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Astable MultiVibrator

jmakwana

Hi, 

I have an input of 5v, and I am trying to create an output of square wave, with frequency around 30kHz and 50%duty. I have made the circuit and I feel it's right but I am not getting the square wave output

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    Dear jmakwana,

    The resolution and colors of your screenshots prevent me from viewing any details of your schematic nor the waveform that you are displaying. I can barely make out that your schematic appears to be a differential pair with positive feedback from its drains or collectors to the opposite gates or bases.

    From what I can tell, I also do not see any bias current to the differential pair. As such, when you apply power to the circuit, how do you know the DC operating point provides sufficient gain to sustain oscillation? Are you setting an initial condition or are you ramping the 5 V supply voltage to set the DC operating points of your differential pair to their high gain regions?

    If you are not seeing any oscillation, I might suggest you perform a DC operating point simulation and examine the small-signal gain of your differential pair using a small-signal AC simulation to validate that sufficient gain exists to initiate and sustain oscillation.

    Shawn

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