I am new to Circuit design. Recently, I tried to build a TIA with OPA355 for a Photodiode (figure added). According to a paper, Peaking in AC frequency response shows Instability. To solve this, I used the Resistor isolation method(Riso). Peaking is now reduced, but the pulse response is changed, which also affects the input signal (signal after photodiode). How to solve this?
figure1: TIA Circuit diagram before Rios




fig 2: Freq. response


Fig3: Pulse. Res before Rios at 100KHz



Fig4: Circuit after adding Rios



fig5: freq res after Rios


fig6: pulse response after Rios

 

If that's an LTspice sim, post the .asc file.

 

If that's an LTspice sim, post the .asc file.

The circuit shown in Figure 1 is indeed from LTSpice, but the frequency response shown here is from an actual experiment. This bump in frequency response is not visible in LTSpice. I only added the first figure to show my circuit design.

 

You figure 4 schematic is different than your figure 1 schematic so we seem to be comparing two different circuits.
For example there is no R2 in the figure 4 circuit.

And I don't understand the Rios circuit.
Is this Cload a capacitance you added?
That makes no sense.
And 18+15 ohms is too low a load resistance for the op amp.

What you are seeing is likely from stray capacitance at the inverting input.
Try removing the Rios circuit and increasing the value of the 1.8pF feedback capacitor to compensate.
Likely something in the tens of pF should work.
You would need to experiment to find the optimum value.