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So if one were to use a high bandwidth Opamp, at say 10GHz, and use it to reproduce a much lower frequency signal, say in 1GHz or 700MHz, would there be attenuation or degradation of the signal?? Or, would they be indistinguishable?? Assuming also that we ignore power requirements and price of the hardware...

This is not for a power supply design.

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    \$\begingroup\$ Using "a high bandwidth Opamp" at 10GHz? What GBWP does the op-amp have? \$\endgroup\$ – Andy aka Apr 16 '15 at 8:04
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In general, using a 'faster' opamp than you need is absolutely fine. An ideal opamp will have as close to flat gain as possible across its entire range; see the graphs in the datasheet if you're uncertain.

However, faster opamps tend to be trickier to use; they're more likely to oscillate, so you need to take care to roll off the gain to prevent that; they'll require more attention and care paid to proper power supply bypassing. Some high speed opamps are not unity gain stable, so you need to be certain you're operating at a gain that they're stable at.

Faster opamps may also make tradeoffs to achieve that speed; for instance, current feedback opamps have a low input impedance on the inverting terminal, so you can't easily use them as differential amplifiers, and need to account for the input impedance when calculating your feedback values.

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  • \$\begingroup\$ Faster opamps often have lower open-loop gain (in part, to make them easier to stabilise) and that can translate to higher distortion (THD or IMD). \$\endgroup\$ – Brian Drummond Apr 16 '15 at 12:23

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