# Bodeplot of simulation and network analyzer difference in magnitude with same characteristics

#### kwoki

Joined Aug 31, 2018
12
Hello,

I have a problem which I can't find the solution. It's related with the determination of the bodeplot of a circuit. According to my bodeplot in the simulation, the flat part of the magnitude plot is -23.02 dB (Simulation.PNG) and the cut-off frequency is equal to 17.67 MHz whereas the flat part of the magnitude plot from the vector network analyzer (Help_VNA) is around -7 dB and the cut-off frequency is around 20 MHz.

Moreover, the frequency characteristic seems the same as given in the simulation, but the magnitude is different. Does anyone know why there is a difference?

Network analyzer:
flat part at -7 dB and cut-off frequency at -10 dB

Simulation:
flat part at -20.02 dB and cut-off frequency at -23 dB

I am using an Agilent 4395A network- spectrum and impedance analyzer with Agilent 87512A which is attached to input A and R.

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#### Papabravo

Joined Feb 24, 2006
20,989
The usual reason for such a shift would be assumptions about source impedance and load impedance. Given the frequencies and the negative magnitudes I'm guessing this is a passive filter.

#### kwoki

Joined Aug 31, 2018
12
The usual reason for such a shift would be assumptions about source impedance and load impedance. Given the frequencies and the negative magnitudes I'm guessing this is a passive filter.
The usual reason for such a shift would be assumptions about source impedance and load impedance. Given the frequencies and the negative magnitudes I'm guessing this is a passive filter.
It's actually a Transimpedance amplifier. I have added a two files how I got the result (Help_vna.png). Is this the right way to connect and to measure the bandwitdh?

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