Bandgap Reference Trimming Using Temperature-Based Voltage Prediction
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Solution Overview
Problem
Conventional bandgap reference circuits exhibit significant variation in output voltage across temperature ranges, leading to errors when trimmed at a single temperature, which are not effectively reduced at other temperatures due to curvature of the bandgap reference output voltage as a function of temperature.
Innovation Solution
A predictive model is used to trim the bandgap reference circuit by determining model parameters during production and adjusting trim parameters based on temperature measurements during actual use, reducing the error between the output voltage and target voltage from +/-1.5% to +/-0.45% through discrete adjustments of resistance or current sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the bandgap reference circuit is trimmed at a single temperature during production test, then the output voltage error is reduced at that specific temperature, but the error increases at other temperatures due to curvature of the output voltage vs temperature relationship
Solution Approach 1:
The patent applies preliminary action by measuring and storing the output voltage of the bandgap reference circuit at multiple temperatures (e.g., -40°C, 25°C, 125°C) during production testing. These pre-measured values are stored in a lookup table in memory, enabling the system to compensate for temperature-induced voltage variations without requiring real-time complex calculations or additional trimming at each temperature point.
Solution Approach 2:
The patent implements feedback by using a temperature sensor to detect the current temperature, then using this temperature information to select the appropriate correction value from the stored lookup table. The correction value is applied to adjust the bandgap reference output voltage, creating a closed-loop feedback system that maintains accurate voltage output across varying temperatures.
2Ease of manufacture
If conventional trimming methods are used without temperature compensation, then the circuit is simple to manufacture, but the output voltage varies significantly across temperature ranges
Solution Approach 1:
The patent uses copying by creating a digital replica of the bandgap reference circuit's temperature characteristics through measurement and storage of output voltage values at multiple temperatures. Instead of physically modifying the circuit for each temperature condition, the system copies the voltage characteristics into a lookup table in memory, allowing software-based compensation that maintains manufacturing simplicity while improving reliability.
3Device complexity
If the bandgap reference circuit operates without temperature-based compensation, then the device complexity is low, but the output voltage curvature causes errors across temperature ranges
Solution Approach 1:
The patent introduces an intermediary element - a lookup table stored in memory - that mediates between the temperature sensor and the bandgap reference circuit. The lookup table contains pre-calculated correction values that translate temperature readings into appropriate voltage compensation amounts, allowing the system to achieve high precision without modifying the fundamental bandgap reference circuit structure.
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
The model effectively reduces the error between the bandgap reference output voltage and target voltage across a wide temperature range, ensuring a stable output voltage by continuously adjusting trim parameters based on predicted output voltages, thereby maintaining a constant target voltage.
Implementation Method 1
A conventional bandgap reference circuit outputs a voltage with a relatively low temperature sensitivity or temperature dependency based on a bandgap principle. The bandgap principle involves adding voltages from a circuit section of the bandgap reference circuit having a positive temperature coefficient and a circuit section of the bandgap reference circuit having a negative temperature coefficient
Implementation Method 2
the PTAT voltage is obtained as a voltage difference between two bipolar transistors which are operated with different current densities
Implementation Method 3
the NTAT voltage is obtained as a base-emitter voltage of a bipolar transistor
Data Source
AI summary
A first error is determined between a bandgap reference output voltage of a bandgap reference circuit at a first temperature and a target voltage. A second temperature of the bandgap reference circuit is measured. A bandgap reference output voltage of the bandgap reference circuit is predicted at the second temperature and based on the first error. A second error is determined between the bandgap reference output voltage and the target voltage. A trim parameter of the bandgap reference circuit is determined based on the second error. The bandgap reference circuit is set with the trim parameter, where a third error between a bandgap reference output voltage of the bandgap reference with the trim parameter is less than the second error.