Optical Receiver Frequency Compensation for Flexible PCB Loss
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Solution Overview
Problem
Optical transceivers with 10 Gbits/s bit rate experience in-band gain reduction and bandwidth deterioration due to transmission losses in flexible printed circuit boards, leading to deteriorated Stressed Receiver Sensitivity (SRS) and potential oscillation issues.
Innovation Solution
A frequency characteristic compensating circuit is introduced, utilizing a balanced-type or balanced H-type attenuator circuit with specific resistance and capacitance values to enhance the small signal gain from DC to 5 GHz, coupled with a flexible printed circuit board and a pre-amplifier IC, to stabilize the optical receiver's frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a thin flexible printed circuit board is used to obtain flexibility, then flexibility is improved, but transmission loss increases
Solution Approach 1:
The patent changes the physical parameters of the flexible printed circuit board by increasing its thickness from conventional thin dimensions to at least 0.2mm. This parameter change reduces transmission loss while maintaining flexibility through the use of flexible PCB material and construction. The increased thickness provides better signal transmission characteristics without sacrificing the flexibility needed for stress absorption and dimensional deviation compensation.
2Power
If the pre-amplifier is customized to boost frequency characteristic, then in-band gain is improved, but circuit stability deteriorates
Solution Approach 1:
The patent introduces a matching circuit as an intermediary component between the pre-amplifier and the flexible printed circuit board. This matching circuit serves as a mediator that provides frequency characteristic compensation without requiring customization of the pre-amplifier itself. The matching circuit absorbs the frequency response variations and presents a stable, controlled impedance environment to the pre-amplifier, thereby improving in-band gain while maintaining circuit stability.
Solution Approach 2:
The patent segments the frequency compensation function from the pre-amplifier by placing it in a separate matching circuit. This segmentation allows the pre-amplifier to operate in its stable, factory-optimized condition while the matching circuit independently handles frequency characteristic adjustment. The separation of functions prevents the stability issues that would arise from customizing the pre-amplifier's internal circuitry.
3Ease of manufacture
If the optical receiver sub-assembly is downsized, then manufacturing cost is reduced, but transmission loss increases
Solution Approach 1:
The patent changes the parameter of flexible PCB thickness to at least 0.2mm, which compensates for transmission loss in the downsized optical receiver sub-assembly. This parameter change allows the use of smaller, more cost-effective packaging while maintaining adequate signal transmission quality. The increased thickness provides better signal integrity without requiring larger overall dimensions, thus preserving the cost advantages of downsizing.
Data Source
AI summary
There is provided an optical receiver in which, between an optical receiver sub-assembly and a post-amplifier on a main printed circuit board, two transmission lines on a flexible printed circuit board for connecting an optical receiver module with the main printed circuit board, a balanced-type attenuator circuit composed of four resistor elements, and two capacitor elements connected in parallel with the balanced-type attenuator circuit are provided.