So I got this problem.

enter image description here

And I know MOSFETs...Sort of.

So the area in red is a NAND gate and the area in blue is an Inverter...I think? So I know what those two pieces are, now how do those connect? Let alone what the other MOSFETs function as. So as the title says I can't "Put the pieces together".

And I know you can't give answers to homework problems. So if you can please give me some breadcrumbs to how these pieces come together, it would be greatly appreciated.


I tried the suggestion in the comments and I got 0001. I saw that C is always 1 so I can treat it as a straight wire (correct me if I'm wrong). I thought if D or E is one then the MOSFET without the label would treated as a wire and A,B or C would short circuit, I thought the only way is if D and E are both 0. What am I doing wrong?


I am now getting 1001.

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    \$\begingroup\$ I wouldn't immediately jump to "This is a nand gate" and "This is an inverter". Carefully go through each input and think about what happens when it's low or high. Alternatively, just make a big truth table (this will take a while) and figure out the output z for each combination of inputs. It may help to break the truth table into two smaller ones, one of both D and E with the output taken at the drain of D or E (I shall call it N), and the other one of A, B, C, and N \$\endgroup\$ – C_Elegans Mar 19 '19 at 16:29
  • \$\begingroup\$ I see, I'll work on it and see what I get. \$\endgroup\$ – user213230 Mar 19 '19 at 16:31
  • \$\begingroup\$ I tried what you said and I got 0100. What did I do wrong? @C_Elegans \$\endgroup\$ – user213230 Mar 19 '19 at 17:16
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    \$\begingroup\$ Can't really tell what you did wrong if you don't show your work \$\endgroup\$ – C_Elegans Mar 19 '19 at 17:19
  • \$\begingroup\$ So I caught my mistake and now I calculated 0001. Am I heading in the right path? @C_Elegans \$\endgroup\$ – user213230 Mar 19 '19 at 17:45

No, your current guess of "0001" is still wrong.

Here are some hints to get you going:

  • There are two separate logic functions here, one associated with each of the load resistors.
  • One of those functions has inputs D and E. Call its output Y.
  • The other function has inputs A, B, C and Y, and its output is Z.
  • Start by working out the full truth table for Y (four entries).
  • Then work out the full truth table for Z (16 entries).
  • Finally, in your tables, find the four specific results asked for in the problem statement.
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simulate this circuit – Schematic created using CircuitLab

If you redraw the circuit like this, you will get more clarity. Then deduce Z as:

  • Can you write the boolean expression for Z in terms of A,B,C,X ?
  • After that, write the expression for X in terms of D and E.
  • Substitute and reach the final expression for Z.
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