Bandgap Reference Voltage Tuning via Calibration Transistors
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Solution Overview
Problem
Bandgap voltage generators in integrated circuits suffer from temperature drift due to variations in processing, leading to unreliable reference voltages across different semiconductor dies.
Innovation Solution
A tunable bandgap voltage generator with a calibration mechanism using programmable transistors, where the control circuit measures and adjusts the bandgap voltage by enabling or disabling calibration transistors based on pre-stored calibration codes to stabilize the output voltage across a range of temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bandgap voltage generator uses fixed circuit parameters to generate reference voltage, then the circuit design is simple, but the temperature drift and process variations cause unacceptable voltage variation
Solution Approach 1:
The patent implements a tunable bandgap voltage generator where the calibration transistor group can be dynamically configured by enabling or disabling individual transistors through control signals. This dynamic reconfiguration allows the circuit to adapt its characteristics to compensate for process variations and temperature drift, transforming a static circuit into a dynamically adjustable system that maintains reliable reference voltage output.
Solution Approach 2:
The patent changes the electrical parameters of the bandgap voltage generator by selectively enabling calibration transistors with different current gains (beta values). By varying the number and configuration of enabled calibration transistors, the overall current gain and voltage output characteristics are adjusted to compensate for manufacturing variations, achieving reliable reference voltage without requiring complex circuit redesign.
2Reliability
If the bandgap voltage generator is designed to compensate for process variations, then the reference voltage reliability improves, but the circuit complexity and number of components increase
Solution Approach 1:
The patent segments the calibration functionality into multiple independent calibration transistors (Q3-1 through Q3-n) rather than using a single complex compensation circuit. Each calibration transistor can be independently enabled or disabled, allowing fine-grained adjustment of the reference voltage characteristics. This segmentation approach achieves reliable reference voltage consistency across different semiconductor dies while keeping the added complexity manageable through modular design.
Solution Approach 2:
The patent employs a group of calibration transistors that provides more adjustment capability than theoretically minimum required. By having multiple calibration transistors with varying beta values, the system can achieve reliable reference voltage output even when the exact compensation amount is uncertain due to process variations. This partial/excessive action ensures coverage of a wide range of process variation scenarios.
3Temperature
If calibration transistors are added to adjust the reference voltage, then the temperature drift is reduced, but the manufacturing process complexity increases
Solution Approach 1:
The patent merges the calibration transistors with the existing bandgap voltage generator circuit structure, integrating them into the same current mirror configuration and sharing common components like resistors and amplifiers. This merging approach allows the calibration functionality to be implemented using the same fabrication process steps as the main circuit, avoiding additional manufacturing complexity while achieving reduced temperature drift through selective transistor enabling.
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 ensures a stable and accurate bandgap reference voltage, reducing temperature-related variations and achieving a consistent output within tolerance limits, even across different processing conditions.
Implementation Method 1
Bandgap voltage generators rely on the bandgap between the conduction band and the valence band of a semiconductor. Bandgap energy is the energy required for an electron to make the transition from the valence band of a semiconductor material to the conduction band of the semiconductor material.
Implementation Method 2
The reference voltage VG is based on the base emitter voltage Vbe1 of the transistors Q1 and the factor m. In particular, the voltage VG is given by the following relation: VG=VC+VP*K where VC=Vbe1, VP=ln(m)*Kb*T/q
Data Source
AI summary
A bandgap voltage generator includes a plurality of calibration transistors. A test circuit measures the bandgap reference voltage generated by the bandgap voltage generator and enables a subset of the calibration transistors to correct to the bandgap reference voltage.