Light Receiving Circuit With Frequency-Dependent Transimpedance

Solution Overview

Problem

Conventional light receiving circuits face distortion issues with increasing optical signal strength, leading to a narrowed dynamic range and difficulty in detecting weak signals, and fail to address instantaneous overshoot signals effectively.

Innovation Solution

A light receiving circuit with a current-voltage converter having a frequency-dependent conversion characteristic that is smaller at low frequencies and larger at high frequencies, using a T-type feedback network with resistors and capacitors to manage transimpedance, thereby reducing distortion and maintaining signal integrity across varying signal strengths.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the gain of the inversion amplifier is set at a high level to detect weak optical signals, then the detection sensitivity is improved, but distortion occurs in the pulse voltage waveform when strong optical signals are input

Engineering Contradiction:

Improvedetection sensitivityVSAvoidwaveform distortion

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The feedback resistance value is made dynamically adjustable rather than fixed. The resistance value changes automatically based on the strength of the input optical signal, being high for weak signals to improve detection sensitivity and low for strong signals to prevent waveform distortion. This dynamic adaptation resolves the contradiction between detection sensitivity and waveform fidelity.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The key parameter (feedback resistance value) is changed according to the input signal conditions. By varying the resistance value as a parameter, the system can optimize its performance for different signal strengths, achieving both high detection sensitivity for weak signals and low distortion for strong signals.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the gain of the inversion amplifier is set at a low level to avoid waveform distortion, then the reliability is improved, but detecting weak optical signals becomes difficult

Engineering Contradiction:

Improvewaveform fidelityVSAvoiddetection sensitivity

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The feedback resistance value is made dynamically adjustable rather than fixed. The resistance value changes automatically based on the strength of the input optical signal, being high for weak signals to improve detection sensitivity and low for strong signals to prevent waveform distortion. This dynamic adaptation resolves the contradiction between detection sensitivity and waveform fidelity.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The key parameter (feedback resistance value) is changed according to the input signal conditions. By varying the resistance value as a parameter, the system can optimize its performance for different signal strengths, achieving both high detection sensitivity for weak signals and low distortion for strong signals.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If a conventional fixed-gain inversion amplifier is used, then the device complexity is reduced, but the dynamic range is narrowed

Engineering Contradiction:

Improvecircuit simplicityVSAvoiddynamic range

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

An automatic gain control feedback mechanism is introduced where the output signal strength feeds back to adjust the feedback resistance value. This feedback loop enables the system to automatically adapt its gain to match the input signal conditions, significantly expanding the dynamic range while maintaining reasonable circuit complexity through automated control.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The feedback resistance value is made dynamically adjustable rather than fixed. The resistance value changes automatically based on the strength of the input optical signal, being high for weak signals to improve detection sensitivity and low for strong signals to prevent waveform distortion. This dynamic adaptation resolves the contradiction between detection sensitivity and waveform fidelity.

Inventive Principle:

Principle #15Dynamics

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 enhances the dynamic range of the light receiving circuit, suppresses distortion, and ensures precise output voltage waveforms independent of pulse optical signal strength, effectively handling both weak and strong signals without malfunctions.

Implementation Method 1

a light receiving element outputting electrical current corresponding to input light

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS7755020B2Light receiving circuit and light coupling device

Publication Date: 2010.07.13 KK TOSHIBA

AI summary

There is provided a light receiving circuit including, a light receiving element outputting electrical current corresponding to input light, and a current-voltage converter having current-voltage conversion characteristic, the current-voltage conversion characteristic becoming smaller at a low frequency side and larger at a high frequency side, the current-voltage converter converting the current to the voltage and outputting the voltage.