# Improve DAC Pulse Rise/Fall Time

I have an older NI DAQ (PCI-6251) which comes equip with a bunch of ADC's, two DAC's and a hand full of DIO ports. I need to output a pulse of variable width, amplitude and DC offset which the DAQ can do but once you fall below about 5us pulses the rise and fall times become a considerable amount of the actual pulse. For example, I would like to idle the DAC at 5V and then have it pulse to 0.5V for 1us and return to 5V without having the pulse be too distorted.

Is there a simple circuit that could sharpen the edges of the pulse while still allowing me to keep a DC offset?

My first thought was to use a P-TYPE MOSFET in a pull-up configuration with the gate tied to a Digital Output signal but then I wouldn't be able to use just any DC offset or pulse amplitude. The rise/fall times of a Schmitt trigger would be perfect but I'm not sure how I could use the digital output in an analog signal.

Let me know if there is more information I can provide. Any help would be very much appreciated!

• Do you have any waveforms? Are you using a coax cable? If so, what is $Z_0$ and how long is it? What is the load you are trying to drive? Are you using $10\times$ probes for your measurements? – Zulu Apr 7 '15 at 3:59