Electronics > Projects, Designs, and Technical Stuff
High frequency photodiode transimpedance amplifier design
awallin:
Here's a few python scripts that compute transimpedance, bandwidth, and noise for a simple one op-amp TIA:
https://github.com/aewallin/TIASim
comparisons against real-world measurements show good(ish) agreement with a few OPA657 designs.
if anyone has insight on how to compute stability (vs oscillations), phase-margin, etc then that would be a good addition to these scripts.
Marco:
--- Quote from: grouchobyte on June 13, 2020, 10:41:56 pm ---With 33K TIA gain, it's johnson-noise limited
--- End quote ---
Seems unlikely, datasheet current noise 2.6 pA/rtHz, Johnson-Noise 0.7 pA/rtHz.
Marco:
To really get close to Johnson Noise for these larger feedback resistors and at high bandwidth I don't see any other way than using a discrete JFETs or GaAs FETs common source amplifier. By themselves JFETs at least won't really have the bandwidth to be able to handle a 33k feedback resistor from drain to gate though, so you'll need an extra non-inverting amplifier.
Maybe a GaAs FET could do it with just a resistor from drain to gate and no extra amplification stages? (Well, a resistor plus something to add some voltage drop.) Dunno.
PS. all assuming inputs without huge capacitances, where Phil Hobbs wizardry comes into play.
nfmax:
Although I wasn't personally responsible for the design, I have seen a GaAs HEMT followed by a CFA used successfully with ~100k feedback resistors giving bandwidths around 50MHz to 100MHz, from a low-capacitance APD detector. DC performance is terrible, but that didn't matter for the application.
awallin:
FWIW, I added a model for the OPA818 op-amp to TIASim, and then compared the TIASim bandwidth-predictions to those in the TI datasheet.
When I add an extra sqrt(2) factor to the computation of the optimal C_F (in parallel with R_F) I get reasonable agreement.
opamp https://www.ti.com/lit/ds/symlink/opa818.pdf
script: https://github.com/aewallin/TIASim/blob/master/opa818_bw_figure.py
so this (maybe) adds some confidence to the predictions for BW and noise give by TIASim.
AW
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