Broad tuning microwave oscillators utilising multilayer technology and SiGe devices

This paper describes the design of a low phase noise 3.27-5.27 GHz VCO demonstrating phase noise performance varying from -96 to -102 dBc/Hz at 100 kHz offset over the whole band. The VCO incorporates a silicon germanium transistor as the active device. The resonator consists of a printed electrically short transmission line with printed shunt inductors at either end. Two varactor diodes are coupled in parallel to the centre of the resonator. The amplifier is placed on the other side of a 3-layer board and coupled to the resonator using capacitive vias. The oscillator operates at V_CE=2 V and I_C=30 mA. The design of a broadband (3-6 GHz) negative group delay equaliser capable of cancelling the phase shift in the amplifier is also described although this was not used in the final design due to the high insertion loss.