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Intergarting in analog and digital domians

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luben111

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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
 

BradtheRad

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Digital methods bring some benefits over analog. In other ways digital requires more work.

Say you take 5 digital samples and average them. A single rogue spike of noise can have a disproportionate effect. You should therefore increase the number of samples (which becomes a problem as you know).

With the analog method (RC), averaging is automatic and proportionate. An advantage.

However now go back and look at the digital method. And suppose you throw out the highest and lowest samples. Take the average of the remaining 3 samples. This reduces the effect of the worst spurious noise.

On the other hand the RC (analog) method must accept spurious noise spikes.

Therefore suddenly the digital method can give you a more sensible reading than the analog method can. Even if it takes a little more work.

It all depends how you can extract best performance from one way versus the other way.
 
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andre_teprom

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If the processing cost in uC is not significant it is prefereable to perform al filtering operations digitally; unless analogiclly would avoid reach excursion range (level saturation). That´s because it´s possible implement filters of any selectivity digitally.

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luben111

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Hi BradtheRad,

Thank you for the explanations. In my case there is no way to make hardware filtering, is it possible to say that the software filtering if adequate can completely replace the hardware filtering? This is actually my main concern - if there is no hardware filtering can the software filtering replace the hardware one.

Regards
Luben
 

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