Bandgap Reference Circuit Offset Voltage Elimination
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Solution Overview
Problem
The bandgap reference circuit disclosed in H. Neuteboom, B. M. J. Kup, and M. Janssens' work faces errors in generating a current with positive temperature dependence due to the offset voltage of the operational amplifier, which affects the accuracy of the constant reference voltage output irrespective of temperature.
Innovation Solution
A current generation circuit is designed with first and second bipolar transistors, NMOS transistors, and operational amplifiers, where the operational amplifiers generate control voltages based on drain voltages and a reference bias voltage, eliminating the operational amplifier from the PTAT current generation loop to avoid offset voltage errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If an operational amplifier is disposed on the current path through which the current having positive temperature dependence flows, then the bandgap reference circuit can generate a constant reference voltage irrespective of temperature, but errors occur in the current flowing through that current path due to the influence of the offset voltage of the operational amplifier
Solution Approach 1:
The patent extracts the operational amplifier from the PTAT current generation loop by implementing a separate current mirror circuit. The PTAT current is generated through bipolar transistors and resistors without passing through the operational amplifier, thereby eliminating the offset voltage error while maintaining temperature compensation functionality.
2Measurement precision
If the operational amplifier is removed from the PTAT current generation loop to eliminate offset voltage errors, then current generation accuracy is improved, but the circuit complexity increases due to additional current mirror circuits and control voltage generation stages
Solution Approach 1:
The patent segments the reference voltage generation circuit into distinct functional blocks: a PTAT current generation section using bipolar transistors and resistors, a current mirror section for current distribution, and a separate operational amplifier section for generating control voltages. This modular segmentation improves accuracy while organizing complexity into manageable functional units.
Data Source
AI summary
A current generation circuit including a first and a second bipolar transistors, a current distribution circuit that makes a first current and a second current flow through the first and second bipolar transistors, respectively, the first current and the second current corresponding to a first control voltage, a first NMOS transistor disposed between the first bipolar transistor and the first current distribution circuit, a second NMOS transistor disposed between the second bipolar transistor and the first current distribution circuit, a first resistive element, a first operational amplifier that outputs the second control voltage to the gates of the first and the second NMOS transistors according to a drain voltage of the first NMOS transistor and a reference bias voltage, and a second operational amplifier that generates the first control voltage according to a drain voltage of the second NMOS transistor and the reference bias voltage.