How much variation in the transimpedance gain of the TIA is acceptable?

[VisheshG24]

Hi,
I have designed a transimpedance amplifier with a transimpedance gain that varies from 113.1dB to 111.46dB over a current input range from 200nA to 6uA. Is this variation in transimpedance gain acceptable?

I know the answer depends on my application, but what I want to know is:
1) Whether the variation in the trans-impedance gain is a normal problem while designing a TIA and whether one is always aiming to get a really precise trans-impedance gain?
2) Or, in general, people can't get a precise trans-impedance gain and one can live with a variation unless and until it is a really big variation and creates a big problem with his application?

I will appreciate any help in understanding this.

Thanks and Regards,
Vishesh

 

[crutschow]

I expect that variation is normal.
Typically negative feedback is used to reduce such variation.

 

[VisheshG24]

Hi crutschow, I made the tia using a negative feedback using a resistor to a voltage amplifier opamp. The opamp was made using a single stage differential amplifier with a single output. Is the variation still normal?

 

[KlausST]

Hi,

I assume you're the designer... so I expect you to know the answer.

*Either you should have decided before starting the design
*or you should have gotten your client's requirements

I don't expect any of us to be able to tell you how your design should work.

Klaus

 

[BradtheRad]

You're encountering similar questions as those who design VOM's. The ohmmeter function reads in reverse manner as we'd expect. That is, upscale readings indicate lesser resistance, because less resistance conducts greater Amperes.

Inside the meter, internal resistors must have certain values themselves, in order to produce the intended ranges for a Device-under-test. Often these ranges are in steps of 10X. The scale markings are usually non-linear and must be customized to the needle readings.

Your specified range is 30:1. You must tailor voltages and gain at the op amp so as to obtain sensible readings, prospectively across the widest span of voltage from zero to supply_V. You might decide to create more than one range. Decisions are many.