PLL frequency synthesizer with multi-curve VCO implementing closed loop curve searching

摘要

A phase-locked loop circuit using a multi-curve voltage-controlled oscillator (VCO) having a set of operating curves, each operating curve corresponding to a different frequency range over a control voltage range. The phase-locked loop circuit includes a digital control circuit configured to generate a curve select signal using a closed loop curve search operation to select one of the operating curves in the multi-curve VCO, the selected operating curve being used by the VCO to generate an output signal with an output frequency being equal or close to a target frequency of the phase-locked loop. In one embodiment, the digital control circuit implements a binary jump method and an operating curve is selected when the operating curve has an output frequency meeting the target frequency with the control voltage being within a first voltage range being a narrowed and centered voltage range within the control voltage range.

主权项

1. A phase-locked loop circuit using a multi-curve voltage-controlled oscillator (VCO) having a plurality of operating curves, each operating curve corresponding to a different frequency range over a control voltage range, the phase-locked loop configured to receive an input signal having a reference frequency and to generate a control voltage to control the multi-curve VCO to generate an output signal using the one of the plurality of operating curves, the output signal having a fixed relation to the phase of the input signal, the phase-locked loop circuit comprises:
a digital control circuit configured to generate an n-bit curve select signal using a closed loop curve search operation to select one of the plurality of operating curves in the multi-curve VCO where the plurality of operating curves include 2n operating curves and n is an integer greater than zero, the selected operating curve being used by the VCO to generate an output signal with an output frequency being equal or close to a target frequency of the phase-locked loop, wherein the digital control circuit implements a binary jump method for choosing one or more operating curves from the plurality of operating curves to search for the selected operating curve, the digital control circuit generates the curve select signal to select one of the one or more operating curves as the selected operating curve when the operating curve has an output frequency meeting the target frequency with the control voltage being within a first voltage range being a narrowed and centered voltage range within the control voltage range; and wherein the digital control circuit implements the binary jump method to choose the one or more operating curves by changing the logical state of a subset of q bits of the n-bit curve select signal, q being an integer between 1 and less than n−1, the subset of q bits of the curve select signal being selected starting from the most significant bit of the n-bit curve select signal to the least significant bit of the n-bit curve select signal over successive searches using the binary jump method.