Patent ID: 6825729
Filing Date: 2004-11-30
Classification: G06F,H03L,H03M

Abstract:
A frequency synthesizer, which transforms a digital input signal at a first frequency to a digital output signal at a second frequency, comprising:a phase detector having first and second inputs and an output, with the first input receiving the digital input signal; a filter to receive the output from phase detector and produce an output signal; a voltage controlled oscillator driven by the output signal of the filter to produce the digital output signal; and a digital synthesizer to transform the digital output signal to a signal at a third frequency, which is fed back to the second input of the phase detector for the phase detector to compare the phase of the signal at the third frequency with the phase of the digital input signal, the digital synthesizer comprising: a first sigma-delta modulator; and a digital oscillator supplied with the digital output signal to drive the first sigma-delta modulator, the digital oscillator comprising a series circuit of a second sigma-delta modulator and a digital integrator.