Spread spectrum code tracking loop

Details Spread spectrum code tracking loop Spread spectrum code tracking loop

1978-02-28

1981-08-18

Birmiel, Howard A.

Pulse or digital communications

Repeaters

Testing

375120, 455304, H04B 1510

Patent

active

042850606

ABSTRACT:
A code tracking loop for a spread spectrum receiver includes a pair of mixer circuits to which phase offset or relatively delayed pseudo noise code signals are applied and combined with an incoming IF spread spectrum signal. The output of the mixers are coupled to a sum and difference hybrid. The hybrid produces a sum signal corresponding to the sum of the mixer outputs and a difference signal corresponding to the difference between the mixer outputs. These sum and difference signals are separately filtered, amplified and then coupled to a further mixer or phase detector. Appropriate AGC circuitry is controlled by the envelope of the sum signal to adjust the gains of the respective amplifiers. The output of the phase detector is proportional to the difference between the squares of the outputs of the hybrid and represents the phase of the sum signal relative to the difference signal. This phase-representative signal is coupled through a tracking loop filter to control the voltage controlled clock for the local PN code generator. A significant advantage of the inventive system is that even if the gains of the separate channels are not equal, this gain difference does not erroneously affect the output of the phase detector.

REFERENCES:
patent: 3646446 (1972-02-01), Rittenbach
patent: 3745255 (1973-07-01), Fletcher
patent: 4017798 (1977-04-01), Gordy
patent: 4038540 (1977-07-01), Roberts
patent: 4041391 (1977-08-01), Deerkowski
patent: 4053834 (1977-10-01), Lerner
patent: 4123718 (1978-10-01), Lampert et al.

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