Optical Receiver Photocurrent Sensing With Diode-Clamped Headroom

Solution Overview

Problem

Optical receivers face challenges in accurately measuring photocurrent due to its large dynamic range, where low currents are difficult to detect and high currents violate the headroom required by the photodiode, making reliable RSSI and LOS indicator measurements unreliable.

Innovation Solution

The optical receiver circuit employs a first current path with a sensing resistor in parallel with a diode circuit to limit voltage and a current mirror to mirror current to a second path, allowing the use of large sensing resistors for increased sensitivity while preventing voltage violations, and incorporates a transimpedance amplifier and shunt circuit to improve measurement accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a large sensing resistor is used to increase measurement sensitivity, then low current detection accuracy is improved, but voltage across the resistor violates the headroom required by the photodiode for high current measurements

Engineering Contradiction:

Improvelow current detection accuracyVSAvoidvoltage violation of photodiode headroom

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The current measurement function is segmented into two separate paths: a first current path with a large sensing resistor for low current measurements, and a second current path with a small sensing resistor for high current measurements. This segmentation allows each path to be optimized for its specific current range without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The circuit dynamically switches between the first and second current paths based on the magnitude of the photocurrent. A switching mechanism selects the appropriate path automatically, allowing the system to adapt to varying current conditions and maintain optimal measurement accuracy across the entire dynamic range.

Inventive Principle:

Principle #15Dynamics

2Object-affected harmful factors

If a small sensing resistor is used to prevent voltage violation of photodiode headroom, then high current measurement is enabled, but low current detection accuracy deteriorates

Engineering Contradiction:

Improvephotodiode headroom preservationVSAvoidlow current detection accuracy

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The current measurement function is segmented into two separate paths: a first current path with a large sensing resistor for low current measurements, and a second current path with a small sensing resistor for high current measurements. This segmentation allows each path to be optimized for its specific current range without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The circuit dynamically switches between the first and second current paths based on the magnitude of the photocurrent. A switching mechanism selects the appropriate path automatically, allowing the system to adapt to varying current conditions and maintain optimal measurement accuracy across the entire dynamic range.

Inventive Principle:

Principle #15Dynamics

3Device complexity

If a single current path with fixed sensing resistor is used, then circuit complexity is minimized, but measurement range and accuracy across different current levels deteriorate

Engineering Contradiction:

Improvecircuit structure simplicityVSAvoidmeasurement range and accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The current measurement function is segmented into two separate paths: a first current path with a large sensing resistor for low current measurements, and a second current path with a small sensing resistor for high current measurements. This segmentation allows each path to be optimized for its specific current range without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The circuit dynamically switches between the first and second current paths based on the magnitude of the photocurrent. A switching mechanism selects the appropriate path automatically, allowing the system to adapt to varying current conditions and maintain optimal measurement accuracy across the entire dynamic range.

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

This solution enables accurate measurement of both low and high photocurrents, maintaining a wide measurement range and improving the sensitivity and reliability of RSSI and LOS indicators, while minimizing noise and headroom violations.

Implementation Method 1

a photodiode generating a photocurrent

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

a first diode circuit connected in parallel across said first sensing resistor so as to limit the voltage across the first sensing resistor

Methodology Applied

Scientific EffectDiode voltage clamping: Diode

Implementation Method 3

a current mirror circuit arranged to mirror current from said first diode circuit to said second current path

Methodology Applied

Scientific EffectCurrent mirroring:

Data Source

PatentUS8450676B2Optical receiver

Publication Date: 2013.05.28 NVIDIA DENMARK APS

AI summary

An optical receiver suitable for connecting to a photodiode generating a photocurrent with a sensing resistor and a diode circuit in parallel with the sensing resistor to limit the voltage across the sensing resistor. The diode circuit allows for a larger resistor providing greater sensitivity without risking violating the necessary headroom available to the photodiode.