# [moved] What is the output waveform in the 2nd circuit ? RC vs CR

Status
Not open for further replies.

#### Ayman Essam

##### Member level 2
i have this question that want me to draw the waveform of both circuits, the 1st is OK, its just an RC delayed version of the original. what about the 2nd ?

#### CataM

First one --> low pass filter (LPF)
Second one --> high pass filter (HPF)

Analytical response of HPF: Vout(t)=5·e^(-1000t)

NOTE: In my graphs goes to 1 V because that is the step function. For 5 V means that goes to 5 V the plot. (is the same the transient response, just changes the final value).

#### Audioguru

You should have learned that in an RC circuit the capacitor charges from the resistor exponentially which is not a delay.
The second circuit is CR where the capacitor cannot charge immediately so it passes the entire 0V to +5V leading edge then it charges into the resistor exponentially.

#### Attachments

• exponential.png
45.8 KB · Views: 17

#### c_mitra

Case 1: Initial voltage across the capacitor is zero. The capacitor charges via R and we get an exponential graph that reaches 5V with a time constant determined by RC.

Case 2: Initial voltage across the capacitor is 5V. The capacitor discharges via R and we get a negative exponential graph that reaches zero with a time constant determined by RC.

What do you mean by RC delayed version of the original?

#### Audioguru

Case 2 is confusing in this thread that has a +5V sudden rise into an RC for A and into a CR for B. The capacitor always begins discharged.
The sudden rise would originally sound like POP. A delayed version would also sound like POP. But the RC cuts high frequencies which would sound like THUD and the CR cuts low frequencies which would sound like TICK.

Status
Not open for further replies.