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# hello, anyone can give me some advice?

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#### samuel

##### Full Member level 3
Now, I am design readout circuit from infrared detector. I want to do some sum function and average function. That is to say, first sum current signal from infrared detector signal and then take sixty pecent of average current from summation current.

thanks, anyone.

samuel.

Well, summing two currents is just joining the two branches with the current in the same direction

Tacking 60 percent is also easy, just a current mirror with that factor.

I'm not sure what you mean with average. Is it a sinusoidal signal and you want the rms value, or you want to eliminate noise,or what?

### samuel

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hello, PaloAlto

i want to make sum of 320 infrared singals, then averege them, at last, take 60 percent of the average signal. each infrared singal is 300nA.

thanks again.

Join them all into one single line
Use current mirrors to scale by 0.6
Now you have the (60%) sum of them all, if you scale it down 320 times, that's the average

That would give you the result, you need to calculate the error that the current mirrors are introducing to see whether it is feasible or not. Do some numbers and check it

### samuel

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Now i want to arbitrarily take percentage of the summation, for example,0.4 0.5,0.6.0.7 and so on by external control signal.

how to implement this function?

as PaloAlto mentioned - use current mirrors. You can have multiple current mirrors with different ratios and select them by external digital signal.

### samuel

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But external signal can not control this percentage continuously.

If you control signal is analog then it is quite more difficult. I guess we assumed that control signal is digital.
But you can still use similar approach by implementing A/D and again select the current mirrors. - But it would be discrete again.

I suppose you can use transimpedence amplifier to transform the sum of current to voltage,then amplify it with a factor.

Added after 3 minutes:

Well,if you want to get athe average,you can amplify the voltage with a factor of half.

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