Re: Radiofrequency amplifier.

On Nov 16, 5:35 am, hahn.a...@xxxxxxxxx wrote:
On Nov 16, 12:10 am, jon...@xxxxxxxxx wrote:



Hi,

    I am trying to build an amp capable of driving +/- 12 volts into a
50 ohm load over a range of frequencies from DC - ~100 mhz. As if that
wasn't hard enough, it needs to be about 2 cm^2 in size. Additionally
the output must be able to go into a high impedance state which
presents very little capacitance to the bus. I've gone through a lot
of different design ideas and have settled on this kind of weird
architecture. The schematic is here:

http://prymfg.com/schema.jpg

The output transistors are 2sk1403 and 2sc3597. The opamps are
actually ad8045's. Even with only one half of the push-pull, this
design isn't stable. At least according to spice it oscillates in the
5-65GHZ region. I'm not really sure if spice can be trusted at all.
How would a circuit like this be analyzed? Will it work or how can I
make it. I've tried things like using transconductance amplifiers,
using a mosfet as a second stage and adding feedback filters.

Thanks in advance.

Jon Pry

Jon, Perhaps using the Wilson Current Mirror for the output stage is a
solution. It has good linearity if you use matched transistors like
the lm394, etc..  Just parallel enough of them to drive 50 ohms at
12v. It's not rocket science, you should get a flat response out to
100k without feedback. You cant use feedback , it will lower your
output impedance.

Good luck and let me know what happens.

I don't understand how a current mirror is going to work. I need the
common emitter outputs because they allow me to make the output
impedance go high. Also, a push-pull amp is necessary for that reason
and heat reduction.
.

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