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Old 13th November 2007, 01:33 PM   #1
d1983 is offline d1983  Canada
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Join Date: Mar 2007
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Hey all.
I'm designing myself a (hopefully) higher order sigma delta modulator using op amps.
As of right now I have a working computer model of a 1st order system, but it doesn't seem to want to work properly past 10kHz.
I'm thinking it's the integrator, and I've tried to set the 0dB point all the way up to like 50kHz, and still it doesn't look quite right.
Here's the set up:
Input to summing amp (+), integrator, comparator (+ rail, 0), d-flip flop, comparator (+/- rail), to input summing amp(-).
I've looked at all the waveforms, and I don't think it's the clock speed.
Any hints/tips/ideas?
I'm using general purpose opamps and comparator opamps so that I can make use of a 2V input from a CD player or other input device.
If it'd help, I can include a schematic and some waveforms, or if it'd help I can include the OrCAD files.
Thanks all!
(I'm pretty new to this design stuff, so take it easy! haha)
-Dave
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Old 14th November 2007, 02:17 AM   #2
fdeck is offline fdeck  United States
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Join Date: Feb 2006
Location: Wisconsin
In my own fiddling with a similar circuit (sans flip flop, so it was really a self oscillating Class-D), it turned out that I needed at least a high speed comparator to get the oscillation frequency up into the hundreds of kHz.
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