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Old 6th March 2004, 02:44 PM   #1
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Default totally ridiculous digital amplifier (power DAC) idea

well... i just got this totally ridiculous idea . how about a power DAC? hear me out... say we have a digital parallel n-bit stream of unsigned audio. we'll discuss this for the positive part of the signal (we asume the signal to be n-bit POSITIVE) right... also suppose we have n independent voltage sources V[i] where i=0..n-1 with the property that V[i]=2xV[i-1].
for every voltage source we have 2 switches, that insert, or take out the voltage source from the circuit...
just take a look at the picture... it's a 4 bit d/a converter...
of course this basic design can be implemented in any way... the way i thought of it was with mosfets as the switches, driven by a microprocessor with highly oversampled signal.
just a crazy idea i thought i'd share with the rest of the world ...
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Old 6th March 2004, 03:26 PM   #2
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Err.. As you said, this is a DAC. What is so crazy about it??

Jan Didden
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Old 6th March 2004, 05:39 PM   #3
mwh-eng is offline mwh-eng  United States
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Good idea! How would you make all the different voltages - multi-output switching converter? I'm sure you realize you need the negative side (voltages) also. I think you will end up with a lot of parts, but it would be a fun project. Build it and tell us how it turns out.
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Old 7th March 2004, 12:41 AM   #4
djk is offline djk
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Up-sample the multi-bit to a 1-bit, then you can do a straight PWM (2.8Mhz).
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Old 7th March 2004, 12:51 AM   #5
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Actually, I have toyed around a bit with a similar idea, although
I was thinking of current switches instead (ie. binary controllable
CCSes). I suppose it might perhaps be possible for DIY purposes
to trim the CCSes relative to each other. However, I also suppose
it would be much harder to get good precision from a power DAC
than from a small-signal one, consider eg. that power devices are
slower and have longer rise and fall times. A compromise might
be to use fewer bits but oversampling, as in early CDPs. Another
possibility might be to have some self-calibration, or manual,
where the output errors for every pair of subsequent input values
is logged and a correction table is calculated and used to modify
the input (what would this be? Off-line feedforward correction???)
interesting potential feature is that it might be possible to have
the volume control set the DAC reference level, which would have
the benefit of not needing a better dynamic range than the source.

Please note, I have only toyed around with a loose idea, so I have
no good guess at how feasible such a project would be. Besides,
it is probably only of interest for people having digital sources only,
making it of less interest to me, for instance. It is a fun idea though.
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Old 7th March 2004, 02:29 PM   #6
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The multibit power DAC (with switched voltages) is a very nice idea in theory, but will be a nightmare to put in practice.
A controllable current-source will be easier to build but the load must be pure resistive (not suitable to drive directly a speaker)...
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Old 8th March 2004, 06:14 AM   #7
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This principle is used as modulator stage in large AM broadcast transmitters.


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