Class D Auto-Bias

An auto bias scheme for class D amplifiers, where the triangle/sawtooth wave's amplitude is independent of the amplitude/DC offset of the input signal. The resultant outputs will always have a zero offset against each other (blue/green), to ensure the class D amplifier is working within the optimal range. P.S. The 47kOhm/4.7nF values have been chosen for quick settling here in the simulation (with a corner frequency of 720Hz). In reality, one would be aiming to a lower corner frequency, as to attenuate the sawtooth ripple as much as possible, and reduce the error from the low frequency oscillator. Anything below the hearing range is okay (5-20Hz).Given the high frequency of the sawtooth generator, even now we're getting a good attenuation. It's just about balancing the settling time vs ripple rejection.

published 2 years ago