## Integration in analog and digital domains

## Integration in analog and digital domains

(OP)

Intergarting in analog and digital domians

Hi,

One theoreitical question about signal integration.

Imagine that you have 10 bit ADC which measures the changing voltage on some capacitor. The signal is quite noise so there are mainly two approaches:

1. Increase the RC constant on the system and measure the voltage (integration in digital domain)

2. Don't change the RC constant but make several samples and integrate the results digitally (integration in digital domain, for example simpel averaging).

The question is - do these two methods yeild the same result if both operations are executed for the same time - i.e. if the added time from increased RC constant in case 1 is equal to the time spent to get extra samples in case 2?

From oversampling theory is known that in order to get more bits and/or better SNR the input signal should be filtered from HF otherwise signal aliases will appear and will compromise the result.

Or I can redefine the question as: In which conditions the integration in digital and analog domain are equivalent?

Best regards

Luben

Hi,

One theoreitical question about signal integration.

Imagine that you have 10 bit ADC which measures the changing voltage on some capacitor. The signal is quite noise so there are mainly two approaches:

1. Increase the RC constant on the system and measure the voltage (integration in digital domain)

2. Don't change the RC constant but make several samples and integrate the results digitally (integration in digital domain, for example simpel averaging).

The question is - do these two methods yeild the same result if both operations are executed for the same time - i.e. if the added time from increased RC constant in case 1 is equal to the time spent to get extra samples in case 2?

From oversampling theory is known that in order to get more bits and/or better SNR the input signal should be filtered from HF otherwise signal aliases will appear and will compromise the result.

Or I can redefine the question as: In which conditions the integration in digital and analog domain are equivalent?

Best regards

Luben

## RE: Integration in analog and digital domains

TTFN

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## RE: Integration in analog and digital domains

I'll put it other words - say I have in one case 10x bigger capacitor 10*Cs where I accumulate 10 charge transfers and then measure the voltage. In other case I have small capacitor Cs and measure 10 times the voltage. In both cases the measured voltage like value is the same.

The question is - in which case I get better noise immunity. Notice that when I use small capacitor I don't have LP filtering on the input so all noises dirrectly impact the ADC.

## RE: Integration in analog and digital domains

What you appear to be looking for is what is the level of noise compared to the level of measurement. Obviously if the magnitude of measurement increases compared to a stable magnitude level of noise, the signal-to-noise ratio goes up and the measurement looks better. But it's still the same noise level, and neither is less "immune".

Dan - Owner

http://www.Hi-TecDesigns.com

## RE: Integration in analog and digital domains

Thank you for the response.

In oversampling the gain in the SNR and/or the additional bits comes after applying LP filtering on the measured samples. So my concerns are about the LP filtering

## RE: Integration in analog and digital domains

Cheers

Greg Locock

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## RE: Integration in analog and digital domains

Thank you for the idea - see attached the file where are shown 3 cases:

1. ADC with hardware LP filter on the input is acquiring multiple samples. The final result is the average value of all samples

2. ADC without hardware LP filter is acquiring multiple samples. The final result is the average value of all samples

3. ADC without hardware LP filter is acquiring multiple samples, each new sample is filtered in the software (IIR and/or slew rate). The final result is the average value of all samples

For sure the best way to measure the values is 1, but we can't implement LP on the ADC by many reasons.

The question is - if using software LP filtering (case 3) is it close like noise suppression to case 1? I guess one of the problems by not filtering the signal on the source (no hardware LP filter on ADC) is that we'll get aliases of the HF noises and hence this will compromise somehow the final result.

Also - case 2 (no hardware LP filter and no LP software filter - just averaging) what kind of noise levels we get?

regards

Luben

## RE: Integration in analog and digital domains

needfor a LP filter, it merely relaxes therequirements(e.g., you may get away with a 3dB/decade filter rather than a 6dB/decade).Dan - Owner

http://www.Hi-TecDesigns.com

## RE: Integration in analog and digital domains

So you think that case 3 is the best in my case - ADC sampling and LP on the acquired samples before they added in the accumulator for averaging.

regards

Luben

## RE: Integration in analog and digital domains

Jumping into the middle of process and asking for comparisons of point designs without knowing the point requirements is a poor way to select the appropriate design. Moreover, in all 3 cases, you're already doing an average, which you yourself have noted has lowpass characteristics. In 2 of the 3 cases, you double band your latency, because you have both filter latency and averaging latency.

There are recursive filters that have better time series characteristics, and there are maximum likelihood filters that hage both better performance and lower latency.

TTFN

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## RE: Integration in analog and digital domains

Dan - Owner

http://www.Hi-TecDesigns.com

## RE: Integration in analog and digital domains

I can understand 6 dB/octave, but how do you get 3 dB/octave? And is there anything to gain from that?

Gunnar Englund

www.gke.org

--------------------------------------

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## RE: Integration in analog and digital domains

TTFN

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## RE: Integration in analog and digital domains

Dan - Owner

http://www.Hi-TecDesigns.com

## RE: Integration in analog and digital domains

Gunnar Englund

www.gke.org

--------------------------------------

Half full - Half empty? I don't mind. It's what in it that counts.