• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Interview questions

Status
Not open for further replies.
Hi, i've been asked today few questions but i were suspecting of the answers

1. what is the difference between RC circuit and RC with an op-amp ? i said the gain , he said suppose its 1 , he answered that in the RC-op-amp the capacitor will charge lineary , is this correct ??

2. what's the difference between butterworth and cheybychev filters ?
3. what happens when there are ripples in a low pass filter circuit in the pass band area ??
 

Sceadwian

Banned
An RC with an opamp is an active filter, it can maintain the original voltage levels of the signals with only the filtered frequencies being lower. A passive RC filter is going to have loss in amplitude even at the unfiltered frequency.

A butterworth filter has flat frequency responce, the chebyshev filter has ripple in the passband.

When there's ripple in the passband it's not ideal so your frequency response will not be flat like ideally you would want it to be.
 
So he is wrong when he said the difference between active and passive filter ?? he said , the cap will charge lineary ..

and he said about the ripples that , the gain will be different at different ripples , is this correct also??
 

Sceadwian

Banned
I didn't say he was wrong, there's more than one reason why active filters are better. You'd have to provide circuit examples to comment further, and yes the ripples will produce different gains at the given frequency.
 
1. what is the difference between RC circuit and RC with an op-amp ? i said the gain , he said suppose its 1 , he answered that in the RC-op-amp the capacitor will charge lineary , is this correct ??

Really need more information here, as this depends on what you're discussing. For a first order filter, there is very little difference. If it's a linear integrator, then the active integrator will see the capacitor charging linearly, as opposed to the passive integrator.

2. what's the difference between butterworth and cheybychev filters ?

Butterworth filters are an extension to higher orders of the first order RC or RL LPF. The poles of the Butterworth characteristic are equally spaced around a circle. The Chebychev characteristic derives from the Chebychev Polynomials: C(x)= cos(Karccos(x)). The poles are arranged around an ellipse.

3. what happens when there are ripples in a low pass filter circuit in the pass band area ??

This is usually accompanied by sharp skirt selectivity and a nasty, nonlinear phase characteristic. (I.e. Chebychev or Elliptic filters. You wouldn't want to use it where fidelity is the goal.
 
Last edited:

audioguru

Well-Known Member
Most Helpful Member
The capacitor in an RC integrator circuit that uses an opamp charges linearily. Look up integrator circuit in Google.
A capacitor charged by a simple resistor charges exponentially.
 
Status
Not open for further replies.

EE World Online Articles

Loading
Top