# Photodiode Trans impedance amplifier design

Am designing a trans impedance amplifier for photodiode from first sensor PS-100E.Am using LM 358 op-amp.To calculate the feedback resistance ,I should know the short circuit current of the photodiode.However I could'nt find it in the datasheet.I need help to calculate the short circuit current.Thank you

• Please can you link to the datasheet of the photodiode you are using? I searched for PS-100E but could not find a photodiode with that part number. – MIL-SPEC Jul 20 '18 at 8:00

## 1 Answer

The photocurrent is determined by the amount of light falling on the photodiode. You can use other parameters such as the Responsivity to calculate the amount of expected photocurrent.

$$R(\lambda) = \frac{I_{phot} (A)}{P_{opt} (W)}$$

This responsivity changes depending on the wavelength of the light. In general, knowing the spectral components of the light source $P_{opt}(\lambda)$ you can calculate the total photocurrent using

$$I_{phot,tot} = \int_0^{+\infty} R(\lambda)P_{opt}(\lambda)d\lambda$$

Of course, this is a kind of annoying expression. Depending on the light source, you can probably approximate above expression with a much more simple expression. For LED's for example, you can assume all spectral power to be at a specific wavelength $\lambda_{LED}$, allowing you to just use the simple expression

$$I_{phot,tot} \approx R(\lambda_{LED})\cdot P_{LED}$$