The difference between large signal gain and small signal gain for particular opamp

[rampat]

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?

 

[trashbox]

Re: OP-AMP ac analysis

OP-AMP works at some operation point, for example the A(x,y). For large signal gain is y/x, for small signal gain is the slope at this point dy/dx.

 

[Sadegh.j]

Re: OP-AMP ac analysis

Hi there

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.

Cheers

 

[rampat]

Re: OP-AMP ac analysis

small signal gain part i understood,But for opamp where i will get 50V/mV large signal gain.How to check this spec?

 

[analog_prodigy]

OP-AMP ac analysis

Large signal gain is the DC gain and the small signal gain is ac gain.

 

[rampat]

OP-AMP ac analysis

if u don mind can u tell me the testbench setup to chk this DC gain?