Bandgap Reference Circuits Using Negative PN Junction Bias
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Solution Overview
Problem
Conventional bandgap circuits face challenges in operating at lower supply voltages due to conflicting requirements between transistor voltage scaling and diode voltage stability, leading to accuracy and robustness issues in sub-threshold designs.
Innovation Solution
Implementing bandgap circuits with PN junctions that utilize negative voltage biases and negative supply references, such as gate-all-around transistors, to generate precise reference voltages even at low supply voltages, avoiding the need for deep N-well and P-well isolation and maintaining temperature independence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional bandgap circuits use PN junctions with positive supply references, then diode voltage stability is maintained, but the circuit cannot operate at lower supply voltages due to headroom requirements
Solution Approach 1:
The patent inverts the conventional supply reference approach by using negative supply references instead of positive ones. The bandgap circuit employs PN junctions biased with negative voltages, allowing the circuit to operate with lower positive supply voltages while maintaining diode voltage stability. This inversion of the supply reference polarity resolves the contradiction between stability and low-voltage operation.
Solution Approach 2:
The patent changes the supply voltage parameters by introducing negative supply references (e.g., -1.2V, -1.8V) instead of conventional positive references. This parameter change enables the bandgap circuit to maintain proper PN junction biasing and temperature compensation while operating with reduced positive supply voltages, thus achieving both stability and low-voltage compatibility.
2Ease of operation
If sub-threshold transistor designs are used to reduce headroom, then lower supply voltage operation is enabled, but accuracy and robustness deteriorate due to leakage and threshold voltage dependencies
Solution Approach 1:
The patent changes the operating parameters by using PN junctions in their normal forward-bias region rather than forcing sub-threshold transistor operation. By employing negative supply references, the circuit maintains adequate voltage headroom for accurate PN junction operation, eliminating the need for sub-threshold designs and their associated accuracy problems while still enabling low-voltage operation.
Solution Approach 2:
The patent avoids the complex sub-threshold transistor designs by using standard PN junctions with negative biasing. This approach sacrifices the theoretical ultra-low voltage capability of sub-threshold devices but gains robustness, accuracy, and ease of implementation using conventional junction structures that are less sensitive to process variations and leakage.
3Reliability
If deep N-well and P-well isolation is used to protect PN junctions, then junction reliability is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent inverts the biasing approach by using negative supply references, which naturally protects the PN junctions from over-stress conditions. This inversion eliminates the need for complex deep N-well and P-well isolation structures, as the negative biasing inherently prevents junction breakdown and reduces the requirement for extensive isolation engineering.
Data Source
AI summary
In some embodiments, bandgap reference circuits are provided that are capable of using PN junctions while transistors in the circuits can operate at reduced supply voltage levels.