Analog Electronics Circuits Differential amplifier, Slides of Analog Electronics

Download Analog Electronics Circuits Differential amplifier and more Slides Analog Electronics in PDF only on Docsity!

EC 402

Analog Electronics Circuits

Lecture # 23 Differential Amplifiers

IInnstructor:

Chiranjib Goswami, PhD

asansol engineering college asansol EC

Lec#

June © Chiranjib

Agend

a

Differential Amplifiers

Differential Mode Operation

Common Mode Operation

Use of Constant Current Source 2

EC

Lec#

^23

June © Chiranjib

Basic Internal Arrangement of an Op-Amp. EC

Lec#

^23

June © Chiranjib 4

Single-Ended Input & Double-Ended (Differential) Input 5

EC

Lec#

,^

June © Chiranjib

Common Mode Operation

This operating feature is referred to as common-mode rejection.

7

Ideally, the two inputs are equally

amplified, and since they result in

opposite-polarity signals at the

output, these signals cancel, resulting

in 0-V output.

Practically, a small output signal will

result.

• (^) Common-Mode Rejection

Noise (any unwanted input signal) is generally common to

both inputs, the differential connection tends to provide

attenuation of this unwanted input while providing an

amplified output of the difference signal applied to the inputs.

EC

Lec#

June © Chiranjib

Differential Amplifier Circuit

Input signal combinations:

Double-ended : If two opposite-polarity input signals are applied.

Single-ended : If an input signal is applied to either input with the

other input connected to ground.

Common-mode : If the same input is applied to both inputs.

EC

Lec#

,^

June © Chiranjib

Problem 10

EC

Lec#

June © Chiranjib

Calculate the dc voltages and currents in the circuit of Fig.

Solution 11

EC

Lec#

June © Chiranjib

The collector current is then

resulting in a collector voltage of

AC Operation..

EC

Lec#

June © Chiranjib

AC Operation..

EC

Lec#

June © Chiranjib

Single-Ended AC Voltage Gain

AC Operation...

The single-ended voltage gain magnitude at either collector

EC

Lec#

June © Chiranjib

AC

Operation..

H.W.  Derive the Ad equation

2- Double-Ended AC Voltage Gain

A similar analysis can be used to show that for the condition of signals

applied to both inputs, the differential voltage gain magnitude is:

EC

Lec#

June © Chiranjib 17

EC

Lec#

June © Chiranjib 19 Problem

Problem EC

Lec#

June © Chiranjib 20