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Quote# QACF040 - Suitable operational amplifier

Other Parts Discussed in Thread: OPA857, OPA855

can you possibly suggest a suitable operational amplifier for the customer's application as per the below description?
We are looking for amplifiers on DIE-level which we can integrate into our terahertz detectors.
These detectors are down-converting the incoming terahertz signal, so that the detector current is either in the kHz to MHz range, or extends into the lower GHz range, depending on the application.
The noise current of our detectors is between 20 pA and 100 pA, which is why we need very low-noise amplifiers.
The signal amplitude reaches up to a few µA. Signals with around 10 nA should be able to be detected by the amplifier in any case.
The output amplitude should then be large enough for the signals to be digitized by an ADC.
A cascading of several amplifiers is of course conceivable.
The requirements regarding the bandwidth are concrete:
For spectroscopy and measurement technology, the amplifier should have a bandwidth of > 500kHz.
Bandwidths> 5 GHz are required for communications applications.
I would be very grateful for your recommendation.

Can you possibly suggest possible op amps that could be suitable for this use?
Would you need any additional details before you can suggest a specific part?

Thank you very much.
Best regards

  • Hi Adnan, 

    If I understand correctly, are you only looking for devices that are sold as a die sale? (e.g. they are not in a package?). We do not have any devices that can cover the 5 GHz use case, but we may have some parts that would work for the 500 kHz application. 


  • Hi Jacob,

    thank you.

    We checked with the customer and he told us that the 500 kHz and 5 GHz applications can be viewed separately.
    Of course they would be happy if there was a solution for both cases, but only a 500KHz amplifier would help a lot.

    He mentioned:
    "I would actually prefer a device over a package. The background is that we want to integrate the amplifiers into our sensor heads. For this we
    would best build the amplifier ourselves via wire bonding.
    If suitable amplifiers are only available in the housing, we would have to discuss internally to what extent this could still be a solution.

    In addition, I can think of another detail that I forgot when I first asked for it:
    Since our sensor chips are operated without bias voltage, the amplifier input should be unbiased, or optionally be able to be connected with a bias block (capacitor)."

    Thank you.

    Best regards

  • Hi Adnan, 

    Can you clarify what you mean by the amplifiers being unbiased? Do you mean that they do not have a standard voltage applied at the inputs, or do you mean that there is no actual power supply connection? 


  • Hello Jacob,

    many thanks for your response. Instead of answering your question, our customer now responded:


    After consultation with my colleague, we came to the conclusion that we were looking for an integrated (transimpedance) amplifier circuit.
    The problem with discrete OpAmps is that we still have to embed them in a suitable circuit, which in turn takes up space in the form of a PCB.
    In order to be able to integrate the amplifiers into our sensor modules, we therefore imagine complete TIA ICs.
    According to my understanding the OPA857 would be such an amplifier.

    Unfortunately bandwidth and Input-Referred Current Noise do not match our requirements yet."


    Can you possibly advise on the above are there possibly better choice of the now mentioned transimpedance amplifiers, which might help the customer's application?

    Thank you very much.

    Best regards


  • Hi Adnan, 

    Unfortunately the OPA857 is the fastest fully integrated transimpedance amplifier that we have currently. However, we can create a fairly small circuit with the OPA855 using 0201 sized components for the feedback network.