Design of a VCO for rubidium atomic frequency standard

The rubidium atomic clock based on coherent population trapping (CPT) has advantages of low power consumption, small size and quick start-up. It is potential to be applied in many fields of science. The rubidium atomic clock requires a microwave signal source whose center frequency is 3.417GHz (half of the rubidium atomic hyperfine energy difference) with the ability to be tuned during a certain frequency range. A transistor with high cut-off frequency and low noise figure is selected in this design to constitute the amplifier circuit. At the emitter of the transistor, a varactor and other components are used to make up the resonance circuit. The circuit parameters are optimized by using the negative resistance analysis method to meet the power and phase noise requirements. Finally, a voltage controlled oscillator (VCO) based on the rubidium atomic frequency standard is designed. The frequency is 3.417GHz, the phase noise is -53dBc/Hz@1kHz, and the output power is about 1.4dBm. By adjusting the reverse DC bias voltage of the varactor between 0V and 2.5V, the output frequency varies about 100MHz.