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I'm looking for help designing a constant current pulse through a variable load impedance of 10-100k (R4). The ideal response is shown below. This waveform was measured from an off the shelf instrument without access to the design files.

The attractive component is the square wave that it generates. It spends a solid couple of milliseconds at my intended current.

Ideal circuit response

My current design results in a circuit response as shown below with a sharp rise then fall (not ideal).

Circuit response

I'm hoping for my circuit response to more closely match that of the response shown above. What modifications could be made in order to square out the waveform?

Circuit schematic

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  • \$\begingroup\$ Your ideal response looks rather less than ideal so could you specify what it is about the trailing edge slowly decaying back to zero that is at all attractive to you? What circuit produced the "ideal" waveform? \$\endgroup\$ – Andy aka Oct 22 '18 at 19:48
  • \$\begingroup\$ Sure, the ideal waveform was measured from an off the shelf instrument without access to the design files. The attractive component is the square wave that it generates. It spends a solid couple of milliseconds at my intended current. \$\endgroup\$ – zciwor Oct 22 '18 at 19:54
  • \$\begingroup\$ Is the ideal response required to integrate to something near zero? \$\endgroup\$ – Scott Seidman Oct 22 '18 at 20:02
  • \$\begingroup\$ If so, you might try differentiating an asymmetric triangle wave. \$\endgroup\$ – Scott Seidman Oct 22 '18 at 20:15
  • \$\begingroup\$ IMO it has to be at least 2nd order, or maybe more. You circuit has a 2st order response. \$\endgroup\$ – Marko Buršič Oct 22 '18 at 20:39

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