Bandgap Voltage Reference Offset Calibration

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Solution Overview

Problem

Existing band-gap reference voltage source calibration methods are time-intensive and require multiple temperature measurements, as well as additional chip area for clock presence, making them inefficient for high accuracy and space optimization.

Innovation Solution

A bandgap reference voltage source with a calibration technique using phase switches to measure and adjust trim resistors in two phases, allowing for temperature-stable voltage generation without the need for two-temperature trimming, utilizing a differential amplifier and adjustable resistance to correct for both slope and offset errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If two-temperature trim is used to calibrate the band-gap reference, then high accuracy voltage generation is achieved, but calibration time increases significantly

Engineering Contradiction:

Improvevoltage accuracyVSAvoidcalibration time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The calibration process is segmented into two distinct phases: a first calibration phase that measures and corrects the slope error (temperature coefficient), and a second calibration phase that measures and corrects the offset error. This segmentation allows each phase to be optimized independently, enabling accurate calibration at a single temperature rather than requiring two-temperature measurements.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The method performs preliminary calibration actions by first measuring the slope error in the first phase and applying correction, then measuring the offset error in the second phase and applying correction. This preliminary action sequence enables the system to achieve high accuracy calibration at one temperature by systematically addressing each error component in sequence.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If additional components like clock are added to the calibration circuit, then calibration functionality is enhanced, but chip area increases

Engineering Contradiction:

Improvecalibration functionalityVSAvoidchip area

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The calibration circuit is designed with multi-functionality, where the same circuit components and switches are used for both slope calibration and offset calibration operations. The differential amplifier, switches, and resistors serve multiple purposes across different calibration phases, eliminating the need for separate dedicated circuits for each calibration function and thereby reducing overall chip area.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The method merges the slope calibration and offset calibration operations into a unified calibration sequence using the same hardware resources. The switches and amplifiers are shared between the two calibration phases, combining multiple calibration functions into a single integrated circuit block rather than requiring separate independent circuits.

Inventive Principle:

Principle #5Merging (Combining)

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

Enables high accuracy band-gap reference voltage generation at one temperature, reducing calibration time and chip area requirements, while maintaining stability and accuracy without the need for additional components like a clock.

Implementation Method 1

a differential amplifier having a positive input, a negative input, a positive output and a negative output used in single ended configuration

Methodology Applied

Scientific EffectDifferential amplification:

Implementation Method 2

VBE is a base-to-emitter voltage of one of the PNP transistors 103, and it has a negative temperature co-efficient, that is, it decreases as temperature increases

Methodology Applied

Scientific EffectBand-gap voltage generation:

Implementation Method 3

ΔVBE is the difference of the base-to-emitter voltages of the two PNP transistors (101 and 103), and is a positive quantity with a positive temperature coefficient

Methodology Applied

Scientific EffectTemperature coefficient compensation:

Data Source

PatentUS8680839B2Offset calibration technique to improve performance of band-gap voltage reference

Publication Date: 2014.03.25 TEXAS INSTRUMENTS INC

AI summary

Offset calibration technique to improve performance of band gap voltage reference. An example of a bandgap reference source includes an output resistor, a first and second transistors and a differential amplifier. A positive-input calibration phase switch is in communication with a positive amplifier input, a emitter of the first and second transistor and a negative-input calibration phase switch in communication with the negative amplifier input, the emitter of the first and second transistor. A positive-output calibration phase switch is in communication with the positive amplifier output, the first and second terminal of the output resistor and a negative-output calibration phase switch is in communication with the negative amplifier output, the first and second terminal of the output resistor. An adjustable resistance is in communication with the emitter of the first transistor, the emitter of the second transistor, and the second terminal of the output resistor.