Spread spectrum signal demodulation circuit
First Claim
1. A spread spectrum demodulation circuit, comprising:
- a variable frequency oscillator a frequency of which is changed in accordance with a control signal as applied;
PN code generating means for generating a demodulation PN code by using an oscillation signal of said variable frequency oscillator as a clock thereof;
multiplying means for multiplying an input spread spectrum signal and said demodulation PN code;
filter means for receiving an output of said multiplying means;
first holding means for holding a first value associated with an output of said filter means at a first time;
second holding means for holding a second value associated with the output of said filter means at a second time later than said first time;
comparing means for comparing said first value and said second value being respectively held in said first holding means and said second holding means; and
controlling means for outputting said control signal in accordance with an output of said comparing means to control said variable frequency oscillator so that said demodulation PN code from said PN code generating means can be synchronized with a modulation PN code included in said input spread spectrum signal.
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Abstract
A spread spectrum signal demodulation circuit includes a multiplier which multiplies an input spread spectrum signal by a demodulation PN code, and a demodulation PN code generator generates the demodulation PN code by utilizing an oscillation signal from a VCO as a clock signal thereof. An output of the multiplier is given to a bandpass filter and an output of which is integrated by an integration circuit. A first integrated value for a first time is compared with a second integrated value for a second time later than the first time and, in accordance with a comparison result, a frequency of the oscillation signal of the VCO is changed so that the demodulation PN code is synchronized with a modulation PN code included in the input spread spectrum signal.
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Citations
7 Claims
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1. A spread spectrum demodulation circuit, comprising:
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a variable frequency oscillator a frequency of which is changed in accordance with a control signal as applied; PN code generating means for generating a demodulation PN code by using an oscillation signal of said variable frequency oscillator as a clock thereof; multiplying means for multiplying an input spread spectrum signal and said demodulation PN code; filter means for receiving an output of said multiplying means; first holding means for holding a first value associated with an output of said filter means at a first time; second holding means for holding a second value associated with the output of said filter means at a second time later than said first time; comparing means for comparing said first value and said second value being respectively held in said first holding means and said second holding means; and controlling means for outputting said control signal in accordance with an output of said comparing means to control said variable frequency oscillator so that said demodulation PN code from said PN code generating means can be synchronized with a modulation PN code included in said input spread spectrum signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification