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-   -   Alternative modulation schemes for class d amps (http://www.diyaudio.com/forums/class-d/42371-alternative-modulation-schemes-class-d-amps.html)

Nirav Desai 11th October 2004 10:12 AM

Alternative modulation schemes for class d amps
 
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 11th October 2004 08:54 PM

Quote:

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 12th October 2004 02:45 AM

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

analogspiceman 12th October 2004 03:24 AM

Quote:

Originally posted by Nirav Desai
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 9th January 2005 12:21 PM

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 10th January 2005 09:19 AM

2 Attachment(s)
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 10th January 2005 09:26 AM

2 Attachment(s)
And now without input signal:


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