Optical Transceiver Impedance Balancer Circuit
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Solution Overview
Problem
Conventional optical transceivers are vulnerable to supply voltage fluctuations and substrate noise due to single-ended structures in laser diode driving circuits and photoelectric diode amplifiers, leading to poor noise characteristics and increased chip area with RC passive filters.
Innovation Solution
The optical transceiver employs a differential structure with impedance balancers in the transmitter and multi-stage amplifiers with replica circuits in the receiver to maintain impedance matching and reduce noise, eliminating the need for RC passive filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fixed resistance resistor is used for impedance matching in the laser diode driving circuit, then the circuit is simple to manufacture, but the impedance matching becomes inaccurate when temperature varies, degrading noise characteristics and gain
Solution Approach 1:
The patent replaces the fixed resistance resistor with a variable resistance element whose value dynamically adjusts based on temperature conditions. The impedance balancer circuit actively monitors and adjusts the resistance of the second output terminal to match the impedance changes of the laser diode caused by temperature variation, maintaining accurate impedance matching across different operating conditions.
Solution Approach 2:
The impedance balancer implements a feedback mechanism where the impedance state of the first output terminal (connected to the laser diode) is fed back to control the resistance of the second output terminal. This feedback loop ensures that impedance matching is continuously maintained despite temperature-induced impedance changes in the laser diode.
2Reliability
If an RC passive filter is added to the optical receiver to filter noise and hold input voltage, then noise characteristics improve, but chip area increases and response time increases
Solution Approach 1:
The patent extracts and removes the RC passive filter from the optical receiver circuit. Instead of using a passive filter that occupies chip area and introduces delay, the invention uses an active differential amplifier structure with impedance balancing that achieves noise filtering without requiring separate filter components, thereby reducing chip area and maintaining fast response time.
Solution Approach 2:
The patent merges the noise filtering function with the signal amplification function by using a differential amplifier structure that inherently rejects common-mode noise while amplifying differential signals. This integration eliminates the need for separate RC passive filters, combining multiple functions into a single circuit block that maintains fast response.
3Device complexity
If a single-ended structure is used in the laser diode driving circuit and photoelectric diode amplifier, then the circuit structure is simple, but the system becomes vulnerable to supply voltage fluctuations and substrate noise
Solution Approach 1:
The patent introduces asymmetry in the circuit structure by adding an impedance balancer that creates a differential structure. The first output terminal connects to the laser diode while the second output terminal has its impedance actively adjusted to match the first terminal's impedance state. This asymmetric configuration enables common-mode noise rejection while maintaining signal integrity.
Solution Approach 2:
The impedance balancer uses feedback to monitor the impedance state of the first output terminal and adjust the second output terminal's impedance accordingly. This feedback mechanism ensures that both output terminals maintain matched impedance conditions, enabling the differential structure to reject common-mode noise from supply voltage fluctuations and substrate noise.
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 configuration enhances noise removal, maintains high gain, and reduces chip area while ensuring fast response times and stable bandwidth, even with temperature-induced impedance changes.
Implementation Method 1
an optical transmitter configured to generate a first current signal for driving a laser diode in response to a data signal, and to provide the first current signal to the laser diode, such that the laser diode converts the first current signal into an optical signal
Implementation Method 2
an optical receiver configured to receive a second current signal from a photoelectric diode that converts the optical signal into the second current signal
Data Source
AI summary
An optical transceiver includes an optical transmitter and an optical receiver. The optical transmitter includes a laser diode configured to convert a current signal into an optical signal; a main driver comprising first and second output terminals that have a differential structure, the main driver configured to drive the first and second output terminals in response to differential input signals and to provide the current signal to the laser diode through the first output terminal; and an impedance balancer configured to match impedances of the first and second output terminals by adjusting the impedance of the second output terminal according to signal states of the first and second output terminals.