Low phase noise MMIC oscillators in InGaP HBT technology

Low phase noise oscillators in cross-coupled and balanced Colpitts topologies have been designed and implemented in InGaP GaAs technology. A 6.9 GHz cross-coupled oscillator has a measured phase noise of X(100kHz)=-117 dBc/Hz and a 5.5 GHz fixed-frequency balanced Colpitts oscillator has a measured phase noise of X(100kHz)=-120 dBc/Hz. Voltage controlled oscillators (VCOs) have also been designed. For both the cross- coupled and the balanced Colpitts topology, the phase noise of the VCOs is roughly 8 dB higher than that of the fixed-frequency oscillators when the varactor is reverse biased. Beside comparing fixed-frequency oscillator to VCOs, VCOs based on finger varactors are also compared to VCOs based on conventional square varactors. A cross-coupled VCO using finger-varactors has 7 dB lower phase noise and 5 times lower power consumption than a similar cross-coupled VCO based on rectangular varactors.