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High frequency Operation of Op amps

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saad

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Hi
Whats the frequncy above which we consider op amp to work as high frequency device.

If 1KHz signal is fed as input to an op amp, will it be considered as High Frequency Operation??

Wating for reply
 

This can be a very controversial issue ..

For the "old" 741 opamp 10-100kHz (gain drops to 1 at 100kHz) will be high frequency operation, for some "contemporary" opamps, where the rolloff of gain starts at, say, 500MHz, one can say 50-500MHz is high frequency operation ..

Regards,
IanP
 

if i assume the op amp to be ideal one then?
 

In theory, an ideal opamp should have flat response from 0Hz to ∞ ..

Regards,
IanP
 

Hey IanP, 741 can operate with unity gain up to 1MHz, not only 100kHz.

nguyennam
 

so 1 khz will be considered as low frequency for 741 op amp?? please correct me if i am wrong.
 

Hey nguyennam! Dont confuse things! U urself say that 741 can operate up to 1MHtz with unity gain. I repeat unity gain! can u think of how an op amp with unity gain operates? Effective operation of op amp requires high gain, thats why we assume op amps to have infinite gain. As for u saad, 1KHz is considered high frequency for 741. As a simple rule of thumb be sure that the op amp has at least 10 times gain relative the gain of the amplifier (if the device is to function as an amplifier)

Regards!
 

i m totally confused :cry: can anyone summarize things up again plzzz
 

Take a look at the attached graphs ..

Fig.4 shows theoretical frequency v gain response, whereas Fig.5 shows the same relationship for a more practical situation ..

As a simple rule of thumb be sure that the op amp has at least 10 times gain relative the gain of the amplifier (if the device is to function as an amplifier)

One has to be consequent and call thing as they are: 1kHz, according to the attached frequency-spectrum graph falls into ELF/VLF (very low frequency) category ..

However, ..

From a certain point of view 1$ is a lot of money, therefore, if you think of µA741 working at 1kHz, it is "high(er) frequency operation" ..

Regards,
IanP
 

hey i think slew rate concept involved here............
i would like to look if i have resources for slewrate and then would post again ......
 

op-amps have a very low bandwidth...abt 5-10 hz for a good gain...as the frequency increases...the gain drops gradually...until the gain reaches unity.
 

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