Due to the varying phase difference between the two inputs, a pulse-width modulated (PWM) signal is produced. When a low-pass filter is applied to those pulses, the filter's output rises as the pulses grow longer and its output falls as the pulses grow shorter.
The varying timing discrepancy between the two signals results in the production of a pulse-width modulated (PWM) wave. This PWM wave's behavior is analogous to that of a low-pass filter, which responds by increasing its output with growing pulse duration and decreasing it with shrinking pulse duration.