Switched-Capacitor Bandgap Voltage Reference Curvature Compensation
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Solution Overview
Problem
Bandgap voltage references exhibit significant temperature sensitivity due to curvature in output voltage, making them unsuitable for many applications where low temperature variation is required.
Innovation Solution
A switched-capacitor amplifier is used to sample and scale voltage differences across diodes with unequal current densities and currents exhibiting little temperature dependency, combining these scaled voltages to compensate for both linear and non-linear temperature-dependent components, thereby reducing temperature sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bandgap voltage reference is used to generate a temperature-independent reference voltage, then the reference voltage can be produced, but the output voltage exhibits significant curvature and temperature sensitivity that makes it unsuitable for many applications
Solution Approach 1:
The patent segments the temperature compensation into multiple distinct components: a PTAT voltage component (proportional to absolute temperature) and a CTAT voltage component (complementary to absolute temperature). By generating these separate voltage components and combining them with specific weighting factors, the circuit achieves curvature compensation and reduced temperature sensitivity that cannot be obtained with a single conventional bandgap configuration.
Solution Approach 2:
The patent changes the operating parameters of the diodes by biasing them with different current densities. Specifically, it uses multiple diodes with different emitter areas operated at different current densities to generate the PTAT voltage difference. This parameter variation enables the extraction of temperature-dependent voltage components that are then used for curvature compensation.
2Reliability
If curvature correction techniques are incorporated to reduce temperature sensitivity, then the reference voltage stability improves, but the circuit complexity and component requirements increase
Solution Approach 1:
The operational amplifiers in the circuit serve multiple functions: they act as voltage followers to buffer the diode voltages, as differential amplifiers to generate the PTAT and CTAT voltage components, and as summing nodes to combine these components with appropriate weighting. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby managing complexity while achieving curvature compensation.
Solution Approach 2:
The patent introduces intermediate voltage nodes that represent the PTAT and CTAT components separately before combining them into the final reference voltage. These intermediate nodes act as mediators that allow independent adjustment and optimization of the temperature compensation characteristics without directly modifying the core bandgap structure.
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 solution results in a stable bandgap voltage reference with reduced temperature sensitivity, minimizing the effects of temperature variations and reducing manufacturing costs by minimizing resistor requirements.
Implementation Method 1
The PTAT voltage difference is sampled and scaled using a switched-capacitor amplifier. The switched-capacitor amplifier also is used to sample and scale a difference in voltages across a second pair of diodes
Data Source
AI summary
In a novel aspect, producing a reference bandgap voltage includes generating a proportional to absolute temperature (PTAT) voltage difference based on respective voltages across a first pair of diodes. The PTAT voltage difference is sampled and scaled using a switched-capacitor amplifier. The switched-capacitor amplifier also is used to sample and scale a difference in voltages across a second pair of diodes, one of which is biased with a PTAT current and the other of which is biased with a current that exhibits little or no linear temperature dependency. The scaled voltage differences are combined with a voltage corresponding to a voltage across the diode that is biased with the PTAT current so as to at least partially compensate for linear and non-linear temperature-dependent components of the voltage across the diode.