working of active lead-lag compensator.

[Muhammad Khurram Khalil]

hello everyone,
can anyone please help me in understanding the working of the active lead lag compensator circuit in the link below
thank you in advance

https://obrazki.elektroda.pl/9186522900_1405240777.png

 

[crutschow]

The input R1C1 is a high-pass (lead) filter and the feedback R2C2 is a low-pass (lag) filter. It's commonly used to compensate and stabilize PID controller loops.

 

[Muhammad Khurram Khalil]

but..how R2 and C2 are making a low pass filter as the c2 is in series with R2..just like C1 is in series with R1...!!
yep i am actually implementing the transfer function of this loop filter in designing the software-defined PLL...but there is no help available at internet regarding the working of this circuit.

 

[crutschow]

It's related to the fact that the gain of an inverting op amp is ideally equal to the Feedback-Impedance divided by the Input-Impedance.

As the frequency increases the impedance of C1 goes down. Since a reduction of the input impedance increases the gain of the op amp, the input RC causes the gain to increase with frequency (a high-pass, lead type function).

The impedance of C2 also goes down with an increase in frequency but this reduction in the feedback impedance causes the amp gain to decrease with frequency (a low-pass, lag type function).

 

[Muhammad Khurram Khalil]

thank you so very much...sir
your post is really helpful...
thanx alot