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TDMA mobile unit frequency synthesizer having power saving mode during transmit and receive slots

  • US 5,541,929 A
  • Filed: 01/24/1995
  • Issued: 07/30/1996
  • Est. Priority Date: 04/10/1992
  • Status: Expired due to Fees
First Claim
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1. A frequency synthesizer of a mobile unit for a time division multiple access (TDMA) cellular communication system, said system having a plurality of cell sites each being assigned a channel of unique frequency for carrying a TDMA frame having a sequence of receive and transmit slots and at least one idle slot, comprising:

  • a reference pulse source for generating a train of reference pulses;

    a phase comparator for generating a phase difference signal indicative of the phase difference between two input signals applied thereto;

    a switched filter bank comprising a plurality of loop filters each of said loop filters having a unique cutoff frequency;

    selector means for selecting one of the loop filters in response to a channel selection signal;

    switch means for establishing a connection between the output of said phase comparator and the selected loop filter in response to a close-loop command signal to cause the selected loop filter to develop a voltage according to said phase difference signal and clearing said connection in response to an open-loop command signal, wherein the voltage developed in the selected loop filter is maintained after said connection is cleared and is maintained when another loop filter is selected;

    a voltage-controlled oscillator connected to the selected loop filter for generating an output signal at a frequency corresponding to the voltage developed by the selected loop filter;

    a frequency divider connected to said voltage-controlled oscillator for producing an output pulse at a submultiple of an output frequency of the voltage-controlled oscillator;

    a phase alignment circuit for establishing initial phase alignment between an output pulse from said frequency divider and a reference pulse from said reference pulse source in response to an enable signal applied thereto and applying the phase-aligned signals to said phase comparator as said two input signals; and

    control means for causing the mobile unit to scan a different one of the plurality of cell sites during each of a plurality of idle slots and to return to a receive or transmit frequency during the respective receive and transmit slots by providing a series of channel selection signals which alternately select between one of the plurality of loop filters during an idle slot and a loop filter which corresponds to the receive or transmit frequency during the respective receive and transmit slots so that a different one of the plurality of loop filters is selected for each of a plurality of successive idle slots by generating said open-loop command signal during said receive and transmit slots of the TDMA frame, and generating said close-loop command signal, said enable signal and said channel selection signal during the idle slot of the TDMA frame, and for deactivating said reference pulse source during said receive and transmit slots and activating said reference pulse source during said idle slot of the TDMA frame.

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