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enter image description here

I have a 50 ohm BNC cable which connects to a coaxial connector on a PCB.

I want to invert the signal from the cable with an op amp.

If I use the top circuit from the image, will the cable be terminated correctly, or should I add a buffer with high input impedance like the circuit in the bottom of the image to achieve 50 ohm termination ?

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  • \$\begingroup\$ Explain why you believe you need to terminate the cable in 50 ohms. What signal frequencies are you using? \$\endgroup\$ – Andy aka Apr 3 at 10:30
  • \$\begingroup\$ @Andyaka , hello my signals are around 50 Mhz . The termination must be done to 50 ohms according to the datasheet of the bcn cable. Best regards \$\endgroup\$ – Suparman Sy Apr 3 at 10:32
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You will more-than-likely get away with scenario 1 but if you were to be picky you would terminate in 52.63 ohms: -

enter image description here

52.63 || 1000 = 50.

Nearest value to 52.63 ohms is 52.3 ohms and this, in parallel with 1 kohm gives 49.7 ohms i.e. 0.5% away from perfection.

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  • \$\begingroup\$ So , i have to use a resistor which will be equivalent (or close to 50 ohms) when put in parallel with the 1k . Than you very much Sir \$\endgroup\$ – Suparman Sy Apr 3 at 10:39

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