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Old 27th September 2005, 08:56 AM   #1
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Join Date: Oct 2003
Location: Helsinki
Default coding your own PCM to PWM converter?

Hi,

I've started experimenting with the Freescale 56F8300DSK DSP developer starter kit (small 56F8323 DSP, 60 MIPS) and "generic" <600kHz 500Wrms half-bridge modules that I made.

Easily doing some very trivial 8kHz PCM to PWM@400kHz on the DSP got me curious if anyone here has done experiments with their own PCM to PWM converter?

12-bit ADC peripheral output data, LP filtered, output to 16-bit PWM peripheral did sound acceptable but not that good (partly bad ADC, partly 16bit PWM).

Maybe you could recommend some nice algorithm?

There are a zillions of different PCM2PWM papers, like
http://www.imec.be/esscirc/esscirc20...gs/data/62.pdf
but do you have a particular favorite? One that would be light-weight and could run on 60MIPS for subwoofer e.g. 8kHz sampling freq? (I know DSP only from Matlab and F2812, and there lowish MIPS isn't a problem... that's the reason i ask...)

Oh and another one: could someone kindly reveal the patent number and ptoffice for the EquiBit algorithm? I couldn't locate it in uspto search (Texas, equibit, pcm, pwm, ..., nada )

- Jan
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Old 27th September 2005, 09:13 AM   #2
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Join Date: May 2002
Location: Switzerland
I think the conversion a such is just a noise-shaping loop converting low-rate high resolution data into high-rate low resolution, followed by acounter that converts this noise-shaped PCM into PWM. But there might also be some additional proprietary functions implemented that deal with the non-idealities of the switching devices etc.

Regards

Charles
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Old 15th November 2005, 09:06 PM   #3
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Join Date: Nov 2005
Save yourself a lot of time and use the TI TAS5010 converter driving a hi-lo side driver chip like TAS5182. On the input side you can drive it from a CODEC in a few different modes, but I prefer 24 bit IIS.
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