| 摘要 |
Methods and circuits for synthesizing two or more signals phase-locked to a common reference frequency signal are disclosed. In one embodiment, a method comprises generating first and second output signals phase-locked to a reference clock signal, using first and second phase-locked loop circuits. In response to a detected frequency error in the first output signal, the first output signal is corrected by adjusting a frequency-division ratio in the first phase-locked loop circuit. The second output signal is corrected, separately from the correction to the first output signal, by adjusting a frequency-division ratio in the second phase-locked loop circuit, using an adjustment parameter calculated from the detected frequency error. In another exemplary method, first and second output signals are generated as described above, using first and second phase-locked loop circuits. The first output signal is corrected by adjusting a frequency-division ratio in the first phase-locked loop circuit and generating a control signal to adjust the frequency of the reference clock signal, in response to detected frequency error in the first output signal. Because the second output signal is derived from the common reference clock signal, adjustments to the reference clock frequency will also adjust the frequency of the second output signal. Additional adjustments to the second output signal may be applied in some embodiments by adjusting a frequency-division ratio in the second phase-locked loop circuits. Circuits for implementing the described methods are also disclosed.
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