Current-Shunt Bandgap Reference Circuit for Sub-0.7 V Operation
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Solution Overview
Problem
Conventional bandgap reference (BGR) circuits face limitations in low-voltage operation due to their fixed output voltage of 1.25 V and require high impedance resistors, which occupy large chip area, and operate near sub-threshold regions, degrading performance.
Innovation Solution
The proposed BGR circuit includes a current-shunt path with multiple current sources, transistors, and resistive elements, along with comparators to regulate current flow and provide a reference voltage of less than 0.7 V, allowing operation under 1.0 nA bias current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional BGR circuits use fixed output voltage of 1.25 V, then the reference voltage is stable, but low voltage operation is limited
Solution Approach 1:
The patent implements dynamic voltage selection by providing multiple bandgap voltage references (1.25V, 0.7V, and adjustable voltages) and using a voltage selector circuit that can dynamically choose different reference voltages based on operational requirements. This allows the BGR circuit to adapt between stable high-voltage operation and low-voltage operation modes, resolving the contradiction between voltage stability and low-voltage adaptability.
2Temperature
If high impedance resistors are used to meet low voltage specification, then the reference voltage can be provided under 1.0V, but chip area increases
Solution Approach 1:
The patent changes the impedance parameter of resistors from high impedance (greater than 200 mega ohms) to low impedance values. By using low impedance resistors in conjunction with current-mode operation and voltage selector circuits, the circuit achieves sub-1.0V reference voltage output without requiring high impedance components, thereby reducing chip area while meeting low voltage specifications.
3Temperature
If current mirrors operate near sub-threshold region to meet low voltage spec, then operation under 1.0V is achieved, but performance degrades
Solution Approach 1:
The patent dynamically adjusts the operating region of current mirrors by providing multiple operation modes. In normal mode, current mirrors operate in saturation region for optimal performance. In low-voltage mode, the circuit switches to alternative configurations using voltage selectors and current-shunt paths that maintain functionality without forcing current mirrors into sub-threshold operation, thus preserving performance while enabling low-voltage operation.
4Temperature
If additional clocks are used in switched capacitor network to achieve sub-1.0V reference, then low voltage operation is enabled, but voltage ripple increases
Solution Approach 1:
The patent replaces the switched capacitor network approach (which uses clocked switching mechanisms) with a current-mode BGR circuit that operates continuously without requiring additional clocks. This substitution eliminates the switching-induced voltage ripple while maintaining sub-1.0V reference voltage capability, resolving the contradiction between low-voltage operation and voltage ripple generation.
Data Source
AI summary
A bandgap reference (BGR) circuit is provided. The BGR circuit includes a first node, a second node, and a third node. A first resistive element is connected between the second node and the third node. The BGR circuit is operative to provide a reference voltage as an output. The BGR circuit further includes a current shunt path connected between the first node and the third node, the current shunt path being operable to regulate a voltage drop across the first resistive element.