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Total harmonic problem on 3 stage opamp circuit

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BRIAN_PENG

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Dear all:
I got a problem with high THD degradation on simple 3 stage opamp circuit.
The THD is normal and the same as loop back from PXI-5422 (SG) to PXI-5122 (SA) on Ft(input frequency)=1Mhz sinewave or below. If inputing 10Mhz signal, THD degrad seriously per stage. I've calculated the THD degradation of THS4011, it's around -70dBc in 1Mhz, shouldn't be so worse as in figure I show you in attachment. Is that related to the RF reflection between stages? The PCB routing between stages are short.

Appreciate for your help!

Brianbrian_peng1@yahoo.com.tw
 

cmontoya

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Hi Brian,
it's me from TEV how is it going? Tell your father thank you for the calligraphy it's beautiful my wife loves it.

I saw your post. The first thing that comes to mind is did you do a loop back test and account for the THD of your generator and digitizer ? it may be that the PXI generator is generating it's own harmonics as well.

cmontoya
 

BRIAN_PENG

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Thank you! Chris, nice to hear from you. I am fine and how's your new life? The problem has been solved with alternative OPAmp (THS3091) for high voltage +-10V and low distortion at 10Mhz sine wave input.


Brian
 

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