CROSS-COUPLED VOLTAGE CONTROLLED OSCILLATOR WITH IMPROVED PHASE NOISE PERFORMANCE

摘要

A cross-coupled voltage controlled oscillator having reduced phase noise. A pair of bipolar transistors having common emitter connections are coupled to reduce that oscillation frequency which is determined from a tuning circuit connected across the collectors of transistors. First and second varactor diodes provide analog tuning of the circuit, and a digitally controlled capacitor provides for a selection of a band of frequencies to be tuned by the varactor diodes. A current source provides the current to the emitter connections of the bipolar transistors. Second harmonic signals generated at the emitter of the transistors are significantly suppressed by a tuned filtered trap connected to the common emitter connections. By reducing the second harmonic signals, the phase noise or the voltage controlled oscillator can be significantly improved.