| 摘要 |
A frequency synthesizer includes a controlled oscillator which is responsive to a frequency control input signal, to generate an output frequency. A programmable frequency divider is responsive to the output frequency and to a divider control input, to divide the output frequency by a first integral ratio or by a second integral ratio in respons e to the divider control input, to thereby produce a divided signal. A phase comparator is responsive to areference frequency signal and to the divided signal, to compare the reference frequency signal and to the divided signal, and thereby produce a first error signal. A sigma deltamodulator is responsive to a modulation input to produce the divided control input. A loop filter is responsive to the first error signal , to thereby produce the frequency control input signal. Ripple compensation signals and direct modulation signals may also be provided, to provide three-point modulator for a frequency synthesizer. Analog and digital embodiments may also be provided.
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