ADC in a digital world
Simonmada & Roff,
I still do not know what speed you want.
A Successive approximation ADC with a 100mhz clock will convert at 10mhz.
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People reading this thread will say “buy a ADC”. For the last hard ASIC I made there was a huge price advantage to not go mixed signal. (development cost) In a digital only ASIC we made ADCs using 3 pins and a RC. Ask you boss; Should I use a $5.00 ADC or a $0.01 R+C? Multiply by 100,000 unites per year.
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I have used an ADC much like the ramp ADC but faster.
Modify the ramp ADC to have a Up/Down counter. The output of the analog voltage comparator drives the U/D pin on the counter. The ramp heads up until it crosses the unknown analog voltage. Then the ramp heads down until it crosses again (one count). If the analog voltage is at a value of 200.3 then the output of the U/D counter will = 200, 201, 200, 200, 201, 200, 200, 201 etc. The bad news is it takes a while to find the voltage. The good news; when it is close there is an output every clock.
To speed things up I tried to combine the successive approximation idea with the UpDown idea. The DAC counts up by +32 until the voltages cross. Then it counts down by –8 until the voltages cross. Then counts up by +2, then counts Up/Down/Up/Down etc.
I struggle with logic to detect when the unknown voltage is many counts from the DAC output. If the unknown voltage moves up fast then the counter needs to up1, up1, up1, up2, up4, up8, up16, up32, (too high) down 16, up 8, down 4, up2, down, up down, up down, up etc.
This crazy method works when you want to over sample a signal. (OR) If you want to have very low delay to output. (Leave the UpDown ADC running all the time, read the output when you want the information.)
Simonmada; You are not alone. There are people get “free” analog functions out of a digital part. Keep working. Please post your results!