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I've designed cascode telescopic op amp with feedback resistor loop to control on its gain but my problem is that i've a problem in ac response like as in picture can any one help me ?
Without an output stage it is possible that your gain will be very low to use it as a programmable gain array unless you use megaohms of feedback resistors which are quite unreliable. From the diagram I can understand that you are going for a fast opamp. It will be power hungry if you design it with an output stage I believe. To use this as it is you might want to consider switched capacitor equivalent if it works for you.
If you have an output stage then it is possible that in your feedback configuration, the input capacitance plus your load capacitance generates a slower pole than the internal node in your Opamp. So you are losing your phase margin. As a rule of thumb for 60 degrees of phase margin your output stage should have a pole nearly three times faster than your internal node. I'm not sure whether it is stable or at the edge of the stability but considering this diagram it will definitely have a bad settling response. Depending on your application it might be harmful. For example driving a sampled data system like an ADC it is quite destructive. Also when you lower your gain this peak will be worse than before.
Can you please add the transient settling response also?
I guess it is the closed loop gain., if it is, then it is quite normal to see peaking near UGB, but it is quite over pronounced in your case. Some frequency compensation would do good
Such a peak in the response can be caused by stray capacitance at the inverting input. You can generally compensate for this with a small capacitor across the feedback resistor. You will have to determine the value experimentally as it depends upon the gain the the resistance of the input and feedback resistors. Generally a value in the tens of picofarads region should work.
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