Measuring Resistance with SPICE

Discussion in 'Electronics Resources' started by GlobalFPGAEntineer, Jan 28, 2011.

  1. GlobalFPGAEntineer

    Thread Starter New Member

    Jan 28, 2011
    I am trying to understand BJT amplifiers better, and I would like to investigate input and output resistance of these small circuits with SPICE.

    How can I measure input and output impedance? For the DC circuits on this website, I've noticed that 0V DC sources are inserted, and then by knowing the node voltage and the current through a 0V DC source, I could then compute the impedance. Will this work for BJT amplifiers?

    I normally just use a regular SPICE, but I also have access to HSpice.

    Any suggestions would be greatly appreciated!
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    Here's a way to measure impedances in LTspice. Basically, you just apply a voltage to the node you want to measure, and plot AC V/I in a Bode plot. Plot the resistance (vertical axis) on a linear scale instead of in decibels. To do this, right-click on the vertical axis and choose the Linear button.
    I've included the .ASC file, if you want to run the same sim that I ran.