[SOLVED] Current Amplification (nA => uA)

[flote21]

Hi!
I agree with your suggestion. But the only inconvenience is that i think that it is not very easy design of the switches for the reset circuit. I think that steps 3 and 4 is something that it is very difficult to do with a low noise and high efficiency. The design of the reset circuit is not very complicated itself using a charge AO + cap. The problem is how to design a good switch with low noise. Using mosfet trt could be a good option. But any suggestion to achieve a good mosfet switch with low noise? Any mosfet in particular with a special circuit around it?
Thanks

 

[Analog Ground]

Hi!
I agree with your suggestion. But the only inconvenience is that i think that it is not very easy design of the switches for the reset circuit. I think that steps 3 and 4 is something that it is very difficult to do with a low noise and high efficiency. The design of the reset circuit is not very complicated itself using a charge AO + cap. The problem is how to design a good switch with low noise. Using mosfet trt could be a good option. But any suggestion to achieve a good mosfet switch with low noise? Any mosfet in particular with a special circuit around it?
Thanks

There is a type of part called an "analog switch" which has the MOSFETs and control circuitry in one device. Analog Devices has some precision parts. Here is a link:

https://www.analog.com/en/switchesmultiplexers/analog-switches/products/index.html

A key parameter for your application is "Charge Injection". When a switch is opened or closed a small amount of charge is injected into the switch. This would appear as an offset on your integrating capacitor at the start of the collecting period when the switch is opened. When you close the switch to reset, the charge injection is not important. It will go away along with the other charge on the capacitor. Most other parameters are fairly self explanatory. Analog Devices will have app notes to help you get familiar with these parts. They should show ways predicting and minimizing the effect of charge injection.

 

[flote21]

Hello Analog Ground.

I was doing several researches about your suggestion and there is another commercial swithced integrator with a lower input offset voltage: ACF2101. This could be another interesting solution for my problem.

On the other hand I have been also thinking in the posibility of setting on my own reset circuit with analog switches and basically I have to set up something like this:

**broken link removed**

But in that circuit I will use the ADG821 for switching the cap and the AO will be another one with a lower input offset voltage and lower noise...

What do you think? Shoud it be work right?

Thanks again.