Dynamic RDAC Offset Trimming for Bandgap Reference Amplifiers
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Solution Overview
Problem
Conventional band gap reference circuits in semiconductor devices suffer from significant errors due to amplifier offset voltages, which result in variations in reference voltage generation, especially when transistors have mismatches, leading to instability over temperature and voltage corners, affecting the reliability and efficiency of microprocessor operations.
Innovation Solution
The implementation of an integrator to amplify offset voltages, a comparator to determine their sign, and a controller to adjust a resistive digital-to-analog converter (RDAC) settings dynamically, which drives a differential pair of transistors in an operational transconductance amplifier (OTA) to minimize amplifier offset without relying on stored trim data, ensuring stable reference voltage generation across varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional band gap reference circuits are used with fixed trim data, then the circuit structure is simple, but the reference voltage varies significantly over temperature and voltage corners due to amplifier offset errors
Solution Approach 1:
The patent implements dynamic offset compensation by continuously adjusting the RDAC settings based on real-time offset detection, transforming the static trim approach into a dynamic adaptation mechanism that maintains reference voltage stability across varying operating conditions
Solution Approach 2:
The patent introduces a feedback loop where the offset detector monitors amplifier offset errors and feeds this information to the controller, which then adjusts the RDAC to compensate for detected offsets, creating a closed-loop system that actively maintains reference voltage accuracy
2Measurement precision
If trimming is performed at system startup, then the trim code can be stored, but the reference voltage is not available to operate storage devices and complications arise
Solution Approach 1:
The patent performs offset detection and compensation actions preliminarily during system startup before the reference voltage is fully stabilized, allowing trim settings to be established in advance and stored, eliminating startup delays while ensuring reference voltage accuracy
3Device complexity
If amplifier offset is not compensated, then the circuit operation is simple, but the offset error is multiplied by band gap loop gain resulting in up to 20 mV error
Solution Approach 1:
The patent introduces an intermediary offset detector and controller system that measures and compensates for amplifier offset errors, acting as a mediator between the amplifier and the reference voltage generation to eliminate the harmful effect of offset multiplication while maintaining overall system simplicity
Data Source
AI summary
An amplifier system includes a low offset amplifier having a first signal input, a second signal input, an output, a resistive digital to analog converter (RDAC) coupled between a first amplifying terminal and a second amplifying terminal of the amplifier that provides offset control, and a current supply coupled to the RDAC. The amplifier system further includes a low offset amplifier having a first signal input, a second signal input, an output, a resistive digital to analog converter coupled between a first amplifying terminal and a second amplifying terminal of the amplifier that provides offset control, and a current supply coupled to the RDAC. The amplifier system also further includes a load coupled to the output and to the second input of the amplifier and a controller coupled to the RDAC that provides an offset control of the first and second inputs by controlling the RDAC.