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   Common Source Amplifier
   Common Source Amplifier with Source Degeneration.
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Common Source Amplifier

Common Source Amplifier.
We’ve studied MOSFET small-signal equivalent models and the biasing of MOSFET amplifiers in the previous three lectures. We’ll now apply those skills by looking closely at three basic MOSFET amplifier types:
1. Common source amplifiers, including configurations with a source resistor (called source degeneration).
2. Common gate amplifiers.
3. Common drain (or source follower) amplifiers.
All of these amplifier types are appropriate for discrete component designs. In the case of IC amplifiers, we’ll also show corresponding designs implemented in CMOS, beginning in
Common Source Small-Signal Amplifier
This type of amplifier is shown in Fig. 4.43a, as biased by a combination of voltage and current sources:

Assuming sufficiently large values for the coupling capacitors (CC1 and CC2) and the bypass capacitor (CS) – so that their reactances are very small at the frequency of operation – the equivalent small-signal circuit for this amplifier is shown in

The text mentions performing the small-signal analysis directly on the amplifier circuit, as illustrated in Fig. 4.43(c). We do not recommend this approach. It is better to take the time and construct the small-signal equivalent circuit, as we’re doing here.
Small-Signal Amplifier Characteristics
As we did when studying BJT amplifiers, we’ll calculate the following quantities for this MOSFET common source amplifier: Rin, Av, Gv, Gi, and Rout.
• Input resistance, Rin. From the small-signal circuit above, and noting that ig =0 , then
Rin = R G
• Partial small-signal voltage gain, Av. From the output side of the small-signal circuit
V 0 = - GmV gs (r0||RD||RL)
while at the input,
V i=Vgs
Substituting (3) into (2), we find that the partial voltage gain as

• Overall small-signal voltage gain, Gv. As we did with BJT amplifiers, we can derive an expression for Gv in terms of Av. By definition,

Applying voltage division at the input of the small-signal equivalent circuit,

Substituting (6) into (5) and using (4) we find

• Overall small-signal current gain, Gi. Using current division at the output in the small-signal model above

while at the input,
Vgs= iiRG Substituting (9) into (8) we find that the overall small-signal current gain is

Notice that as RG ®¥ in this last expression, i G i® ¥. Is thisa problem? (To help answer this question, notice that as RG ®. ¥, ii® 0.) Also, what does Gi as RG ¥ mean for the overall small-signal output power of this amplifier?
• Output resistance, Rout. To calculate the output resistance, we first set vsig =0 , which also means that gm vgs =0 . The input impedance of the dependent current source is infinite. Consequently,
Rout= r0|| RD
Summary
In summary, we find for the CS small-signal amplifier that it has a
o High input resistance [see (1)].
o Relatively high small-signal voltage gain [see (7)].
o Very high small-signal current gain [see (10)].
o Relatively high output resistance [see (11)].



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Type of diode
I need short notes for all type of diode.


Posted By :-
 imteyaz86
Oct 27, 11:50:24 AM 0 9674
signals and system
hi i am venkatesh which author use in signal and system for gate


Posted By :-
 venkatesh.dace2
Oct 13, 4:38:08 PM 0 9231
Thank u
i need some links to download free ebooks multiple choice for my gate preparation - V.Vivek Sharma.


Posted By :-
 vvivekxp@yahoo.com
Oct 4, 9:56:42 AM 0 7081
study materials
i want to study materials of digital communication.


Posted By :-
 titon
Feb 6, 3:43:05 PM 4 18538
More examples of non linear circuit analysis
Notes are very simple to understand the concepts.


Posted By :-
 ruby2810
Sep 9, 3:17:49 PM 0 12825
study materials
can i get some study materials by online


Posted By :-
 shyama.km
Sep 4, 9:05:49 AM 0 9090
hiii plz give me basic information about electromegnetics
i have a dout between combination of electrostatics and megnetostatics


Posted By :-
 pandya.saga
Jul 29, 2:38:13 PM 0 7527
hi
pls send me a link on answered problems on electronic devices and circuit theory by boylestad and nashelsky.. ty


Posted By :-
 flux089
Jul 25, 11:21:28 PM 0 8670
electronics and communication
i am in 4th year


Posted By :-
 gauravjai24.ece.uit@gmail.com
Jun 10, 6:02:44 AM 0 7616
bjt
about bipolar device


Posted By :-
 vikashgupta160489
Feb 13, 2:11:36 PM 2 14683
h parameters of transister
i want h parameters of transister


Posted By :-
 vijaybaviskar007
Feb 11, 7:52:45 AM 3 21218
very good tutorials
the explanations r very easy to understand


Posted By :-
 blues2torn@rediffmail.com
Dec 7, 8:38:09 PM 0 7877
ECE
the explanation was nice...more of these explanations on other topics would be of much help and is expected urgently...


Posted By :-
 pallavi.sist@gmail.com
Dec 2, 10:32:29 PM 0 8496
e.d.c
i want to simple way abt all the diode n jfet


Posted By :-
 vijayjyani@gmail.com
Jun 4, 10:25:28 AM 1 11439
Thanks for nice tutorials
Thanks for nice tutorials


Posted By :-
 my.gateprep
Nov 26, 8:29:06 AM 0 8051

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