Sub-Bandgap Reference Circuit for Low-Voltage Stable Output
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Solution Overview
Problem
Existing bandgap reference voltage sources face high power consumption, making them unsuitable for low supply voltages and requiring innovative solutions to achieve stable, temperature-independent voltage references.
Innovation Solution
A sub-bandgap reference voltage source circuit utilizing a current mirror circuitry with two branches of bipolar junction transistors operated at different current densities, combined with resistance-based voltage dividers, to generate a stable output voltage with reduced temperature variation and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap reference voltage sources are used, then stable and temperature-independent voltage references are achieved, but power consumption is high
Solution Approach 1:
The circuit is divided into two separate branches: a first branch with a first BJT operated at a first current density and a second branch with a second BJT operated at a second current density. This segmentation allows independent optimization of each branch's operating conditions to achieve both low power consumption and temperature stability.
Solution Approach 2:
The patent changes the operating parameters by utilizing different current densities in the two branches. The first BJT operates at a lower current density while the second BJT operates at a higher current density, creating different voltage drops that can be combined to achieve a stable reference voltage with reduced power consumption.
2Reliability
If conventional bandgap reference voltage sources are used, then stable output voltage is achieved, but the solution is not suitable for supply voltages at or below 1 V
Solution Approach 1:
By changing the operating current densities and utilizing the different voltage characteristics of BJTs operated at different current densities, the circuit achieves a reference voltage that is stable and suitable for low supply voltages. The sub-bandgap reference approach allows operation with supply voltages at or below 1 V.
3Adaptability or versatility
If resistive sub-divisions are used to realize sub-bandgap references, then supply voltage compatibility is improved, but power consumption increases
Solution Approach 1:
The patent replaces the resistive division approach with a transistor-based approach using BJTs operated at different current densities. This substitution eliminates the need for large resistors that consume power, while achieving the same sub-bandgap reference function with significantly reduced power consumption.
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 stable output voltage with minimal temperature variation and low power consumption, allowing for accurate voltage references even at low supply voltages, as demonstrated by simulation results showing improved accuracy and reduced standard deviation after trimming.
Implementation Method 1
two bipolar transistors operated at differing current densities to generate respective base-emitter voltages
Data Source
Figure 1
Figure 2a~3b
Figure 4a~4b
AI summary
The present application relates to a sub-bandgap reference source circuit, which comprises a current mirror source, a first branch comprising a first BJT and a second branch comprising a second BJT, the first BJT having an emitter current density lower than an emitter current density of the second BJT, the first branch and the second branch being connected at a first node coupled to ground; a first voltage divider comprising first and second resistances coupled in series, the first resistance being coupled between a base terminal of the first BJT and a second node, the second resistor being coupled to ground; a second voltage divider comprising first and second resistances coupled in series, the first resistance being coupled between the second node and a base terminal of the second BJT, the second resistance being coupled to the first node; and an output terminal coupled to the second node.