12 bit resolution using a pic

Eugeneo · Joined: 30 Aug 2005 Posts: 155 Location: Calgary, AB

Is it possible to achieve 12 bit resolution using 4 offset analog inputs using a pic. Is it possible to offset each input by 1/4 of its 10 bit resolution then use code to determine what it actually is.

Or use one input as a reference AD then use another with varing charge times so the capacitor is not fully charged and extrapolate the AD value.

I'm just curious if anybody has tried this something like this with good results.

kender · Joined: 09 Aug 2004 Posts: 768 Location: Silicon Valley

A few days ago SherpaDoug had mentioned this method in the other thread http://www.ccsinfo.com/forum/viewtopic.php?t=27261.

My personal oppinion is that this fractional bit offset method is not worth it. To make 4 offset signals, you'll need 4 opamps (quad opamp: 14 pins, about $3) plus qite a few discretes. On the other hand, if you have I2C or SPI bus in your system, you can add a 12-bit A/D, which requires minimum descretes, in an 8-pin package for $5-$7.

butterfly · Joined: 04 Jun 2006 Posts: 35

PIC HAS 10 BÝT RESOLUTIONS BUT WE CAN USE IT 12 BIT RESOLUTION. BUT YOUR SYSSEM NOISE IS IMPORTANT TOO. LOOK UP HE LINK

http://archive.chipcenter.com/TestandMeasurement/tn033.html

GOOD LUCK

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

If you already have an amp in the circuit that has offset capability, like maybe an instrumentation amp, then the offset method does not require any additional amps. Just make an R2R ladder of cheap resistors to drive the reference pin of the instrumentation amp.
The technique is not useful very often, but it is cheap. The biggest problem is that the A/D is probably not linear to 1/4 lsb.
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