Single-Ended Optical Receiver Offset Compensation for Low-Power Sensing

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Solution Overview

Problem

State-of-the-art optical receivers face challenges in accurately measuring very low power electrical signals, particularly at power levels around −40 dBm, due to sensitivity issues related to resistance and gain variations, and the need for negative voltage supplies, which are noisy and costly.

Innovation Solution

A single-ended optical receiver design incorporating a transimpedance amplifier with an electrical switch to directly measure and compensate for the offset voltage applied to the operational amplifier, allowing for precise measurement and removal of the offset voltage from the signal, thereby improving power accuracy and reducing the need for stable voltage sources.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a transimpedance amplifier with high gain is used to measure very low power signals, then measurement sensitivity is improved, but the impact of gain variations and offset voltage becomes more significant, worsening measurement accuracy

Engineering Contradiction:

Improvesensitivity to very low power signalsVSAvoidaccuracy affected by gain and offset variations

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent applies preliminary action by measuring and storing the offset voltage before the actual signal measurement. The system performs an offset measurement phase where it captures the baseline offset voltage and stores it in memory. During the subsequent signal measurement phase, this pre-measured offset is subtracted from the total measurement, effectively compensating for offset variations and improving accuracy without requiring ultra-stable components.

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If stable voltage sources and high-precision components are used to reduce gain and offset variations, then measurement accuracy is improved, but device complexity and cost increase

Engineering Contradiction:

Improvepower measurement accuracyVSAvoidrequirements for stable voltage sources and precision components

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system applies self-service by using its own measurement capability to characterize and compensate for its own imperfections. The optical receiver performs self-calibration by measuring its own offset voltage and using that information to correct subsequent measurements. This eliminates the need for external calibration equipment and allows the system to automatically compensate for component variations, reducing the need for ultra-stable components.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent implements feedback by using the measured offset voltage to adjust and correct the measurement process. The system measures the offset, stores it, and then subtracts it from subsequent signal measurements. This feedback loop continuously compensates for offset variations, allowing the use of less stable components while maintaining high measurement accuracy.

Inventive Principle:

Principle #23Feedback

3Measurement precision

If negative voltage supplies are used to enable the transimpedance amplifier operation, then the ability to measure low power signals is improved, but noise and cost increase

Engineering Contradiction:

Improvecapability to measure very low power signalsVSAvoidnoise from negative voltage supplies

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent extracts and removes the problematic negative voltage supply from the system. By using a single-ended architecture with a virtual ground reference, the design eliminates the need for negative voltage supplies entirely. The system achieves the same measurement capability by referencing all voltages to the virtual ground point, thereby removing the noise source while maintaining the ability to measure very low power signals.

Inventive Principle:

Principle #2Taking out (Extraction)

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 enhances the accuracy of low-power signal measurement, reduces the impact of gain and offset voltage variations, and allows for the use of less stable components, lowering costs and footprint while maintaining high sensitivity.

Implementation Method 1

the photodiodes in the optical receivers may generate current signals that range from tens of microamperes down to sub-nanoamperes

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

Transimpedance amplifiers convert the current generated by a photodetector to a voltage

Methodology Applied

Scientific EffectCurrent-to-voltage conversion:

Data Source

PatentUS8867929B2Optical receiver using single ended voltage offset measurement

Publication Date: 2014.10.21 II VI DELAWARE INC

AI summary

An optical receiver includes an optical detector that generates a photocurrent at an output. A transimpedance amplifier generates an amplified voltage signal corresponding to the photocurrent generated by the optical detector. An offset voltage generator generates an offset voltage that biases the voltage signal generated by the transimpedance amplifier. A switch having a first input electrically connected to the output of the transimpedance amplifier and a second input electrically connected to the output of the offset voltage generator switches between the offset voltage and the voltage signal generated by the transimpedance amplifier.