Bandgap Voltage Reference Circuit with PTAT Compensation

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Solution Overview

Problem

High precision electronic systems require stable reference voltages, but existing voltage reference circuits face challenges in reducing power consumption and noise while maintaining temperature stability and accuracy, especially as device performance increases and battery-powered devices become more functional.

Innovation Solution

A voltage reference circuit using a PTAT cell with transistors operating at different current densities, controlled by a control circuit to set collector currents to a desired ratio, and incorporating correction circuitry to compensate for base current flow effects, along with additional PTAT and CTAT cells to enhance temperature stability and noise reduction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If base current flow is present in PTAT transistors, then the circuit operates normally, but output voltage varies due to base current effects

Engineering Contradiction:

Improveoutput voltage stabilityVSAvoidvoltage reference accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

A compensation transistor is introduced as an intermediary element that replicates the base current effects of the PTAT transistors. The compensation transistor is configured to generate a compensating voltage that counteracts the base current-induced voltage variations, thereby improving output voltage stability without affecting the normal operation of the PTAT cell

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The circuit employs a feedback mechanism where the voltage generated by the compensation transistor is fed back to counterbalance the base current effects. The compensation transistor's base is connected to the PTAT cell output, creating a feedback loop that automatically adjusts the compensating voltage to maintain accurate output voltage reference

Inventive Principle:

Principle #23Feedback

2Use of energy by moving object

If power consumption is reduced in voltage reference circuits, then battery life extends, but noise performance and voltage stability may deteriorate

Engineering Contradiction:

Improvepower consumptionVSAvoidnoise and voltage instability

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The invention changes the operational parameters of the transistors by operating them at different current densities rather than identical currents. This parameter change allows the circuit to achieve the required PTAT voltage with lower overall current consumption, thereby reducing power consumption while maintaining voltage stability and minimizing noise through optimized current density distribution

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If transistors operate at higher current densities to improve resolution, then device performance increases, but power consumption and noise increase

Engineering Contradiction:

Improveanalog to digital converter resolutionVSAvoidnoise and power consumption

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

Different transistors in the circuit are operated at different current densities tailored to their specific functions. The PTAT transistors operate at optimized current densities for generating the temperature-proportional voltage, while the compensation transistor operates at a different current density suited for base current compensation. This local optimization of current density improves measurement precision without unnecessarily increasing overall noise and power consumption

Inventive Principle:

Principle #3Local quality

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 provides improved temperature stability and reduced noise in voltage reference circuits, enabling better performance in high precision electronic systems without compromising voltage stability or increasing power consumption.

Implementation Method 1

a first PTAT cell, the first PTAT cell comprising first and second transistors operating at first and second current densities, respectively, such that the transistors have first and second base-emitter voltages that differ from each other

Methodology Applied

Scientific EffectBase-emitter voltage difference effect:

Implementation Method 2

a control circuit for controlling the base voltage difference between the first and second transistors of the first PTAT cell so as to set collector currents flowing the first and second transistors to a desired ratio

Methodology Applied

Scientific EffectElectrical conduction control: Conduction (electrical)

Implementation Method 3

correction circuitry or other correction means for compensating an output voltage of the voltage reference circuit against changes in output voltage due to current flow into the base of the first and second transistors

Methodology Applied

Scientific EffectVoltage compensation effect:

Data Source

PatentUS10809752B2Bandgap voltage reference, and a precision voltage source including such a bandgap voltage reference

Publication Date: 2020.10.20 ANALOG DEVICES INT UNLTD CO

AI summary

A technique for improving the stability of a voltage reference is provided. The implementation of technique is simple and elegant and does not involve a noise penalty. A compensation resistor is provided on one end of a string of resistors used to set a ΔVBE in a PTAT cell and to set a gain applied to the PTAT cell voltage.