Piezoresistive
sensor
2. RESISTIVE CIRCUITS
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CIRCUITS by Ulaby & Maharbiz
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Ohm’s Law
Voltage across resistor is proportional to current
iR
R
i
Resistance: ability to resist flow of electric current
r resistivity
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Conductivity
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Resistor Codes
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Example 2-1: dc Motor
What fraction of power supplied by the
battery is dissipated in the motor?
Solution:
= 98% of P
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Tech Brief 2: Superconductivity
Critical temperature TC is the
temperature at which a material
becomes superconducting (zero
resistance & no power dissipation)
Kirchhoff’s Current Law
Sum of currents entering a node is zero
Also holds for closed boundary
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Example
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Kirchhoff’s Voltage Law (KVL)
Sum of voltages around a closed path is zero
Sum of voltage drops = sum of voltage rises
Example : KCL/KVL
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Solution:
Loop 1
Loop 2
Three equations w/three unknowns:
Determine all currents & voltages
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Equivalent Circuits
If the current and voltage characteristics at nodes are
identical, the circuits are considered “equivalent”
Identifying equivalent circuits simplifies analysis
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Resistors in Series
Equivalent resistance (series) is sum of resistances
Voltage divided over resistors (voltage divider)
Adding Sources In Series
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Combining voltage sources
Unrealizable Circuit
Resistors in Parallel
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Source Transformation
Hence,
For the two circuits to be equivalent :
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Example 2-10: Source Transformation
R1,R2,R3=Delta
R3,R4,R5=Delta
R1,R3,R4=Y
R2,R3,R5=Y
Circuit with no two resistors sharing the same current or same voltage
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Hence,
( Assuming no connection at node 3)
Simultaneous solution leads to:
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Example 2-12: Y-Δ Circuit
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Wheatstone Bridge
Measurement instrument
based on differential
measurement
Balanced Condition:
Determine unknown
resistance based on
“balanced” condition
For balanced condition
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Wheatstone Sensor
Determine Vout
Tech Brief 3: Resistors As Sensors
Piezoresistive Sensors
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Tech Brief 3: Resistors As Sensors
Tech Brief 3: Resistors As Sensors
Thermistor Sensors
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Example 2-16: Piezoresistor Cantilever
(400 times greater than w/o cantilever)
Linear i-v relationships
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The Diode
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Current can flow only from + to – through a diode.
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Multisim
SPICE simulator software
Powerful tool for analyzing circuits
See tutorial and examples on CD that accompanies
the text
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Multisim: Creating a Circuit
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Multisim: DC Operating Point Solution
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Multisim Solution Window
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Summary
