Transcript Types of comparator

GOKUL TECHNICAL CAMPUS
HANSABA COLLEGE OF
ENGINEERING &
TECHNOLOGY, SIDHPUR
Subject – Analog Electronics
Branch: Electrical
Semester: 3nd
Year: 2014
Topic: Types of comparator
Types of comparator:
 Comparators are classified into two
categories.
 (1) Non-inverting comparator.
 (2) Inverting comparator
(1) Non-inverting comparator.
 The schematic diagram of a non-inverting
comparator is as shown in fig.
 Positive dc reference voltage is applied to
the inverting terminal (-) and an ac
sinusoidal signal is applied to the noninverting (+) terminal.
 The signal is connected to the noninverting (+) terminal, this comparator is
called as non-inverting comparator.
(1) Non-inverting comparator
Operation of the circuit of Noninverting comparator
 The current through resistors R1 is almost zero, the voltage
drop across them will be equal to zero. Hence V1=Vin
and V2=V ref differential voltage V d is given by,
 V d = V1-V2 =Vin-V ref
 When Vin is less then V ref the inverting (-) is as
higher potential non-inverting (+). The OP-AMP
output will swing to the –V(sat).
 When Vin is greater then V ref the non-inverting (+)
and higher potential then the inverting (-) the OPAMP output will swing to +V(sat).
Operation of the circuit of Noninverting comparator
 If the reference voltage is made negative (- V raf ) and
applied to the inverting (-) terminal and output
voltage waveforms are modified as shown in fig.
 The we will get either +V set or GND at the
comparator output. OP-AMP Ics such as IC LM324
is capable of working on a single polarity supply.
Operation of the circuit of Noninverting comparator
Operation of the circuit of Noninverting comparator
Transfer characteristics of Noninverting comparator:
 The ideal transfer characteristic of a non-inverting
comparator is as shown in fig.
 It shows that the output voltage is equal to –V sat for
Vin<V ref and it switches to +V sat as soon as Vin is
slightly greater then V ref.
 The practical transfer characteristic of the commercial
OP-AMPs is as shown in fig.
Transfer characteristics of Noninverting comparator:
Transfer characteristics of Noninverting comparator:
(2) Inverting comparator
 The schematic diagram of an inverting comparator
is as shown in fig and the relevant waveforms
are as shown in fig .
 The reference voltage V ref has now been
applied to the non-inverting (+) and the input
voltage is applied to the inverting (-) terminal.
(2) Inverting comparator
(2) Inverting comparator
(2) Inverting comparator
Operation of the circuit of inverting
comparator:
 The OP-AMP to have a very high input resistance.
Hence the currents flowing through the resistors
R1 and R of fig is very small.
 Hence the voltage drop across them is close to
zero.
 V1 = V ref and V2 = Vin
 Differential input voltage is as,
 When Vin is less then V ref ,the voltage at the noninverting (+) is higher then the voltage at the
inverting (-).
Operation of the circuit of inverting
comparator:
 This makes the differential input voltage V d positive
and the OP-AMP output will swing to +V(sat).
 When Vin is greater then V ref the voltage V d positive
and the inverting (-) is greater then the voltage at the
non-inverting (+) terminal.
 Therefore the differential input voltage V d is negative
and the OP-AMP output will be – V (sat).
Operation of the circuit of inverting
comparator:
 If the reference voltage is made negative ( - V ref ) then
the input and output voltage waveforms get modified
as shown in fig.
Transfer characteristics of inverting
comparator:
 Fig shows the ideal transfer characteristic of an
inverting comparator.
 It shows that the output voltage is equal to + V set for V
in less than V ref. It switches instantaneously from + V
set to –V sat when Vin becomes just slightly greater
then V ref.
 The commercial OP-AMPs have the transfer
characteristic as shown in fig.
 The change in output state takes place when the
differential is about 2 mV.
Transfer characteristics of inverting
comparator:
Transfer characteristics of inverting
comparator: