Filtering device for use in a phase locked loop controller
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United States of America Patent
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Jun 13, 1995
Grant Date -
N/A
app pub date -
Dec 22, 1993
filing date -
Dec 22, 1993
priority date (Note) -
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status (Latency Note)
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Abstract
A phase lock loop (PLL) frequency synthesizer is used in a radiotelephone to provide a reference frequency to a transmitter or a receiver. This particular PLL frequency synthesizer has a wide bandwidth control loop having a high current charge pump (417) and a narrow bandwidth control loop having a low current charge pump (411). A deadzone circuit (413) is used at an output of a phase detector (405) to control the application of an error signal to the high current charge pump (417). Additionally, the PLL frequency synthesizer utilizes a loop filter (419). The loop filter (419) receives two correction signals (409', 415') and provides a single control signal for the VCO (voltage controlled oscillator) (423). The loop filter contains two time constants formed from resistive and capacitive elements. The two time constants control the bandwidth of the two control loops.
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