| 摘要 |
A phase lock loop for use in carrier acquisition employing a predetection filter and a loop filter switchable between a constant phase margin and second order characteristic. In the acquisition mode, the constant phase margin characteristic is employed to acquire the carrier and the second order characteristic is thereafter employed to track the carrier. The second order characteristic retains only the pole at the origin and the lowest frequency zero of the constant phase margin characteristic. The filter parameters are selected to minimize the mean square deviation of a phase margin expression which includes contributions from the predetection filter pole and from positive poles generated by the loop's voltage controlled oscillator. The loop filter is further provided with gain coefficients selected to maximize the probability of carrier acquistion at a plurality of frequencies and carrier to noise density ratios.
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