Explain to me all these offset concepts

[variable]

Maybe I'm just really dense here but can someone please explain to me all these offset concepts like what does it mean to add a DC offset and what does adding a DC offset do to an AC signal? For instance, adding it to a sine wave or whatever other waveforms and decreasing it. Can someone please explain the general concept of it. Also, what is offset voltage? I just don't really understand these concepts. Thank you!

 

[berkeman]

If you have an AC voltage like V(t) = Asin(wt), then adding a DC offset just is adding a DC term V(t) = Vdc + Asin(wt). Or if you have the second waveform with the DC offset and you want to eliminate the DC offset, you can often just use a DC blocking capacitor in series with the signal source to get back to the AC-only waveform (where the average voltage over time is zero).

One practical example is a POTS line (plain old telephone service). The telco standard is a -48V DC voltage across the tip and ring wires when the phone is on-hook. To ring the mechanical bell for an incoming call, a large AC voltage is added to the -48Vdc. When you pick up the handset, the DC voltage falls from -48V to about -5V or so (I forget). When you speak into the microphone or push the DTMF tone buttons to dial, the AC audio waveform is combined with the DC offset as the waveform that is on the tip-ring wire pair. If you are using an oscilloscope at 1V/div to watch the waveform (careful -- the POTS voltages are already referenced to Earth ground, so you have to be sure to put your scope ground on the correct wire), you would see about a 5 division offset down from 0V when the phone is offhook, and then as you push the buttons, you'd see the AC audio dual tone riding on top of the average -5Vdc. Make sense?

The most common use of a DC offset is to combine power with data transmission. That's why the POTS has a DC offset -- to power the telephones from the central office.

 

[ravenprp]

Sure, I'd be happy to explain these offset concepts for you. Offset refers to the addition or subtraction of a constant value from a signal. This constant value is called the offset voltage. It is represented by a straight line on a graph and does not change with time.

Adding a DC (direct current) offset to an AC (alternating current) signal means adding a constant voltage to the original signal. This shifts the entire waveform up or down, depending on the polarity of the offset voltage. For example, if you add a positive DC offset to a sine wave, it will shift the entire waveform upwards, and if you add a negative offset, it will shift the waveform downwards.

The effect of adding a DC offset to a sine wave or any other waveform is to change its average value. This means that the signal will no longer oscillate around the zero axis, but rather around the new average value. This can be useful in certain applications, such as in audio amplifiers, where a small DC offset can help prevent distortion in the output signal.

On the other hand, decreasing the DC offset means subtracting a constant voltage from the original signal. This has the opposite effect of adding an offset and shifts the waveform in the opposite direction. Decreasing the offset can be useful for removing any unwanted DC components from a signal.

Offset voltage, as mentioned earlier, is the constant voltage added or subtracted from a signal. It is important to note that offset voltage can also refer to the error in a measurement or the difference between the actual value and the expected value. In electronics, offset voltage can cause inaccuracies in circuit measurements and must be taken into account.

I hope this explanation has helped clarify these concepts for you. If you have any further questions, please don't hesitate to ask.