Flexible PCB Microstrip Impedance Matching Common Mode Noise
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-speed optical transceiver modules face issues with unintentional electromagnetic radiation and increased power consumption due to impedance mismatch between semiconductor laser devices and transmission lines, particularly with common mode signals, which existing technologies fail to adequately address.
Innovation Solution
A flexible printed circuit board design incorporating a thin film resistor layer and microstrip lines that consume common mode components as heat, eliminating the need for resistor elements between the optical device and ground potential, thereby reducing electromagnetic radiation and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If resistor elements are inserted in series in signal wiring to improve impedance matching, then electromagnetic radiation is reduced, but power consumption increases
Solution Approach 1:
A common mode choke is introduced as an intermediary component in the signal wiring between the driver IC and semiconductor laser device. The choke provides impedance matching for common mode signals without creating a direct resistive path that would consume differential signal power, thus reducing electromagnetic radiation while maintaining power efficiency
Solution Approach 2:
The impedance characteristics of the signal transmission path are modified by adding the common mode choke, which changes the electrical parameters of the circuit to achieve better common mode signal matching without adversely affecting differential signal transmission and power consumption
2Device complexity
If the semiconductor laser device is left in open state for common mode operation, then differential signal transmission is simple, but common mode signal reflection causes electromagnetic radiation
Solution Approach 1:
The common mode choke acts as an intermediary that terminates common mode signals without requiring changes to the basic open-state configuration of the semiconductor laser device for differential operation, thus maintaining circuit simplicity while preventing common mode signal reflection and electromagnetic radiation
Solution Approach 2:
The signal transmission path is segmented into differential mode and common mode components, with the common mode choke specifically addressing the common mode portion while leaving the differential mode transmission path unchanged and simple
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 solution effectively reduces unintentional electromagnetic waves and power consumption by consuming common mode signals as heat, improving impedance matching and maintaining differential signal integrity without increasing power requirements.
Implementation Method 1
when the high frequency signal is transmitted through the microstrip line, eddy current is generated in the thin film resistor layer by a variation of magnetic fluxes generated in the vicinity of the microstrip line, and a part of the high frequency signal is consumed as heat
Data Source
AI summary
A flexible printed circuit board includes: a signal wiring pattern including: a transmission line for connecting an end of an optical device with an end of a signal generation circuit; and another transmission line for connecting another end of the optical device with another end of the signal generation circuit; a thin film resistor layer formed in a region including a region facing the signal wiring pattern so as to constitute a first microstrip line together with each of the transmission lines; a ground conductor formed in a region except a part of a region facing the thin film resistor layer within a region including a region facing the signal wiring pattern so as to constitute a second microstrip line together with each of the transmission lines; and an insulating layer formed between each two of the signal wiring pattern, the thin film resistor layer, and the ground conductor.