# Two-port circuit with input/output duality

Suppose I have a circuit with two ports. One port is considered the input, and the second port is considered the output.

Assume it's described via

$$V_{out} = \frac{V_{in}}{2}$$

Now assume there's no voltage applied to the input terminals.

Supply the output port with 5 V. If I measure the terminals of the input port, will I see 10 V?

In general, the answer is no, of course, as a voltage divider will show.

What do you call circuits that do satisfy the behavior where you measure 10 V at the input port given a supplied 5 V source at the output port? I'm asking for a general term, but using an example to illustrate what I mean.

• which behavior? .... you talked about two – jsotola Jan 11 at 1:46
• Hmmm... Reversable? Bidirectional? Ambivalent? I move that we all use "Ambivalent voltage converter" from now on. Seriously though probably bidirectional. – K H Jan 11 at 2:19
• @KH I like that term. It's intuitive, and simple. If you answer with this same comment, I'll accept it. – Metric Jan 11 at 2:32
• We'll wait a while to see if one of the engineers pops in, as they could comment with greater certainty than I and there may be an existing accepted term. – K H Jan 11 at 2:44
• You got it! I'm just trying to avoid one of those cases where a question has a good answer in the comments but never becomes an actual "answer" for years and years. – Metric Jan 11 at 2:46

• In the specific case where $$\V_\text{out}\$$ and $$\V_\text{in}\$$ take on only two possible levels, the device is known as a bidirectional (logic) level translator/converter/shifter.
• In the specific case where $$\V_\text{out} = V_\text{in}\$$, it is of course a wire or transmission line.
• In the specific case where the device can be switched between $$\V_\text{out} = V_\text{in}\$$ and no connection, it is a switch — or, if implemented in semiconductors rather than mechanically, specifically an analog switch or transmission gate.