Bandgap Reference Circuit Using CTAT Cancellation for Temperature Stability
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Solution Overview
Problem
Existing bandgap reference circuits face challenges in maintaining a constant voltage level across temperature changes, requiring additional calibration and consuming excessive power and area, with existing calibration techniques lacking accuracy due to nonlinearity and performance differences between devices.
Innovation Solution
A bandgap reference voltage generating circuit comprising a first and second current generator that produce complementary-to-absolute temperature (CTAT) and proportional-to-absolute temperature (PTAT) currents, with an output circuit generating a reference voltage based on the difference between these currents, ensuring the reference voltage remains constant regardless of temperature changes by equalizing the CTAT currents and adjusting the PTAT currents through a variable resistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing bandgap reference circuits use additional calibration techniques, then voltage stability across temperature changes is improved, but power consumption and circuit area increase
Solution Approach 1:
The patent combines CTAT and PTAT current generation into a unified circuit architecture where two current generators work together to produce complementary temperature-dependent currents. This merged approach eliminates the need for separate calibration circuits, reducing power consumption while maintaining voltage stability across temperature variations.
Solution Approach 2:
The patent utilizes parameter changes in transistor characteristics (Vbe voltage and Ptat current) with respect to temperature to generate compensating currents. By controlling the ratio of transistor sizes and resistor values, the circuit automatically adjusts current magnitudes to achieve temperature-independent reference voltage without additional calibration power.
2Reliability
If existing bandgap reference circuits use additional calibration techniques, then voltage stability across temperature changes is improved, but circuit area increases
Solution Approach 1:
The patent integrates multiple functions (CTAT current generation, PTAT current generation, and temperature compensation) into a compact circuit structure using shared transistors and resistors. This merging eliminates the need for separate calibration circuits, significantly reducing the overall circuit area while maintaining voltage stability.
Solution Approach 2:
The current generators in the patent serve multiple functions simultaneously: generating CTAT currents, generating PTAT currents, and providing temperature compensation. This multi-functionality reduces the number of dedicated components needed, thereby reducing circuit area compared to conventional designs that require separate calibration circuits.
3Reliability
If existing calibration techniques are used, then some voltage stability is achieved, but calibration accuracy is insufficient due to nonlinearity and device performance differences
Solution Approach 1:
The patent exploits the nonlinear parameter changes of transistor Vbe voltage and Ptat current with temperature to generate compensating effects. By carefully designing the circuit to utilize these inherent nonlinear characteristics, the patent achieves high calibration accuracy without external calibration equipment, overcoming the limitations of linear approximation methods.
Solution Approach 2:
The patent implements implicit feedback through the interconnection of CTAT and PTAT current generators, where the temperature-dependent characteristics of one generator automatically compensate for the variations in the other. This feedback mechanism ensures high calibration accuracy by continuously balancing the temperature effects without requiring external calibration inputs.
Data Source
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AI summary
A bandgap reference voltage generating circuit includes a first current generator generating a first complementary-to- absolute temperature (CTAT) current and a first proportional-to-absolute temperature (PTAT) current, a second current generator generating a second CTAT current and a second PTAT current, and an output circuit outputting a reference voltage based on a difference between a first voltage based on the first CTAT current and the first PTAT current and a second voltage based on the second CTAT current and the second PTAT current, wherein the first CTAT current is cancelled by the second CTAT current.