0
\$\begingroup\$

I have been reading the Digital Design: Principles and Practices 3rd Edition as a hobby. Unfortunately, I am stuck at page 103 of Section 3.5.2: Circuit Behavior with Resistive Loads.

In Figure 3-27: https://ibb.co/v1BVXrK, a resistive model of a CMOS inverter with a resistive load has been illustrated. (a) showing the actual load circuit and (b) using the Thevenin equivalent of the load.

To understand how Figure 3.27(a) is equivalent to Figure 3.27(b), I learned how the Thevenin theorem works. I watched a brilliant course about the theorem: https://www.youtube.com/watch?v=25axDabtoFk.

However, as far as I understand from the Thevenin theorem, we remove a circuit component and make it an open circuit. After the removal, we have only 2 open terminals. Whereas in Figure 3.27(a), by removing the components in the right-hand-side blue rectangle, we are making 3 open terminals, not 2.

So, how does the author convert Figure 3.27(a) to Figure 3.27(b) using the Thevenin theorem?

\$\endgroup\$
0
\$\begingroup\$

I think your confusion comes from the fact that both the inverter and the load use the same power supply voltage source.

You can replace the single power supply with two identical supplies, one for the inverter and one for the load. As long as these are assumed to be ideal voltage sources with the same voltage then the circuit behavior does not change. Of course, the ground terminals of the two sources must be connected together.

Now, the load is connected to the inverter at just two nodes: the inverter output and ground. The Thevenin equivalent of the load must be constructed with these two nodes being the "output" nodes of the equivalent circuit.

\$\endgroup\$
  • \$\begingroup\$ Can you further elaborate your last sentence? What do you mean by the "output" nodes? I tried to draw based on what you have said (ibb.co/fYcW2z5) but I am still confused. If you think I lack some prerequisite knowledge, can you list what they are? \$\endgroup\$ – bmm Jan 2 at 18:12

Your Answer

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

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