Why PLLs Are Cool (yes I'm a huge geek)

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PLLs or phased locked loops is a technique used in electrical engineering to lock one oscillator to another using a feedback loop. When used in musical applications the results are often unpredictable but sometimes beautiful. From an electrical engineering perspective PLLs can be used to generate, demodulate, recover or filter a signal.

The basic principle behind a phase locked loop is that the phase of two oscillators are compared when they are not the same a voltage is generated to adjust the frequency of one of the oscillators. this oscillator is bumped up and down in frequency until it is in phase with the other oscillator. by definition if the two oscillators are in phase they are also in tune aka the same frequency.

from wikipedia "A phase-locked loop or phase lock loop abbreviated as PLL is a control system that generates an output signal whose phase is related to the phase of an input signal. There are several different types; the simplest is an electronic circuit consisting of a variable frequency oscillator and a phase detector in a feedback loop. The oscillator generates a periodic signal, and the phase detector compares the phase of that signal with the phase of the input periodic signal, adjusting the oscillator to keep the phases matched.

Keeping the input and output phase in lock step also implies keeping the input and output frequencies the same. Consequently, in addition to synchronizing signals, a phase-locked loop can track an input frequency, or it can generate a frequency that is a multiple of the input frequency. These properties are used for computer clock synchronization, demodulation, and frequency synthesis.

Phase-locked loops are widely employed in radio, telecommunications, computers and other electronic applications. They can be used to demodulate a signal, recover a signal from a noisy communication channel, generate a stable frequency at multiples of an input frequency (frequency synthesis), or distribute precisely timed clock pulses in digital logic circuits such as microprocessors. Since a single integrated circuit can provide a complete phase-locked-loop building block, the technique is widely used in modern electronic devices, with output frequencies from a fraction of a hertz up to many gigahertz."

another interesting use for phase locked loops in a musical sense is for frequency multiplication and clock multiplication. Dividing a clock is fairly easy, using a simple counter or a function generator that cannot be re-triggered on rise will allow clock division in the digital and analog realms respectively. However multiplication becomes trickier. I am sure there are ways to multiply a clock using analog circuitry without a PLL but I know of non. To achieve clock multiplication with PLL is simple and achieved by placing a clock/frequency divider in the feedback loop right before the phase detector.

if the divider is set to divide by two then this will result in the frequency being multiplied by two because the oscillator will need to go twice as fast for the result of the division to be in phase with the input signal.

anyways I'm a big PLL geek, I hope you enjoy this post and video. If you did please Upvote and follow!

Diagram From Wikipedia

thanks to @dtube for putting together this platform!

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