Spaceborne MEMS atomic clock frequency stabilization system optimization and Exp
3.1 Modulator
The servo control system design, circuit, want to use 10 kHz sine signal as a modulation signal, so use RC oscillator circuit. Sine wave generator Signal 2 Road, a road used as a modulation signal, a road used as a demodulation signal. Wien oscillator using improved circuit RC sinusoidal oscillator signal to obtain the actual frequency of 9.79 kHz, 9.95 kHz with the theoretical difference between the 160Hz, amplitude adjustment range of 50 ~ 1 100 mV. Frequency and amplitude can meet the system design requirements.
3.2 Phase Shifter
Used mobile phase phase shift compensation, or inverting the signal processing. Need to achieve the range of 0 ° ~ 360 ° phase shift, and there are fine-tuning phase function. All-pass filter design, characterized by maintaining a gain of 1, adjust the time constant adjustable phase range. Figure 1 is a schematic diagram and the phase shifter phase shift curve. The transfer function is:
9.79 kHz to make the signal phase shift 90 °, phase shifter design parameters are as follows: R = 1.6 , R1 = 10 k , C = 10 nF; To achieve -90 ° phase shift, just to Figure 1a in R with C exchange. It is used with 90 ° phase shifter can achieve the same parameters -90 ° phase shift. 180 ° phase inverter can be used to achieve. Phase tuning can achieve all-pass filter to the one R or C can be replaced by adjustable devices. Keeping C constant, changes in the range of set R 1 ~ 7 k , to meet the range of -47 ° ~ 50 ° within the fine-tuning.
3.3 Phase Detector
Phase is controlled by analog multiplier and low pass filter structure, the signal can be detected by detecting the phase relationship with the reference signal is given and the corresponding phase error signal for adjusting the calibration device to use. Analog multiplier a variety of purposes, such as gain control, an additional gain to adjust for division, voltage controlled filter, phase detector and so on. Used here is the phase detector function. When Two sinusoidal signal input multiplier, by difference frequency, and frequency of two component signal. When the signal frequency is the same, filtered and the frequency signal, received difference frequency signal is a DC signal, reflecting the phase difference of two signals. Meanwhile, the phase difference is 0 ° or 180 ° when the DC signal by the maximum, which is to be increased to compensate for the phase shifter the phase error signal the best reason.
3.4 Calibrator
Calibration is controlled by PI controller, triangular wave generator, analog switch 3 parts, its role is to correct the phase error signal output, improve system speed and accuracy. When the laser beyond the locking range by outside interference, can automatically find the peak points, automatic locking. Functional requirements according to the setting, Figure 2 for the calibrator principle.
Figure 2, the error is zero is the role of regulation by the PI controller error signal output frequency discriminator calibration curve corresponds to zero and the center frequency. PI controller zero adjustment and gain amplifier circuit shown in Figure 3, where R1 = 2 k , R2 = 500 , R3 = 10 k , the gain A = 0.25 ~ 5.25.
PI controller is used to filter out high frequency noise, and low frequency signal amplification points. Accordingly, functional requirements, design as shown in Figure 4, the PI controller schematic.
The transfer function is:
Phase detector in the low-pass filter cutoff frequency of 200 Hz, so set the cutoff frequency for the Pl controller 200 Hz. After repeated experiments, select C1 = 220 nF, C2 = 15 nF, R1 = 30 k , R2 = 50 k .
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