Linearization technique for phase locked loops employing differential charge pump circuitry

摘要

A differential linear fractional N-synthesizer includes a phase and frequency detection module, a linearized charge pump, a low pass filter, a voltage controlled oscillator, and a fractional N divider feedback. The phase and frequency detection module is operably coupled to produce a differential charge-up signal, a differential charge-down signal, or a differential off signal based on phase and/or frequency differences between a reference oscillation and a feedback oscillation. The feedback oscillation is generated by the fractional N divider feedback, which divides an output oscillation by a divider value to produce the feedback oscillation. The linearized charge pump includes a 1^st current source, a 2^nd current source and a modulation module. In response to the differential off signal, the modulation module produces a modulated differential off signal that causes the 1^st and 2^nd current sources to produce a zero current signal in an alternating fashion. The low pass filter is operably coupled to attenuate the high frequency signal components produced by the modulation module of the linearized charge pump and to pass the positive, negative or zero current signals to produce a filtered signal. The voltage control oscillator produces the output oscillation based on the filtered signal.