Differential Optical Receiver Circuit for Low-Delay Noise Immunity

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Solution Overview

Problem

Existing optical receivers face challenges in converting wide dynamic range optical light into a fully differential signal without significant delay, especially at high speeds, while maintaining immunity to noise and electromagnetic interference, particularly in DC to multiple megahertz frequency applications.

Innovation Solution

The optical receiver employs a differential transimpedance amplifier with input cascodes, peak detectors, and a differential summing amplifier to produce a fully differential output, which is then processed by a comparator with built-in hysteresis and automatic gain control, ensuring low pulse width distortion and noise immunity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If low pass filters are used to process differential TIA outputs, then noise immunity is improved, but signal delay increases

Engineering Contradiction:

Improvenoise immunityVSAvoidsignal delay

Core Design Contradiction:

Object-affected harmful factorsVSLoss of time

Solution Approach 1:

The patent introduces an intermediary circuit between the TIA and comparator that processes signals without using traditional low pass filters. The differential summing amplifier with peak detectors acts as a mediator that achieves noise immunity through differential processing rather than temporal filtering, thereby avoiding the delay inherent in LPF-based approaches.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If feedback control is used to correct DC offset, then accuracy is improved, but response speed decreases due to signal delay

Engineering Contradiction:

ImproveDC offset correction accuracyVSAvoidresponse speed

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

The patent applies preliminary action by performing DC offset correction through the differential summing amplifier architecture before the signal reaches the comparator. The peak detectors and summing amplifier proactively establish the correct reference levels, eliminating the need for delayed feedback control and enabling immediate accurate response.

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If a pseudo differential signal is used from TIA, then circuit complexity is reduced, but comparator reference accuracy deteriorates

Engineering Contradiction:

ImproveTIA output structureVSAvoidcomparator reference accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent transforms the static pseudo differential signal into a dynamic fully differential signal through the differential summing amplifier. The circuit dynamically processes both differential outputs and their corresponding peak detected references, converting the inadequate pseudo differential signal into a fully differential signal with accurate references for the comparator.

Inventive Principle:

Principle #15Dynamics

4Adaptability or versatility

If automatic gain control is implemented for wide optical power range, then adaptability is improved, but device complexity increases

Engineering Contradiction:

Improveoptical power range handlingVSAvoidgain control circuitry

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent merges the gain control function into the differential summing amplifier architecture. The same circuit that performs differential summing and reference generation also handles automatic gain control, eliminating the need for separate gain control circuitry and reducing overall device complexity while maintaining wide optical power range adaptability.

Inventive Principle:

Principle #5Merging (Combining)

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 enables the optical receiver to provide a fully differential output with minimal delay and improved noise immunity, effectively handling wide optical power ranges and high-frequency signals, ensuring accurate signal detection and reduced distortion.

Implementation Method 1

The conversion of optical light into a voltage is usually implemented using a photodiode and a transimpedance amplifier (TIA)

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS10333472B2Optical receiver

Publication Date: 2019.06.25 FIRECOMMS

AI summary

A receiver has a differential transimpedance amplifier (4) with two inputs and two outputs. The differential transimpedance amplifier (4) provides a differential output and this is peak-detected (15, 16) to provide amplitude reference signals. The differential transimpedance amplifier output and the amplitude reference signals are fed to a differential summing amplifier (10), which provides a fully differential signal to a comparator, or to an automatic gain control circuit (5) to regulate the differential transimpedance amplifier gain. The differential summing amplifier (10) output is a fully differential signal, thereby having lower distortion for DC and burst mode receiver applications.