enter image description here

I know that whenever you have series transistors multiply the equivalent W/L of the inverter by the number of series transistors. In the parallel case W/L remains the same. I don't know how to apply those two rules to this problem. All of the examples I can find are far simpler than this and more symmetric.

How do I apply parallel and series rules to transistors?

  • 1
    \$\begingroup\$ Start by drawing the transistor level schematic of this function, ignore the W/L first, just draw the circuit. After that worry about W/L \$\endgroup\$ – Bimpelrekkie Jan 10 '18 at 20:47
  • \$\begingroup\$ that's not the problem i already drew it. \$\endgroup\$ – Mostafa Mekawy Jan 10 '18 at 20:52

If you have already sketched out the transistor diagrams take the worst case N path (4 transistors if I am not mistaken) and size these to give you the required overall w/l. The other transistors on the N side can be smaller, you have a set of three one of which is already sized from the above. Size the other two to match the needed overall W/L. Finally you have one which acts on its own size that one accordingly.

Repeat the exercise for the P side transistors and you are done.

  • \$\begingroup\$ okey, so they can be the same size as the critical path ?! \$\endgroup\$ – Mostafa Mekawy Jan 10 '18 at 21:07
  • \$\begingroup\$ Yes they can but silicon area is expensive and the extra gate capacitance reduces performance you would get extra marks from me for making them as small as possible. \$\endgroup\$ – RoyC Jan 10 '18 at 21:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.