Bandgap Reference Circuit Using Darlington Pairs for Temperature Stability
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Solution Overview
Problem
Conventional bandgap type reference voltage generation circuits have a positive temperature coefficient due to base resistance, leading to unstable reference voltage variations with temperature changes.
Innovation Solution
The proposed bandgap type reference voltage generation circuit employs Darlington pairs and inverted Darlington pairs to reduce the influence of base resistance, using identical resistance values for current sources and amplifying output currents, thereby stabilizing the reference voltage across a broad temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap type reference voltage generation circuit is used, then reference voltage can be generated, but temperature coefficient is positive due to base resistance causing unstable reference voltage variations with temperature changes
Solution Approach 1:
The patent converts the harmful effect of base resistance (which causes positive temperature coefficient) into a beneficial effect by using it to generate a compensation voltage. The base resistance of the first BJT, when multiplied by a specific current, produces a voltage that compensates for the temperature drift in the bandgap reference voltage, thereby reducing the overall temperature coefficient.
Solution Approach 2:
The patent changes the electrical parameters (current values and resistance ratios) to achieve temperature compensation. By setting specific relationships between currents I1 and I2, and between resistances R3 and R4, the circuit transforms the temperature-dependent base resistance effect into a compensating mechanism that stabilizes the reference voltage across temperature variations.
2Reliability
If base resistance is reduced to improve temperature characteristic, then temperature coefficient improves, but device complexity and manufacturing constraints are affected
Solution Approach 1:
Instead of trying to minimize base resistance (which would require complex device design), the patent accepts the inherent base resistance and converts it into a useful compensation element. This approach avoids the need for complex base resistance control while achieving improved temperature characteristics through electrical parameter optimization.
3Reliability
If emitter area ratio N is increased to reduce base resistance influence, then reference voltage stability improves, but transistor area and device complexity increase
Solution Approach 1:
The patent achieves base resistance compensation through optimal selection of electrical parameters (current ratios and resistance values) rather than relying solely on increasing transistor emitter areas. This approach reduces the required transistor area while maintaining effective base resistance compensation and reference voltage stability.
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 configuration significantly improves the temperature characteristic of the reference voltage, reducing its temperature coefficient and providing a stable output voltage with minimal variation due to base resistance changes, even under high base resistance conditions.
Implementation Method 1
A bandgap type reference voltage generation circuit that utilizes a bandgap voltage (that is a specific voltage of a semiconductor, and in a case of silicon, is about 1.2 V) has been known conventionally.
Implementation Method 2
A difference voltage ΔVBE between base-emitter voltages of the NPN type BJTS 50 and 60 is caused between both ends of the resistor R3. A difference voltage ΔVBE is represented by (kT/q)·lnN by using a Boltzmann constant k, an absolute temperature T, a charge q of an electron, and a ratio N of emitter areas
Data Source
AI summary
According to an embodiment, a bandgap type reference voltage generation circuit includes a first node that is connected to an output terminal, second and third nodes that are connected to current sources, a fourth node, first and second bipolar junction transistors with bases that are connected to the first node, a third bipolar junction transistor that is provided with an emitter-collector path that is connected between the second node and the fourth node and amplifies an output current of the first bipolar junction transistor, and a fourth bipolar junction transistor that is provided with an emitter-collector path that is connected between the third node and the fourth node and amplifies an output current of the second bipolar junction transistor.