NG-SPICE: Low-Powered Saw-Wave Generator

The goal of my latest exercise at using the Open-Source circuit simulation software named ‘NG-SPICE’ consisted of designing a low-powered saw-wave generator. Here were the premises of the project:

  • A train of pulses is to be taken as input, that are approximately of 1μS duration, 2V in amplitude, and that have a steady rate of recurrence of 100kHz.
  • They are to be converted into a saw-wave that has an attack as fast as the pulses are short, and which has approximately linear falloff after each input pulse.
  • One active component is a monolithic N-channel enhancement-mode MOSFET transistor with a gate size of approximately 100 microns squared – which therefore has poor qualities if compared to discrete components – but which is plausible as part of an IC with Medium Scale Integration (:2)
  • The other active component is a bipolar diode of unknown weaknesses, which has been approximated as a discrete 1N4148 switching diode.
  • The entire circuit is to operate off a 3V power supply.
  • The maximum output load is in the vicinity of 100kΩ – 40kΩ, and must not change the internal workings of this circuit block. (:1)
  • The output amplitude is to reach approximately +1V with respect to the circuit ground.

What was observed:

  • The diodes were difficult to get into a conductive state at the low pulse-voltage.
  • The chosen MOSFET makes a very poor output driver.




The experiment seems to have been successful.

(Updated 7/3/2019, 8h35 : )

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