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OPA4872: OPA4872: OPA4872 50R termination causes distorted input

Prodigy 140 points

Replies: 3

Views: 57

Part Number: OPA4872

Dear Sir/Madam,

I built the following circuit. There are three OPA4872 in the first stage, one OPA4872 in the second stage and OPA695 in the last stage to form a 10:1 multiplexer.
I have a total of eight, 10:1 multiplexers. Supplies are +/-4V5.

I find that the input at R4 (the input to U1) is distorted or possibly unstable for square wave. 

The square wave below is 400KHz for 50R input termination (R4).

I have removed the cable and the signal looks normal. I have changed 50R to 1K and the signal looks better but is still distorted or possibly unstable.

The square wave below is 400KHz for 1K input termination (R4).

Any ideas?

Regards Joe