I have an application that requires a square wave pulse with the following characteristics:

• frequency = 10-200 Hz
• width \(\geq\) 20 \(\mu\)s
• risetime < 100 ns

Additionally, the application requires a very flat top to the pulse. Specifically:

• ringing falls to within 10 mV of steady state value after 100 ns
• droop/sag does not exceed 20 mV over 10 \(\mu\)s
• variable amplitude up to 10 V

Overshoot and ringing themselves are not so big of a deal, just as long as they die out very very quickly, and that after 100 ns the pulse reaches its steady state value and stays within 10-20 mV of it for most of the pulse.

I can't use an off-the-shelf pulse generator for this, because I need to change the amplitude with every shot, and I don't have a programmable pulse generator that works at 200 Hz.

I've tried wiring up a MOSFET, but the droop is too significant.

My question: Can anyone suggest a square wave generator IC that might meet these characteristics, or maybe point my search in the right direction?

Edit:
I think the problem is that I don't know what words to search for. "Square wave oscillator"? "Square wave generator"? "Comparator"? Of course it'd be lazy of me to ask someone to do a Google search for me - really what I need is advice on:
1.) do "square wave/pulse generator IC's" exist?
2.) what are they called, so I may search for them?

 

I was able to find a couple with 12 ns rise, MAX038 and AD5932.

 

The AD5932 is still available from some authorized distributors, but unfortunately the MAX038 is no longer available. Back around 1993, there was a tsunami which destroyed the Japanese manufacturing facility for the MAX038, and the technology to produce the IC was lost.

If you find any MAX038 IC's for sale, they are most likely forgeries, and won't perform like the real MAX038 did.

 

This isn't a plug-and-play solution, but they do sell mighty fast DACs that can make whatever waveform you can think of, within reason. If you're handy with microcontrollers, you can go that route.

Alternatively, a well-tuned 555 circuit followed by a fast power op-amp (which you vary the gain or input level to get your variable amplitude) might work as well.

 

Hi,

Try these.....

1. 555 astable
2. XR2206
3. SG3525