Digital Logic – Digital Gate in LTspice Not Available and No Generic NOR Gate

Some PSpice models won't import into LTSpice, and those that do aren't always accurate. Before going through the hassle of finding out you should look for equivalents that might already be in LTSpice.

You can ignore package type, and often the same part is made by several manufacturers who use their own prefixes.

MMBT2907 is the same as 2N2907.

OPA192 is a precision rail-to-rail CMOS op amp with Gain Bandwidth Product of 10MHz. Depending on the circuit you are attempting to simulate, a variety of Linear technology op amps may be near enough to equivalent. LTSpice is provided for free because they want you to use their parts, so why not take a look at them?

Remember that models are just that - they don't mimic all the characteristics of the physical part. But for many simulations they don't have to. Therefore you can often get away with using a different part without invalidating the results, so long as the essential parameters are close enough.

The P-tree (pull-up network) needs to be driven the same as the N-tree (pull-down network). The circuit is a four input NOR, but you are driving it with 8 inputs. The result is that sometimes neither the P-tree nor N-tree are conducting and therefore the output is floating. Or, both the P-tree and the N-tree are conducting causing the output to be mid-level (and lots of current consumption).

The proper way to test a 4 input NOR is to use only 4 voltage sources and drive I0=I2, I1=I3, I4=I6, and I5=I7.