A compact Ka-band MMIC voltage controlled oscillator: Comparison of MESFET and HEMT implementations

A novel, compact Ka-band MMIC (monolithic microwave integrated circuit) voltage controlled oscillator (VCO) has been designed, fabricated and tested. The VCO design is a ´ring´ configuration using two FETs with two isolated control terminals, which provides increased tuning bandwidth. This design uses an active feedback topology, resulting in greater device size for higher output power and circuit Q. This VCO was fabricated with both 0.25 mu m gate length MESFET and HEMT (high electron mobility transistor) processes designed to have similar RF equivalent circuits by engineering the device doping. The measured MESFET VCO demonstrated a tuning bandwidth of 740 MHz centered at 35 GHz and an output power of 8.3 dBm. The measured HEMT VCO tuning bandwidth is greater, but phase noise is worse than that of the MESFET implementation.<>