A CMOS spectrum sensor using injection locking of two voltage-controlled oscillators for cognitive radio system

This paper presents a CMOS spectrum sensor to detect spectral usage and spectrum holes for cognitive radio system. The sensor mainly consists of a swept oscillator and a frequency discriminator, both of which use the injection locking of voltage-controlled oscillator (VCO) to process the sensed signal without requiring a frequency synthesizer. As a demonstration, the sensor is designed to operate in the 2.4 GHz industrial-scientific-medical (ISM) band and implemented using 0.18 μm CMOS technology. It can detect the frequency and power for wireless communication signals with high accuracy at a spectrum scanning speed of 100 MHz/ms. The sensitivity can be below -100 dBm when an external low-noise amplifier (LNA) is used in front of the sensor IC.