Curvature-Compensated Bandgap Circuit Without Individual Trimming
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Solution Overview
Problem
Existing bandgap reference circuits require complex calibration and individual device tuning to compensate for process variations, leading to increased manufacturing costs and complexity.
Innovation Solution
A precision bandgap reference circuit is designed with a core bandgap circuit and a proportional-to-absolute-temperature (PTAT) circuit, which produces a sigmoidal voltage temperature curve with minimal voltage variation, reducing the need for individual device tuning and simplifying production testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If curvature compensated circuits are added to traditional bandgap circuits, then voltage variation across temperature is reduced, but circuit complexity increases and factory calibration is required
Solution Approach 1:
The patent merges the curvature compensation function into the existing bandgap circuit by having the operational amplifier control multiple transistors (Q1-Q4) with different emitter areas to generate compensation currents. This integrates the compensation mechanism within the standard bandgap architecture rather than adding separate compensation circuits, thereby reducing overall device complexity while maintaining voltage precision.
Solution Approach 2:
The circuit uses its own internal components (transistors Q1-Q4 with different emitter areas, resistors R1-R4) to generate compensation currents that automatically correct for curvature effects. The operational amplifier self-regulates these compensation currents based on the temperature-dependent voltage drops, eliminating the need for external calibration or additional compensation circuits.
2Manufacturing precision
If curvature compensated circuits with uncorrelated temperature coefficients are used, then voltage variation is compensated, but individual die serialization and trimming are required
Solution Approach 1:
The patent changes the approach from using uncorrelated temperature coefficients to using correlated coefficients that vary together with process parameters. By designing the circuit with transistors having different emitter areas and resistors with specific ratios, the compensation mechanism relies on parameters that scale together during fabrication, making the circuit insensitive to process variations and eliminating the need for individual die trimming.
Solution Approach 2:
The circuit uses homogeneous materials and process-compatible components (all bipolar transistors, all resistors of the same type) that exhibit correlated behavior across process variations. This homogeneity ensures that temperature compensation works effectively across different dies without requiring individual calibration, simplifying manufacturing.
3Manufacturing precision
If multiple different types of resistors with different temperature coefficients are used, then curvature compensation is achieved, but the number of components and calibration steps increases
Solution Approach 1:
The patent makes the resistors and transistors serve multiple functions: they establish bias currents, generate voltage drops for comparison, and simultaneously provide temperature compensation through their correlated variations. This multi-functionality reduces the total number of components needed and eliminates separate calibration steps, as the same components that set the operating point also provide curvature compensation.
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 reduced sensitivity to temperature and supply voltage variations, minimizing production testing costs and complexity by using a correlated PTAT output to flatten the bandgap voltage curve over a temperature range.
Implementation Method 1
a proportional-to-absolute-temperature (ptat) circuit coupled to the core bandgap circuit, wherein the coupled core bandgap and ptat circuits produce a bandgap voltage having a varying sigmoidal shape by the temperature
Data Source
AI summary
A curvature compensated bandgap circuit that is capable of matching best-in-class two (2) parts-per-million performance without over-temperature trimming. This improves performance metrics for precision voltage reference products without requiring individual device tuning during production thereof. A core bandgap circuit comprises a main operational amplifier having a second order bowed voltage response over temperature. A ptat circuit is coupled to the core bandgap circuit to provide a sigmoidal third order shape for the bandgap voltage.