audio – reference circuit

U20, a class-D amplifier on +5V with 100 nF, its bridge-tied outputs to the speaker LS20; its input from GP8 through the PWM DAC's low-pass R20 1 kΩ / C21 10 nF (C0G) – an AC run expects its corner at 15.9 kHz: flat at 1 kHz, the upper −3 dB corner between 10 and 25 kHz.

Why: A PWM pin through a low-pass into a class-D amplifier is how a microcontroller board makes sound. It holds the bridge-tied outputs, which must not touch ground, and an AC run that finds a filter corner in the wrong place.

Domains on: core audio · SVG