This document summarizes the operation of various logic gates using NPN BJTs in LtSpice. It describes the inputs, outputs and operating points for:
1) A NOT gate with 0V and 5V inputs.
2) An AND gate with various combinations of 0V and 5V inputs.
3) An OR gate with various combinations of 0V and 5V inputs.
4) A NOR gate with 0V and 5V inputs on both transistors.
For each configuration it analyzes whether the transistors are on or off based on the 0.7V threshold, and whether this results in output or not.