Choice of Diode to prevent

[LoveLaika]

I'm running a sim of a trans-impedance amplifier that takes two current sources. I'm modelling my current sources as two exponential currents using the following parameters:

EXP(0 -20m 10n 500p 5n 250n)

• Initial Current = 0 A
• Pulsed Current = -20 mA
• Rise Tau = 500ps
• Fall Delay = 5 ns
• Fall Tau = 250ns

The two sources differ in their activation time by 25 ns, and they both go into a TIA to convert their current sum into a voltage. Straightforward, but I wanted to prevent from current backflow from one source to the other, so I'm thinking of adding a Schottky diode in series with my sources to prevent unwanted backflow, but I can't find a good Schottky diode model that would prevent backflow. What parameters should I look for here?

To add more information, while my current source is a simple, ideal one for testing purposes, the actual current source is a photodiode, two of them. Once they 'activate', they generate a voltage of -35 mV at the summing node, passing through the feedback resistor of the TIA to convert the current to a voltage signal. Given how the voltage difference is so tiny, should the diode forward voltage be tiny as well? The lowest forward voltage I found was 140 mV on Digikey.

[rs20]

Since you seem to be staying firmly planted in the virtual (simulation) world, maybe just use an ideal diode?

https://electronics.stackexchange.com/questions/353826/how-to-make-an-ideal-diode-model-in-ltspice

[LoveLaika]

I think I'm not seeing it intuitively. Looking at the wiki's model of the TIA, the current flows into the feedback resistor, which the TIA converts to a negative voltage. Now, like with my sim, if the current flowed into the opposite direction away from the feedback resistor, the output becomes a positive voltage. In order for it to flow in the opposite direction, the voltage at inverting terminal (or summation node) where the source drops with respect to the other end of the current source, connected to ground. So if that's the case, the backflow diode should follow the direction of the current source?

https://en.wikipedia.org/wiki/Transimpedance_amplifier

[LoveLaika]

Thanks; sorry, I get what you're getting at now, using the ideal diode model and adjust as needed to see how it works.