Native Transistor Startup Current Source for Bandgap Reference
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Solution Overview
Problem
Existing bandgap reference voltage circuits face challenges in achieving stable operation over wide temperature variations and supply voltage ranges without causing oxide damage, particularly in ensuring proper startup and minimizing power consumption and area requirements.
Innovation Solution
A self-biased current source circuit utilizing native transistors with threshold voltage near 0V, which allows for efficient startup and operation across a wide supply voltage range with minimal power consumption, by using a low-voltage nmos transistor and high-voltage native transistors to manage current flow and voltage stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a typical startup circuit is used to initialize the bandgap circuit, then the bandgap circuit can start operation, but the circuit requires large resistors (several Megohms) and has poor supply stability, overall power consumption, and area characteristics
Solution Approach 1:
The patent changes the operating parameters of the startup circuit by using native transistors with threshold voltage near 0V instead of conventional transistors. This parameter change allows the circuit to achieve proper startup functionality without requiring large resistor values, thereby reducing the circuit area while maintaining startup reliability
Solution Approach 2:
The startup circuit is designed to be self-biased and self-limiting. The native transistors automatically regulate the startup current based on the supply voltage, eliminating the need for external control mechanisms and large resistors. The circuit serves itself by using the supply voltage characteristics to control the startup current magnitude
2Reliability
If the startup current is increased to ensure proper initialization, then the bandgap circuit starts more reliably, but the power consumption increases and oxide damage risk increases
Solution Approach 1:
The startup current is made dynamic rather than fixed. The native transistors cause the startup current to automatically adjust based on the supply voltage level, being higher when needed for reliable startup and lower during normal operation. This dynamic behavior ensures startup reliability while minimizing power consumption during steady-state operation
Solution Approach 2:
The circuit incorporates implicit feedback through the native transistor characteristics where the startup current is automatically regulated based on the supply voltage. The transistors sense the voltage level and adjust the current accordingly, providing self-regulation that prevents excessive current and power consumption
3Use of energy by moving object
If the circuit is designed for low minimum supply voltage operation, then power efficiency is improved, but the maximum supply voltage range is limited due to oxide damage risk
Solution Approach 1:
The patent employs native transistors that can tolerate higher voltage stress during brief startup periods. These transistors are designed to handle the temporary high-field conditions during startup without permanent damage, enabling the circuit to operate efficiently at low voltages during normal operation while safely accommodating wide supply voltage ranges during initialization
4Device complexity
If conventional transistors are used in the startup circuit, then the circuit design is simpler, but the threshold voltage variation with temperature and process reduces precision
Solution Approach 1:
The patent changes the transistor parameter by using native transistors with threshold voltage near 0V instead of conventional transistors with higher threshold voltages. This parameter change eliminates the dominant threshold voltage term from the startup current equation, making the current primarily dependent on supply voltage and transistor geometry, which are more stable and predictable parameters
Data Source
AI summary
A start-up circuit for a bandgap reference voltage generator circuit, including a first native transistor with a drain connected to a supply voltage of the bandgap reference voltage generator circuit and a source connected to a gate of the first native transistor; a low voltage transistor with a source connected to ground, a drain connected to the source of the first native transistor, and a gate connected to a resistor; a second native transistor with a source connected to the resistor, a gate connected to the source of the first native transistor; a high voltage transistor with a drain connected to a drain of the second native transistor and a source connected to the supply voltage; and a transistor with a gate connected to the gate of the first high voltage transistor and a drain which provides a start-up current for the bandgap reference voltage generator circuit.