ADC on dual layer board?

I have a mature design on a dual layer board to which I now want to add the ADC function (presently not utilized but pins are available). I understood that a 4 layer board is best for this, but is it possible to get the ADC working properly and accurately on a dual layer board? Thanks.

In my view .....when you are dealing with ADC the input signal and stable and accurate reference voltage is very important and it should be noise free....It is independent of no of layers that you use....try to put the proper filters for getting proper input signals such that ADC sampling will be accurate....Also make referecence voltage clean....

Good Luck

blapcb said:

is it possible to get the ADC working properly and accurately on a dual layer board? Thanks.

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Need more info. How many bits, what resolution, what ADC? 8-bit low-speed ADC with on-chip ref? Sure, probably. 12-bit with external ref, maybe harder. 24-bit? Depends on how you route power and grounds, the particular ADC, how much noise on the supply bus, what the PSRR for the ADC might be, and another couple dozen things. I've done many data acq projects on just double-sided boards. Needs more careful attention to part selection, signal routing, partitioning ground and power traces, decoupling. You can do a multilayer design that doesn't work well or a 2-layer that does. Just a multilayer board is no magic bullet. Upgrade to a micro with on-chip ADC? Can simplify things.

Robert Hoffman said:

Need more info. How many bits, what resolution, what ADC? 8-bit low-speed ADC with on-chip ref? Sure, probably. 12-bit with external ref, maybe harder. 24-bit? Depends on how you route power and grounds, the particular ADC, how much noise on the supply bus, what the PSRR for the ADC might be, and another couple dozen things. I've done many data acq projects on just double-sided boards. Needs more careful attention to part selection, signal routing, partitioning ground and power traces, decoupling. You can do a multilayer design that doesn't work well or a 2-layer that does. Just a multilayer board is no magic bullet. Upgrade to a micro with on-chip ADC? Can simplify things.

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Hi Robert, thanks a lot for your reply. The processor is a MSP430F1612 with an on-board 12 bit ADC. I plan to use an external reference with a TL431 (as I understand that the on-board ref is susceptible to temperature influence). The signal I want to acquire is slow moving, basically a DC voltage (if you discount the noise that may be there on the line) and a sample rate of a few Hz no more (i.e. I will sample on demand in single-shot conversion and then do a moving average in software).

Do you need an actual 12-bit +/- 1/2 LSB conversion? TL-431 has anywhere from 6 to 25 mv change on the 2.5V ref output over temp and time and anywhere up to 2% accuracy of the actual ref voltage. 12-bit accuracy needs more like 1mv stability. The on-chip ref is around 100 ppm/deg C. Over 20 C ambient range, that's somewhat better than an external TL-431. I'd try with the on-board ref first and if it isn't good enough try a better ref like a MAX 6126 or LM4030. Those may be overkill and expensive, but many other options. Assuming you solve the noise issues, the on-chip ref will give you closer to 9 or 10 bits accuracy assuming you calibrate or trim out the absolute reference accuracy. If you put a simple RC filter on the ADC input sufficiently close to the micro, I'd think you won't have a problem there. The bigger issue is routing the analog input to the ADC without noise on the ground or signal lines. That depends on your layout. With something approximating a single-point ground and no ground loops I think you have good chance of success with a 2-layer board. If you do a whole new layout with 4-layer you have a whole new set of issues to debug. To test, just use your existing board, solder a resistor, cap, twisted pair and write your code. Simple is good.