Compound Configurations, Lecture notes of Electronics

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Compound Configurations

CASCADED SYSTEMS

 The output of one amplifier is the input to the next amplifier

 The overall voltage gain is determined by the product of gains of the

individual stages

 The DC bias circuits are isolated from each other by the coupling

capacitors

 The DC calculations are independent of the cascading

 The AC calculations for gain and impedance are interdependent

CASCODE CONNECTION

This example is a CE – CB

combination. This arrangement

provides high input impedance

but a low voltage gain.

The low voltage gain of the

input stage reduces the Miller

input capacitance, making this

combination suitable for high-

frequency applications.

CASCODE CONNECTION

DC BIAS OF DARLINGTON CIRCUITS

I E =(D + 1 )IB DIB

VE = IERE

B D E

CC BE B R R

V V

I

Base current:

Emitter current:

Emitter voltage:

Base voltage:

VB = VE +VBE

FEEDBACK PAIR

This is a two-transistor circuit that operates like a

Darlington pair, but it is not a Darlington pair****.

It has similar characteristics:

• High current gain
• Voltage gain near unity
• Low output impedance
• High input impedance

The difference is that a Darlington

uses a pair of like transistors,

whereas the feedback-pair

configuration uses complementary

transistors.

CURRENT SOURCE CIRCUITS

Constant-current sources can be built using FETs, BJTs, and

combinations of these devices.

IE  IC

E

Z BE E R

V V I I

−  =

more…

CURRENT SOURCE CIRCUITS

VGS = 0V

ID = IDSS = 10 mA