Bandgap Current Reference Circuit With Single Stable PTAT Bias

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Solution Overview

Problem

Existing bandgap current reference circuits face challenges in achieving precise temperature stability and reducing circuit area and component mismatch, leading to multiple stable operating points and increased trim requirements.

Innovation Solution

The proposed bandgap current reference circuits incorporate a bandgap core circuit with a bipolar transistor and resistors, coupled with an error amplifier featuring a differential input stage, to generate a zero temperature coefficient current, ensuring operation at a single stable point and reducing circuit area and mismatch variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If existing bandgap current reference circuits are used, then temperature stability is achieved through PTAT and CTAT combination, but circuit area increases and multiple stable operating points occur

Engineering Contradiction:

Improvetemperature stabilityVSAvoidcircuit area

Core Design Contradiction:

Stability of the object's compositionVSArea of stationary object

Solution Approach 1:

The patent combines the PTAT and CTAT generation functions into a unified bandgap core circuit structure where bipolar transistors with different emitter areas and resistors work together to produce both temperature coefficients simultaneously, reducing overall circuit area while maintaining temperature stability

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent uses bipolar transistors with deliberately different emitter areas (Q1 with area A1, Q2 with area A2) to create local variations in current characteristics, enabling one transistor to generate PTAT current while another generates CTAT current, thus achieving temperature compensation without increasing overall circuit area

Inventive Principle:

Principle #3Local quality

2Measurement precision

If existing bandgap current reference circuits are used, then reference voltage is generated, but component mismatch increases and trim requirements increase

Engineering Contradiction:

Improvereference voltage precisionVSAvoidcomponent mismatch

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The patent implements an error amplifier that continuously monitors the bandgap core circuit output and provides feedback control, detecting and correcting component mismatch variations in real-time, thereby maintaining high reference voltage precision despite manufacturing tolerances

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The bandgap core circuit is designed to self-compensate for component mismatch through its inherent PTAT and CTAT current combination mechanism, where the temperature-dependent characteristics automatically adjust to counteract mismatch effects, reducing external trimming requirements

Inventive Principle:

Principle #25Self-service

3Stability of the object's composition

If existing bandgap current reference circuits are used, then temperature stable voltage is produced, but power supply rejection is insufficient

Engineering Contradiction:

Improvetemperature stable voltageVSAvoidpower supply rejection

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The error amplifier in the patent provides high-gain feedback control that actively rejects power supply disturbances, maintaining stable bandgap voltage output despite variations in power supply conditions, thus improving power supply rejection ratio

Inventive Principle:

Principle #23Feedback

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 solution achieves reduced circuit area, improved power supply rejection, and minimized variations in reference current over temperature, voltage, and process, thereby reducing trim requirements and associated costs.

Implementation Method 1

A bandgap reference circuit generates a complementary-to-absolute-temperature (CTAT) voltage/current and a proportional-to-absolute-temperature (PTAT) voltage/current. The PTAT component increases with increasing temperature (i.e., the PTAT component has a positive temperature coefficient)

Methodology Applied

Scientific EffectThermal voltage: Seebeck Effect

Implementation Method 2

Bandgap voltage reference circuits generate a temperature-stable voltage by combining a p-n junction voltage with a thermal voltage. The CTAT component decreases with increasing temperature (i.e., the CTAT component has a negative temperature coefficient)

Methodology Applied

Scientific EffectBandgap effect: Seebeck Effect

Implementation Method 3

The error amplifier includes a differential input stage and a gain stage. The differential input stage is coupled to the bandgap core circuit. The gain stage includes a first input, a second input, and an output

Methodology Applied

Scientific EffectDifferential amplification:

Data Source

PatentUS20230324941A1Bandgap current reference

Publication Date: 2023.10.12 TEXAS INSTRUMENTS INC

AI summary

A bandgap current reference circuit includes a bandgap core circuit and an error amplifier. The bandgap core circuit is configured to generate a zero temperature coefficient bandgap current. The bandgap core circuit includes a bipolar transistor. The bipolar transistor is configured to pass a current that is proportional to absolute temperature (PTAT current). The error amplifier is coupled to the bandgap core circuit and includes a bipolar differential input pair. The bipolar differential input pair is configured to ensure that the PTAT current is flowing in the bipolar transistor.