| 摘要 |
A charge pump circuit for a phase locked loop includes series-connected FETs in which a reference current flows and other series-connected FETs in which sourcing and sinking currents flow. The junctions of the two series-connected FETs are connected to the non-inverting and inverting input terminals of an operational amplifier. The amplifier detects the voltage difference between a reference side junction and the output voltage of the charge pump circuit and provides an amplified voltage of the detected voltage difference. In response to the amplified voltage, the charge pump circuit sources to and sinks current from an external circuit to which the charge pump circuit is connected. Due to the definite and high input impedance of the operational amplifier, there is no mismatch between the source and the sink currents. A start-up FET initializes the charge pump circuit so that current flows in the series-connected FETs.
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