Which component in a phase-locked loop is responsible for generating the error voltage?

In a phase-locked loop (PLL), the phase detector plays a crucial role in generating the error voltage. The primary function of the phase detector is to compare the phase of the input signal (the reference) to the phase of the output signal from the voltage-controlled oscillator (VCO). The phase detector measures the difference in phase between these two signals, and this phase difference is converted into a voltage signal known as the error voltage.

This error voltage indicates how much and in which direction the VCO needs to adjust its frequency to lock onto the input signal's frequency. If the output phase lags behind the reference phase, the error voltage will be positive, prompting the VCO to increase its frequency. Conversely, if the output phase leads the reference phase, the error voltage will be negative, leading to a reduction in the VCO frequency.

Coherent operation of the phase detector is essential for the PLL to function effectively, as it directly influences the stability and accuracy of frequency locking. Thus, the phase detector’s function in generating the error voltage is fundamental to the operation of the entire phase-locked loop.