ChipCraft is a good course for beginners to learn chip design. I found it is compelling to break down some of its 300+ slides and hopefully it may help other newcomers with understanding the concepts when feeling confused with them.
Today I’ll show how I approached and solved the NAND Challenge.
We are given two circuits to make a NAND gate: the first one, default on, is only on when the current is zero and the second one, default off, is only on when the current is one. Both circuits have an input, an output, and a current. The current determines if the circuit will be on or off. If so, the input will be given to the output. Otherwise, the output is zero regardless of the value of the input.
In order to make a NAND gate, we need to make an AND gate and a NOT gate.
Build AND Gate
The AND gate’s truth table is:
Input A will be the current and input B will be the input for the circuit. Firstly, we need to determine which circuit to use. Since an AND gate only outputs 1 when both A and B are 1, we need the current to be 1 for the output to receive the input. Therefore, the circuit we will use is the default off circuit.
Note: We know that this is an AND gate because the truth table on the left is the truth table for a NAND gate and all four rows have an X.
Add NOT Gate
The NOT gate’s truth table is:
For this gate, we first need to determine whether the output for the AND gate should go to the current or the input of the circuit. If the current always remains the same, then the output will either always be 0 or whatever the input is, which is not what we want. Thus, the current will be given the output of the AND gate.
Next, we need to figure out what the input will be. If the input is always 0, then the output will always be 0 regardless of the current. Accordingly, the input will always be 1.
Finally, we will figure out what type of circuit we should use. When the current is 0, the circuit should return 1. Otherwise, it will return 0. From the above description of the circuits given in the first paragraph, we are positive that the circuit is the default on circuit.
