Reference Voltage Generator Using MOS and Bipolar Transistors
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Solution Overview
Problem
Integrated circuit designs for mobile devices face challenges in generating accurate reference voltages in low power environments, as conventional resistor-based solutions require large chip areas, which is inefficient for small form factor devices.
Innovation Solution
A reference voltage generator using a combination of MOS and bipolar transistors, where the MOS transistor is biased with a current proportional to T^2*μ(T) and the bipolar transistor's base-to-emitter voltage is combined with the MOS transistor's gate-to-source voltage to produce a stable output without the need for resistors, reducing chip area requirements and minimizing manufacturing variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional resistor-based circuits are used to generate accurate reference voltage, then manufacturing precision is improved, but chip area increases significantly
Solution Approach 1:
The patent changes the fundamental parameters of the reference voltage generation by replacing resistors with transistors operating in specific regions. MOS transistors are biased to operate in the subthreshold region where their current-voltage characteristics provide temperature compensation, while bipolar transistors operate in the forward active region. This parameter change allows achieving accurate reference voltage without large resistors, resolving the contradiction between manufacturing precision and chip area.
Solution Approach 2:
The patent substitutes the passive resistor-based mechanism with an active transistor-based mechanism. Instead of relying on resistor ratios for voltage reference, the invention uses the exponential current-voltage relationships of MOS and bipolar transistors, combined with their temperature coefficients, to generate the reference voltage. This substitution eliminates the need for large-area resistors while maintaining or improving accuracy.
2Use of energy by moving object
If low power operation is implemented in mobile devices, then energy consumption is reduced, but reference voltage generation becomes more challenging
Solution Approach 1:
The patent exploits the temperature coefficient parameters of MOS and bipolar transistors to achieve power-efficient operation. By biasing MOS transistors in the subthreshold region, the circuit operates at very low currents while the inherent positive temperature coefficient of subthreshold MOS transistors compensates for the negative temperature coefficient of bipolar VBE, maintaining reference voltage stability without requiring high power consumption.
Solution Approach 2:
The patent creates a composite transistor circuit combining MOS and bipolar transistors to achieve both low power consumption and high stability. The MOS transistors provide low-power operation with positive temperature coefficient, while bipolar transistors provide stable VBE with negative temperature coefficient. The combination of these two different transistor types creates a composite system that cancels temperature effects and maintains reliability at low power levels.
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
This solution provides a highly accurate reference signal in a low power environment while conserving chip area, as the positive temperature coefficient of the MOS transistor cancels the negative temperature coefficient of the bipolar transistor, resulting in a stable output voltage with reduced error rates.
Implementation Method 1
the positive temperature coefficient of the MOS transistor cancels the negative temperature coefficient of the bipolar transistor, resulting in a stable output voltage with reduced error rates
Data Source
AI summary
A reference voltage generator circuit may include at least one MOS transistor and at least one bipolar transistor coupled together to provide an electrical path from an input reference potential to an output of the generator circuit. The electrical path may extend through a gate-to-source path of the MOS transistor and further through a base-to-emitter path of the bipolar transistor. The MOS transistor may be biased by a bias current that is proportional to T2·μ(T), where T represents absolute temperature and μ(T) represents mobility of a MOS transistor in the bias current generator. Optionally, the reference voltage generator may include N MOS and M multiple bipolar transistors (N≧1, M≧1), and the output reference voltage may be N*VGS+M*VBE as compared to the input reference potential.