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Class D Switching Power Amplifiers and Power D/A conversion

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Old 23rd August 2005, 02:06 PM   #11
diyAudio Member
Join Date: Aug 2005
The Wolfson micro parts are awesome.
I will get one and experiment with it.

I am not a seasoned DSP programmer, and to implement this I would have to stick to the only one I have expecience with-- dsPIC from Microchip.

In worst case, I could indeed implement the PCM-to-PWM conversion in firmware. But I assumed a dedicated chip could do it better, faster, more accurately.

Think about it: if you have a 16 bit signal to convert to PWM-- that's 64,000 individual timing quanta. Superimpose that on a PWM base frequency of 50 KHz, and you'd need a 3200 MHz clock to resolve 16 bits in PWM.

I can't implement that in a DSP, unless I reduce something.

Reduce bandwidth: (for subwoofer) 100Hz passband, with 1KHz PWM carrier.

Reduce resolution, 12 bit instead of 16.

That's 4096 x 1000, or about 4MHz PWM timing clock. Although doable, this stretches the limit of a DSP, since you will need to execute more than 1 instruction per PWM step.

But then you have a PWM carrier in the audible range. A subwoofer channel will imply hefty class D amplification post-processing.
A class D amp operating at 1KHz! -- great; the MOSFETS will like it.
Unless the whole circuit is dunked in epoxy and cemented, there may be some audible whine coming out of that.

I'll try both approaches
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Old 24th August 2005, 09:59 AM   #12
i-s is offline i-s  United Kingdom
diyAudio Member
Join Date: Nov 2003
Location: UK
I remember reading something like this at Zetex. Unfortunately I don't know the part number
ZXCW8100 and ZXCW6100
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