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I am trying to design a transimpedance amplifier to fabricate on silicon without using any IC with the following specs:

  1. Input current range: 50 nA to 10 uA.
  2. No bandwidth requirement.
  3. I want the output voltage to be max 5 V.
  4. I have a Vdd supply of +5 V.

I am not able to find any work similar to the specs that I mentioned. Most of them focused on bandwidth, but I have no bandwidth requirement. Additionally, the work area is mostly a small signal for the existing work that I can find. I just want to input the current from a sensor and convert it into voltage. Can someone help me guide how to approach this problem or share any pre-existing work? I would appreciate any help.

Thanks and Regards, Vishesh

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    \$\begingroup\$ I suspect you have some input requirements as well, otherwise the cheeky answer of "just use a 500k resistor" would be relevant. \$\endgroup\$
    – W5VO
    Commented yesterday
  • \$\begingroup\$ Thanks a lot for the reply. But the problem with resistor (correct me if I am wrong) is, first it makes the input resistance really high which is not good for a current inputting system, secondly, the noise related to use this big of a resistor will be huge. is there any work that you know that did somewhat like I want to achieve? \$\endgroup\$ Commented yesterday
  • \$\begingroup\$ If you require low input impedance, please state so in your question. \$\endgroup\$
    – winny
    Commented yesterday
  • \$\begingroup\$ I don't require it, but I guess a good trans-impedance amplifier should have a low input resistance. \$\endgroup\$ Commented yesterday
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    \$\begingroup\$ If you want an improved BW over other types of amplifier you would go for a TIA so, in opting for a TIA you are also sending the message that you want high BW. Then saying BW isn't important is like saying it's not important that it's a TIA. See the problem? I'm not saying that if you fully disclosed the application that a TIA wouldn't be the most suitable choice of course. In other words there are less obvious reasons for choosing a TIA but, you haven't said one of them. \$\endgroup\$
    – Andy aka
    Commented yesterday

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A transimpedance amp is an opamp with resistive feedback. The feedback resistor is the difficult part here, too large to conveniently implement on an ASIC.

A hundred resistors in series would give you a rather large phase shift due to stray capacitance, not good for stability when used for feedback. But maybe you don't care here. Just compensate with a capacitor in parallel with the monster resistor: that'll reduce your bandwidth but you say you don't care about bandwidth.

Another approach is an active resistor circuit. There are examples in Hirokazu Ikeda's OpenIP, unfortunately no longer directly accessible online. However, you can find it at https://web.archive.org/web/20211229121629/https://research.kek.jp/people/ikeda/openIP/. See Chapter 6.

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  • \$\begingroup\$ Hi, Thanks a lot for the reply. Can you please send the link that contains the information in English? Another approach that I have in mind (correct me if I am wrong here) is to use a common gate at the input of the current as a current buffer and then use a big resistor for the current to voltage converison? \$\endgroup\$ Commented yesterday
  • \$\begingroup\$ @VisheshGupta Google translate does a decent job with the 日本語. \$\endgroup\$
    – John Doty
    Commented yesterday
  • \$\begingroup\$ Thanks. I will try it. \$\endgroup\$ Commented 7 hours ago

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