Digital frequency synthesizer having selectable frequency offset between transmit and receive frequencies
AssigneeMotorola, Inc.
InventorL. J. Reed
Life of this patent
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Abstract
A digital frequency synthesizer includes a phase locked loop having dual presetting means for enabling the loop to generate a first frequency signal (e.g., "transmit" signal) for each of many selectable channels and generate a second frequency signal (e.g., "receiver" signal) in the form of the first frequency signal set off by an intermediate frequency (e.g., IF frequency) and programmable means for varying the frequency offset.
Claims4
In a frequency synthesizer of the type including a phase locked loop for providing a first frequency output or a second frequency output the frequency of which is set off from that of the first frequency output by an intermediate frequency, the improvement which comprises:
- presetting means for enabling said synthesizer to selectively generate one of the first and the second frequency outputs;
- and
- programmable means coupled to said presetting means for programmably setting the value of said intermediate frequency to any desired frequency within the capabilities of the frequency synthesizer.
A frequency synthesizer comprising:
- a forward path having a reference oscillator, a phase detector, a low pass filter and a voltage controlled oscillator connected in series;
- a feedback path coupled between said phase detector and an output of said voltage controlled oscillator, said feedback path including a programmable counter having a plurality of programming inputs and control means for setting the synthesizer to operate in a first mode and a second mode selectively;
- programming means having predetermined programming capabilities and coupled to the programming inputs of said programmable counter for programming substantially any desired first number, N.sub.1, and substantially any desired second number, N.sub.2, within the predetermined capabilities of said programming means;
- and
- means for enabling said programming means to set said programmable counter to said first number, N.sub.1, for enabling said synthesizer to generate a first frequency output equal to the output frequency of the forward path divided by N.sub.1 for the first mode of operation and to set said programmable counter alternately to the first number, N.sub.1, and the second number, N.sub.2, for enabling said synthesizer to generate a second frequency output signal the frequency of which is equal to the output frequency of the forward path divided by N.sub.1 plus N.sub.2 for the second mode of operation.
Dependencies are inferred from the claim text.