Curvature-Corrected Bandgap Reference Using BJT Current Density Segmentation
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Solution Overview
Problem
Bandgap voltage references in integrated circuits face limitations due to residual temperature curvature, which affects their temperature stability, and existing curvature correction techniques are either process-sensitive or difficult to incorporate into canonical topologies like the Brokaw bandgap circuit.
Innovation Solution
A curvature-corrected bandgap reference is developed, utilizing three BJT devices with specific current densities and resistors to generate a temperature-independent reference voltage, canceling curvature-related terms and maintaining the benefits of the Brokaw topology, including insensitivity to base currents and operational amplifier offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap voltage references are used, then a reference voltage is provided, but residual temperature curvature affects temperature stability
Solution Approach 1:
The patent changes the operating parameters of the BJT devices by utilizing two different current densities (first current density substantially proportional to absolute temperature, second current density substantially independent of temperature) to generate different voltage components that compensate for each other's temperature dependence, thereby eliminating residual temperature curvature
Solution Approach 2:
The patent creates a composite voltage reference by combining multiple voltage components from BJT devices operating at different current densities. The reference voltage is formed as a weighted combination of voltages from BJT devices with different operating characteristics, achieving temperature independence through the composite structure
2Reliability
If existing curvature correction techniques are applied, then temperature stability improves, but the techniques are either process-sensitive or difficult to incorporate into canonical topologies
Solution Approach 1:
The patent achieves curvature correction by changing the current density parameters of the BJT devices rather than relying on process-sensitive matching. The first BJT operates at a current density proportional to absolute temperature while the second operates at a temperature-independent current density, creating a process-insensitive correction mechanism
Solution Approach 2:
The patent segments the bandgap reference function into distinct BJT devices operating at different current densities, with each device contributing a specific voltage component. This segmentation allows the curvature correction to be incorporated into the canonical Brokaw topology without requiring complex additional circuitry
3Reliability
If curvature correction is implemented, then temperature stability improves, but device complexity increases
Solution Approach 1:
The patent achieves multi-functionality by having the same BJT devices serve dual purposes: generating the reference voltage while simultaneously providing curvature correction through their different operating current densities. The correction voltage is derived from the same devices that generate the main reference, eliminating the need for separate correction circuitry
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 achieves improved temperature stability by directly relating curvature correction to resistor values, simplifying production trims and reducing systematic errors, while ensuring the output voltage remains independent of temperature variations.
Implementation Method 1
The first BJT device operates at a first current density that is substantially proportional to absolute temperature
Implementation Method 2
The second BJT device operates at a second current density that is substantially independent of temperature
Implementation Method 3
a correction voltage proportional to a voltage difference of the first and second emitter terminals, wherein the correction voltage substantially cancels a curvature of the reference voltage
Data Source
AI summary
A curvature-corrected bandgap reference is disclosed. The curvature-corrected bandgap reference comprises a Brokaw bandgap circuit. The Brokaw bandgap circuit includes an output node providing a reference voltage. The Brokaw bandgap circuit further comprising a first BJT device including a first base terminal coupled to the output node and a first emitter terminal. The first BJT device operates at a first current density that is substantially proportional to absolute temperature. The curvature-corrected bandgap reference also includes a second BJT device including a second base terminal coupled to the output node and a second emitter terminal. The second BJT device operates at a second current density that is substantially independent of temperature. Finally the curvature-corrected bandgap reference includes a correction voltage proportional to a voltage difference of the first and second emitter terminals, wherein the correction voltage substantially cancels a curvature of the reference voltage.