Filtering adjacent channel blockers using signal-transfer-function of continuous-time ΣΔ modulators

Abstract

Abstract-In this paper, we show that the signal transfer function of continuous-time Σ∆ modulators can be used to remove the baseband analog filters in radio receivers. General expressions for the signal transfer function of continuous-time Σ∆ modulators are derived. Comparisons between the frequency response of feedforward and feedback architectures of discrete-time and continuous-time Σ∆ modulators are established. Filtering of GSM adjacent channel blockers using a 5 th order continuous-time Σ∆ is given as an example.

Sensitivity of single-bit continuous-time ΔΣ analogue-to-digital converters to out-of-band blockers

“…1 for a block diagram of a fifth-order CT DS modulator) have recently gained significant attention in wideband wireless receivers because of their amenability for operating at a higher speed with lower power consumption compared to discretetime (DT) counterparts, inherent anti-aliasing, and robustness to sampling errors in the quantiser. Furthermore, the lowpass filtering (LPF) signal transfer function (STF) (STF is the loop transfer function over the signal path from the modulator input terminal to the loop filter output) offered by cascade of resonator feedback (CRFB) CT DS structures can adequately attenuate OOB blockers before they reach the quantiser input [1] and hence avoid loop desensitisation (due to the integrators' saturation) and instability (due to internal quantiser overloading) that can be caused by OOB interferers. Although multi-bit DS modulators relax the noise shaping requirement on the loop filter and show better robustness to clock-jitter in the feedback digital-to-analogue converter (DAC) sampling clock [2], when compared to single-bit implementations, they suffer from limited linearity in the feedback multi-bit DAC owing to inherent mismatch between DAC unit cells.…”