Parallel Base-Emitter Reference Current Circuit for Low Voltage Operation
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Solution Overview
Problem
Conventional bandgap circuits are unable to operate at voltages below 2V, making them unsuitable for new electronics trends requiring reduced power consumption, and redesigning with different semiconductor materials is expensive and challenging.
Innovation Solution
A reference current circuit design that uses parallel base-emitter voltage drops instead of series connections, maintaining silicon-germanium transistor technology while enabling operation down to 1V to 1.5V with temperature compensation and low power bias networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional bandgap circuits use series-connected BE-junctions with silicon germanium transistors, then temperature compensation is achieved, but the minimum operating voltage is limited to above 2V
Solution Approach 1:
The patent inverts the conventional series connection topology to a parallel connection topology for the base-emitter junctions. This inversion changes the voltage requirements: while series connections require the sum of individual voltage drops (2×0.8V=1.6V minimum), parallel connections allow operation at lower voltages (down to 1V-1.5V) while still achieving temperature compensation through the parallel configuration's current division characteristics.
Solution Approach 2:
The patent changes the connection parameter from series to parallel, which fundamentally alters the electrical characteristics. The parallel configuration maintains the temperature compensation function (positive temperature coefficient from one branch combined with negative temperature coefficient from another) while changing the minimum operating voltage parameter from >2V to 1V-1.5V, enabling low-power applications.
2Reliability
If silicon germanium transistors are used in bandgap circuits, then temperature-stable reference current is provided, but supply voltages above 2V are required
Solution Approach 1:
The patent applies the inversion principle by switching from series to parallel connection of the silicon germanium transistor base-emitter junctions. This allows the circuit to maintain temperature stability (a key advantage of silicon germanium) while reducing the supply voltage requirement from above 2V to 1V-1.5V, making it suitable for low-power applications.
3Use of energy by moving object
If conventional bandgap circuits are redesigned for lower voltage operation, then power consumption is reduced, but expensive semiconductor materials with smaller bandgap voltages are required
Solution Approach 1:
The patent changes the connection parameter (from series to parallel) rather than changing the semiconductor material parameter. This allows the circuit to operate at lower voltages (1V-1.5V) while continuing to use standard silicon germanium transistors, avoiding the need for expensive alternative materials and simplifying the manufacturing process.
Solution Approach 2:
The patent creates a new circuit configuration (parallel connection) that copies the temperature compensation functionality of conventional bandgap circuits but implements it in a topology that enables lower voltage operation with existing materials, rather than requiring material substitution.
Data Source
AI summary
A reference current circuit has an input configured to receive an input current, a first transistor, a second transistor, and an output configured to provide a reference current. The input is directly connected to a control input of the second transistor and a first terminal of the first transistor, and is connected via a first resistor to a control input of the first transistor. The output is connected to a first terminal of the second transistor. A reference node is connected via a second resistor to the control input of the first transistor, directly to a second terminal of the first transistor and via a third resistor to a second terminal of the second transistor.