Bandgap Circuit Adaptive Start-Up to Prevent Initialization Deadlock
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Solution Overview
Problem
Conventional bandgap circuits face issues with premature power line disconnection during start-up, leading to potential deadlock regions due to the use of threshold voltage from an inverter as a reference, which can result in incomplete initialization of the bandgap core.
Innovation Solution
The proposed bandgap circuit incorporates a start-up circuit with a reference BJT that provides a threshold voltage reference to ensure the power line remains connected to the emitter terminal of the first BJT until it is fully turned on, utilizing a comparator and MOS transistors to manage this process, thereby preventing premature disconnection and ensuring adaptive operation across various PVT corners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the power line is disconnected from the emitter terminal using inverter threshold voltage as reference, then the start-up circuit can simplify the control logic, but the bandgap core may not be fully initialized leading to deadlock regions
Solution Approach 1:
The patent introduces a reference BJT as an intermediary component that provides a reliable voltage reference for the comparator. This reference BJT acts as a mediator between the power line and the comparator, ensuring accurate detection of the emitter terminal voltage without requiring complex control logic in the start-up circuit.
Solution Approach 2:
The start-up circuit performs preliminary action by maintaining the power line connection to the emitter terminal through the reference BJT voltage reference before the bandgap core is fully operational. This preliminary voltage reference establishment ensures the bandgap core is properly initialized before normal operation begins.
2Reliability
If the power line remains connected to the emitter terminal during start-up, then the bandgap core can be fully initialized, but the circuit consumes more power during the start-up phase
Solution Approach 1:
The start-up circuit operates periodically rather than continuously. The reference BJT provides voltage reference only during the critical start-up phase when the bandgap core needs initialization. Once the bandgap core is operational, the start-up circuit's active control function is completed, reducing power consumption to minimal standby levels.
Solution Approach 2:
The circuit performs the power-consuming initialization action preliminarily during start-up when necessary, establishing the bandgap core's operational state. After this preliminary action completes successfully, the circuit transitions to normal operation with significantly reduced power consumption from the start-up circuitry.
3Measurement precision
If a reference BJT is used to provide threshold voltage reference, then the start-up control precision is improved, but the device complexity increases
Solution Approach 1:
The reference BJT exploits the inherent physical parameter of base-emitter voltage (Vbe) which naturally provides a stable voltage reference. By changing the approach from using inverter threshold voltage to using BJT Vbe reference, the circuit achieves higher precision with a simple, well-understood physical effect rather than complex voltage division or regulation circuits.
Solution Approach 2:
The reference BJT is configured in a diode-connected form, copying the structure of the first BJT in the bandgap core. This structural copying ensures that the reference BJT experiences similar operating conditions and provides an accurate voltage reference that matches the electrical characteristics of the main bandgap circuitry.
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 adaptive start-up design ensures the bandgap circuit generates a temperature-independent voltage by maintaining power to the bandgap core until it is fully operational, preventing deadlock regions and ensuring reliable operation across different power supply and temperature conditions.
Implementation Method 1
a reference BJT that provides a threshold voltage as a reference for disconnecting the power line from the emitter terminal of the first BJT
Implementation Method 2
a comparator, having a positive input terminal receiving a sensed voltage related to a sensed current sensed from the bandgap core, a negative input terminal coupled to the emitter terminal of the reference BJT, and an output terminal outputting the control signal
Implementation Method 3
a start-up control MOS, having a gate terminal coupled to the output terminal of the comparator, a source terminal coupled to the power line, and a drain terminal coupled to the emitter terminal of the first BJT
Implementation Method 4
The bandgap core uses paired bipolar transistors (BJTs) to eliminate temperature-sensitive factors and thereby generate a bandgap voltage independent of temperature variations
Data Source
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AI summary
A bandgap circuit with adaptive start-up design is shown, which includes a bandgap core and a start-up circuit. The bandgap core uses paired bipolar transistors (BJTs) to eliminate temperature-sensitive factors and thereby generate a bandgap voltage that is independent of temperature variations. The start-up circuit couples an emitter terminal of a first BJT of the paired BJTs to a power line to start up the bandgap core. The start-up circuit includes a reference BJT that provides a threshold voltage as a reference for disconnecting the power line from the emitter terminal of the first BJT.