Why DC source is replaced by AC ground in AC analysis?

[neofrkh]

Why in AC analysis of Common Emitter amplifier the dc source is replaced by a ground (ac ground) which is treated same as the actual ground?

 

[necolei]

Re: AC Ground

I think it is not replaced it is removed. You must not look at any parameters of dc source if your doing an AC analysis. Try to search about the two port system of a common emitter amplifier. Remember to short all capacitor when your doing an AC analysis.


Necolei

 

[jonw0224]

AC Ground

neofrkh,

A DC source provides an alternating voltage of zero.

From an AC analysis point of view, an ideal DC source is an AC short.

The only thing a DC source will do is change the DC offset of an AC signal but it doesn't attenuate or amplify the AC signal.

-Jonathan

 

[magnetra]

AC Ground

Jonathan is correct!. From ac analysis perspective, a DC source is zero voltage which is same as ground. Even from the mathematics point of view, in ac analysis only the time varying components are considered while the constant (DC componets) are eliminated!

M

 

[A.Anand Srinivasan]

Re: AC Ground

here superposition theorem is being used and hence the AC contribution of each of the components and supplies is only taken into account,,,,...

 

[saas123qa]

Re: AC Ground

As far as I know, the transistor analysis should be done in AC, and DC as well. In the AC analysis, they look at the frequency response which is zero in DC. while the DC analysis look at the operation points and so on.