Bandgap Reference Circuit With DAC Offset Correction for Low Drift
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Solution Overview
Problem
Existing bandgap reference circuits face performance degradation due to additional noise, offset, and temperature drift when a gain stage is used to adjust the output voltage to a fixed reference voltage different from the bandgap voltage, leading to unacceptable variations across process, voltage, and temperature.
Innovation Solution
A digital-to-analog converter (DAC) is used to add or subtract a correction voltage derived from the attenuated bandgap voltage, eliminating the need for a gain or buffer stage, thereby reducing noise and temperature drift, and providing programmability of the current source to achieve a precision reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a gain stage is added to raise the output voltage to a fixed reference voltage different from the bandgap voltage, then the output voltage can be adjusted to the desired reference voltage, but additional noise, offset and temperature drift are introduced leading to performance degradation
Solution Approach 1:
The patent extracts and removes the gain stage from the reference voltage generation circuitry. Instead of using a gain stage to raise the bandgap voltage to the desired reference voltage, the invention directly outputs the bandgap voltage or uses a voltage divider to scale it down, eliminating the source of additional noise, offset and temperature drift that the gain stage would introduce.
Solution Approach 2:
Rather than amplifying the bandgap voltage up to the desired reference voltage level using a gain stage, the patent inverts the approach by using a voltage divider network to scale the bandgap voltage down to the desired reference voltage level. This inversion eliminates the need for active amplification and its associated performance degradation.
2Adaptability or versatility
If a gain stage is added to produce the reference voltage from the bandgap voltage, then the desired reference voltage level can be achieved, but the variations across process, voltage and temperature increase
Solution Approach 1:
The patent removes the gain stage that would amplify PVT variations along with the signal. By directly outputting the bandgap voltage or using passive voltage division, the circuit maintains the excellent PVT stability inherent in bandgap references without the additional variability introduced by active amplification stages.
Solution Approach 2:
The patent introduces a voltage divider network as an intermediary between the bandgap voltage source and the output. This passive intermediary scales the voltage to the desired level while maintaining stability, avoiding the use of active gain stages that would degrade PVT performance.
3Adaptability or versatility
If a DAC is used to add correction voltage to translate the bandgap voltage to any reference voltage, then programmability and precision are achieved, but circuit complexity increases
Solution Approach 1:
The patent applies a DAC-based correction circuit that provides only the necessary adjustment amount rather than fully regenerating the reference voltage. The DAC adds or subtracts a correction voltage to the bandgap voltage, providing just enough adjustment to achieve the desired reference voltage level while maintaining simplicity.
Solution Approach 2:
The patent uses a DAC to digitally control the correction voltage parameter. By changing the digital input code to the DAC, the correction voltage is adjusted in discrete steps, enabling programmable output voltage levels while keeping the circuit structure relatively simple compared to fully digital reference voltage generation.
Data Source
AI summary
An electronic device includes a precision reference circuit, which contains a bandgap reference circuit and an offset-correction circuit. The bandgap reference circuit has an output that is coupled to provide a bandgap reference voltage and an intermediate node that is separated from the output by a transimpedance resistor. The offset-correction circuit is coupled to the bandgap reference circuit and includes a DAC. The DAC is coupled to the intermediate node and is also coupled to receive an external digital value. The external digital value determines a fraction of a correction current that will be passed by the DAC.