1 [GHz] high frequency Colpitts oscillator

As progress in the information and communication infrastructure toward the broadband network, rapid and accurate transmission of vast amounts of data is required. In accordance with it, the crystal oscillator as a frequency generator is required to improve the frequency short-term stability as well as to achieve higher frequency. The frequency short-term stability can be specified with two domains, one is time-domain and the other is frequency domain. Each domain is used according to application and condition as below; time domain: Allan variance, TDEV, jitter; frequency domain: phase noise. In the past, the crystal oscillator using PLL was popular for the high frequency oscillator. But since the oscillator using PLL multiplies frequency, it deteriorates jitter characteristics by the influence of spurious at the fundamental oscillation and it could result in causing bit error in the equipment. In order to improve the frequency short-term stability, we think that the best way is a fundamental oscillation by the Colpitts circuit. However, a conventional Colpitts circuit could not get a sufficient negative resistance in higher frequency range more than 600 [MHz] bandwidth. In this paper, we suggest that such the high frequency Colpitts oscillator can get a sufficient negative resistance even in [GHz] bandwidth. In addition, we report the efficiency of our high frequency Colpitts oscillator, which was confirmed by measurement with prototype of VCSO at 1 [GHz] using the SAW resonator.