Hello , I have purchest recently an Evaluation Board containing the Op Amp LMP7712 and LMP7715 (LMP7721 Multi-Function Evaluation Board Users' Guide© 2009) ,
This evaluation board(http://www.ti.com/lit/ug/snou004/snou004.pdf) is working with a triax cabels.
I am using there the non inverting option and i am conecting a resistor of 10k at the end of the triax cabel (about 40cm long with 180pf capcitance).
i trying to get a flat response of the noise of this 10k resistor till 100khz . eventualy i am measuring this noise at the spectrum but at about 70khz
the spectrum response rise , i guess from peaking of one of the amplifiers . i have tried to put the Cf capcitor to lower the bandwidth but this didnt work,
i also tried to build it with different amplifers with higher GBW, the response have improved but still i have peaking.
also tried without the feedback amplifer LMP7715 just connecting the inverting leg to the guard shield but still there is peaking.
may i add that as the cable is longer the response rise earlier , also i rise the value of the resistor.
i will happy to recieve an advise.
Thanks
