning method using interstage feedback

Abstract

A cascaded continuous-time SigmaDelta modulator with programmable NTF zero and simple mismatch correction method is proposed. By using interstage feedback the loop filter resonator is not needed to introduce an NTF zero. As a result of the absence of resonators very simple mismatch tuning methods can be applied because the interstage feedback does not have influence in the mismatch properties. Moreover the loop filter stability is improved when the resonator is removed. Analytical expressions to calculate the interstage feedback gain are proposed to place the NTF zero in the desired location in the continuous-time case. To validate the proposed method several Monte Carlo analyses have been carried out showing an improvement in the mean SNR value of 10dB.