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?

 

[XNOX_Rambo]

Check if this high power operational amplifier, or a similar type, could do the trick:
https://focus.ti.com/docs/prod/folders/print/opa549.html

/Rambo

 

[evandude]

You, sir, are my hero. I never even thought to look for a single-chip solution. I had envisioned some sort of complicated circuit with push-pull MOSFET outputs or something.

with a slew rate of 9v/uS that should be capable of a triangle wave at 250 KHz at 18Vp-p (by my quick, offhand calculation) so i think it will work marvelously. I think i may build a couple different output driver circuits... one with this chip for low-frequency, high power, and another for high-frequency, low power operation...

thank you a lot...

 

[Borber]

OPA603 from TI has slew rate 1000V/µs, output current is ±150mA, but supply voltage is only ±18V. This current feedback OPA will give you higher upper frequency limit.

 

[evandude]

the OPA603 appears to be obsolete, according to the TI website. thanks though, I will look around the TI site for a similar one, so I can have a high-frequency amp too.

 

[VVV]

This is another circuit I like, the LT1010 from Linear Technology: www.linear.com/pc/productDetail.do?navId=H0,C1,C1154,C1009,C1028,P1219
National used to make LH0033, if you find one of these oldies, it can work, too.