Wayne wrote...
Could anyone help. I am trying to find either a circuit or a piece
of equipment for a pre amp.
It needs to have a flat response from 0.1Hz to 2MHz (without switching
in diff. comps.) and capable of an input imp. of 100MR and able to deal
with an input voltage switch of +/-10v (down to 1uV).
A oscilloscope buffer would be perfect if I could find one.
colin answered...
lm6152 is one op amp that springs to mind, 75mhz gain bandwidth product.,
should be easy to use, although might fall short of 100M ohm but theres
plenty of others, to chose from, dont know what gain/input ofset you need
tho.
Wayne responded...
This device tails off close to 400Hz at 5v.
See image att. form datasheet
That's 400kHz, not 400Hz, and it's the slew-rate-limited maximum
frequency for 5Vp-p output swing, not the gain frequency response.
You didn't specify your required gain or maximum rate of change.
Slew rate is S = 2pi f A. For a full +/-10V output swing at 2MHz,
that's a serious 125V/us. You'll also need a +/-15V supply opamp.
I like Burr-Brown OPA627's nice JFET input, but at 55V/us it's
too slow. Their OPA637 does 135V/us, but you'd have to wire it
in input-compensated mode for G = 1, which could compromise Zin.
The LM6321 and LM6325 were nice 800V/us G=1 buffers. The LM6313
works well, but is hard to get. I also liked the LM6362, R.I.P.
Guess you'll have to consider Analog Device's bipolar AD817, with
350V/us, even tho it has 3.3uA of input current. Ouch! Other
fast-slewing +/-15V opamps are LT1355, LT1357, LT1358 and EL2244.
The LT1229 is an exceptionally-fast current-feedback opamp, rated
up to 1000V/us and with a lower Ibias = 0.3uA typ for the + input.
Now, if you create an input attenuator to allow using +/-5V supply
opamps, you'll need less slew rate, and you'll have many more ICs
to choose from, like the elegant OPA655, a JFET rated at 290V/us.
For this opamp you'd need to restrict your input signal to +/-2.5V,
but then it would give you full-range swing capability up to 16MHz.
Thanks,
- Win
(email: use hill_at_rowland-dot-org for now)