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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.

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First Claim