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Cancellation of reconstructed digital signal

Started by alexia March 9, 2010
Hello,

I have an instrumentation amplifier with a gain of 100. 
The positive input (AO) is connected to a DAC. The negative input is taken
from a previous analog stage and also connected to a ADC --> recorded
signal (AI1).

I put a replicate of the recorded signal (AI1) at AO. However, I got an
amplified signal of quantization, noise, etc.

I want to ask which is the best way to reconstruct the analog signal. Is
wavelett algorithm to remove noise is good enough? Any other method
available (ICA, etc)?

Thanks a lot.


alexia wrote:
> Hello, > > I have an instrumentation amplifier with a gain of 100. > The positive input (AO) is connected to a DAC. The negative input is taken > from a previous analog stage and also connected to a ADC --> recorded > signal (AI1). > > I put a replicate of the recorded signal (AI1) at AO. However, I got an > amplified signal of quantization, noise, etc. > > I want to ask which is the best way to reconstruct the analog signal. Is > wavelett algorithm to remove noise is good enough? Any other method > available (ICA, etc)?
This makes no sense -- if you already have the signal recorded, why do you need to measure it? It sounds like your 'real' problem is that you are successfully amplifying quantization noise, and now you want to get rid of it. The problem that you are going to run into is this: for a filter to work there has to be something that distinguishes the two signals that you are trying to separate. "Straight" quantization noise is not all that stationary -- sometimes it has all it's content at DC, sometimes it's pretty well spread over the spectrum. Because of this any linear filter (and to my knowledge wavelet filters are linear) is going to have a hard time consistently distinguishing quantization noise from signal. It's like pouring beer through a towel, hoping that water will come out the other side: the ingredients all 'look' the same to the weave of the towel, so it can't work as a filter. All you can do is to change your quantization noise. _If_ the recorded version of your signal is not where the quantization noise is then you are stuck with improving your DAC. This may mean that you have to revise your hardware with a higher precision DAC. If your sampling rate out to the DAC is generous enough, you may be able to dither the signal going to it -- see http://www.wescottdesign.com/articles/sigmadelta.html for details, or some other reference on sigma-delta modulators. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com

alexia wrote:

> Hello, > > I have an instrumentation amplifier with a gain of 100. > The positive input (AO) is connected to a DAC. The negative input is taken > from a previous analog stage and also connected to a ADC --> recorded > signal (AI1). > > I put a replicate of the recorded signal (AI1) at AO. However, I got an > amplified signal of quantization, noise, etc. > > I want to ask which is the best way to reconstruct the analog signal. Is > wavelett algorithm to remove noise is good enough? Any other method > available (ICA, etc)?
No matter what magic spells do you cast (ICA, wavelets, fuzzy logic, genetic algotithms, turbo codes...) it is impossible to get cancellation in this setup because ADC-DAC pair introduces delay. If you want to entertain your professor, put a FIR filter between ADC and DAC and update it by LMS stochastic gradient. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com