Optical Receiver Gain Control With Variable TIA and VGA

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Solution Overview

Problem

Conventional optical receivers face limitations in achieving high dynamic range and linearity due to noise-performance tradeoffs, particularly with fixed trans-impedance amplifiers and variable gain amplifiers, which affect signal-to-noise ratio and bandwidth, especially in high-order modulation schemes.

Innovation Solution

Implementing a variable gain trans-impedance amplifier (VGTIA) with a single variable gain amplifier (VGA) and an automatic gain control loop that generates separate gain control signals for both the VGTIA and VGA, allowing for independent control of their gains and improving noise and linearity performance across a wide range of input currents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a fixed trans-impedance amplifier and variable gain amplifier are used in conventional optical receivers, then the device complexity is reduced, but the dynamic range and linearity performance deteriorate due to noise-performance tradeoffs

Engineering Contradiction:

Improveamplifier configurationVSAvoiddynamic range

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent applies dynamics by making the trans-impedance amplifier gain variable instead of fixed. The VGTIA uses a control voltage to dynamically adjust its trans-impedance gain based on input signal conditions, enabling the system to adapt to varying input current levels and overcome the limitations of fixed-gain amplifiers in achieving high dynamic range.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent segments the gain control function by introducing separate control mechanisms for the VGTIA and VGA. The automatic gain control loop generates distinct control signals for each amplifier stage, allowing independent optimization of their respective gain characteristics and enabling better overall dynamic range performance.

Inventive Principle:

Principle #1Segmentation

2Device complexity

If a fixed trans-impedance amplifier is used, then the device complexity is reduced, but the signal-to-noise ratio and linearity deteriorate across varying input current levels

Engineering Contradiction:

Improveamplifier configurationVSAvoidsignal-to-noise ratio

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The variable gain trans-impedance amplifier dynamically adjusts its gain based on input signal conditions through a control voltage. This dynamic adjustment optimizes the signal-to-noise ratio across varying input current levels by preventing saturation at high levels and maintaining adequate gain at low levels, which a fixed-gain amplifier cannot achieve.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The automatic gain control loop implements feedback by sensing the output signal level and generating appropriate control voltages for both the VGTIA and VGA. This feedback mechanism ensures that the amplifiers operate in their optimal linearity regions, maintaining high signal-to-noise ratio and linearity performance across the full dynamic range.

Inventive Principle:

Principle #23Feedback

3Device complexity

If conventional amplifier configurations are used, then the device complexity is reduced, but the bandwidth is limited and power consumption increases

Engineering Contradiction:

Improveamplifier configurationVSAvoidbandwidth

Core Design Contradiction:

Device complexityVSSpeed

Solution Approach 1:

The variable gain trans-impedance amplifier uses dynamic gain control to maintain optimal bandwidth performance across different operating conditions. By adjusting the trans-impedance gain based on input signal levels, the system prevents saturation effects that would limit bandwidth, thereby achieving wider effective bandwidth compared to fixed-gain configurations.

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 configuration enhances signal-to-noise ratio by optimizing noise and linearity performance across varying input current levels, achieving a wider bandwidth with reduced power consumption and overcoming the noise-linearity tradeoff in conventional designs.

Implementation Method 1

a photodetector for converting an optical signal into an input electrical current signal

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

a variable gain trans-impedance amplifier (VGTIA) for converting the input electrical current signal into an input voltage signal

Methodology Applied

Scientific EffectTrans-impedance amplification:

Implementation Method 3

a variable gain amplifier (VGA) for amplifying the input voltage signal to a desired voltage level

Methodology Applied

Scientific EffectVoltage amplification:

Data Source

PatentUS10454441B2Automatic gain control loop

Publication Date: 2019.10.22 NOKIA SOLUTIONS & NETWORKS OY

AI summary

In conventional optical receivers the dynamic range is obtained by using variable gain amplifiers (VGA) with a fixed trans-impedance amplifier (TIA) gain. To overcome the SNR problems inherent in conventional receivers an improved optical receiver comprises an automatic gain control loop for generating at least one gain control signal for controlling gain of both the VGA and the TIA. Ideally, both the resistance and the gain of the TIA are controlled by a gain control signal.