Optical Driving Circuit Crosstalk Noise Suppression
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Solution Overview
Problem
In high-capacity optical communication systems, power supply noise from one differential amplifier circuit can affect other circuits through shared power lines, deteriorating the quality of modulated light output due to crosstalk noise, especially at high modulation speeds like 28 Gbaud to 56 Gbaud.
Innovation Solution
The driving circuit incorporates a series resistance circuit with a line element and a resistor connected in series between the center node of a differential pair circuit and a static potential line, which includes a signal line extending straight with a distance from ground lines, effectively suppressing crosstalk noise by varying impedance frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If multiple differential amplifier circuits share a common power supply line, then power supply efficiency is improved, but power supply noise causes crosstalk between circuits deteriorating signal quality
Solution Approach 1:
The common power supply line is segmented into multiple independent power supply lines, each dedicated to a specific differential amplifier circuit. This segmentation prevents noise from one circuit from affecting others through the power supply line, while still maintaining efficient power distribution to each circuit individually.
Solution Approach 2:
A series resistance circuit is introduced as an intermediary element between the power supply line and the differential amplifier circuit. This resistance circuit acts as a noise filter, blocking high-frequency noise from entering the circuit while allowing the DC power supply component to pass through, thus eliminating crosstalk without compromising power supply efficiency.
2Productivity
If high modulation speeds are implemented, then optical transmission capacity is improved, but power supply noise and crosstalk become more significant deteriorating signal quality
Solution Approach 1:
The series resistance circuit serves as a noise isolation intermediary that becomes increasingly important at high modulation speeds. By placing resistance elements in series with the power supply lines, the circuit blocks high-frequency noise components that become more prominent at 28-56 Gbaud modulation speeds, allowing clean power delivery while maintaining high transmission capacity.
Solution Approach 2:
The impedance characteristics of the power supply line are modified by adding series resistance elements. This changes the frequency response of the power supply network, creating a low-pass filter effect that attenuates high-frequency noise while passing the DC and low-frequency power components needed for high-speed modulation operation.
Data Source
AI summary
A driving circuit includes a plurality of differential amplifier circuits each electrically connected to a power supply line. Each differential amplifier circuit includes a differential pair circuit and a series resistance circuit. In the differential pair circuit, a first transistor and a second transistor are electrically connected to the power supply line through a first load resistor and a second load resistor, respectively. A center node is electrically connected between the first transistor and the second transistor. Each differential amplifier circuit generates a differential output signal in accordance with a differential incoming signal. The series resistance circuit includes a resistor and a line element. The line element includes a signal line which extends straight with a distance between the signal line and a ground line extending in parallel thereto. The resistor and the line element are connected in series between the center node and a static potential line.