Fasedetektor

Fasedetektor, or phase detector, is an electronic circuit that compares the phase of two input signals and produces an output that depends on their phase difference. The detector itself does not generate synchronization; it provides an error signal used by a control loop, such as a phase-locked loop (PLL), to adjust a controlled oscillator until the signals are in phase.

Common implementations include analog and digital topologies. Analog phase detectors often use mixers or multipliers, which yield an output proportional to the sine or cosine of the phase difference when the input frequencies are close. Digital phase detectors include exclusive-OR (XOR) detectors for digital square-wave inputs, producing a DC level that represents the phase difference over a limited range and with certain nonlinearity. Phase-frequency detectors (PFDs) use flip-flops to detect both phase and frequency differences; they are widely used in PLLs because they offer a wide pull-in range and a reduced risk of false locking when combined with a charge pump.

In a phase-locked loop, the phase detector output is filtered and fed to a voltage- or digitally controlled oscillator to correct the output frequency. The loop seeks to minimize the phase error, achieving synchronization between the reference signal and the oscillator. Applications include frequency synthesis, clock generation and distribution, demodulation, and data recovery in telecommunications.

Key characteristics of phase detectors include linear range, sensitivity (output per unit phase difference), dead zones, pull-in or lock range, and noise susceptibility. The choice of detector topology depends on the desired trade-off between linearity, speed, noise performance, and implementation complexity.