SOI CTAT Current Mirror With Self-Biased Back Gate
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Solution Overview
Problem
Existing reference circuits require precise and constant reference voltages and resistors to maintain a stable reference current over temperature variations, which can be challenging and costly due to the use of bipolar devices and additional manufacturing steps.
Innovation Solution
A circuit design utilizing fully depleted SOI transistors in current mirror configurations, where the back gate contact of one transistor is connected to the drain of another, generates a CTAT current that is self-biased and provides a relatively linear current over a wide temperature range, combined with a PTAT current to produce a reference current or voltage that is stable over a wide temperature range without requiring bipolar devices or additional manufacturing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If precise resistors and constant reference voltage are used to maintain stable reference current over temperature, then temperature stability is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The back gate voltage of the SOI transistor is generated self-generously from its own drain voltage through the capacitance coupling, eliminating the need for external reference voltage sources and complex biasing circuits. The transistor's own operation creates the necessary gate voltage to maintain stable current.
Solution Approach 2:
The invention exploits the temperature-dependent characteristics of SOI transistors, specifically the variation of threshold voltage with temperature, to inherently compensate for temperature effects. By operating in the sub-threshold region and utilizing capacitance coupling, the circuit transforms temperature-dependent parameters into a stabilizing mechanism.
2Stability of the object's composition
If precise resistors and constant reference voltage are used to maintain stable reference current over temperature, then temperature stability is improved, but manufacturing cost increases
Solution Approach 1:
The back gate voltage is generated self-generously from the transistor's own drain voltage, eliminating the need for precision reference voltage sources and reducing component requirements. This self-biasing mechanism simplifies the bill of materials and reduces manufacturing cost.
Solution Approach 2:
The invention replaces expensive precision resistors and reference voltage sources with standard SOI transistors and simple capacitors. The use of readily available standard components instead of precision components reduces manufacturing cost while maintaining performance.
3Stability of the object's composition
If bipolar devices or complex threshold voltage altering techniques are used to generate CTAT current, then current stability is improved, but device complexity increases
Solution Approach 1:
The invention changes the operating parameters of the SOI transistor by operating in the sub-threshold region and utilizing capacitance coupling between drain and back gate. This parameter change enables the generation of CTAT current using simple transistor configurations without requiring bipolar devices or complex threshold voltage altering techniques.
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 circuit achieves a reference current or voltage that is relatively constant over a wide temperature range, reducing the need for precise resistors and constant reference voltages, and minimizing manufacturing complexity while maintaining accuracy.
Implementation Method 1
a back gate contact of the first SOI transistor is capacitively coupled to a gate and drain of the first SOI transistor
Implementation Method 2
utilizing fully depleted SOI transistors in current mirror configurations with self-biased back gate contacts to generate a CTAT current
Data Source
AI summary
A CTAT circuit that generates a CTAT current. The circuit includes two SOI transistors of a first conductivity type arranged in a current mirror configuration where the gates of the two transistors and the back gate contact of one of the transistors is connected to the drain of the other transistor. The SOI transistor of the first conductivity type whose back gate contact is connected to the drain of the other SOI transistor of the first conductivity type is located in current path that carries a CTAT current. In some embodiments, the drains of the two transistors are each coupled to a drain of a respective one of a second pair of SOI transistors of a second conductivity type, where the second pair of SOI transistors are also configured in a current mirror configuration.