| 摘要 |
A circuit for generating an output signal having an output frequency that varies linearly with time, and to an FM CW radar system utilizing such a circuit. The circuit includes a voltage controlled oscillator that produces an output signal at its output terminal at an output frequency that corresponds to the voltage of an input tuning signal. A comparison signal circuit receives the output signal and produces a periodic comparison signal such that when the output frequency varies by DELTA f, the comparison signal frequency varies by DELTA f/N where N is a positive integer. An update counter periodically causes the value of N to change by a predetermined integer amount. A phase detector compares the comparison signal to a periodic reference signal, and produces a correction signal that is filtered to provide the tuning signal for the VCO. The value of N is preferably changed at an update frequency that is equal to the frequency of the reference signal times an integer. The comparison signal circuit preferably includes a local oscillator for converting the output signal into a periodic IF signal for input to a divider. A high side local oscillator is preferred to minimize loop gain variation with frequency.
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