Low Voltage (LV) Overvoltage Protection

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bhc
Posts: 4
Joined: Mon Nov 16, 2020 2:20 am

Low Voltage (LV) Overvoltage Protection

Post by bhc » Mon Nov 16, 2020 4:53 am

TL:DR

Is there a recommended circuit (e.g. diode clamp) that folks have used or recommend to fully leverage the ADC in the LV position? I need full resolution in this range but transient signals can exceed 1V.

Extended Question:

I have an application that uses a high gain, current-voltage amplifier (10^9) to measure transient currents in the pA range. However, to do so the experiment requires the pulsing of a high voltage electrode which capacitively couples with the detector. While very short (i.e. 10s of ns), this coupling can cause the amplifier to output voltages that exceed 1V. Additional information worth mentioning is that the signals I'm trying to measure have rise times in the 100s of ns range. Because the voltages of the true signal rarely exceed 1V, I really need the resolution in the LV setting.

Are there any recommended circuits that would help protect the ADCs without sacrificing sampling performance too much? Ultimately, I'd like to sample with a decimation of 1024.

Relevant links that I've considered but haven't tried as I don't want to break things include:

https://www.eevblog.com/forum/projects/ ... ode-clamp/
https://forum.arduino.cc/index.php?topic=611356.0

Cheers

bhc
Posts: 4
Joined: Mon Nov 16, 2020 2:20 am

Re: Low Voltage (LV) Overvoltage Protection

Post by bhc » Mon Nov 16, 2020 9:19 pm

After doing some digging, it appears as though a standard clipping circuit using diodes may not be suitable for the LV setting. This has a fair bit to do with the limitations of diodes operated on such low voltages. While I haven't tried it, the following may be a strategy for some folks:

https://www.radiolocman.com/shem/schema ... ?di=589807

This circuit uses the behavior of a couple of op-amps to clip the circuit. Upon further reflection, it may be worth considering adding yet another amplifier stage to my setup so that I can boost the signal to levels where I can more fully leverage the resolution of the ADC in the HV setting.

Other suggestions would be appreciated. Does anyone know why such a low voltage range was chosen? Would it not be more advantageous to have the input swings conform to a more standard voltage range (e.g. 3.3? or 5V)?

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