SaM - MEMORIZE (Temperature Sensors)

List of things to memorize:

SaM - Temperature Sensors

• SaM - Different Types of Temperature Sensors
  • SaM - Thermocouples
  • SaM - RTD Sensor
  • SaM - Thermistor
  • SaM - Sensors Based on Silicon Junctions (BJT and Integrated Circuits)
    • SaM - Classical Band Gap Based Temperature Sensor (3 Pins)
    • SaM - Classical Band Gap Based Temperature Sensor (2 Pins)

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SaM - Different Types of Temperature Sensors

• Table:
  (Both RTDs and thermocouples can operate at very high temperatures)
  (Thermocouples have a really simple structure and the best accuracy and high repeatability, however they need cold junction compensation to be used as absolute sensors, and they have a low voltage output)
  (SaM - Thermistor have the lowest cost)
  

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Study these:

• SaM - MEMORIZE (Thermocouple)
• SaM - MEMORIZE (RTD Sensor)
• SaM - MEMORIZE (Thermistor)

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SaM - Sensors Based on Silicon Junctions (BJT and Integrated Circuits)

• Characterisitcs:
  • Absolute temperature sensors.
  • We can find integrated circuits which behave linearly, and have very good performances.
  • Limited temperature range, like most IC $\approx 150°\text{C}$.
• BjT used as a constant current generator:
  (There is a short-circuit between the base and the collector, therefore this device operates in the active region)
  
• BjT active region formula:$V_{out}=V_{BE}=\frac{kT}{q}\ln \left(\frac{I_C}{I_S}\right)$
• Real World Measures:
  • For $T=T_A$ (ambience temperature), so $300\text{°K}$.
  • $V_{BE}=V_{out}=600\text{mV}$.
  • Ideally its sensitivity would be $2\frac{\text{mV}}{\text{°K}}$.
  • Around $300°K$ if $I_S$ is not compensated, we have $\alpha =-4\frac{\text{mV}}{\text{°K}}$.NOT_SURE_ABOUT_THIS (It is a huge difference)
• Terminology:
  • C is the collector, E the emitter, and B the base.

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SaM - Classical Band Gap Based Temperature Sensor (3 Pins)

• $N$ parallel BjTs:
  
• Formula:$I_C=N\cdot I_{C_2}$Or:$I_C=N{I}_{S_2}{e}^{\frac{q{V}_G}{KT}}$
• Classical band gap based temperature sensor structure:
  
  • Output formula:
    (It has a linear dependance on temperature)$V_{out}=\frac{R_T}{R_1}\cdot \frac{kT}{q}\cdot \ln (N)$
  • Real World Measures:
    • Usual values for the sensitivity for this kind of devices are in the range: $\alpha \in \left[2\frac{\text{mV}}{°\text{C}}÷10\frac{\text{mV}}{°\text{C}}\right]$

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SaM - Classical Band Gap Based Temperature Sensor (2 Pins)

• Circuit:
  
• Equivalent circuit:
  (The user has to select the resistance $R$)
  
• There are also integrated circuits that behave not as current generators but has voltage generators: