Reference Voltage Circuit Using Temperature-Coefficient Matching
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Solution Overview
Problem
Conventional reference voltage circuits using depletion-mode field-effect transistors suffer from significant temperature drift, making it difficult to maintain precision and stability at low voltages, especially below 2V, due to the high impact of temperature on the output reference voltage.
Innovation Solution
A reference voltage circuit design that utilizes first and second voltage units with the same positive or negative temperature coefficients to calculate and implement a K times' amplification unit, ensuring that the output reference voltage is independent of temperature by matching their temperature coefficients, thereby reducing temperature-related fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If depletion-mode field-effect transistors are used to ensure normal operation under extremely low voltage, then the circuit can operate at low voltage, but the temperature coefficient of the output reference voltage cannot be guaranteed and temperature fluctuation is significant
Solution Approach 1:
The patent converts the harmful temperature-dependent characteristics of depletion-mode field-effect transistors into a beneficial compensation mechanism. By intentionally designing the circuit to exploit the temperature coefficients of multiple transistors (including both enhancement-mode and depletion-mode devices), the temperature variations that would normally cause drift are instead used to generate compensating voltages that cancel out the drift, thereby achieving stable reference voltage output.
Solution Approach 2:
The patent changes the operating parameters and characteristics of the transistors by utilizing both enhancement-mode and depletion-mode field-effect transistors with different temperature coefficients. Through careful selection and configuration of transistors with opposite temperature characteristics, the circuit achieves temperature compensation without requiring operational amplifiers, enabling low-voltage operation while maintaining stability.
2Temperature
If conventional bandgap reference voltage design is used to generate reference voltage with zero temperature coefficient, then temperature compensation is achieved, but the circuit requires operational amplifier and larger transistor sizes which increase layout area and cost
Solution Approach 1:
The patent extracts and removes the operational amplifier from the conventional bandgap reference voltage circuit, retaining only the essential transistor-based voltage generation and compensation mechanisms. By eliminating the operational amplifier and using direct transistor configurations with complementary temperature coefficients, the circuit achieves temperature compensation with significantly reduced complexity and smaller layout area.
Solution Approach 2:
The patent replaces expensive and complex operational amplifiers with simpler, more economical transistor-based voltage generation circuits. By using readily available enhancement-mode and depletion-mode field-effect transistors in a direct compensation configuration, the design achieves comparable or superior temperature stability without the overhead of operational amplifiers, reducing both cost and layout area.
3Measurement precision
If larger number of transistors with larger sizes are selected to reduce matching error, then matching precision is improved, but the integrated circuit has larger layout and higher cost
Solution Approach 1:
The patent applies different characteristics to different transistors in the circuit by using both enhancement-mode and depletion-mode field-effect transistors with opposite temperature coefficients. Instead of using identical large transistors throughout, the design strategically places transistors with specific local characteristics (different modes and temperature coefficients) to achieve compensation, thereby reducing the required size while maintaining precision.
Data Source
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AI summary
Disclosed is a reference voltage circuit with low temperature drift, including a first voltage unit, a second voltage unit and a K times' amplification unit. The first voltage unit is configured to generate a first voltage, with a first end thereof being grounded. The K times' amplification unit is configured to amplify the first voltage by K times, with a first end thereof being connected to a second end of the first voltage unit, and with a second end thereof being connected to a first end of the second voltage unit, wherein K is a constant greater than zero. The second voltage unit is configured to generate a second voltage, with the first end thereof being connected to a current source circuit, and a second end thereof being connected to a third end of the first voltage unit to serve as an output end of a reference voltage (VREF). The reference voltage circuit with low temperature drift makes relevance between an output reference voltage (VREF) and a temperature extremely low, and has a simple structure, and few device types are required, thereby greatly reducing difficulty and risks in design. The reference voltage circuit has very high practicality and versatility.