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wat is de difference between large signal gain and small signal gain.for particular OPAMP they hv mentioned Large signal voltage gain=50V/mV and Av(small signal gain)=40dB.They are not matching .Can anybody plz xplain it?
Well, if you consider the characteristic graph of a transistor, you will certainly realize its non linearity. When a small signal is applied at the bias point, the transistor's gain can be regarded to be constant since the deviation from this point is small. This is the case in many amplifiers that you come across in electronic text books. (Razavi, Sedra, Gray). But another case should also be mentioned, what if the swing is so much that it moves the bias point considerably, for example in an oscillator. Then the gain will not be the same as the previous case. In fact, B. Razavi in his famous CMOS book mentions this point so nicely and uses the reasoning that I used above to justify the phenomenon.