icsoul said:
Where should I begin from?
How to define the basic parameters?
How to simulate the circuit completely?
papers,datum,advice etc all welcome!
Thanks very much!
What a good opamp? The first requirement for a good opamp is that it must be suitable for one's applications. Then next requirement is that its cost and power consumption should be as lower as possible.
To design a opamp, the first step is to understand its specifications, such as input common mode range, output swing, slew rate, bandwidth, gain, phase margin,etc.
Then, the next step is to determined which structre should be used according to the parameters required by the applications. For example, If your application need deal with a signal whose common mode is always above the middle supply, you shoud select a NMOS transistor as your input stage.
The third step is to calculate the basic parameter tail curren, gm of input stage, output driven capability.
The fourth step is to simulate your design using CAD tools. The DC. AC. and tran simulation must be done for a opamp. During simulation you can find if you design has met the requirement of your applications, if not, modify the deisgn and simulate again until everhing is ok.