Fasestyringskredsløb

Fasestyringskredsløb, often translated as phase-locked loop (PLL), is an electronic control system that generates a signal that has a fixed relationship with the phase of an input signal. It is a feedback control system that synchronizes an output oscillator with an input reference signal. The core components of a typical PLL are a phase detector, a loop filter, and a voltage-controlled oscillator (VCO).

The phase detector compares the phase of the input signal with the phase of the output signal from the VCO. Any difference between these phases is converted into an error voltage. This error voltage is then passed through a loop filter, which smooths out rapid fluctuations and removes unwanted frequencies, producing a DC or low-frequency control voltage. This control voltage is then applied to the VCO, adjusting its frequency. If the VCO's output frequency is too high, the control voltage will decrease its frequency; if it's too low, the control voltage will increase it. This feedback mechanism continuously adjusts the VCO's frequency until its phase is locked to the phase of the input signal, at which point the loop is considered "locked."

PLLs have a wide range of applications. They are commonly used in radio receivers for demodulating frequency-modulated (FM) and phase-modulated (PM) signals, as well as in frequency synthesizers to generate stable, precise frequencies. Other uses include clock recovery in digital communication systems, motor speed control, and in audio signal processing for effects like pitch shifting. Their ability to track and synchronize with input signals makes them a fundamental building block in modern electronics.