Communications Blockset

Phase Detector

The Logical Operator block, from the Simulink Math library, functions as a phase detector. It compares the frequencies of the frequency-divided reference signal and the frequency-divided synthesized signal. Since the block's Operator parameter is set to XOR in the mask, the output signal is 0 where the two input signals are equal, and 1 where they are not equal.

At steady state, the signal is a pulse train with frequency of 20 MHz. The reason for this is that both inputs to the block have a frequency of 10 MHz, but they are out of phase by 1/4 of their period. As a result, the XOR'ed signal is a periodic pulse train with frequency 20 MHz.

You can compare the two input signals to the Phase Detector with the output signal by clicking on their respective Scope blocks, as shown below.

Divide Frequency by M

Analog Filter Design