Charge pump phase locked loop with improved power supply rejection
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United States of America Patent
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Nov 8, 2005
Grant Date -
Sep 8, 2005
app pub date -
Mar 3, 2004
filing date -
Aug 29, 2003
priority date (Note) -
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status (Latency Note)
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Abstract
A phase lock loop circuit (60) has a phase frequency detector (62), a charge pump (64), an active filter (87) and a voltage-controlled oscillator (100). The phase detector generates signals responsive to reference signal FR and VCO output signal FV. A charge pump generates a voltage at the input of a first transmission gate (76) according to the values of the phase detector signals. A predetermined voltage is generated at the input of a second transmission gate (112). When the transmission gates (76, 110) are closed (low impedance) the charge pump may sink or source current to the inverting input of the operational amplifier (86) of the active filter 86 and the predetermined voltage is applied to the non-inverting input. When the transmission gates are open (high impedance state) the inverting input is electrically isolated from the node and the non-inverting output is isolated from the power supply.
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