Multiple pll system with phase locking and phase noise cancellation

Abstract

An integrated, distributed, multiple Phase Locked Loop (multi-PLL) system locks the frequency and phase of multiple secondary PLLs to that of a primary PLL. The VCOs in all PLLs receive both first and second control signals. The primary PLL's primary VCO control signal is generated conventionally. using a reference periodic signal input, and is output to all secondary PLLs: hence the secondary PLLs operate at the primary PLL frequency. The primary PLL also outputs its divided periodic signal. Each secondary PLL compares its local divided periodic signal to the one received from the primary PLL (rather than to a reference signal input) in its phase locking loop. generating a secondary VCO input that locks the secondary PLL circuit phase to that of the primary PLL circuit. Selected secondary PLLs can be set to a phase offset from the primary PLL, such as by controlled DC current injected into the charge pump output. Phase noise generated by the primary PLL VCO is detected and corrected by one or more secondary PLLs in a second charge pump circuit that outputs a correction current having an inverse polarity. The correction currents are summed, and a correction loop filter generates a third VCO control signal which is provided to the second primary VCO input to correct the phase noise. Either the charge pumps scale output current (1/N) or the correction loop filter scales impedance (1/N) to account for the number (N) of secondary PLLs generating correction currents. A common mode voltage circuit may monitor selected VCO control signals of all PLLs. and maintains the common mode input level within a predetermined voltage range.