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ELEC207 LINEAR INTEGRATED CIRCUITS
23/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
SUMMING AMPLIFIER/VOLTAGE ADDER
It is based upon the standard Inverting
Operational Amplifier configuration that
can be used for combining multiple inputs
It amplify each individual input voltage and
produce an output voltage signal that is
proportional to the algebraic "SUM" of all
the individual input voltages
General output equation is given by
ELEC207 LINEAR INTEGRATED CIRCUITS
23/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
SCALING SUMMING AMPLIFIER
When the individual input resistors are "NOT" equal, it is a scaling summing
amplifier
General output equation is given by
ELEC207 LINEAR INTEGRATED CIRCUITS
23/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
EXAMPLE:
1. Find the output voltage of the circuit shown in the figure
ELEC207 LINEAR INTEGRATED CIRCUITS
23/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
SOLUTION:
1. Find the output voltage of the circuit shown in the figure
ELEC207 LINEAR INTEGRATED CIRCUITS
23/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
DIFFERENTIAL AMPLIFIER
Differential amplifiers amplify the difference between two voltages making this type
of operational amplifier circuit a Subtractor
By connecting one voltage signal onto one input terminal and another voltage
signal onto the other input terminal, the resultant output voltage will be proportional
to the "Difference" between the two input voltage signals of V1
and V2
If all the resistors are of the same value, i.e R1
= R2
= R3
= R4
then the circuit will
become a Unity Gain Differential Amplifier and the voltage gain of the amplifier will
be exactly one or unity. Then the output expression would simply be
Vout
= V2- V
1
Va
Vb
ELEC207 LINEAR INTEGRATED CIRCUITS
23/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
DIFFERENTIAL AMPLIFIER
Va
Vb
ELEC207 LINEAR INTEGRATED CIRCUITS
23/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
INSTRUMENTATION AMPLIFIER
Instrumentation amplifier is a kind of differential amplifier with additional input
buffer stages. The addition of input buffer stages makes it easy to match
(impedance matching) the amplifier with the preceding stage
Commonly used in industrial test and measurement application
ELEC207 LINEAR INTEGRATED CIRCUITS
23/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
ANALYSIS OF INSTRUMENTATION AMPLIFIER
The proof for instrumentation amplifier
transfer function starts with Super position
theorem.
Case 1: (Figure 1a)
Make V12
= 0 by connecting U2
input to
ground and calculate for Vout1
Figure 1a
ELEC207 LINEAR INTEGRATED CIRCUITS
23/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
ANALYSIS OF INSTRUMENTATION AMPLIFIER
Case 2: (Figure 1b)
Make V21
= 0 by connecting U1
input to
ground and calculate for Vout2
Figure 1b
Final Equation: Vout
=Vout1
+Vout2
ELEC207 LINEAR INTEGRATED CIRCUITS
25/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
COMPARATOR
Voltage comparator is a circuit which compares two voltages and switches the output
to either high or low state depending upon which voltage is higher.
Non-inverting comparator
Reference voltage is applied to the
inverting input and the voltage to be
compared is applied to the non inverting
input
Whenever the voltage to be compared (Vin)
goes above the reference voltage , the
output of the op-amp swings to positive
saturation (V+) and When V
ingoes below
reference voltage, the output swings to
negative saturation(V-)
Vref
Vin>V
ref, V
out=V
+
Vin
ELEC207 LINEAR INTEGRATED CIRCUITS
25/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
Inverting comparator
Reference voltage is applied to the non-
inverting input and the voltage to be
compared is applied to the inverting input
Whenever the voltage to be compared (Vin)
goes above the reference voltage , the
output of the op-amp swings to negative
saturation (V-) and When V
ingoes below
reference voltage, the output swings to
positive saturation(V+)
COMPARATOR
Vref
Vin>V
ref, V
out=V
-
Vin
ELEC207 LINEAR INTEGRATED CIRCUITS
25/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
Non-inverting and Inverting Comparator waveforms
Non-inverting Comparator Input and
Output Waveforms
Inverting Comparator Input and
Output Waveforms
ELEC207 LINEAR INTEGRATED CIRCUITS
25/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
SCHMITT TRIGGER
Designed with a positive feedback and hence will have a regenerative action which
will make the output switch levels. Hence it is also called a regenerative
comparator circuit
The use of positive voltage feedback instead of a negative feedback, aids the
feedback voltage to the input voltage
The purpose of the schmitt trigger is to convert any regular or irregular shaped
input waveform into a square wave output voltage or pulse. Thus, it can also be
called a squaring circuit
ELEC207 LINEAR INTEGRATED CIRCUITS
25/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
SCHMITT TRIGGER
Applying Super position Theorem at V1,
For switching the output from Vsat+
to Vsat-
, V1=0 V1
When Vout = Vsat-, value of Vin to switch output state from Vsat- to Vsat+ is
When Vout = Vsat+, value of Vin to switch output state from Vsat+ to Vsat- is
ELEC207 LINEAR INTEGRATED CIRCUITS
25/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
SCHMITT TRIGGER
Hysteresis width VH
is
Vsat+
Vsat-
Hysteresis Loop
ELEC207 LINEAR INTEGRATED CIRCUITS
25/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
EXAMPLE
1. For the Schmitt trigger shown below calculate the upper threshold voltage, lower
threshold voltage and the hysteresis width if the saturation voltages are 12V.
1k
3k
ELEC207 LINEAR INTEGRATED CIRCUITS
25/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
SOLUTION
1. For the Schmitt trigger shown below calculate the upper threshold voltage, lower
threshold voltage and the hysteresis width if the saturation voltages are 12V.
1k
3k
ELEC207 LINEAR INTEGRATED CIRCUITS
25/02/2014
DEPARTMENT OF
ELECTRICAL & COMPUTER
ENGINEERING
DIFFERENCE BETWEEN COMPARATOR AND SCHMITT TRIGGER
Comparator change its state when the voltage exceeds a threshold and return to
the initial state when the voltage drops below this threshold.
Schmitt trigger change its state when the voltage exceed a threshold and will not
return to the initial state until the voltage drops at a certain value below the initial
threshold.
Comparator Output Schmitt trigger Output