# How Does a Capacitor Introduce Phase Delay in a Circuit?

• PhysicsTest
In summary: When you are using the term "delay" - which signals do you have in mind? Such a delay is the delay between two signals (voltage and/or current) resp. the corresponding phases of these signals, in time. When you remember your own definitions, you will know what you have to measure/simulate.When you are using the term "delay" - which signals do you have in mind?You are asking about the delay between voltage and current signals, right? If so, then the delay is the time it takes for the voltage to go from one phase to the next. This delay is always the same for signals that are in phase. In summary, you
PhysicsTest
TL;DR Summary
Understanding the phase delay
I simulated the below circuit to capture the phase delay between input voltage and output current in LTSpice

How do i measure the phase delay introduced due to capacitor?

#### Attachments

• lfresponse1.txt
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The rule is that currents in a series circuit are ALWAYS in phase. So I'll ask you what can you conclude from that rule and the circuit you have drawn.

When you are using the term "delay" - which signals do you have in mind? Such a delay is the delay between two signals (voltage and/or current) resp. the corresponding phases of these signals,
When you remember your own definitions, you will know what you have to measure/simulate.

This would normally be done with sine waves, not square waves. This is because the phase delay depends on the signal frequency. A pulse waveform contains many frequencies. It still can have a phase shift, but it's complicated. So sine waves, which are a single frequency, often swept through a range to make a frequency response (Bode) plot, is what most EEs use.

In any case, you need to specify the conditions, like the input waveform, for phase delay to make sense.

hutchphd
PhysicsTest said:
TL;DR Summary: Understanding the phase delay

I simulated the below circuit to capture the phase delay between input voltage and output current in LTSpice
It looks like you are using a Transient Analysis -- that is not the type of analysis that you should use to see the Frequency Domain characteristics of a circuit. Have a look at this article, and let us know what a better SPICE analysis mode would be...

https://techweb.rohm.com/know-how/simulation/7916/

hutchphd and DaveE
I am analyzing the circuit and will come up with the exact problem i am facing.

PhysicsTest said:
I am analyzing the circuit and will come up with the exact problem i am facing.

A square wave will charge a capacitor up as soon as it is applied because it is similar to direct current.

Are you wanting to test the time constant, tau, as it is charging?

Last edited:
DaveE
osilmag said:
A square wave will charge a capacitor up as soon as it is applied
More accurately, a square wave will start to charge up a capacitor with the initial application of the first pulse. Subsequent pulses alternately start to discharge it and recharge it... (see the OP's transient SPICE simulation):

hutchphd and Tom.G
Ok

As has been noted the term phase delay (better called phase lag) is defined as the response to a particular frequency sine wave. So your question is not well formulated. Please try again.

DaveE and berkeman

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