[Qucs-help] toying digital

[Raimund 'R. J. <ra...@lk...>]

hello *,

Florian and me were playing around, trying to start a digital 
simulation. Attached are NOR, OR, NOT, NAND, AND in TTL (wich seem to 
work) and an attempt of a NOT in CMOS. the CMOS version does not work at 
all and we dont understand why.

symptom is:
ERROR: TR1: Jacobian singular at t = 2.000e-03, aborting transient analysis

does anyone have an idea what may cause this? is the circuit wrong or is 
that a shortcoming of the simulator?

furthermore we have same suggestions:

* when using a subcircuit the ports should be shown with their name, not 
their number. it is really hard to wire a NOR and a NOT together given 
only port numbers 1..5 and 1..3.

* related to this: moving the "pins" of a subcircuit around would 
greatly improve wiring when using a subcircuit.

* for digital circuits we would need some kind of a "table-driven" 
voltage source. something where you just would enter a timespan and a 
voltage:
1ms 1V
2ms 0V
1ms 1V
...

this would be even better when the source had multiple ports, each 
having its own table.

this way one could simulate digital circuits using analog subcircuits as 
building blocks. the simulation would probably be slower than for a 
proper digital simulation, but you could simulate mixed-mode stuff this 
way. ...or simply teach digital circuits :)

keep up the good work, it's really fun using qucs!

	Florian + Raimund

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