Frequency synthesiser with output frequency higher than VCO frequency

摘要

A frequency synthesiser comprises an oscillator 43, for example a numerically controller oscillator, for generating a first signal. An edge combiner 45 is provided for generating a second signal derived from the first signal, for example using two or more tap signals from the oscillator, the second signal having a frequency that is greater than that of the first signal. A detector 33 receives an input reference signal Fin and a feedback signal 35, and generates an output signal 37 that is used to provide an input to the oscillator, such that the oscillator operates in a locked loop mode of operation. The feedback signal to the detector is taken from the output of the edge combiner 45 rather than directly from the output of the oscillator, thus compensating for errors introduced by the edge combiner 45. The feedback signal may also pass through a divider 36. The frequency synthesiser may also include a sigma-delta modulator (47, fig.4) which is clocked by either the first signal or the second signal depending on power requirements. Keywords: synthesizer, synthesizer, edge combiner, frequency multiple.