MDAC output amp

You're probably better off without C2. haven't used this part in particular, but I have some experience with other CFB parts like the AD8000, and normally you want to avoid any capacitance in the feedback loop. Same with capacitance from - to ground. Their gain doesn't fall off with frequency in the conventional VFB sense, so you may see some unwanted peaking with this circuit unless you get rid of the capacitance and/or use a lower Rfb.

The data sheet doesn't seem to have as many dire warnings as the ones for the CFB parts I've used, so maybe it's not a big deal with this part. But if you don't need the inversion, I'd drive the + input instead and keep all of your capacitive strays away from -.

CFB amps are some of the least-appreciated parts out there. They are great when you need flat gain and good drive capability to

100 MHz+ and don't want to use discretes. Once you start using them you may get hooked.

-- john, KE5FX

That is exactly what I expected. Except that Spice says that it likes a few pF of C2. I'm using such big input and feedback resistors - 5K - that this amp is operating in an unusual space; I'm throwing away most of the native GBW.

I'm using a current-output MDAC, with an internal feedback resistor, and it needs an inverting amp. It makes at least poetic sense to drive the inverting input of a curent-mode opamp. It actually seems to work pretty well, at least in Spice. DC performance will be terrible, but I only need the AC signal.

Oh, I love them already. AD8xxx series for small stuff, and the THS parts for big voltage and current swings. There is nothing else out there like the THS3xxx and THS6xxx parts.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics