Apparatus and method for reducing oscillator frequency pulling during AM modulation
AssigneeItron, Inc.
InventorNormand T. Lemay
Life of this patent
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Abstract
The invention discloses an apparatus and method for reducing frequency pulling. Further, the invention provides amplitude modulation techniques to eliminate spurious signals and injection locking of the VCO to the output transmitted carrier. The architecture includes at least one synthesizer, a plurality of frequency dividers, an output VCO, a low pass filter, a mixer, a pretransmission filter and an amplifier connected in a manner to generate an output frequency which is non-harmonically related to the synthesizer VCO and to maintain the magnitude of the output frequency at, preferably, exactly 1.5 times higher than the VCO frequency.
Claims12
Apparatus for reducing frequency pulling of an output VCO involving AM modulation wherein the output frequency is structured to be larger than a synthesizer VCO frequency by a factor greater than unity to maintain a non-harmonic relation between the synthesizer and the output VCO, the apparatus comprising:
- a source for signals;
- the synthesizer for synthesizing said signals being in communication with a first frequency divider;
- a second frequency divider connected to the output VCO;
- a third frequency divider connected to said second frequency divider and further connected to said synthesizer;
- a mixer connected to the transmission side of the output VCO and further connected to the transmission side of said second frequency divider;
- a pretransmission filter connected to said mixer on the transmission side;
- and
- an amplifier connected to the pretransmission filter and further connected to a transmitter;
- the output frequency at said amplifier being non-harmonically related to the synthesizer VCO to thereby minimize frequency pulling during the AM modulation of the output VCO.
A frequency pulling reduction architecture implemented in an AM modulation process wherein spurious responses resulting from mixing products are eliminated, the architecture comprising:
- a frequency transmitter scheme having a 3/2 frequency output;
- a frequency synthesizer;
- and
- said frequency output being developed from a VCO for both said transmitter and being non-harmonically related to a VCO frequency of said synthesizer.
A method of reducing frequency pulling in an AM modulation process wherein spurious responses resulting from mixing devices are eliminated, the method comprising the steps of:
- generating a VCO output frequency equal to a value obtained from a source frequency conditioned by a plurality of frequency dividers and phase detectors;
- introducing said VCO output into a mixer;
- adding ½ of said VCO output into said mixer via one of said frequency dividers;
- introducing ½ of said VCO output into said synthesizer via one of said plurality of frequency dividers;
- and
- producing a frequency output equal to 1.5 times greater than said VCO output frequency at an output amplifier.
Dependencies are inferred from the claim text.