Wide range frequency synthesizer with quadrature generation and spur cancellation

摘要

A frequency synthesizer generates a wide range of frequencies from a single oscillator while achieving good noise performance. A cascaded phase-locked loop (PLL) circuit includes a first PLL circuit with an LC voltage controlled oscillator (VCO) and a second PLL circuit with a ring VCO. A feedforward path from the first PLL circuit to the second PLL circuit provides means and signal path for cancellation of phase noise, thereby reducing or eliminating spur and quantization effects. The frequency synthesizer can directly generate in-phase and quadrature phase output signals. A split-tuned ring-based VCO is controlled via a phase error detection loop to reduce or eliminate phase error between the quadrature signals.

主权项

1. A circuit comprising:
a first phase-locked loop circuit to receive a reference signal having a first frequency and generate an intermediate signal having a second frequency; a feedforward circuit to receive a control signal from the first phase-locked loop circuit and generate a feedforward signal; and a second phase-locked loop circuit to receive the intermediate signal having the second frequency and the feedforward signal, and generate an output signal having a third frequency based on the intermediate signal and the feedforward signal.