| 摘要 |
A phase locked loop provides frequency modulation over an extended frequency range by summing a modulation signal with the loop signal at two separate points within the loop. The modulation signal is directly applied to the control input terminal of the voltage controlled oscillator. In addition, the modulation signal is processed to compensate for the transfer functions of loop components, and the processed signal is summed with the loop signal at an additional point between the output terminals of the phase detector and the lowpass filter of the loop. The processing of the modulation signal consists of preshaping of the signal to compensate for the transfer functions of loop circuitry located between the voltage controlled oscillator and the summing junction.
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