Title: Small Signal Model
1Small Signal Model MOS Field-Effect Transistors
(MOSFETs)
1
2Quiz No 3 DE 27 (CE)
20-03-07
Rout.
- Draw small signal model (4)
- Find expression for Rout (2)
- Prove vo/vsig (ß1a2RC)/(Rsigrp) (4).
3A traveler once came to the mosque to see the
prophet.After greeting the prophet he was asked
where he was from. The traveler replied that he
came from very farjust to get a few questions
answered. Following is thedialogue between the
traveler and the prophet.Traveler I do not
want adhaab to be written in my account.
Prophet behave well with your
parentsTraveler I want to be known amongst
people as anintelligent person. Prophet fear
Allah always.Traveler I want to be counted
amongst Allah's favorites.Prophet recite Quran
every morning and evening. Traveler I want my
heart to always be enlightened.(roshan and
munawer) Prophet never forget death
4Traveler I never want to be away from Allah's
blessing. Prophet always treat fellow creatures
well.Traveler I never want to be harmed by my
enemies. Prophet always have faith in only
Allah.Traveler I never want to be humiliated.
Prophet becareful of your actions.Traveler I
wish to live long. Prophet always do sila-rahm.
(Goodness towards blood relations)Traveler I
want my sustenance to increase. Prophet always
be in wudhoo.Traveler I wish to stay free of
adhaab in the grave.Prophet always wear pure
(paak) clothes. Traveler I never want to burn
in hell.Prophet control your eyes and tongue.
5Traveler how do I get my sins forgiven?
Prophet always ask forgiveness from Allah with
a lot of humility.Traveler I want people to
respect me always. Prophet never extend your
hands of need at people.Traveler I want to
always be honored. Prophet never humiliate or
put down anyone.Traveler I don't want to be
squeezed by fishare qabr.(Squeezing in the grave)
Prophet recite sura e mulk often.Traveler I
want my wealth to increase. Prophet recite sura
e waqia every night.Traveler I want to be safe
and at peace on day of judgment. Prophet do
zikr of Allah from dusk to night.Traveler I
want to be in full attention and concentration
during namaaz. Prophet always do wudhoo with
concentration and attention
6Enhancement-type NMOS transistor
7Figure 4.2 The enhancement-type NMOS transistor
with a positive voltage applied to the gate. An n
channel is induced at the top of the substrate
beneath the gate.
8Enhancement-type NMOS transistor
9MOSFET Analysis
iD iS, iG 0
10Large-signal equivalent-circuit model of an
n-channel MOSFET Operating in the saturation
region.
11Large-signal equivalent-circuit model of an
p-channel MOSFET Operating in the saturation
region.
12Large Signal Model MOSFET
13Transfer characteristic of an amplifier
14Conceptual circuit utilized to study the
operation of the MOSFET as a small-signal
amplifier.
The DC BIAS POINT
To Ensure Saturation-region Operation
15Signal Current in Drain Terminal
16Figure 4.35 Small-signal operation of the
enhancement MOSFET amplifier.
17Total instantaneous voltages vGS and vD
18Small-signal p models for the MOSFET
19Common Source amplifier circuit Example 4-10
20Small Signal T Model NMOSFET
21Small Signal Models
T Model
22Single Stage MOS Amplifier
23Amplifiers Configurations
24Common Source Amplifier (CS) Configuration
25Common Source Amplifier (CS)
- Most widely used
- Signal ground or an ac earth is at the source
through a bypass capacitor - Not to disturb dc bias current voltages
coupling capacitors are used to pass the signal
voltages to the input terminal of the amplifier
or to the Load Resistance - CS circuit is unilateral
- Rin does not depend on RL and vice versa
26Small Signal Hybrid p Model (CS)
27Small Signal Hybrid p Model (CS)
28Small-signal analysis performed directly on the
amplifier circuit with the MOSFET model
implicitly utilized.
29Common Source Amplifier (CS) Summary
- Input Resistance is infinite (Ri8)
- Output Resistance RD
- Voltage Gain is substantial
30Common-source amplifier with a resistance RS in
the source lead
31The Common Source Amplifier with a Source
Resistance
- The T Model is preferred, whenever a resistance
is connected to the source terminal. - ro (output resistance due to Early Effect) is not
included, as it would make the amplifier non
unilateral effect of using ro in model would be
studied in Chapter 6
32Small-signal equivalent circuit with ro neglected.
33Small-signal Analysis.
34Voltage Gain CS with RS
35- Source Resistance can be used to control the
magnitude of the signal vgs thus ensure that
vgs does not become too large to cause non-linear
distortion - vgs ltlt 2(VGS-Vt) ltlt VOV
36Common Source Configuration with Rs
- Rs causes a negative feedback thus improving the
stability of drain current of the circuit but at
the cost of voltage gain - Rs reduces id by the factor
- (1gmRs) Amount of feedback
- Rs is called Source degeneration resistance as it
reduces the gain
37Small-signal equivalent circuit directly on
Circuit
38A common-gate amplifier based on the circuit
39Common Gate (CG) Amplifier
- The input signal is applied to the source
- Output is taken from the drain
- The gate is formed as a common input output
port. - T Model is more Convenient
- ro is neglected
40A small-signal equivalent circuit
41A small-signal Analusis CG
42A small-signal Analusis CG
43Small signal analysis directly on circuit
44The common-gate amplifier fed with a
current-signal input.
45Summary CG
- 4. CG has much higher output Resistance
- CG is unity current Gain amplifier or a Current
Buffer - CG has superior High Frequency Response.
46Common Gate
- Rin in independent of RL Rin 1/gm gm in
order of mA/V. - Input resistance of the CG Amplifier is
relatively low (in order of 1kv) than CS
Amplifier - Loss of signal
- CG is acts as Unity gain current amplifier
current buffer useful for a Cascade circuitry
47A common-drain or source-follower amplifier.
48Small-signal equivalent-circuit model
49Small-signal Analysis CD
50(a) A common-drain or source-follower amplifier
output resistance Rout of the source follower.
51(a) A common-drain or source-follower amplifier.
Small-signal analysis performed directly on the
circuit.
52Common Source Circuit (CS)
53Common Source Circuit (CS) With RS
54Common Gate Circuit (CG) Current Follower
55Common Drain Circuit (CD) Source Follower
56Summary Comparison
57Small Signal Model
58Small Signal Model
VBE0.7 V ß 200 Kn(W/L)2mA/V2 Vt1V
Figure P6.123
59DC Analysis
Figure P6.123
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