Colpitts-type oscillator for high frequency application

Since broadband requires a staggering budget of information to transmit at high speed, it is important for the oscillator, as a frequency generator, to be high frequency and have high frequency stability. The best technique for frequency short-term stability is to use a resonator to oscillate directly at the fundamental. But the usual Colpitts oscillator is difficult to get plenty of negative resistance in the 600 MHz base band. Therefore, a PLL VCXO (voltage controlled crystal oscillator) or delay line type VCSO (voltage controlled SAW oscillator) is generally used to design the high frequency oscillator. However, the short-term frequency stability of these oscillators is worse than that of fundamental oscillation using a Colpitts oscillator. In this paper, we design the oscillator with two transistors, and suggest that the high frequency Colpitts oscillator can get plenty of negative resistance in the GHz frequency range. Furthermore, we build a 622.08 MHz VCSO with a SAW resonator, and confirm that the high frequency Colpitts oscillator could be of practical use.