A 0.25–3.25-GHz Wideband CMOS-RF Spectrum Sensor for Narrowband Energy Detection

A wideband spectrum sensing system for cognitive radio is designed and implemented in a 130-nm radio frequency mixed-mode CMOS technology. The system employs an I-Q downconverter, a pair of complex filters, and a pair of envelope detectors to perform the spectrum sensing from 250 MHz to 3.25 GHz. The design makes use of the bandpass nature of the complex filter to achieve two objectives: 1) separation of upper sideband and lower sideband around the local oscillator signal and 2) resolution of smaller bands within a large detection bandwidth. The measured sensitivity is close to -45 dBm for a single tone test over a bandwidth of 40 MHz. The measured image reject ratio is close to 30 dB. The overall wideband detection bandwidth is 250 MHz, which is partitioned into 40-MHz narrowband chunks with eight such overlapping chunks.