intuition method for pole zero determination ?

Status
Not open for further replies.
C

cmos_ajay

Full Member level 2
Joined
Jan 30, 2007
Messages
126
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,296
Activity points
2,247
-> For the op-amp circuit attached , how do I determine the poles and zeros by intuition only ??
-> Also, what will the frequency response look like when C1 = 10*C2 and R1 = R2 = R
I know the method of writing a transfer function and simplifying it to get pole zero expressions.
Can someone help ?
 

Attachments

  • opamp_pole_zeros.JPG
    58.3 KB · Views: 126

you take a semilog graph paper, figure out the pole frequency and figure out the zero frequency. those are the two points the gain vs frequency will change slope. from flat to 20 dB/decade of the right sign. in the middle somewhere the gain is known just from R2 and R1 (ignore the 2 caps). then draw it all out on the graph paper
 

I am looking for an expression for poles and zeros in the circuit . Is there an intuition based method to determine them ?
Please help.
 

You would write down the transfer function of the inverting amplifier which has two poles at s=1/C1R1 and s=1/C2R2 and a zero at s=0. Then add +1 and rearrange to a single expression which creates additional zeros.

I agree with biff44 that it can be best visualized in a bode diagram.
 

The problem with such an "intuition method" is that you are required to see - by visual inspection - under which conditions the circuit will produce zero or infinite output.
In principle, this is not a severe problem for real frequencies f or w - however, for your purpose you are required to think in terms of s (complex frequency).

EDIT: For the present example, it is relatively simple to "guess" the zero and pole positions.

Because it is a classical bandpass there will be two zeros (0 Hz and infinite) and one single pole pair.
Because all 4 elements will be involved there is only one alternative: wp=1/SQRT(R1R2C1C2).
 
Last edited:

Hello Lvw,
Can you please explain this in detail how you guessed the pole and zero expressions........i mean the 2 zeros and the poles ?
 

cmos_ajay said:
Hello Lvw,
Can you please explain this in detail how you guessed the pole and zero expressions........i mean the 2 zeros and the poles ?
Click to expand...

It is a simple and classical bandpass response - and as such the ouput is zero for w=0 and w infinite.
More than that, I know that for such a simple bandpass the pole frequency and the center frequency are identical.
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…