| 摘要 |
The invention provides an apparatus and method for calibrating both the pole/zero locations and the gain of a charge pump phase-locked loop's (PLL's) frequency response with one calibration operation. In one embodiment, the calibration is performed using a bandgap voltage reference and a stable frequency reference in order to measure a slew rate (I/C), defined as a current-to-capacitance ratio, and then adjusting the RC time constant (tRC) by adjusting the capacitance value. The adjustment setting is used in the loop filter capacitors, thereby calibrating the pole and zero locations of the PLL, which depend on the RC product. The charge pump reference current is proportional to the ratio of the bandgap voltage to the resistor value. When the capacitance is adjusted, the slew rate is calibrated as well, wherein the slew rate represents a portion of the loop gain of the PLL.
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