A 1.9 GS/s 4-bit sub-Nyquist flash ADC for 3.8 GHz compressive spectrum sensing in 28 nm CMOS

Spectral activity detection in wideband radio-frequency (RF) signals for cognitive-radio applications typically necessitates expensive and energy-inefficient analog-to-digital converters (ADCs). In this paper, we present a novel compressive sensing (CS)-based analog front-end, which is able to sample sparse wideband RF signals at low cost and low power. The analog front-end consists of a pseudo-random non-uniform clock generator unit offering the possibility to configure the (average) undersampling factor at run-time, and a low-cost, wideband 1.9 GS/s 4-bit flash ADC. The spectral information acquired at sub-Nyquist rates can be recovered off-line via novel sparse signal dequantization algorithms. The developed analog front-end is implemented in 28nm CMOS, and enables the recovery of spectrally sparse RF signals up to 3.8 GHz by means of CS, which corresponds to a Nyquist-equivalent sampling rate of 7.6 GS/s. The ADC and pseudo-random clock generator together occupy less than 0.1mm², and consume an estimated 4.1mW to 5.4mW for undersampling factors between 4 and 11.5.