Design of X-Band and Ka-Band Colpitts Oscillators Using a Parasitic Cancellation Technique

An X-band and two Ka-band monolithic microwave integrated circuit (MMIC) common drain Colpitts oscillators using a parasitic cancellation technique are designed and fabricated in a 0.2-mu m GaAs pHEMT technology with a f(T) of 60 GHz. The parasitic cancellation technique significantly improves the negative resistance and increases the maximum operating frequency, which is suitable for microwave and millimeter-wave applications. An in-depth theoretical analysis of the Miller effect and insights in the behavior of the input impedance with the parasitic cancellation are provided. The effect of the Q-factor of the inductor used in the cancellation, and the impact of the parasitic cancellation technique on phase noise and frequency tuning range are analyzed and discussed in detail. The X-band design has a measured phase noise of -117.5 dBc/Hz at 1 MHz offset with an output power of -9.3 dBm. The first X-band design has a measured phase noise of -94 dBc/Hz at 1 MHz offset with an output power of +0.2 dBm. The second X-band design providing more flexibility has a measured phase noise of 98.5 dBc/Hz at 1 MHz offset with an output power of +0.3 dBm. The two Ka-band designs achieve very high fosc/f(T) ratios and also demonstrate performance comparable to the best previously published oscillators in a similar frequency range.