Getting "Matrix Error" when using a switch with a subcircuit

[kylepaulsen]

I might be missing something obvious, not sure. I'm tying to simulate a NAND gate as if it were on a breadboard.

Main circuit: https://tinyurl.com/2la74rgh

Subcircuit: https://tinyurl.com/2ju9qf5u

If I open either switch on the main circuit, the simulation stops and I get a "Matrix Error" message on the bottom. Any idea why? Thanks.

Edit: I changed the subcircuit link as I originally posted the wrong url.

[pfalstad]

Hi, if either switch is open, then the voltage of A or B is undefined. A and B are only connected to MOSFET gates, which don't help define the voltage of those lines. If you don't use a subcircuit, then the simulator is smart enough to notice that A and B are undefined and so it will set them to 0. But if you do, then it gets confused. You should probably use logic inputs for A and B instead so that the voltage will always be set.

[kylepaulsen]

Thanks for the reply. I saw the logic inputs, but I was trying to mimic a circuit in real life for learning. If the subcircuit used NPN transistors instead would that have worked?

[pfalstad]

yes that would have worked. or, you could add a 1Meg resistor from each input to ground.

[kylepaulsen]

Thank you!