Quadrature Oscillator with Negative-Resistance Compensated Transformer Couple

A quadrature oscillator with the negative-resistance compensated transformer couple is presented. Two identical LC sub-harmonic oscillators are cross-coupled by the transformer to generate the quadrature outputs. The transformer also serves as the tail current source filtering network for the sub-harmonic oscillators to improve the phase noise performance. The loss of the transformer is partially compensated by the cross-coupled PMOS pair to overcome the possible undesired harmonic couple and to further improve the phase noise performance. The phase noise performance of the quadrature oscillator is 7dB better than the sub-harmonic oscillator itself by the simulation. The quadrature oscillator has been implemented in 0.25mum CMOS process and the measurements show the proposed oscillator could achieve a phase noise of -130dBc/Hz at 1MHz offset from 1.13GHz carrier while it only draws an 8.0mA current from the 2.5V power supply