[time-nuts] new op amp for distribution amplifiers

[John Miles]

> So the THS3491 is an LMH6702 replacement except
> for a slightly elevated noise floor.  Why would
> anyone not want to use the LMH6702?  What does
> the THS3491 have going for it?

Power output is what caught my eye.  After the loss in the series termination, the LMH6702 struggles to put out +15 dBm at 10 MHz without distortion, and you lose a bit more P1dB at 100 MHz and up.  +15 dBm is a pretty reasonable spec for a distribution amp, so you'd like some headroom if possible.

Running the LMH6702 at +/-6 helps a bit, as would using two of them with an output transformer, but a single THS3491 can output +20 dBm on +/- 15V rails by itself.   (There's a note in the data sheet that mumbles something about a +/- 100 mA long-term limit due to electromigration, but that still allows a solid +18 dBm after the series R.)

-- john, KE5FX
Miles Design LLC