Reduced Size Bandgap Reference Circuit for Current and Voltage
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Solution Overview
Problem
Traditional bandgap circuits require large area footprints and high power consumption due to the need for precise temperature compensation of reference currents, which is not always necessary for applications like phase locked loops and voltage regulators, and they often result in significant variations in reference current over temperature.
Innovation Solution
A reduced size bandgap reference circuit that generates both current and voltage using the ΔVBE/R method with an additional 1+βT factor to compensate for second-order temperature coefficients, eliminating the need for a second op amp and reducing the overall size and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional bandgap circuits use precise temperature compensation with multiple op amps, then reference current precision is improved, but circuit area and power consumption increase
Solution Approach 1:
The patent extracts and eliminates the second op amp from the traditional bandgap circuit architecture. By using a simplified topology that relies on the intrinsic properties of BJTs and resistors with specific temperature coefficients, the circuit achieves adequate precision (±2%-±5%) without requiring the full precision compensation mechanism, thus reducing area while maintaining sufficient accuracy for commercial applications.
Solution Approach 2:
The patent changes the operating parameters by selecting resistors with specific positive temperature coefficients that compensate for the BJT's temperature dependence. By carefully choosing resistor values and their temperature coefficient characteristics, the circuit achieves temperature compensation through parameter selection rather than through complex active compensation circuits, reducing the need for additional op amps.
2Reliability
If traditional bandgap circuits use multiple op amps for temperature compensation, then reference current stability over temperature is improved, but power consumption increases
Solution Approach 1:
The patent removes the second op amp from the circuit, directly reducing the power consumption associated with operating additional high-precision operational amplifiers. The remaining single op amp is configured to provide the necessary compensation with lower power draw, achieving acceptable stability over the −40 C to 125 C temperature range without the energy overhead of multiple precision compensation stages.
Solution Approach 2:
The patent employs resistors with positive temperature coefficients as a simpler, lower-power alternative to additional active compensation components. These passive components provide temperature compensation through their inherent physical properties rather than requiring active control, reducing overall power consumption while maintaining reliability for commercial applications.
3Measurement precision
If traditional bandgap circuits are designed for high precision (±0.5%), then reference voltage accuracy is improved, but circuit complexity increases
Solution Approach 1:
The patent applies partial compensation rather than full precision compensation. By targeting a relaxed accuracy range of ±2%-±5% instead of ±0.5%, the circuit uses a single op amp and simpler topology that avoids the complexity of multiple precision compensation stages. This partial action approach provides sufficient accuracy for most commercial and consumer systems without the overhead of high-precision circuitry.
Solution Approach 2:
The patent changes the design parameters by accepting a relaxed accuracy specification that allows for simpler circuit implementation. By selecting resistor values and temperature coefficients that provide adequate compensation within the ±2%-±5% range, the circuit achieves the necessary reference voltage accuracy with reduced complexity compared to high-precision designs requiring multiple op amps and careful matching.
4Reliability
If traditional bandgap circuits are placed far from points of use to minimize interference, then signal integrity is improved, but routing complexity and area increase
Solution Approach 1:
The patent creates multiple distributed reference circuits located near their respective points of use throughout the integrated circuit. Each local reference circuit provides signal integrity for its nearby consumers without requiring long routing paths that would increase area and introduce interference. This local quality approach allows different parts of the chip to have their own reference sources optimized for their specific locations.
Solution Approach 2:
The patent segments the reference circuit functionality into multiple independent units distributed across the chip. Instead of a single centralized reference circuit, multiple smaller reference circuits are placed strategically near their points of use, reducing the need for extensive routing and minimizing interference. Each segment operates independently to serve its local area, reducing overall routing complexity and area requirements.
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 a ±2%-±5% accuracy range over a temperature range of −40 C to 125 C, which is sufficient for most commercial and consumer systems, while significantly reducing the circuit area to 20% of traditional designs, allowing for multiple reference circuits to be integrated near their points of use, thus minimizing interference.
Implementation Method 1
A reduced size bandgap reference circuit that generates both current and voltage using the ΔVBE/R method
Implementation Method 2
precise temperature compensation of reference currents
Implementation Method 3
A high precision bandgap voltage reference is a temperature independent voltage reference circuit
Data Source
AI summary
A simple bandgap current generator combines a PTAT (proportional to absolute temperature) base-emitter voltage (VBE) measured across two binary junction devices (ΔVBE=VBE1−VBE2) with a current that is varied by an nWell resistor with a positive temperature coefficient to produce a CTAT (complementary to absolute temperature) current instead of PTAT reference current. One of the base-emitter voltages is constrained to be VBE1=VBE(1βT). This reduces the temperature dependency of a reference current generated by the bandgap generator. This reference current may be used to generate a bandgap reference voltage by adding an IR drop to a diode voltage or to a base-emitter voltage. The simple bandgap circuit is significantly smaller in size than a precision bandgap circuit, but still provides a voltage and/or a current reference signal having a good accuracy.