Quadrature Generation Techniques in CMOS Relaxation Oscillators

Shunt and series-coupling techniques for quadrature generation are applied to CMOS relaxation oscillators. The 2.4GHz quadrature oscillators are designed and simulated in a UMC 0.18 mu m CMOS process. The shunt-coupled oscillator consumes a current of 12mA from a supply of 1.8V and achieves a phase noise of -99.4dBc/Hz @ 1MHz offset. The series-coupled oscillator consumes a current of 16mA from the 1.8V supply and achieves a phase noise of -98.3dBc/Hz @ 1MHz offset. For a systematic mismatch of 1%, the quadrature phase error of the shunt-coupled and series-coupled circuits are 0.55 degrees and 0.1 degrees respectively.