**Part Number:**TIDA-060025

**Other Parts Discussed in Thread:**OPA858

I have a TIA question concerning a noise calculation in the **TIDA-060025**** **reference design document.

I am calculating a different noise current value than the reference design indicates.

The **TIDA-060025** reference design implements a TIA front end with a 200+ MHz Bandwidth using an OPA858 device.

Section **2.4.1.3 of the TIDA-060025** document indicates a calculated noise level of 132 nArms for the circuit conditions.

Cs = 2 pF

Cf = .75 pf

Rfeedback = 10K

Q=.95

BW=260 MHz

The **TIDA-060025** documents references TI document **SBOA122 – Transimpedance Considerations for Hight-Speed Amplifiers.**

When I calculate the input referred noise equation using equation 13 in the **SBOA122 document** I get 78.8nArms

I am not far off but was concerned that I am missing something.

Equation 13 - Ieq = sqrt(Ib^2 + 4kT/RF + (en/RF)^2 + (en*2*pi()*F*Cs)^2/3)

en = 2.5 nV/rtHz

Ib = 1e-15 Amp

RF = 10K

Cs = 2 pF

F = 260 MHz

Ieq = 4.89 pA/rtHz

Irms = 78.8 nArms (over 260 MHz BW)