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 18.104.22.168 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
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)