Bandgap Reference Circuit Capacitor Layout for EMI Immunity

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Solution Overview

Problem

Existing band-gap circuits for generating temperature-independent reference signals are susceptible to electromagnetic interference (EMI), which alters the value of the reference signal, impacting the operation of electronic systems.

Innovation Solution

The proposed solution involves connecting a capacitor between the base and emitter of at least one of the two bipolar transistors in the band-gap circuit, with the capacitance value being significantly larger than the intrinsic capacitance of the base-emitter junction, to mitigate the effects of EMI.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If a band-gap circuit uses bipolar transistors to generate a temperature-independent reference signal, then the reference signal value remains stable with temperature changes, but the circuit becomes susceptible to electromagnetic interference that alters the reference signal value

Engineering Contradiction:

Improvetemperature stability of reference signalVSAvoidelectromagnetic interference susceptibility

Core Design Contradiction:

TemperatureVSObject-affected harmful factors

Solution Approach 1:

The patent introduces capacitors as intermediary elements connected between the base and emitter of bipolar transistors in the band-gap circuit. These capacitors act as mediators that filter electromagnetic interference signals before they can affect the transistor operation, thereby protecting the reference signal generation while maintaining temperature compensation functionality

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent modifies the electrical parameters of the band-gap circuit by adding capacitors with specific capacitance values (at least five times larger than the intrinsic base-emitter junction capacitance). This parameter change transforms the circuit's frequency response characteristics, creating a low-pass filter effect that attenuates high-frequency electromagnetic interference while preserving the DC and low-frequency temperature compensation signals

Inventive Principle:

Principle #35Parameter changes

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 approach effectively reduces or eliminates the influence of EMI on the reference signal, ensuring a stable temperature-independent reference voltage with minimal variation, even in the presence of strong radio frequency magnetic fields.

Implementation Method 1

a first capacitor is connected between a base and an emitter of the first transistor

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

reduces or even eliminates the influence of electromagnetic interference on the value of the reference signal

Methodology Applied

Scientific EffectElectromagnetic interference filtering: Filter (electronic)

Data Source

PatentUS12287663B2Bandgap circuit

Publication Date: 2025.04.29 STMICROELECTRONICS (GRENOBLE 2) SAS

AI summary

A band-gap circuit for generating a bandgap reference signal includes a first bipolar transistor and a second bipolar transistor of a same type among PNP and NPN types. The first and second bipolar transistors are configured to generate a current varying proportionally with the temperature. A capacitor is connected between a base and an emitter of one or both of the first and second bipolar transistors.