Bandgap Reference Voltage Generator Startup Circuit
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Solution Overview
Problem
Conventional bandgap reference voltage generators fail to maintain a zero temperature coefficient reference voltage due to issues with BJT transistor turn-on conditions, leading to operational errors and unreliable performance.
Innovation Solution
A bandgap reference voltage generator design incorporating a first current generator with a positive temperature coefficient, a second current generator with a negative temperature coefficient, and an output voltage generator that combines these currents to produce a zero temperature coefficient reference voltage, using a voltage clamp circuit to ensure stable operation across temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bandgap reference voltage generator is used, then a reference voltage with zero temperature coefficient can be generated, but the BJT transistor may not turn on reliably at power-up, causing operational errors
Solution Approach 1:
The patent applies preliminary action by introducing a starting circuit that activates before the main bandgap reference circuit. This starting circuit pre-charges the node connected to the BJT transistor base, ensuring the transistor is already in an on-state when the main circuit begins operation. The starting circuit includes a starting transistor and associated resistors that create a preliminary voltage condition, preventing the BJT from being in an undefined or off state at power-up, thus eliminating startup errors.
2Reliability
If the BJT transistor is not turned on, then the current flows directly to ground without producing the required voltage drop, but adding a starting circuit increases circuit complexity
Solution Approach 1:
The patent merges the starting circuit functionality with the existing bandgap reference circuit components. The starting transistor shares the same node connections and voltage references as the main circuit, and the starting resistors are integrated into the existing resistor network. This merging approach allows the starting circuit to be implemented using minimal additional components that work in conjunction with the existing bandgap structure, rather than adding completely separate startup circuitry.
3Measurement precision
If the voltage at the BJT transistor base is not sufficiently high, then the transistor remains off and the reference voltage cannot be generated accurately, but increasing the voltage requires additional components
Solution Approach 1:
The patent uses an intermediate voltage boosting mechanism through the starting circuit that acts as a mediator between the power supply and the BJT transistor base. The starting transistor and associated resistors create an intermediate charging path that raises the base voltage to the required threshold level. This intermediary approach allows the voltage to be boosted locally at the critical node without requiring a global voltage multiplier or additional complex voltage generation circuitry throughout the entire bandgap reference structure.
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 reference voltage that does not change with temperature, preventing operational errors and enhancing performance by ensuring the BJT transistor remains turned on, thus providing a reliable reference voltage.
Implementation Method 1
the voltage V161 on the node 161 is the voltage drop across the BJT transistor 130, the voltage drop V161 decreases with an increase of the temperature (referred to as a negative temperature coefficient)
Implementation Method 2
the ΔV is the voltage drop across the resistor 122. Because a plurality of BJT transistors 131, . . . , 13N are coupled between a terminal of the resistor 122 and the ground, the voltage drop ΔV therefore increases with an increase of the temperature (referred to as a positive temperature coefficient)
Data Source
AI summary
A bandgap reference voltage generator is provided. In one embodiment, the bandgap reference voltage generator includes a first current generator, a second current generator, and an output voltage generator. The first current generator generates a first current with a positive temperature coefficient. The second current generator generates a second current with a negative temperature coefficient. The output voltage generator generates a third current with a level equal to that of the first current, generates a fourth current with a level equal to that of the second current, adds the third current to the fourth current to obtain a combined current with a zero temperature coefficient, and generates a reference voltage according to the combined current.