| 摘要 |
A testing circuit and method for a phase-locked loop allow measurement of leakage currents in the phase-locked loop components. By forcing the output of the phase-frequency detector to a particular state, the charge pump can be disabled. This disables the effect of feedback in the phase-locked loop, and allowing the output frequency to be determined by the voltage on the control voltage node at the time the feedback is disabled. If there is no leakage, the control voltage, and therefore the output frequency, should remain the same as they were at the moment feedback was disabled. Monitoring the output frequency for changes provides an indication of the presence or absence of leakage. Conducting the test using two different charge pump reference currents allows one to detect leakage resulting from charge pump mismatch.
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