Alternative modulation schemes for class d amps

[Nirav Desai]

Can we use modulation schemes like pulse position modulation, sigma-delata modulation for the class d amps instead of the usual pwm? can anyone suggest some resource material on this.

 

[phase_accurate]

sigma-delata modulation for the class d amps instead of the usual pwm?

The Sharp SM-SX100 is using delta sigma modulation. Also the Tripath amps use delta-sigma modulation.
Some self-oscillating class-d amps using hysteresis modulation are said to use sigma-delta modulation by their constructors.

Regards

Charles

 

[Nirav Desai]

I would like to get some resource material on practical circuits using sigma-delta modulation in class d amps. can anyone help.

 

[analogspiceman]

I would like to get some resource material on practical circuits using sigma-delta modulation in class d amps. can anyone help.

There was a recent thread on this subject right here on this forum: Non clocked (e.g. free running, self oscillating) class d

Check it out. It covers why and how free running class d amp oscillate. If you have any further question just post them to that thread.

Regards -- analog(spiceman)

 

[Kenshin]

That's Pulse Density Modulation (PDM).

just insert a D flip-flop between the CMP and gate driver,then drive it with a clock pulse of several MHz,that is OK.

but PDM need a switching frequency higher than hyerstis modulation -- that's not ecomic.

a modulator of high order may be better.
SHARP's HIFI equipment uses a modulator of 7th order!

 

[phase_accurate]

The problem of high switching frequencies is only a problem for no or very low input signal levels.
Enclosed you will find the simulation of a hypothetical class-d amp using SD modulation. The signal frequency is 40 kHz. One can clearly see the phase of the sinusoid lagging behind the switching pattern due to the output filter.

 

[phase_accurate]

And now without input signal: