Variable Sub-Bandgap Voltage Generator for Low-Voltage Operation
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Solution Overview
Problem
Designing bandgap reference circuits that operate effectively at low voltages, such as those used in battery-operated portable devices, is challenging due to the need for stability against temperature and input voltage variations, as well as power supply ripple rejection.
Innovation Solution
A variable sub-bandgap reference voltage generator is developed, utilizing a pair of diodes with different areas, amplifiers with specific gain configurations, and voltage adders/subtractors to generate output voltages with variable temperature coefficients, allowing for operation at low voltages and adaptability to different output voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap reference circuits are designed for stability and ripple rejection, then temperature independence and power supply rejection are improved, but the minimum operating voltage increases making them unsuitable for low-voltage portable devices
Solution Approach 1:
The reference voltage generation is segmented into multiple paths: one generating a voltage with positive temperature coefficient and another with negative temperature coefficient. These segmented paths are then combined to achieve temperature compensation while maintaining low operating voltage capability.
Solution Approach 2:
The circuit employs dynamic element selection through switches that can be controlled to enable different operating modes. This allows the bandgap reference to adapt its internal configuration to maintain stability across varying voltage conditions, including low-voltage operation.
2Reliability
If bandgap reference circuits are designed for high voltage operation with strong ripple rejection, then power supply rejection ratio is improved, but the circuit complexity and power consumption increase
Solution Approach 1:
The circuit employs universal building blocks such as operational amplifiers and voltage adders that can serve multiple functions. These components are used both for ripple rejection and for temperature compensation, reducing overall circuit complexity while maintaining high reliability.
Solution Approach 2:
Multiple functions are merged into shared circuit components. The same operational amplifiers and voltage adders that provide ripple rejection are also utilized for temperature compensation, eliminating the need for separate dedicated circuits and reducing overall complexity.
3Device complexity
If bandgap reference circuits use fixed output voltage design, then circuit simplicity is maintained, but adaptability to different voltage requirements is reduced
Solution Approach 1:
The circuit incorporates controllable switches that can dynamically adjust the output voltage by selecting different diode configurations. This dynamic element allows a single circuit design to provide multiple output voltage levels, enhancing adaptability without requiring multiple fixed designs.
Solution Approach 2:
The output voltage parameter can be changed by controlling the switches to select different diode areas and configurations. This allows the same circuit hardware to generate different reference voltages (e.g., 1.2V, 1.8V, 2.5V) by changing the operational parameters rather than the physical structure.
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 enables bandgap reference circuits to generate stable reference voltages with near-zero temperature coefficients, effectively suppressing noise and ripples, and operates reliably at voltages as low as 1.2 volts, meeting the demands of portable electronic devices.
Implementation Method 1
A bandgap reference circuit operates on the principle of compensating the negative temperature coefficient of VBE—which is the base-emitter voltage of a bipolar transistor—with the positive temperature coefficient of the thermal voltage VT
Implementation Method 2
a first amplifier having a voltage gain of greater than one and configured to amplify the third voltage to generate a fourth voltage; a second voltage amplifier having a voltage gain of smaller than one and configured to amplify the first voltage to generate a fifth voltage
Data Source
AI summary
A sub-bandgap reference voltage generator, generates a pair of variable voltages one having a positive temperature coefficient and one having a negative voltage coefficient. The pair of voltages are added to generate an output voltage whose value and temperature may be varied. To achieve this, a first voltage having a positive temperature coefficient is multiplied by a first ratio defined by first and second resistive values to generate a second voltage. A third voltage having a negative temperature coefficient is multiplied by a second ratio defined by third and fourth resistive values to generate a fourth voltage. The second and fourth voltages are added together to generate the output voltage of the sub-bandgap voltage generator.