Means and method for maintaining synchronization of a spread spectrum or other receiver clock
First Claim
1. A system for locally generating a clock signal in synchronization with a received input signal and for maintaining such synchronization during a temporary loss of said input signal, said system comprising:
- first oscillator means responsive to said input signal for supplying a clock signal to be synchronized with said input signal;
second oscillator means having a greater free running frequency stability than that of said first oscillator means;
means for determining whether or not said clock signal is synchronized with said input signal;
means responsive to said clock signal and input signal being synchronized for causing said second oscillator means to supply an output signal synchronized with said clock signal; and
means responsive to said clock signal and input signal not being synchronized for causing said first oscillator means to supply said clock signal in synchronization with said second oscillator means output signal.
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Accused Products
Abstract
A system for synchronizing a clock signal generated by a lower stability clock generator to a received incoming signal whereby a higher stability clock generator is synchronized to the lower stability clock generator when the clock signal is synchronized to the incoming signal, and the lower stability clock generator is synchronized to the higher stability clock generator when the incoming signal is lost. More specifically, in a spread spectrum receiver for receiving a signal phase modulated by a pseudo-random code, a means for synchronizing a receiver pseudo-random code generator to the incoming code modulation is provided. The code generator is clocked by a relatively low stability voltage controlled crystal oscillator (VCXO) whose output frequency is controlled by an error signal created by a phase difference between the received code modulation and the output of the pseudo-random code generator. As the low stability VCXO tracks the code modulation, a high stability VCXO is provided to track in frequency and phase the low stability VCXO. If the incoming signal is lost, the high stability VCXO is configured to hold its frequency and phase and to control the frequency and phase of the low stability VCXO, thereby tending to retain the same phase and frequency relationship with respect to the modulation as was present when signal was lost.
31 Citations
18 Claims
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1. A system for locally generating a clock signal in synchronization with a received input signal and for maintaining such synchronization during a temporary loss of said input signal, said system comprising:
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first oscillator means responsive to said input signal for supplying a clock signal to be synchronized with said input signal; second oscillator means having a greater free running frequency stability than that of said first oscillator means; means for determining whether or not said clock signal is synchronized with said input signal; means responsive to said clock signal and input signal being synchronized for causing said second oscillator means to supply an output signal synchronized with said clock signal; and means responsive to said clock signal and input signal not being synchronized for causing said first oscillator means to supply said clock signal in synchronization with said second oscillator means output signal.
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2. A system for maintaining synchronization of a clock signal with an incoming signal comprising:
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a first oscillator having an output clock signal to be synchronized with said incoming signal; means for controlling the frequency of said first oscillator by said incoming signal; a second oscillator having a more stable free-running frequency stability than said first oscillator; first means for causing said second oscillator to track said first oscillator when said incoming signal is phase synchronized with said output clock signal; and second means for causing said first oscillator to track said second oscillator when said incoming signal level is below a predetermined threshold level. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. In a spread spectrum receiver, a means for maintaining a clock signal in phase synchronism with a code modulated on a received carrier signal, comprising:
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a first clock signal generator; a code generator having a coded output signal corresponding to said modulated code and whose phase and frequency is controlled by said first clock signal generator; first means for controlling said code generator by said first clock signal generator so that said code generator coded output signal has a predetermined phase relationship with respect to said modulated code when said first clock signal generator is phase synchronized with said modulated code; a second clock signal generator having a more stable free-running frequency stability than said first clock signal generator; means for controlling the frequency of said second clock signal generator by said first clock signal generator when said code generator is phase synchronized with said modulated code; and second means for controlling the frequency of said first clock signal generator by said second clock signal generator when said carrier signal level is below a predetermined threshold level. - View Dependent Claims (13, 14)
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15. A method for maintaining synchronization of a first oscillator with an incoming signal comprising the steps of:
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controlling the frequency of said first oscillator by said incoming signal when said incoming signal is phase synchronized with said first oscillator; controlling the frequency of a second oscillator having a more stable free-running frequency stability than said first oscillator by said first oscillator when said incoming signal is phase synchronized with said first oscillator; and controlling the frequency of said first oscillator by said second oscillator when said incoming signal level is below a predetermined threshold level. - View Dependent Claims (16, 17, 18)
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Specification