Logarithmic Transimpedance Amplifier Temperature Compensation by ADC Sampling

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Solution Overview

Problem

Existing temperature compensation methods for logarithmic transimpedance amplifiers (TIAs) using analog circuitry introduce errors that impede accurate determination of input current, as the base-emitter voltage difference is proportional to absolute temperature.

Innovation Solution

Perform temperature compensation in the digital domain by calculating the logarithm of the input current using analog signals sampled by an analog-to-digital converter (ADC) and a processor, determining a temperature compensation factor based on internal temperature signals to remove temperature dependence from the logarithmic output voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If temperature compensation is implemented using analog circuitry, then temperature dependence is compensated, but measurement precision deteriorates due to introduced errors

Engineering Contradiction:

Improvetemperature compensationVSAvoidinput current determination accuracy

Core Design Contradiction:

TemperatureVSMeasurement precision

Solution Approach 1:

The patent replaces the analog circuitry-based temperature compensation system with a digital signal processing system. The logarithmic transimpedance amplifier output is converted to digital signals through ADC, and temperature compensation is performed digitally by processing the digital signals to calculate the logarithm of the input current. This substitution eliminates the errors introduced by analog circuitry while maintaining temperature compensation capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Temperature

If analog circuitry is used for temperature compensation, then temperature effects are addressed, but device complexity increases due to additional analog components

Engineering Contradiction:

Improvetemperature compensationVSAvoidcircuitry complexity

Core Design Contradiction:

TemperatureVSDevice complexity

Solution Approach 1:

The patent substitutes complex analog temperature compensation circuitry with a digital signal processing approach. Instead of adding analog components to compensate for temperature effects, the system uses existing digital processing capabilities to perform temperature compensation through digital signal manipulation and logarithmic calculation, thereby reducing overall device complexity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The digital signal processing system performs multiple functions: it converts the logarithmic transimpedance amplifier output to digital format, performs temperature compensation, and calculates the logarithm of the input current. By using a universal digital processing platform, the patent eliminates the need for separate dedicated analog temperature compensation circuitry.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If digital signal processing is used for temperature compensation, then measurement precision is improved, but processing time increases due to sequential signal conversion and calculation

Engineering Contradiction:

Improveinput current determination accuracyVSAvoidsignal processing time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent performs the analog-to-digital conversion and initial signal processing in advance, converting the logarithmic transimpedance amplifier output to digital format before temperature compensation is needed. This preliminary conversion enables subsequent rapid digital processing and temperature compensation calculations without time-critical analog processing bottlenecks.

Inventive Principle:

Principle #10Preliminary action

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

Achieves superior performance and flexibility by providing a more accurate determination of input current, enabling corrections like emitter compensation at high input currents, surpassing the limitations of analog circuitry-based methods.

Implementation Method 1

an optical log converter (or optolog converter) is a device used to measure optical power using a photodiode that generates an output current that increases with the optical power

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

an optolog converter includes a logarithmic transimpedance amplifier (TIA) device that relies on the logarithmic relationship between base-emitter voltage and collector current of bipolar junction transistors

Methodology Applied

Scientific EffectLogarithmic relationship in bipolar junction transistor:

Data Source

PatentUS20250244167A1Systems and devices for digital-domain temperature compensation in logarithmic transimpedance amplifiers

Publication Date: 2025.07.31 ANALOG DEVICES INC

AI summary

Technologies are provided to calculate a logarithm of an input current to a logarithmic transimpedance amplifier device at a particular temperature. The logarithm of the current is calculated in digital domain based on sampling of analog signals that are internal to the logarithmic transimpedance amplifier device. The sampling can be performed, in some cases, by an analog-to-digital converter device integrated into the logarithmic transimpedance amplifier device. The calculation in digital domain is performed by one or more processor external to the logarithmic transimpedance amplifier device. The calculation includes a determination of a temperature compensation factor based on an internal analog signal indicative of temperature of the logarithmic transimpedance amplifier device. The temperature compensation factor permits removing temperature dependence from a logarithmic output voltage originating from the input current. Operating in the digital domain permits applying corrections that account for residual leakage current and an emitter-resistance correction at high input currents.