Function Generator output driver

[evandude]

I am working on building the function generator project from EPE magazine. However, the output of it is AC-coupled, and across a 10k pot for voltage adjustment, so obviously the output impedance is pretty high. I know that a function generator output is generally not used for low-impedance inputs anyway, so that shouldn't be an issue, but I have in the past "abused" the function generators in our electronics lab which have decent output drive capability.

Basically what I'm looking for is some circuit that will give me a little more output drive capability, with as much voltage range as possible. The power supply I plan on driving the output drive stage from has +5v, +/-12v, and +24v outputs.

Something in the range of maybe a few hundred milliamps of output current would be fine. I originally thought of using an audio amplifier, but I need to be able to introduce a DC offset to the signal for things like driving logic circuits, and I don't want square waves to get attenuated. The maximum frequency of the function generator chip is 20MHz, but the article says that only about 10MHz is achieved.

If necessary, I would be okay with sacrificing performance at high frequencies. Most likely, at high frequencies (1 MHz and above, probably less) I would only need low-amplitude AC-coupled signals anyway, so this driver stage wouldn't be necessary... so if the driver stage only worked smoothly to several hundred KHz that would probably work okay.

Is it reasonable to build a DC-stable amplifier, good to at least several hundred KHz, that can supply a couple hundred milliamps, at up to about 20V peak-to-peak output?

 

[panic mode]

20MHz is not much by today's standards - did you think of using opamp?
these days they reach high frequency and have high power,
and even continuous short circuit on output tolerant etc.
(look at the specs and proce of chips like LM6640, LM 6181, LMH6672)

 

[Russlk]

This circuit might not handle 20 v p/p without heat sinking, into a 50 ohm load. It is good to 20 mHz at least.

 

[Roff]

Hey Russ,

You can mirror and rotate components in SWitcherCAD III by hitting F7, selecting the part you want to change the orientation of, and then dragging the part up to one of the little icons at the upper right of the toolbar and clicking on it. See below.
You can make that circuit look like push-pull emitter followers, instead of like black magic.

 

[Russlk]

Many thanks, Ron. I get frustrated trying to figure those things out!

 

[Roff]

Many thanks, Ron. I get frustrated trying to figure those things out!

Oh, and one other thing you might find useful. It appears that you print and scan your schematics. You can capture schematics and waveforms directly from SWCAD. I resize the schematic or waveform window to a readable size, then click on Tools - Copy Bitmap to Clipboard. Then I paste into Paint, and save as a GIF file. You know the rest.

 

[Russlk]

Thanks again, Ron