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Original question:

TINA/Spice/OPA855: OPA855 TIA

OPA855: TIA TINA model

Amar Gaikwad1
Prodigy 70 points
Part Number: OPA855
Other Parts Discussed in Thread: LMH5401, , TINA-TI

Hello,

I am trying a TINA model of OPA855 to check what is the lowest value current that I impement in photodiode model to achive a bandwidth of 200MHz. I have added LMH5401 with gain of 2 after OPA855 to increase the SNR. Below is the observation:

  • Intended use for Input of 200MHz, 1uA photodiode model.
  • Based on TIA considerations Rf= 3K, Cf = 0.37pF
  • Minimum current in photodiode model has to be 100uA so that the o/p swings follow the input frequency. Below this current level the o/p does no show any AC. It is just a DC. But OPA855 has 8GBP.
  • If the Cf is removed from the spice model, we do get some level of o/p swing. But it is not upto the satisfaction.

My question is; will the o/p of TIA with OPA855 follow i/p frequency of 200MHz if the current produced by photodiode is 1uA?

Regards,

Amar