PLLkretser

PLLkretser, or phase-locked loop circuits, are closed-loop feedback systems that synchronize an oscillator to a reference signal in frequency and phase. They are widely used to generate, stabilize, and manipulate signals in communications, timing, and signal processing.

A typical PLL consists of a phase detector, a loop filter, a voltage-controlled oscillator (VCO), and a feedback path that often includes a frequency divider. The phase detector compares the reference input with the divided VCO output and produces an error signal proportional to phase/frequency difference. The loop filter smooths this error and drives the VCO to reduce the difference.

In closed loop, the VCO adjusts its output until the phase and frequency errors are within the loop's tolerance. Once locked, the VCO frequency tracks the reference, and the phase error settles to a small, stable value. The loop's performance is influenced by loop gain, order, and the design of the filter, and it determines jitter and noise rejection.

Variants include analog PLLs, digital PLLs (DPLLs), and all-digital PLLs (ADPLLs). Frequency synthesis commonly uses integer-N or fractional-N dividers to achieve fine frequency steps. Fractional-N synthesis often employs sigma-delta modulation and dithering to reduce spurs.

Common applications include clock generation and distribution in microprocessors, radio receivers and transmitters, demodulation of data, and instrumentation. Key performance metrics are capture range, lock range, lock time, phase noise, and jitter, as well as spur performance and power consumption.