# Schematic shows two outputs for Vout. Why?

How do I interpret the fact that Vout has two output points? My guess is that the two Vout points represent where I would place the probes on a multimeter. Is this correct?

See this diagram: The article I'm reading suggests that there is only one signal for Vout, which looks like this: I'm really sorry for if this a basic question, I'm new.

• "My guess is that the two Vout points represent where I would place the probes on a multimeter." I can only speculate why the drawer choose to show two output terminals, but yes this clearly indicates the nodes where you should place your voltmeter (multimeter). Usually ground or the lower rail designates ground (of the voltmeter probe) and you may select the other node (probe) arbitrarily. Either the ground symbol or the lower terminal is redundant. – try-catch-finally Aug 16 '17 at 5:20
• At first I thought why is the graph wrong, then I realize it's just theory that assume the diode forward voltage is 0V. – Jason Han Aug 16 '17 at 5:46
• @try-catch-finally it's really common to see educational circuits drawn like this to give students a clear indication of where to put their probes. Most of the diagrams in my 1st yr notes have two output points as occasionally you measure across components rather than with respect to ground. – BenG Aug 17 '17 at 0:16
• @JasonHan I learned about forward voltages in diodes yesterday! I'm pretty sure the article does state that for simplicity, forward voltage was omitted from the example. – Mark Wears Glasses Aug 17 '17 at 5:40

A voltage is relative between two points. A voltage signal therefore always has two connections.

However, a circuit that has to deal with multiple signals usually wants them all referenced to the same point. Since this comes up a lot, we call that point "ground". We then often talk as if a signal is on a single line, implying that it's actually reference to ground.

Your diagram shows Vout between two points, because that's what it really is. But also notice that the bottom Vout point is shown connected to ground. In electrical engineering context, it would therefore be acceptable, and even common, to talk about Vout as if it were only on the top line. When nothing special is said, the default is that ground is the reference for a signal.

• Ah ok, I think I get it. It needs to be a circuit, it must return to ground. – Mark Wears Glasses Aug 15 '17 at 23:57
• Whoever downvoted this, what exactly do you think is wrong? – Olin Lathrop Aug 16 '17 at 0:42
• @Olin, can you request to appropriate authorities to make it mandatory to give reasons for downvoting an answer? Atleast till answer receives say 5 down votes? – Deep Aug 16 '17 at 5:56
• At least try to motivate your downvote. I can't see anything remotely wrong with this answer. – Bart Aug 16 '17 at 6:22
• Olin's answer is perfectly fine. – BenG Aug 16 '17 at 23:55

Voltage is always relative to a defined point. Notice that the bottom line connects to ground. So Vout is just the top line.

• Now that makes sense, but then why does the diagram have the second Vout point? – Mark Wears Glasses Aug 15 '17 at 23:48
• @Mark Wears Glasses: "relative to" means that you must have a reference point. If there was only one Vout point given (and no line marked as GND), it would not be clear between which two points the voltage is measured. – Curd Aug 16 '17 at 14:00

An output voltage is relative between two points

the high point which is the value of the output voltage

• the reference voltage hear is the ground

in many case it is the ground like the car electronic system

but in other case it may be a negative point