urgent help to calculate the gain of OP AMP

[wael_wael]

calculate the open loop gain op amp

hi everybody,

i have to calculate the open loop gain of OP AMP, so if i need 70db as gain and the input is equal to 1 volt, how much the output by volt ?
thanx alot and i want to till u that i know the result but i need to make sure
best regards

 

[ieropsaltic]

calculate the voltage from gain

Simply calculate the voltage gain which is 10^(70/20)=3162.27766 V/V then multiply it by the input value which is 1 volt ,you'll get the required output value which is 3162.27766 volts .Note that you'll get this output only if you perform AC simulation as the simulator will solve the linearized model .If you try that at the transient simulation, your amplifier transistors would go into triode and you won't get the expected output .If you want to perform transient analysis, you should make your input voltage exteremely small ,say 1uV .

 

[wael_wael]

calculate gain in op-amp

thanx alot, but what do u mean by extreamly small input. i have tried 10 uv and i got same result, could u explain what do u mean
best regards

 

[amarnath]

if you give an extremely large input , your common mode will be disturbed and your bias will be altered.So the input should be as small as possible. Tell us what is the configuration of the opamp you are trying to use, i mean two stage , folded cascode, telescopic etc. The gain for each of these are different. You can also refer to johns and martin for the same.


amarnath