Phase modulator having individually placed edges

Abstract

A phase modulator circuit and method for generating an output signal having individually positionable edges is described. The phase modulator includes a programmable pulse generator, such as an interval counter, a delay, or a ring oscillator for producing the output signal, and a control value source, such as a memory, for delivering a sequence of control values to the generator. The control values determine the time between successive output pulses. A programmable interval counter includes a free running counter, the output of which is compared to a control value, preferably stored as a modulo data value, to generate an output pulse. A first programmable delay circuit includes a ring oscillator having plural delay lines for fine control of edge positioning. To fully synchronize the delay circuit to a coarse control interval counter, the clock input to the interval counter can be provided by the ring oscillator. A second programmable delay circuit uses interpolation to achieve finer resolution between time positions. The interval counter can be combined with the first and second delay circuits to achieve coarse, fine, and very fine resolution, respectively in a phase modulator.