Low phase noise differential LC tank VCO with current negative feedback

摘要

A differential voltage controlled oscillator (VCO) employed in a frequency synthesizer used as a local oscillator of a wireless communication on-chip transmitter/receiver is provided. More particularly, a differential current negative feedback VCO equipped with a current-current negative feedback circuit that suppresses low- and high-frequency noise is provided. ;A differential current negative feedback VCO includes a resonator determining oscillation frequency, and an oscillator generating negative resistance. In the oscillator of the differential current negative feedback VCO, transistors Q1 and Q2 form a cross-coupled pair, and negative resistance is generated by positive feedback of the cross-coupled pair. And, transistors Q1 and Q3 together with an emitter resistor and a capacitor form a current negative feedback part, and transistors Q2 and Q4 together with an emitter resistor and a capacitor form another current negative feedback part which is disposed opposite to a resonator. Thus, the VCO operates differentially. ;In the oscillator of the differential current negative feedback VCO, emitter noise currents generated by base noise voltages of Q1 and Q2 induced by low- and high-frequency noise sources in the bases of Q1 and Q2 are sampled by emitter resistors, amplified through bases of Q3 and Q4, and thus return to the bases of the Q1 and Q2 and suppress the base noise voltages. Measurement of the phase noise of the differential current negative feedback VCO reveals a phase noise reduction of approximately 25 dB compared to a conventional differential VCO.