Abstract: A global positioning system (GPS) receiver includes a phase locked loop that locks to the carrier signal from the GPS satellite at an offset frequency in order to recover the GPS data. The loop includes a phase shifter driven by a system clock through a synchronous clock inversion circuit. The phase of the system clock is periodically inverted synchronously with respect to the clock in order to compensate for the offset loop frequency so that the loop does not lose lock because of the offset error.

Abstract: A Long Loop GPS receiver converts the pseudo random noise code bi-phase modulated input signal to a first IF frequency. The first IF is correlated against a duplicate of the pseudo random noise code that modulates the input signal. The correlator output is converted to a last IF having a frequency of one-half the pseudo random noise code sequence repetition rate. Local oscillator leakage into the receiver input is spread in spectrum by the correlator into spectral lines that do not lie on the received signal. A bandpass filter in the last IF removes the leakage spectral lines. A hard limiter converts the last IF to digital format. A digital phase detector adjusts the local oscillator to lock the local oscillator signal to the receive signal. The correlator pseudo random noise code signal is clocked by the local oscillator.

Abstract: A high-accuracy phase comparison system for noise-contaminated fixed-frequency input signals, such as Omega radionavigation signals, employs a pair of phaselock loops in which output pulses from a high-frequency oscillator are deleted at the frequency of a variable-frequency oscillator which is responsive to the detected phase difference between the associated input signal and an associated reference signal, thereby to provide a high-frequency intermediate signal which is frequency-divided to produce the reference signal continuously and free of noise. The relative phase of the input signals may be determined by phase-comparing the reference signals of the two phaselock loops or, to provide even higher precision, by phase-comparing the variable-frequency signals of the two loops.

Abstract: A high-accuracy phase comparison system for noise-contaminated fixed-frequency input signals, such as Omega radionavigation signals, employs a pair of phaselock loops in which output pulses from a high-frequency oscillator are deleted at the frequency of a variable-frequency oscillator which is responsive to the detected phase difference between the associated input signal and an associated reference signal, thereby to provide a high-frequency intermediate signal which is frequency-divided to produce the reference signal continuously and free of noise. The relative phase of the input signals may be determined by phase-comparing the reference signals of the two phaselock loops or, to provide even higher precision, by phase-comparing the variable-frequency signals of the two loops.