| 摘要 |
A carrier lock detector for a quadrature amplitude modulation system includes Exclusive-OR gating circuits for determining when detected signal points occur within first areas centered on signal point positions in a phase plane diagram or second areas between the signal point positions, and for producing corresponding output signals. An integrated difference between these output signals is produced by an integrator and compared with a threshold level to provide a carrier lock detection signal. The arrangement is such that the integrated difference is substantially zero when the carrier is unlocked, so that the threshold level can be set to a low value to enable reliable operation of the detector at low signal-to-noise ratios.
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