Design Of Coaxial Resonator Based Low Phase Noise Voltage-controlled Oscillators For The Atomic Clocks

The atomic clock can be approximated as a signal generator outputing reference frequency in the working mechanism.With the development of society,there is a growing demand for the miniaturization of the atomic clock.The Coherent Population Trapping?CPT?phenomenon can make the atomic clock to to develop in the direction of low power consumption and small size.The physical system of the atomic clock can be designed into chip-level size theoretically by the CPT phenomenon.The atomic clock system needs a adjustable oscillation signal,which is used to obtain the peak signal of CPT by the small step scanning in the working frequency accessory,and finally realize the closed-loop locking of the atomic clock.Therefore,microwave signal source with low power consumption,small size and low phase noise is very important.Due to the existing voltage-controlled oscillator?VCO?is based on LC resonant circuit with low quality factor,the phase noise can not reach low enough.So,the direct use of VCO can not meet the requirements of atomic clock,and the microwave signal source used internally in the atomic clock is output by the VCO through the phase-locked loop?PLL?.However,the PLL is not conducive to the miniaturization of atomic clock because it will increase the corresponding size and power consumption.Based on this,this thesis developed a kind of VCO which can be directly used for internal system of the atomic clocks.In order to obtain the sufficiently low phase noise,a medium cavity coaxial resonator with high quality factor is applied as a key component of the resonant circuit in the design.According to the corresponding indexs,the size should be less than 1cm²,the power consumption should be less than 30mW,the output power should be higher than-3dBm and the phase noise should be better than-43dBc/Hz@300KHz.In addition,the VCO should oscillate at the operating frequency of the atomic clock and have a good ability to control the frequency.The main work of this paper includs three parts.First,the paper provides a theoretical guidance for the design of VCO according to the introduction of the principles of the oscillator and the parameter extraction and modeling of the key components,particularly the customized coaxial resonater and variode in the paper,provide a guarantee of reliability for the circuit simulation design.Then,the paper designs two kinds of VCOs for ⁸⁵Rb atomic clocks and ¹³³Cs atomic clocks respectively.The start-up process of the oscillator is simulated by the negative resistance analysis method.Based on the oscillation,the transmission analysis method with a virtual ground and the Nyquist stability criterion are used to observe the oscillation circuit and analyze the stability.Then the corresponding circuit structure and simulation results can be best by optimizing the parameters of the components.On the basis of the simulation,the physical design,welding and debugging are carried out.The VCO using for the ⁸⁵Rb atomic clock can get a stable oscillation near the frequency of 3.035GHz and the frequency can be changed according to the controlling voltage,the size is 0.86cm²,the power consumption is less than 28mW,the output power is1.13dBm and the phase noise is-60.49d Bc/Hz@300KHz.The VCO using for the ¹³³Cs atomic clock can get a stable oscillation near the frequency of 4.596GHz and the frequency can be changed according to the controlling voltage,the size is 0.83cm²,the power consumption is less than 28mW,the output power is-0.84dBm and the phase noise is-44.99dBc/Hz@300KHz.So,the performance of the designed VCOs can meet all the design requirements.