White Paper Discuss: Increasing A/D Resolution Using Noise

[Chris Hibner]

Originally posted by KenWittlief
interesting idea
but if you are willing to sacrifice bandwidth to get resolution (sample each reading 10 times)

then why not ride a very precise sawtooth waveform on the input signal, with an amplitude = the lsb resolution of the ADC?

then all you need to do is see which of the ten subsamples pushes the input over the next threshold, and you will know precisely how far below the threshold the real signal is.

?

Ken,

There are a couple of reasons this isn't done in practice.

1) Money. If you can afford to put a very precise waveform generator on your board, you can afford an A/D with much better resolution.

2) Environment. Most of these A/Ds are subjected to though environments (i.e. automotive applications). The temperature can be from -40 to over 100 degrees C. The humidity can vary greatly, and the parts will age over 10 years. All of these factors will affect the A/D as well as any waveform generator. In other words, the waveform generator will not be very precise.

Also, typically bandwidth is not an issue. You are typically trying to measure very low frequency signals and are sampling at a very high rate. For example, if you're integrating angular rate into heading, the real frequency of the signal you're trying to measure is on the order of 10 Hz. With our new controller we should be able to sample at around 500 Hz, so using some of the bandwith is no problem.

-Chris