Why does phase change with frequency in rc circuits

If current is the same then the voltage across C always lags the voltage across R by 90 degrees. It's also true that at very high frequencies Xc is very much smaller than R so the voltage across R closely resembles the input voltage whereas the voltage across C will be very small. At very low frequencies the opposite is true - the voltage across C is very similar to the voltage on the input and the voltage across R is tiny.

Only at these extremes will the phase shift produce close to 90 degrees and that will be seen across the component that has the lowest impedance. Your first circuit is a low pass filter. The second is a high pass filter, all frequencies above the corner same fc are passed. OK, the details are more involved. I think the best thing is to get a 'scope and function generator and see what happens. Next best is maybe to play with LTspice. Then go do the math again.

Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Phase Shifter: why is simple RC circuit's output 0 when phase is 90 deg?

Ask Question. Asked 7 years, 3 months ago. Active 7 years, 3 months ago. Viewed 1k times. MrUser MrUser 2 2 silver badges 10 10 bronze badges. Add a comment. Active Oldest Votes. Andy aka Andy aka k 21 21 gold badges silver badges bronze badges. I'm a little confused, though. But shouldn't it be 45 degrees? Or is the arctan equation for something else? And the book says that Vo goes to 0 as the phase shift approaches It just doesn't sit well with me that both configurations can have an output of 0 at 90 degrees, when the complete voltage in each case will be across different elements.

I think if you had an o-scope and messed around a bit it would start to gel. The output is 90 degrees but infinitely small! Search titles only. Search Advanced search…. New posts. Search forums. Log in. Install the app. Contact us. Close Menu. Welcome to EDAboard. To participate you need to register.

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Hello, Hopefully this isn't duplicating any other thread, I've looked but have not found an answer that I understand. I think I understand how a capacitor stores charge in an electric field, and I believe I understand why there is a phase shift in the output of the capacitor with respect to the input. What I am confused about is how and why the capactive reactance and resistance are used to calculate the phase shift.

I'm not looking for a mathematical proof, just a simple explanation of how the reactance and resistance defines the shift in phase. The total resistance of the entire circuit? The resistance of just the next resistor in series with the capacitor? So if you have two RC elements like , what is the R used to calculate the theta of C1?

Just R1? Does the reactance of C2 contribute to the overall resistance used to calculate the theta of C1? FvM Super Moderator Staff member. The simple formula however doesn't apply to the two-stage RC circuit. Once you have the transfer function, you can calculate the phase. LvW Advanced Member level 5. One can probably assume what you mean for example: phase shift at the node between R2 and C2 - however, for a better understanding it is important for you to realize that these parameters are node dependent.

But it also says that 'When resistors and capacitors are mixed together in circuits, the total impedance will have a phase angle somewhere between 0o and o'. So if you have two RC elements which can apparently have a total phase shift of more than 90 deg , how do you go about constructing this transfer function you are referring to? LvW: the phase shifts that I am curious about are the output versus the input of each RC element.

So for example, what is the phase shift between the input of C1 and the input of C2? Does this shift have any dependency upon the second RC element C2 and R2?