Bandgap Reference Circuit Low Input Voltage Operation
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Solution Overview
Problem
Conventional bandgap reference circuits are limited to using input voltages higher than the base-emitter voltage (VBE) of a bipolar junction transistor (BJT), which is a constraint for energy-constrained electronic systems, and they consume significant power, making them unsuitable for low-power applications such as portable devices and energy harvesting systems.
Innovation Solution
A bandgap reference circuit design that uses a first and second BJT with different device widths, where both BJTs receive currents from nodes with terminal voltages lower than their respective base-emitter voltages, and a reference generation circuit generates a bandgap reference voltage based on these voltages, utilizing switched capacitor charge pumps to operate at input voltages lower than VBE, thereby reducing power consumption and enabling temperature-insensitive voltage references.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional bandgap reference circuits use input voltages higher than VBE, then the circuit can operate with standard BJT biasing, but the minimum input voltage requirement increases power consumption and limits compatibility with energy-harvesting systems
Solution Approach 1:
The patent inverts the conventional approach by using a voltage-boosting mechanism that allows the BJT to operate at lower input voltages. Specifically, it uses a switched-capacitor charge pump or inductor-based boost converter to generate a higher voltage internally that exceeds VBE, while the external input voltage can be lower than VBE. This inversion of the voltage relationship enables low-power operation without sacrificing BJT functionality.
Solution Approach 2:
The patent introduces an intermediary voltage-boosting circuit (switched-capacitor charge pump or inductor-based converter) between the low-voltage input and the BJT. This intermediary generates the necessary higher voltage internally to drive the BJT above its VBE threshold, allowing the overall system to operate from lower input voltages while maintaining proper transistor biasing conditions.
2Stability of the object's composition
If bandgap reference circuits use larger resistors to generate stable reference voltage, then temperature independence improves, but the physical area occupied by the circuit increases
Solution Approach 1:
The patent changes the operating parameters of the BJT by enabling operation at lower currents and voltages through the voltage-boosting mechanism. This parameter change allows the use of smaller resistors with adequate precision, reducing the physical area required while maintaining temperature independence through the bandgap reference principle.
Solution Approach 2:
The patent moves the voltage generation function to a different dimension by using switched-capacitor or inductor-based voltage boosting rather than relying solely on resistor-based voltage division. This dimensional shift allows stable reference voltage generation without requiring large physical resistors, thereby reducing circuit area while maintaining temperature stability.
3Adaptability or versatility
If bandgap reference circuits are designed for low input voltage operation, then compatibility with energy-harvesting systems improves, but the circuit complexity increases due to additional voltage-boosting components
Solution Approach 1:
The patent designs the voltage-boosting circuit to serve multiple functions: it not only provides the necessary voltage boosting for low-voltage operation but also generates the bias currents and signals needed for the bandgap reference operation. This multi-functionality reduces the need for separate dedicated circuits, thereby limiting the increase in overall circuit complexity while achieving broad compatibility with energy-harvesting systems.
Solution Approach 2:
The patent merges the voltage-boosting function with the bandgap reference circuitry by integrating the switched-capacitor charge pump or inductor-based converter directly with the BJT biasing network. This consolidation combines multiple functions into a unified circuit architecture, reducing the number of discrete components and interconnections, thus limiting complexity growth while enabling low-voltage operation.
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 allows for the generation of a temperature-insensitive bandgap reference voltage at lower input voltages, reducing power consumption and extending the operational lifetime of low-power devices, while minimizing the physical area required, thus enhancing the compatibility with sub-threshold digital logic and energy harvesting systems.
Implementation Method 1
a first bipolar junction transistor (BJT) that can receive a current from a node having a terminal voltage and can output a base emitter voltage. The terminal voltage of the first BJT substantially corresponds to or is lower than the base emitter voltage of the first BJT
Implementation Method 2
the reference generation circuit can generate a bandgap reference voltage based on the base emitter voltage of the first BJT and the base emitter voltage of the second BJT
Data Source
AI summary
In some embodiments, an apparatus includes a bandgap reference circuit having a first bipolar junction transistor (BJT) that can receive a current from a node having a terminal voltage and can output a base emitter voltage. The apparatus also includes a second bipolar junction transistor (BJT) having a device width greater than a device width of the first BJT. The second BJT can receive a current from a node having a terminal voltage and output a base emitter voltage. In such embodiments, the apparatus also includes a reference generation circuit operatively coupled to the first BJT and the second BJT, where the reference generation circuit can generate a bandgap reference voltage based on the base emitter voltage of the first BJT and the base emitter voltage of the second BJT.