Self-Heating LDO Trimming for Bandgap Voltage Accuracy
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Solution Overview
Problem
Existing bandgap voltage reference circuits require iterative trimming processes to achieve precise absolute voltage and minimum temperature coefficient, which is cumbersome and affects the accuracy of output voltage over temperature variations, and existing methods for temperature trimming in production quantities are inefficient due to multiple handling and tracking of units.
Innovation Solution
A self-heating trimming technique that increases the external load current in a low-dropout regulator circuit to accurately monitor the change in output voltage versus temperature, allowing for precise adjustment of the bandgap reference temperature coefficient by modifying a resistance value using a polysilicon fuse, thereby improving the temperature bow of the bandgap voltage reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If iterative trimming processes are used to achieve precise absolute voltage and minimum temperature coefficient, then the accuracy of output voltage over temperature variations is improved, but the trimming process becomes cumbersome and time-consuming
Solution Approach 1:
The patent applies preliminary action by performing temperature compensation measurements during the manufacturing trimming process before the device is shipped. The system pre-determines the temperature coefficient (TC) by measuring output voltage at different temperatures (e.g., using self-heating techniques with increased load current) and pre-calculates the compensation values. This eliminates the need for iterative trimming during field operation, as the compensation is already built into the device's operation.
Solution Approach 2:
The patent implements self-service through self-heating trimming techniques where the device uses its own internal resources to perform temperature characterization. By increasing the load current to generate self-heating effects, the system uses its own power consumption to create the temperature gradient needed for measurement, eliminating the need for external temperature chambers or additional test equipment during the trimming process.
2Measurement precision
If multiple handling and tracking of individual units are performed during temperature test for production trimming, then temperature trimming accuracy is achieved, but the manufacturing efficiency is reduced
Solution Approach 1:
The patent merges the temperature testing function with the normal operational function of the device. Instead of requiring separate temperature chambers and multiple handling steps, the system performs temperature characterization during standard operational testing by using self-heating techniques. The same test equipment and handling procedures used for functional testing are also used for temperature coefficient measurement, combining multiple purposes into a single process step.
Solution Approach 2:
The patent replaces the mechanical system of external temperature chambers and physical handling with an electrical self-heating mechanism. By controlling the load current to generate internal heat, the system eliminates the need for mechanical temperature environmental control and multiple unit handling, thereby maintaining measurement accuracy while dramatically improving manufacturing throughput.
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 method achieves improved accuracy of +/-1% output voltage regulation over line, load, and temperature, surpassing the +/-2% accuracy of current LDOs, by accurately compensating for temperature effects and minimizing changes in output voltage versus die junction temperature.
Implementation Method 1
self-heating a voltage regulator circuit, e.g., LDO regulator, by increasing the external load current, thus increasing the power dissipation through the circuit. This results in a thermal increase in die junction temperature
Data Source
AI summary
In one example, a method for compensating for a temperature effect during operation of a voltage regulator circuit includes applying a load current at an output of the voltage regulator circuit, measuring a first output voltage at the output, measuring a reference current or voltage, increasing the load current, measuring a change in the reference current or voltage corresponding to the increased load current, measuring a second output voltage when the measured change in the reference current exceeds a threshold, and determining a temperature coefficient (TC) value based on the measured second output voltage.