Module-1
Part-B
CE amplifier with and without feedback
Common-emitter amplifier without feedback.
The amplifier configuration shown here is a common-emitter, with a resistor bias network
formed by R1 and R2. The capacitor couples Vinput to the amplifier so that the signal source
doesn’t have a DC voltage imposed on it by the R1/R2 divider network. Resistor R3 serves the
purpose of controlling voltage gain. We could omit it for maximum voltage gain, but since base
resistors like this are common in common-emitter amplifier circuits, we’ll keep it in this
schematic. Like all common-emitter amplifiers, this one inverts the input signal as it is
amplified. In other words, a positive-going input voltage causes the output voltage to decrease,
or move toward the negative, and vice versa.
__________________________________________________________________________________
Dr Raghunandan G H 1
, Common-emitter amplifier with feedback.
Negative feedback, collector feedback, decreases the output signal.The resistances of R1, R2,
R3, and Rfeedback function together as a signal-mixing network so that the voltage seen at the
base of the transistor (with respect to ground) is a weighted average of the input voltage and
the feedback voltage, resulting in a signal of reduced amplitude going into the transistor. So,
the amplifier circuit in the figure above will have reduced voltage gain, but improved linearity
(reduced distortion) and increased bandwidth.
Multi-stage amplifier
In practical applications, the output of a single state amplifier is usually insufficient, though it
is a voltage or power amplifier. Hence, they are replaced by multi-stage transistor amplifiers.
In Multi-stage amplifiers, the output of first stage is coupled to the input of next stage using a
coupling device. These coupling devices can usually be a capacitor or a transformer. This
process of joining two amplifier stages using a coupling device can be called as Cascading.
The following figure shows a two-stage amplifier connected in cascade.
The overall gain is the product of voltage gain of individual stages.
AV=AV1×AV2=V2/V1×V0/V2=V0
Where AV = Overall gain, AV1 = Voltage gain of 1st stage, and AV2 = Voltage gain of 2nd stage.
__________________________________________________________________________________
Dr Raghunandan G H 2
Part-B
CE amplifier with and without feedback
Common-emitter amplifier without feedback.
The amplifier configuration shown here is a common-emitter, with a resistor bias network
formed by R1 and R2. The capacitor couples Vinput to the amplifier so that the signal source
doesn’t have a DC voltage imposed on it by the R1/R2 divider network. Resistor R3 serves the
purpose of controlling voltage gain. We could omit it for maximum voltage gain, but since base
resistors like this are common in common-emitter amplifier circuits, we’ll keep it in this
schematic. Like all common-emitter amplifiers, this one inverts the input signal as it is
amplified. In other words, a positive-going input voltage causes the output voltage to decrease,
or move toward the negative, and vice versa.
__________________________________________________________________________________
Dr Raghunandan G H 1
, Common-emitter amplifier with feedback.
Negative feedback, collector feedback, decreases the output signal.The resistances of R1, R2,
R3, and Rfeedback function together as a signal-mixing network so that the voltage seen at the
base of the transistor (with respect to ground) is a weighted average of the input voltage and
the feedback voltage, resulting in a signal of reduced amplitude going into the transistor. So,
the amplifier circuit in the figure above will have reduced voltage gain, but improved linearity
(reduced distortion) and increased bandwidth.
Multi-stage amplifier
In practical applications, the output of a single state amplifier is usually insufficient, though it
is a voltage or power amplifier. Hence, they are replaced by multi-stage transistor amplifiers.
In Multi-stage amplifiers, the output of first stage is coupled to the input of next stage using a
coupling device. These coupling devices can usually be a capacitor or a transformer. This
process of joining two amplifier stages using a coupling device can be called as Cascading.
The following figure shows a two-stage amplifier connected in cascade.
The overall gain is the product of voltage gain of individual stages.
AV=AV1×AV2=V2/V1×V0/V2=V0
Where AV = Overall gain, AV1 = Voltage gain of 1st stage, and AV2 = Voltage gain of 2nd stage.
__________________________________________________________________________________
Dr Raghunandan G H 2
