Bandgap Reference Circuit With Source Degeneration for Stable Current
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Solution Overview
Problem
Bandgap reference circuits face challenges in maintaining temperature stability due to random mismatches in transistor current mirrors, particularly in low power and mobile applications, where increased die area and systematic mismatches exacerbate temperature variations.
Innovation Solution
The implementation of a bandgap reference circuit using source degeneration topology in current mirrors reduces the need for large transistors and allows for convenient tuning of temperature coefficients, thereby minimizing die area and improving matching performance, especially in low power operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If traditional current mirrors are used in bandgap reference circuits, then temperature stability can be achieved through PTAT and CTAT current summation, but random mismatches in transistor current mirrors cause temperature variations that worsen in low power and mobile applications
Solution Approach 1:
The patent introduces source degeneration resistors as intermediary elements between the transistor sources and ground in the current mirror circuit. These resistors act as mediators that reduce the impact of random mismatches in transistor parameters by providing a dominant resistance value that overrides the mismatch effects, thereby improving temperature stability of the reference current in low power applications
2Manufacturing precision
If larger transistors are used to reduce random mismatches, then matching performance improves, but die area increases which is unacceptable in mobile applications
Solution Approach 1:
The source degeneration resistors serve as intermediary elements that improve matching performance without requiring larger transistors. By introducing these external resistance elements, the circuit achieves better matching precision while maintaining compact transistor dimensions, thus reducing overall die area for mobile applications
3Manufacturing precision
If source degeneration is applied to current mirrors, then matching performance improves and die area is reduced, but the circuit complexity increases due to additional components
Solution Approach 1:
The patent modifies the circuit parameters by introducing source degeneration resistors with specific resistance values that optimize the trade-off between matching performance and circuit complexity. By carefully selecting these parameter values, the circuit achieves improved matching while keeping the complexity increase minimal and manageable
Data Source
AI summary
The disclosed bandgap circuit is configured to provide a temperature stable reference current and/or voltage that is also adjustable. The stability can be facilitated by an improved matching of current mirrors provided by a source degeneration topology. The source degeneration can reduce random mismatches without requiring increased size or complexity of the current mirrors and can facilitate operation of the current mirrors in a weak inversion condition, in which random mismatches may be most severe. Further, the source degeneration may be adjusted to adjust a level and/or a temperature coefficient of the generated reference current and/or voltage.