Studies And Designs On Hardware Circuits Of CPT Atomic Frequency Standard

The physical package of the passive coherent population trapping (CPT) atomic frequency standard, since it is free of cavity, can be minimized into chip-scale. A chip-scale atomic frequency standard can be realized with a chip-scale physical package and the corresponding miniature circuits. In principle, the CPT atomic frequency standard is presently the only atomic clock which can be manufactured into wristwatch size and supplied by button battery. In order to realize chip-scale atomic frequency standard, both servo and microwave circuits need to be minimized, this master thesis presents my works on exploiting the miniature circuits, and the experimental results with the realized circuits.In the work, Digital Signal Processor (DSP) was chosen for the digital servo on the consideration of its strong and high-speed ability of data processing. The corresponding works consist of hardware and software parts. The hardware circuit is mainly composed of photo-detection, current-voltage transition and amplification, DSP periphery circuits, analog-digital converter (ADC), bi-channel digital-analog converter (DAC), crystal oscillator, phase-locking loop (PLL), voltage-controlled oscillator (VCO), etc. The functions of software include digital filter, digital demodulation, sweeping and locking, controls of ADC and DAC, control of PLL, external modulation, digital thermal control, constant current for magnetic field generation, etc. Certain functions which are usually realized by analog circuits are realized by digital ones in the DSP scheme, therefore size of the realized circuit is reduced, and flexibility is increased. At the same time the power dissipation of the circuit is basically kept at the same level, although it increases slightly.We have also studied the minimization of the microwave circuit through approaches of Dielectric Resonator Oscillator (DRO) and Step Recovery Diode (SRD) microwave frequency-multiplier. DRO can directly supply the microwave with frequency satisfying physics package, whereas SRD microwave frequency-multiplier generates the required frequency by multiplying the output frequency of a crystal oscillator. The DRO circuit We realized is consisted of three modules:direct current (DC), resonance network, amplification and matching network. Before realizing the circuit, each one was first simulated with Advanced Design System (ADS), followed by simulation of the DRO circuit. The obtained circuit is with the size of40mm x50mm and power dissipation of about37mW. The measured results reveal that this DRO circuit generates3.4GHz microwave with power of-4dBm, satisfying the requirement of the physics package.Through practice on DRO circuit We had accumulated knowledge about the microwave circuits, and then We moved on SRD frequency-multiplier scheme. The SRD frequency-multiplier We realized mainly includes input matching, SRD, and resonance and filter modules. The process was also through first simulating individual modules then simulating the circuit, and followed by realizing the circuit according to the simulation results. The obtained circuit is with the size of20mm×10mm, and the measured results reveal that with a569.5MHz and6dBm input microwave signal, it provides the wanted3417MHz microwave signal with power of-9dBm, also satisfying the requirement.The both exploited microwave generation schemes provide required3417MHz microwave for physics package of the CPT atomic frequency standard. The realized circuits are both with low power consumption, small size and simple structure, which make them the ideal candidates for the miniature CPT atomic frequency standard. However, the circuits of both schemes do not directly output a standard signal of10MHz, which are usually required by electronic devices. Therefore, if the standard out frequency is needed, an additional module needs to be added to the realized atomic standard for converting the exist frequency to the standard one.