How to enlarge bandwidth of an op amp with Miller compensation?

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Hellen Grig

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I need to enlarge the bandwidth of an op amp without decreasing gain , using Miller compesation. How can I do this?
 
What makes you imagine you can?, as far as I'm aware Miller compensation is just to improve stability.

What sort of figures (gain, bandwidth) do you currently have, and what are you looking for?.
 
Nigel Goodwin said:
What makes you imagine you can?, as far as I'm aware Miller compensation is just to improve stability.

What sort of figures (gain, bandwidth) do you currently have, and what are you looking for?.
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With green I have bandwidh of my circuit. With red is the bandwidth of my first op amp . GBW of the op amp influences my final bandwidth. I need to enlarge the GBW of op amp ,and my teacher said that the hint is Miller effect.
 

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not many op amps have exposed pins for compensation capacitors. you didn't provide a schematic of the circuit, so nobody but you has a clue where out1 and out3 are in your amplifier and what makes them different. if you are building a discrete op amp, there are a couple of different ways you can alter the GBW of the amplifier. usually that's done by changing the value of the compensation cap between the B and C leads of the voltage amp stage. you can also choose output transistors that provide a minimum of input capacitance, OR reduce the beta in the output stage (simply put miller capacitance is the input capacitance multiplied by the beta (Hfe) of the output stage).
 
I have to increase the bandwidth of my first op amp OPA2111 externally.
 

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I wouldn't consider it as having anything to do with miller compensation, but you might want to investigate adding a capacitor or a series RC across R1.
 
like i said, if you had external connections for the compensation, that would make sense. if it's some modification being required in the first stage, i would say find an op amp with a higher GBW. the other means of increasing the high frequency gain of the overall circuit, is to reduce the value of C2.
 
There is nothing you can do to increase the bandwidth of the OPA2111, since there is no external access to the compensation points.
 
The OPA2111 is still available in an antique metal can or a DIP and it is very expensive.
 
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