Inverse-Logarithmic Conversion Circuit With Temperature-Free Linearity

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Solution Overview

Problem

Conventional logarithmic/inverse-logarithmic conversion circuits require frequent temperature correction to maintain linearity of output signals, leading to increased time and work in the inverse-logarithmic conversion process.

Innovation Solution

A circuit configuration that includes a logarithmic conversion circuit with an operation amplifier, input resistor, and a device for logarithmic conversion and current feedback, along with an inverse-logarithmic conversion circuit featuring a current/voltage conversion circuit and a subtraction circuit, where the circuit constants are set to ensure linearity proportional to the current signal, eliminating the need for temperature correction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If temperature correction is performed to maintain linearity of output signal, then measurement precision is improved, but loss of time and operational complexity increase

Engineering Contradiction:

Improvelinearity of output signalVSAvoidtime for temperature correction

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent extracts and eliminates the temperature-dependent logarithmic conversion component by using a linear conversion circuit with temperature correction function integrated into the operational amplifier. This separates the temperature correction function from the main conversion process, allowing automatic compensation without manual intervention.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The operational amplifier in the linear conversion circuit is designed with built-in temperature correction capability, allowing the circuit to automatically compensate for temperature effects without external intervention. The circuit serves itself by internally correcting temperature drift through the operational amplifier's characteristics.

Inventive Principle:

Principle #25Self-service

2Manufacturing precision

If temperature correction is performed to maintain linearity of output signal, then manufacturing precision is improved, but device complexity increases

Engineering Contradiction:

Improvelinearity of output signalVSAvoidcomplexity of temperature correction process

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent merges the temperature correction function with the main linear conversion circuit by utilizing the operational amplifier's built-in temperature compensation capabilities. This combines multiple functions (linear conversion and temperature correction) into a single integrated circuit, reducing overall system complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The operational amplifier serves multiple functions simultaneously: it performs the linear conversion operation and provides temperature correction. This multi-functionality eliminates the need for separate temperature correction circuits or manual adjustment mechanisms, simplifying the overall device structure.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 configuration maintains the linearity of output signals during inverse-logarithmic conversion without temperature correction, reducing the time and effort required for temperature adjustments and enhancing detection accuracy.

Implementation Method 1

uses a logarithmic characteristic and an inverse-logarithmic characteristic of the transistor

Methodology Applied

Scientific EffectLogarithmic characteristic of transistor:

Implementation Method 2

uses a logarithmic characteristic and an inverse-logarithmic characteristic of the transistor

Methodology Applied

Scientific EffectInverse-logarithmic characteristic of transistor:

Data Source

PatentUS8972474B2Logarithmic/inverse-logarithmic conversion circuit

Publication Date: 2015.03.03 MITSUBISHI ELECTRIC CORP

AI summary

A logarithmic conversion circuit comprises: an operation amplifier; an input resistor connected at a preceding stage of an inverting input terminal, of the operation amplifier, to which a current signal is inputted; and a logarithmic conversion device and a current feedback device connected in series between the inverting input terminal and an output terminal of the operation amplifier, and an inverse-logarithmic conversion circuit comprises: a current/voltage conversion circuit which, after the current signal having passed through the current feedback device is inputted, converts the inputted current signal to a voltage value corresponding thereto; and a subtraction circuit outputting the difference between an output voltage of the current/voltage conversion circuit and a predetermined reference voltage, a circuit constant of the subtraction circuit being set such that the difference output of the subtraction circuit has a linearity proportional to the current signal.