Modulator Driver Circuit with Integrated Bias Offset

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Solution Overview

Problem

Existing driver circuits for electro-absorption and micro-ring modulators require external bias-T components for high-speed operation, leading to increased complexity, cost, and signal degradation due to large capacitance and inductance values, which are difficult to integrate, and fail to effectively compensate for photocurrent generated during operation.

Innovation Solution

A driver circuit utilizing a differential amplifier with a voltage offset in one branch, allowing direct connection to the modulator without bias-T components, and incorporating a cascode configuration to manage asymmetry and compensate for photocurrent, reducing parasitic capacitance and power requirements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If external bias-T components are used for high-speed operation, then the modulator can operate at high speeds, but the circuit complexity and cost increase

Engineering Contradiction:

Improvemodulation speedVSAvoidcircuit complexity

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

The patent integrates the bias-T functionality directly into the driver circuit by combining the differential amplifier and biasing network into a single monolithic integrated circuit. This merging eliminates the need for external bias-T components while maintaining high-speed operation capability, thereby reducing circuit complexity and cost without sacrificing modulation speed.

Inventive Principle:

Principle #5Merging (Combining)

2Speed

If large capacitance and inductance values are used in bias-T, then the cross-over frequency is reduced, but the integration difficulty increases

Engineering Contradiction:

Improvesignal transmission speedVSAvoidintegration difficulty

Core Design Contradiction:

SpeedVSEase of manufacture

Solution Approach 1:

The patent changes the design approach by implementing the bias-T circuit with standard integrated circuit component values rather than requiring large external capacitance and inductance values. By adjusting the circuit parameters and topology within the integrated driver, the cross-over frequency is optimized without needing large passive components, making the circuit manufacturable as a monolithic IC.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If bias-T components are used, then bias voltage can be provided, but signal degradation occurs due to component limitations

Engineering Contradiction:

Improvebias voltage stabilityVSAvoidsignal degradation

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

By merging the bias voltage generation and high-speed signal path into a single integrated driver circuit, the patent eliminates the signal degradation that occurs at the interfaces of external bias-T components. The integrated design ensures smooth signal transitions and maintains signal integrity while providing stable bias voltage through the differential amplifier configuration.

Inventive Principle:

Principle #5Merging (Combining)

4Ease of operation

If discrete external components are used for bias-T, then the circuit can be assembled, but the density and cost increase

Engineering Contradiction:

Improvecircuit assemblyVSAvoidcomponent count

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The patent combines multiple discrete functions (differential amplification, bias voltage generation, and bias-T functionality) into a single monolithic integrated circuit. This merging eliminates the need for multiple discrete external components, reducing component count and assembly complexity while maintaining the required circuit functionality and improving device density.

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 solution enables higher density, lower cost, and faster signal transmission with reduced cut-off frequency, while effectively compensating for photocurrent, resulting in improved high-speed performance and reduced signal distortion.

Implementation Method 1

A driver circuit utilizing a differential amplifier with a voltage offset in one branch

Methodology Applied

Scientific EffectDifferential amplification:

Implementation Method 2

incorporating a cascode configuration to manage asymmetry and compensate for photocurrent

Methodology Applied

Scientific EffectPhotocurrent generation: Photoelectric Effect

Implementation Method 3

reducing parasitic capacitance and power requirements

Methodology Applied

Scientific EffectParasitic capacitance reduction: Parasitic Capacitance

Data Source

PatentUS9991965B2Driver circuit for an electro-absorption or micro-ring modulator and optical transmitter comprising such driver circuit

Publication Date: 2018.06.05 NVIDIA DENMARK APS

AI summary

A modulator driver circuit for providing a drive voltage to an electro-absorption modulator, such a Franz-Keldysh modulator, or to a micro-ring modulator, and an optical transmitter including such driver circuit, where said driver circuit includes a differential amplifier and at least one differential branch of the differential amplifier being provided with a voltage offset. This provides for a bias voltage being adjustable within the driver circuit itself. Preferably, the differential amplifier is arranged for supplying drive voltage to two complementary driver outputs providing a reverse bias relative to the modulator. In one embodiment, the differential amplifier includes a cascode in the differential branch not being provided with the voltage offset.