Quenchable vco for switched band synthesizer applications

Abstract

A quenchable VCO that is adapted to be used in switched band synthesizer applications. The VCO may be formed from a heterojunction bipolar transistor (HBT) in a common collector configuration. A quenching circuit which includes a p-i-n diode, is electrically coupled in series with the collector of the HBT. The p-i-n diode is adapted to be monolithically integrated with the HBT. Since the p-i-n diode is electrically connected to the collector of the HBT, as opposed to the base and emitter terminals of the HBT, which forms the main oscillator feedback loop, the Q-factor of the p-i-n diode will have relatively less loading on the phase noise of the HBT oscillator. Moreover, since the p-i-n diode is isolated from the base-emitter junction, the configuration will result in reduced frequency pulling and generation of spurious oscillation and transient effects due to the switching of the p-i-n diode quenched circuit. The use of a p-i-n diode for quenching of VCO also provides other inherent advantages over other types of semi-conductor switches, such as FET, Schottky diodes, PN diodes for quenchable VCO applications because p-i-n diodes are relative insensitive to RF and noise modulation. Because the p-i-n diode can be constructed from existing HBT collector-base MBE epitaxy layers, the quenching circuit can be manufactured relatively inexpensively.