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Old 11th October 2004, 10:12 AM   #1
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Default 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.
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Old 11th October 2004, 08:54 PM   #2
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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
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Old 12th October 2004, 02:45 AM   #3
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I would like to get some resource material on practical circuits using sigma-delta modulation in class d amps. can anyone help.
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Old 12th October 2004, 03:24 AM   #4
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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)
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Old 9th January 2005, 12:21 PM   #5
Kenshin is offline Kenshin  China
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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!
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Old 10th January 2005, 09:19 AM   #6
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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.
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File Type: gif ds_out.gif (12.0 KB, 260 views)
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Old 10th January 2005, 09:26 AM   #7
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And now without input signal:
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File Type: gif ds_out_no_drv.gif (11.7 KB, 235 views)
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