Phase locked loop design with reduced VCO gain
Abstract:
A PLL includes a phase frequency detector (PFD) receiving an input signal and feedback signal, and producing a control signal. A charge pump receives the control signal and produces an initial VCO control. A loop filter generates a fine VCO control and intermediate output based upon the initial VCO control. A coarse control circuit includes an integrator having a first input receiving the intermediate output, a second input, and generating a coarse VCO control, a first switch coupling a reference voltage to the second input, a buffer buffering output of the integrator, and a second switch coupling output of the integrator to the second input of the integrator. A VCO receives the fine VCO control and the coarse VCO control, and generates an output signal having a frequency based thereupon. A feedback path receives the output signal and produces the feedback signal.
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