Adjustable Bandwidth Current-to-Voltage Converter for Optical Receivers

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Solution Overview

Problem

Conventional transimpedance amplifiers (TIAs) in optical receivers face challenges in achieving adjustable bandwidth, high gain, and low input noise, particularly in applications requiring ultrawideband operation and variable channel conditions.

Innovation Solution

A dual-mode current-to-voltage converter that switches between a photodetector amplifier with dynamic load (PADL) and an integrate-and-dump (I&D) receiver, using CMOS transistors for active dynamic loads and feedback control, allowing adjustable bandwidth operation and high sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional TIA designs are used, then high gain and low input noise can be achieved, but bandwidth is fixed and not easily adjustable

Engineering Contradiction:

Improvebandwidth adjustabilityVSAvoidcircuit complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent implements dynamic bandwidth adjustment by making the feedback resistance variable through switching between multiple feedback resistors (Rf1, Rf2, Rf3, Rf4) based on baud rate. This allows the TIA to adapt its bandwidth dynamically - higher resistance values for lower baud rates and lower resistance values for higher baud rates - resolving the contradiction between fixed conventional designs and the need for adjustable bandwidth.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the resistance parameter of the feedback element to control bandwidth. By selecting different feedback resistor values (e.g., 500 ohms for 28 GBaud, 2 kohms for 5.6 GBaud), the system achieves wide bandwidth adjustment from DC to 30 GHz while maintaining optimal performance for each operating condition without excessive circuit complexity.

Inventive Principle:

Principle #35Parameter changes

2Speed

If bandwidth is increased for higher baud operation, then data rate capability improves, but input noise increases and sensitivity decreases

Engineering Contradiction:

Improvebaud rate capabilityVSAvoidinput noise

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The patent optimizes the feedback resistance parameter to balance bandwidth and noise. For high baud rates (28 GBaud), lower feedback resistance (500 ohms) provides sufficient bandwidth while minimizing noise. For lower baud rates (5.6 GBaud), higher feedback resistance (2 kohms) improves sensitivity and reduces noise while maintaining adequate bandwidth. This parameter optimization resolves the contradiction between speed and noise.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If fixed feedback resistance is used, then circuit simplicity is maintained, but bandwidth cannot be adjusted for different data rates

Engineering Contradiction:

Improvebandwidth adjustabilityVSAvoidcircuit implementation simplicity

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The patent segments the feedback resistance into discrete selectable values using multiple parallel feedback resistors (Rf1, Rf2, Rf3, Rf4) with switching elements. This segmentation allows bandwidth adjustment for different data rates while keeping each individual resistor simple and manageable, resolving the contradiction between adaptability and manufacturing simplicity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The feedback network is designed to serve multiple functions: it provides bandwidth adjustment for different baud rates, maintains circuit stability, and works across a wide frequency range (DC to 30 GHz). This multi-functional design achieves adaptability without proportionally increasing circuit complexity, as the same feedback network structure handles multiple operating conditions.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 converter provides programmable bandwidth from sub 1 GHz to many 10's of GHz with low parasitics, low power consumption, and high sensitivity, suitable for diverse optical applications including satellite links and terrestrial free space optical links.

Implementation Method 1

there is a need to convert photocurrent from a photodetector into a voltage signal

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS20250247156A1Adjustable bandwidth current-to-voltage converter that operates in a dynamic load mode or in an integrate-and-dump mode for use in an optical receiver

Publication Date: 2025.07.31 CIENA CORP

AI summary

An adjustable bandwidth current-to-voltage converter for use in an optical receiver includes an input configured to receive current from a photodetector; an amplifier stage connected to the input; a feedback path connected to the amplifier stage and to an output, wherein the feedback path includes a feedback element and an operating mode switch configured to set one of photodetector amplifier with dynamic load (PADL) mode and an integrate-and-dump (I&D) mode. The PADL mode is for higher baud operation than the I&D mode.