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

The sensitivity of single-bit continuous-time (CT) ΔΣ analogue-to-digital converters to out-of-band (OOB) blockers received in companion with desired signals is investigated. In essence, the residual interferer signal appearing at the output of the CT loop filter can flip the single-bit quantiser decision near the zero crossings of the loop filter output signal. An intuitive analysis of this effect on the performance of single-bit ΔΣ modulators in the presence of OOB interferers is provided. System level simulations for a single-bit fifth-order CT ΔΣ modulator at an oversampling ratio of 40 have been carried out. A reduction in the achievable signal-to-noise-plus-distortion ratio, that can be as large as 10 dB when applying a 0 dBFS OOB blocker tone along with a weak -75 dBFS desired tone, has been observed. The simulation results show good agreement with the adopted theoretical discussion.