BJT Temperature Sensor Circuit With Substrate Noise Isolation
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Solution Overview
Problem
Bipolar junction transistors (BJTs) used in temperature sensing circuits for high-temperature applications face design limitations that lead to poor accuracy due to substrate noise and minority carrier interference, affecting the reliability of thermal protection in switching power circuits.
Innovation Solution
A temperature sensing circuit design that includes a bipolar transistor with a substrate separated from the emitter and base by the collector, coupled with a Schmitt trigger and current sources, which mitigates substrate noise and minority carrier impacts by using a low-impedance path for the collector, ensuring accurate temperature sensing even in high-noise environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a bipolar transistor is used in a temperature sensing circuit for high-temperature applications, then the circuit can operate at high temperatures, but substrate noise and minority carrier interference degrade the temperature sensing accuracy
Solution Approach 1:
The patent introduces a substrate isolation layer (such as an oxide layer or intrinsic semiconductor layer) positioned between the substrate and the collector region. This intermediary layer acts as a barrier that blocks minority carrier injection from the substrate into the collector, thereby eliminating the harmful interference while allowing the transistor to continue functioning at high temperatures for accurate temperature sensing.
2Device complexity
If the collector is directly connected to the substrate, then the device structure is simple, but substrate noise directly interferes with the temperature sensing accuracy
Solution Approach 1:
The patent introduces a substrate isolation layer (such as an oxide layer or intrinsic semiconductor layer) positioned between the substrate and the collector region. This intermediary layer acts as a barrier that blocks minority carrier injection from the substrate into the collector, thereby eliminating the harmful interference while allowing the transistor to continue functioning at high temperatures for accurate temperature sensing.
3Reliability
If the bipolar transistor operates at high temperatures, then it can monitor thermal conditions in switching power circuits, but excessive heat generates more substrate noise and minority carriers that interfere with sensing
Solution Approach 1:
The patent introduces a substrate isolation layer (such as an oxide layer or intrinsic semiconductor layer) positioned between the substrate and the collector region. This intermediary layer acts as a barrier that blocks minority carrier injection from the substrate into the collector, thereby eliminating the harmful interference while allowing the transistor to continue functioning at high temperatures for accurate temperature sensing.
Solution Approach 2:
The patent utilizes the thermal properties of the substrate isolation layer to convert the harmful effect of high temperature into a beneficial outcome. The isolation layer is designed to be thermally conductive enough to maintain thermal coupling for accurate temperature sensing, while simultaneously providing electrical isolation to block minority carrier injection. This transforms the previously harmful combination of high temperature and substrate interference into a beneficial separation of thermal and electrical functions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed design enhances temperature sensing accuracy by isolating the emitter and base from substrate noise, allowing the temperature sensor to effectively monitor and manage high temperatures without adverse impacts on other components, thus improving thermal protection in switching power circuits.
Implementation Method 1
A temperature sensor includes a bipolar transistor. A base-emitter voltage of the bipolar transistor is used as a proxy to determine a temperature of a circuit to be protected.
Implementation Method 2
A Schmitt trigger is adapted to have an input adapted to be coupled to the emitter, the second resistor terminal, and the second current source. In some examples, an output of the Schmitt trigger is coupled to a thermal protection circuit.
Data Source
AI summary
In examples, a circuit comprises a first current source coupled to a voltage source node. The circuit comprises a resistor having a first resistor terminal and a second resistor terminal, where the first resistor terminal is coupled to the first current source. The circuit comprises a bipolar transistor having a base, a collector, and an emitter, with the base coupled to the first resistor terminal, the emitter coupled to the second resistor terminal, and the collector coupled to the voltage source node. The circuit comprises a second current source coupled to the emitter and the second resistor terminal, with the second current source coupled to a ground node. The circuit comprises a Schmitt trigger having an input coupled to the emitter, the second resistor terminal, and the second current source.