Experimental evaluation of wide range injection locking in a CMOS RC oscillator

CMOS RC oscillators have low area, can be built with a low cost technology, and have a wide tuning range, but they have higher phase-noise than LC oscillators. This can be overcome by synchronizing the oscillator by injection-locking with an low phase-noise external source. We present here an experimental study of injection-locking in an RC two-integrator oscillator. First and second harmonic injection in different locations of the oscillator are investigated. A test circuit was fabricated using a standard CMOS technology with 1.2 V supply. Measurement results show that a phase noise improvement of more than 30 dB, can be obtained with only -30 dBm injected signal between 100 kHz and 10 MHz frequency offset over a wide frequency range (600 MHz to 3 GHz).