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now I want to design an op-amp with the structure that I attached but I dont know I should start from where, can anybody help me? wich parameters are important in op-amp desin? Is this structure a good one?
In fact, it depends on your application.
Generally, opamp spec are: input range, output range, min supply voltage, current consumption, slew rate, noise, offset, gain, phase margin, bandwidth, PSRR, CMRR.
The opAmp you are planning to use will have to sink current from the RL resistor, what you trying to use is really an OTA, which usually handles only capacitive loads or very small currents. Unless RL is very large, you should probably add a buffer stage.
I think you should consider these specs at the least:
stability(loop gain, phase margin, bandwidth), driving capability, input voltage range, slew rate, offset influence.
The opAmp you are planning to use will have to sink current from the RL resistor, what you trying to use is really an OTA, which usually handles only capacitive loads or very small currents. Unless RL is very large, you should probably add a buffer stage.
a two stage Miller opamp seems a better fit but it really depends on the signal coming from Zin and its impedance (looking in the opposite direction to the arrow in your schematic), basically what determines the load of the op amp
As simple way to verify you have the right specs for your op amp (DC gain, bandwidth, output resistance, slew rate,...) is to implement it first as an ideal op amp with the specs you are planning to target in the actual design; until the ideal design works there is no reason to start designing the real thing
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