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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | Here are a few strings of NMOS inverters.
NMOS is harder to simulate than CMOS.
nmos22.ckt all one power supply
nmos30.ckt
nmos100.ckt
nmp100.ckt separate power supplies
The number is the number of gates.
Power supply coupling can hinder convergence, so the big circuits
have separate power supplies for each gate. At 1000 gates it makes
the difference between convergence and non-convergence. At 100
gates, it slows it down a bit but doesn't change the number of
iterations. The latency exploitation doesn't work as well with
common power supplies. The reason for the problem is that the
voltage source in ACS is non-ideal. A future release will have an
ideal voltage source.
Still... Spice 2g6 doesn't converge on either 100 gate circuit.
Another point is that these large circuits show why ACS doesn't
automatically print everything when you do an "op" analysis.
Everything Spice gives you is available. We just don't print it
automatically.
The two .c files nmosgen.c and nmpgen.c are what I used to generate
these circuits.
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