On impedance matching when a single-ended signal from a preamplifier is fed into a post single-ended-to-differential amplifier to be converted into a differential signal

Hi,

Due to the preamplifier's low output impedance, a termination resistor on the FDA's unused input is typically unnecessary. Should a termination become necessary, ensure that the FDA's gain is adjusted to preserve the intended system gain avoiding the said attenuation.

Regards,
Goz

That means that this R7 should not be needed, in which case the input impedance seen from the differential amplifier input port is at 665 Ω. Is there still an impedance match to consider here?

Thanks！

Hi,

I assume your FDA should be gain of 1 right? In that case for feedback matching you should short R11 to ground instead of having the 25Ω resistor there.

-Goz

Yes. I'm just confused about the resistor located at R7, in the chip manual he is there for impedance matching, but it affects the gain, there is confusion about this place.According to you, since the impedance of the front-end op-amp output is very small, then R7 should not be needed here, right? If it's not needed, the differential input impedance will be large, and will this process affect the signal?

Yes. I'm just confused about the resistor located at R7, in the chip manual he is there for impedance matching, but it affects the gain, there is confusion about this place.According to you, since the impedance of the front-end op-amp output is very small, then R7 should not be needed here, right? If it's not needed, the differential input impedance will be large, and will this process affect the signal?