| 摘要 |
The switching time of a phase-locked loop (PLL) circuit can be reduced by increasing circuit bandwidth. A charge pump system is commonly used in the PLL circuitry to drive the voltage control oscillator (VCO) (113). The increase in bandwidth intensifies the noise that is contributed by the charge pump system. To reduce charge pump noise, a chopper stabilizer circuit (301a, 301b, 303) modulates the noise to a sufficiently high frequency so that a low-pass filter (109) may filter out the modulated noise. The chopper stabilizer may be implemented using two multiplexers (301a, 301b) that are controlled by a switch (303). One multiplexer (301a) may be coupled e.g. between the phase comparator (105) and a charge pump (107). When triggered by the switch (303), multiplexer (301a) swaps the output signals of the phase comparator and the second multiplexer (301b) serves to reorient the outputs modified by the reversal of inputs by the first multiplexer (301a).
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