A high frequency cascode oscillator with negative resistance enhancement circuit and its analysis

We have proposed a cascode piezoelectric oscillator circuit with negative resistance enhancement circuit for the use in the frequency range from 100 MHz to 1GHz. The proposed oscillator is composed of a cascode oscillator and a two-stage common-emitter amplifier. The amplifier picks up the signal from the emitter of the oscillator transistor and feeds back the amplified and phase-shifted signal to the base of the oscillator transistor by small capacitance. We have derived the approximate equation of negative resistance and showed the mechanism of the negative resistance enhancement. The proposed oscillator circuit is designed at 311 MHz, 622 MHz and 1GHz and its frequency dependence of the negative resistance is evaluated by simulation. Simulation has shown that sufficiently large negative resistance can be obtained compared to the usual Colpitts oscillator. The steady-state oscillation is simulated at 622 MHz and pure sinusoidal output of magnitude 1V is obtained