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Thank you MikeMl!!!!I found the problem with your AC analysis. At the time you are doing the frequency sweep, the transistor has no bias (is effectively turned off), so when you do the AC analysis, you are seeing the open loop gain of the 741.
I re-ran my simulation of your circuit, but I specified that during the time I do the AC analysis, I first put 10mA into the current-to-voltage converter, and then let the AC analysis vary the current +-9.9mA centered on 10mA. This turns on the PNP transistor, and give a true picture of the frequency response. Note that in my attached sim, the d.c. bias and the a.c. amplitude are both specified independently (10m and AC 9.9m)
I am plotting the magnitude and phase of the trans-impedance (gain) =V(out)/I(I1). Note that at frequencies below ~100kHz, the gain is correct 66 @ -180 degrees (-66 comes directly from R1), and then some funny stuff happens between 100kHz and 10Mhz. Note that I am using a much better opamp than a 741. To get rid of the peaking, I would put a 10nF capacitor in parallel with R1.
View attachment 83797
Thanks for the help, can you show me just the picture of the final circuit?Put the second figure here: https://www.linear.com/docs/1683 of the LT1010 etc within the feedback loop of your I-V converter at the output and it will work like a charm. Basically the input is from the output of your OP amp (Pin 6).
The feedback resistor gets moved to the output of the LT1010.
Then put a capacitor across your feedback resistor to restrict the bandwidth of your I-V converter to whatever by the relationship F=1/(2*PI*Rf*Cf)
For really precise measurements, you could add zero check and zero correct and use the offset pots., but 15 uV of Vos will make a BIG DIFFERENCE. e.g. V = -I*Rf; You have 15uV/Rf which is probably around 100 ohms or so which the OP amp can't drive without a booster. The 15 uV translates to about 15 uA of error. The closer you can get that to zero, the better the converter. The bigger issue is Vos is temperature dependent.
I have used this configuration with another OP amp and it worked really well. You also get current limiting for free.