Hysteresis prediction in autonomous microwave circuits using commercial software: application to a Ku-band MMIC VCO

In this paper, a new method is presented for the simulation of autonomous microwave circuits, using commercial software. The method, especially suitable for voltage-controlled oscillators (VCO's) and phase-locked circuits, allows the simulation of the whole solution curves as a function of any parameter, enabling the prediction of hysteresis phenomena, and thus a realistic determination of the operating bands. Immittance diagrams, providing all of the coexisting oscillating solutions, are traced using commercial software by means of a new technique. As a parameter varies, a switching-parameter continuation method is also used for tracing the possible turning points of the solution curve. The new simulation method has been applied to the design of a Ku-band monolithic microwave integrated circuit (MMIC) VCO. This circuit, which has been integrated using a commercial monolithic technology based on 0.2 /spl mu/m gate length pseudomorphic HEMT's, constitutes a good example to illustrate the new simulation method capabilities. Frequency tuning and output power control are, respectively, obtained by varying the varactor and transistor voltage bias. On-wafer measurements and simulation results showed excellent agreement.