Summary A concise guide to amplifiers. Everything you need to remember about amplifiers for an exam

1 .
AMPLIFIERS :
in waveform is considered to be distortion and is
Any change
~



undesirable /




>
-
An amplifier that preserves the details of the signal waveform
is characterized by the relationship volt) Avilt) =




↳emput signate
&
disput
VOLTAGE GAIN :
qual

E A linear amplifier accepts an input
signal vI(t) and provides at the output
,
accross a load resistance R , an output
signal volt) that is the magnified
replica of VI(t)
voltage gain (AV) =

No
Transfer characteristic
of a

linear voltage amplifier
&
with vottage gain of Av


POWER GAIN E CURRENT GAIN :




Power gain (Ap) load power (P1)
=
=

input power (P1)
where io= and it is the current the amplifier draws from
the signal .
source

current gain = I



voltage gain in decibels = 20
log/AvldB
Current gain in decibels = 20
log/Ail dB
Power gain in decibels = 10
log1ApldB

The .
entra power comes from the ac
power supplies

Amplifier saturation For an amplifier operated from
:
two

power supplies the output voltage cannot exceed a
I
,



specified positive and
negative limit
.

, : the input signal must

swing between I distortion

↓ ↳ vi
I
(
range
Av
maincar




CIRCUIT MODELS FOR AMPLIFIERS :



In
figure (b),

vo = AroVi
RL + Ro

and voltage gain is
given by :




Av
== Avo Rock


An ideal voltage amplifier has

Ro = 0 and R1 = 0
,
and Avo = Av

Thus , Avo is the voltage gain of
the unloaded amplifier or the
, open-circuit voltage gain
if specified
I -


is it
* a load resistance not ,
s
-
normally
assumed that the voltage gain the
given is

circuit
open gain Avo


Vi
R(vs)
=
ve in order to not lose significant portion
of
the signal , Ri Rs

An ideal voltage amplifier was Rs =
0 & Ri =
: Overall ,
voltage gain

Avo XRs
!




=
Vout cannot
go beyond
the C inputs