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Inverting amplifier / positive pulse problem

I built a pulse generator that produces ~1.5 ns pulses that go from

0-3V. (Use Linear app note 98 if you want to build one.) I would like to put it into an RF amp to produce the 7V pulses needed for my application. My problem is that my amp is an inverting amp. Thus, when I put in my positive pulse (actually attenuated down for the amp), it produces a negative pulse of ~4.5 V (corresponding to the bottom rail).

I thought that I could switch the polarity of the SMA connector on my board -- attaching ground to the middle pin and the pulse output to the case. However, I don't think this will work as the ground from the amp and scope will then have to float. I thought of using a NOT gate, but wouldn't that just give a pulse that goes from -5 to 0? Also, the gate would likely increase the pulse width, which we would like to keep as short as possible.

What would be ideal is to have some simple device that takes a positive voltage and flips it to negative, while keeping the pulse width short. At low frequencies, an op-amp could do it, but I'm not sure of any op-amp that will do it at these frequencies. Does anyone know something that will do it? Has anyone done something like this before?

Obviously, it would be better to just use a non-inverting amp. The spec sheet on the amp (JDSU H301) doesn't even mention that it is inverting. Are all Optical Modulator Driver amps inverting, so that it is just an understood?

Thanks

Reply to
O. P. E.
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Most packaged rf amplifiers are not characterized as inverting or not inveting, just as an amplifer. ie gain input vswr output vswr and 1 dB compression point, plus "bandwidth".. You can make a modest gain 10-20 db amplifier with a single active decie, some input match, bias and output match. with a single devcie if you wiggle the base (gate) and take the signal off the collector (drain) you have an inverter. you coul use two in series!

For a 1-2 nS pulse you could use an avalanche tx and hen atenuate the signal down to 7 volts, as the avalacnhe tx will produce about 100 Volt

1 ns rise 1.5 ns fall the signal has a nice impulse shape..

Marc

Reply to
LVMarc

Perhaps I should have said "GHz amp" instead of "RF amp." For most radio signals I doubt polarity matters. However, since this is an amp to interface a signal source with something else, the polarity does matter. Doing some more research, it looks like the amp expects a signal from -.7V to -2V. So, I think it may be expecting some kind of ECL signal. I hope that I can find some kind of translator circuit.

I looked at a few circuits with avalanche transistors. However, with the delay line/AND gate circuit you can change the pulse width by turning a pot, and set the rep rate by using the square wave of an external function generator. The design I found with avalanche circuits with variable pulse widths required a BNC cable cut to length, and had much lower rep rates to allow capacitors to recharge. Also, I worry about the noise 100V pulses create, as I am getting enough with TTL.

I'll have to look into your active device suggestion. That sounds like a circuit I looked at that was posted on Microwaves101. However, that circuit was to produce pulses of RF, while I am just looking to produce square/guassian pulses.

Thanks for your response.

Reply to
O. P. E.

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I found a nifty circuit for doing this while looking for something else. HP did it by using a simple transformer, then, of course, discontinued the product. Here is a link, and the data sheet shows how they hook it up.

formatting link

I think HP has discontinued more useful equipment than 90% of companies have ever made.

Hopefully, this will help anyone in the future who follows this thread, and is looking for a solution. I'm going to look for some transformers to hook it up. As I've never worked with RF transformers, does anyone have suggestions?

Thanks

Reply to
O. P. E.

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