A Continuous-Time Delta-Sigma Modulator for RF Subsampling Receivers

We propose a new continuous-time (CT) delta-sigma modulator (DSM) to be utilized in radio-frequency (RF) subsampling receivers for analog-to-digital conversion. Subsampling DSMs employ sub-Nyquist sampling with respect to the input signal frequency and oversampling with respect to the signal bandwidth. The proposed CT-DSM mitigates the effects of subsampling by modifying the feedback path of the modulator to accommodate the RF replica of the feedback signal and by enhancing the quality (Q) factor of the loop filter. The novel modulator has significant improvements over previously published subsampling modulators as it provides jitter and image suppression and excess loop delay compensation to improve the dynamic range, thus enabling the modulator to be utilized in subsampling receivers when a relatively low sampling rate is desired.