Need a simple circuit idea to generate an Impulse Response

Discussion in 'The Projects Forum' started by Mugwump101, Oct 28, 2011.

  1. Mugwump101

    Thread Starter New Member

    Oct 28, 2011
    I'm connecting a signal generator that generates STEP waves to my breadboard and DAQ card, which is used to allow the signal to be picked up by LabView. Now, from the step wave, I want to build a circuit that will generate an impulse response (output) from the breadboard that will display that signal on LabView.

    So, basically, I need a basic circuit that will generate an impulse response (output) from step waves (input).

    Thanks a bunch in advance!!
  2. steveb

    Senior Member

    Jul 3, 2008
    Can you be a little clearer on what you are trying to do? Do you wish to make an impulse for the input function and then drive the system with that pulse to get the impuse response out directly? Or, do you want to add another system to output of your system to make the output step response look like an impulse response, of your present system?

    The solutions are different because one is the modification of the input signal and the other is the modification of the output signal.

    Assuming you have a generator with a 50 ohm source impedance and BNC connector, you could generate a short pulse from your step function by attaching a splitter at the output of the generator and putting a shorted transmission line on the other path. The length of the line will determine the pulse time. The reflected wave from the short at the other end of the transmission line will cancel out the step output after the propagation delay. The propagation delay should be longer than the rise time of the step edge, and it should be much shorter than the system time constants. The amplitude of the generator would then be scaled to give you an integrated area of 1 Vs under the pulse, so that you have a unit impulse function for the input.

    If you want to modify the output, you can note that the impulse is a derivative of a step. So, if you have a linear system, you can move the derivative to the output side. Hence a differentiator on the output can give you the impulse response of the system when it is driven by a step response. The difficulty of implementing the differentiator depends on what bandwidth you are dealing with. With audio frequencies, an OPAMP differentiator is easy to make.