CMOS Inverter DML Driver Reduces Input Voltage Amplitude

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Solution Overview

Problem

The existing DML drivers require high input voltage amplitudes to modulate current in laser diodes, leading to high power consumption and inefficient modulation in fiber-optic communication networks.

Innovation Solution

A DML driver utilizing a CMOS inverter circuit with PMOSFET and NMOSFET, where the gate of both transistors are connected to the signal input terminal, and their sources are connected to different DC voltage terminals, reducing the input voltage amplitude required for modulation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a conventional DML driver is used to modulate current in laser diodes, then the modulation function is achieved, but high input voltage amplitude is required leading to high power consumption

Engineering Contradiction:

Improvepower consumptionVSAvoidinput voltage amplitude requirement

Core Design Contradiction:

Use of energy by moving objectVSEase of operation

Solution Approach 1:

The driver circuit is segmented into multiple stages: a low-voltage CMOS logic stage that generates modulation signals, and a high-voltage current drive stage that actually modulates the laser diode current. This segmentation allows the low-power CMOS stage to operate at low voltage while the power-intensive current modulation occurs at the laser diode, reducing overall power consumption.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A voltage amplifier stage acts as an intermediary between the low-voltage CMOS logic output and the high-voltage laser diode current drive. This amplifier converts the low-voltage logic signals to the appropriate voltage levels for driving the current modulation, eliminating the need for high-voltage signals throughout the entire circuit.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If high input voltage amplitude is applied to modulate laser diode current, then sufficient modulation depth is achieved, but power consumption increases

Engineering Contradiction:

Improvemodulation depthVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

High voltage amplitude is applied locally only where needed - at the laser diode current drive stage - rather than throughout the entire circuit. The CMOS logic stage operates at low voltage, and only the final current modulation stage requires high voltage to achieve sufficient modulation depth, minimizing overall power consumption while maintaining reliable modulation.

Inventive Principle:

Principle #3Local quality

3Productivity

If conventional current modulation method is used, then laser diode current is modulated, but high voltage amplitude is required reducing modulation efficiency

Engineering Contradiction:

Improvemodulation efficiencyVSAvoidinput voltage amplitude

Core Design Contradiction:

ProductivityVSPower

Solution Approach 1:

The conventional direct voltage-to-current modulation approach is replaced with a two-stage system: first, low-voltage CMOS logic generates modulation signals, then a dedicated voltage amplifier and current drive stage convert these to the required current modulation. This substitution of the modulation mechanism improves efficiency by separating signal generation from power delivery.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS11462883B2DML driver

Publication Date: 2022.10.04 NIPPON TELEGRAPH & TELEPHONE CORP

AI summary

A CMOS inverter circuit is provided as a circuit to modulate a current flowing into a laser diode on the basis of a digital signal. An amplitude of a current flowing in a PMOSFET in the CMOS inverter circuit is made to contribute to an amplitude of the current flowing into the laser diode, to reduce an input amplitude.