1 comparator with hysteresis window comparator basic comparator circuits
TRANSCRIPT
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COMPARATOR WITH HYSTERESIS WINDOW COMPARATOR
BASIC COMPARATOR CIRCUITS
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BASIC COMPARATOR CIRCUITS
Effect of noise on comparator circuits
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Effect of noise on comparator circuits
BASIC COMPARATOR CIRCUITS
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Effect of noise on comparator circuitsIn many practical situation , noise appears on the input line
The noise cause a comparator to erratically switch output state
How to reduce?One way to reduce the effect of noise is by using a comparator with positive feedback called Hysterisis also called as Schmitt trigger
The positive feedback produce two separates trip points that prevents a noisy input from producing false transitions for example UTP and LTP – Hysterisis
BASIC COMPARATOR CIRCUITS
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Schmitt trigger symbol
The symbol for Schmitt triggers in electronic diagrams is a triangle with a hysteresis symbol:
BASIC COMPARATOR CIRCUITS
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SCHMITT TRIGGER
satUTP VRR
RV
21
2
+
-
R1
R2
Vin
Vout
+V
-V
satLTP VRR
RV
21
2
- Inverting Schmitt trigger
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When Vout = +Vsat, the fed-back voltage is called the upper-threshold voltage, VUT.
For Vin < VUTP Vout is locked at +Vsat
If Vin > VUTP Vout begins to drop in value until –Vsat
Upper Threshold Voltage (VUTP)
SCHMITT TRIGGER
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Lower Threshold Voltage (VLTP)
When Vout = -Vsat, the fed-back voltage is called the lower-threshold voltage, VLT.
For Vin > VLTP Vout is locked at -Vsat
If Vin < VLTP Vout will switch back to +Vsat
SCHMITT TRIGGER
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SCHMITT TRIGGER
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What is Hysteresis? Technique of showing comparator performance on
one graph instead of two graphs
+Vsat
-Vsat
Vout
Vin
VUTPVLTP
Hysteresis voltage
BASIC COMPARATOR CIRCUITS
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The difference in voltage between VUTP and VLTP is called hysteresis voltage, VHYS
Whenever any circuit changes from one state to second state at some input signal and then reverts from the second state to the first state at a different input signal, the circuit is said to exhibit hysteresis.
LTPUTPHYS VVV If VHYS > Vnoise peak-peak there will be no false
output crossings VHYS tells us how much peak-peak noise the circuit
can withstand
BASIC COMPARATOR CIRCUITS
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Non-inverting Schmitt trigger
+
-
R1 R2
Vout
Vin
Vin
Vout
+Vsat
-Vsat
VHTPVLTP
VHYS
satUTP VR
RV
2
1 satLTP VR
RV
2
1
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Example 1 If Vsat = 13.5 V, what are the trip points and
hysteresis in Figure below?
+
-Vin
Vout
-15V
+15V
47 k1 k
VVk
kVUTP 281.05.13
48
1
VVk
kVLTP 281.05.13
48
1
VVVVVV LTPUTPHYS 562.0281.0281.0
Non-inverting Schmitt trigger
Answer :Trip points
Answer :Hysteresis voltage
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Window Comparator
It detects when the input voltage is between two limits called window.
Use two comparators with different thresholds.
BASIC COMPARATOR CIRCUITS
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Inverting Window Comparator
Vin
+
-
+
-
VoutVin
Vout
VLTP
VUTP
+V
+V
-V
-V
VUTPVLTP
+Vsat
Window Comparator
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Example 2 In previous figure, the VLTP and VUTP are
changed to +3.5 V and +4.75 V. If Vsat = 12 V and the input is a sine wave with a peak of 10 V, what is the output voltage waveform?
Output is low when input is between 3.5 and 4.75V
Vin
Vout
12V
3.5V 4.75V
Window Comparator
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Comparator ApplicationsSmoke DetectorBar graph DisplayOver-Temperature sensing circuit
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Comparator Applications
A/D converter