Feed Forward Equalizer Test Ports Impedance Matching
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Solution Overview
Problem
Testing feed-forward equalizers (FFE) individually is challenging due to their integration with other electronic components on a Printed Circuit Board (PCB), as adding test ports degrades signal quality and bandwidth, especially at high frequencies.
Innovation Solution
Incorporating test input and output ports located separately from the normal input and output ports, with associated buffers to allow for impedance matching and independent testing without disrupting the FFE's operation or signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If test ports are added next to conventional input and output ports to enable individual FFE testing, then the FFE can be tested individually, but extra circuitry introduces additional parasitics that degrade signal quality and bandwidth
Solution Approach 1:
The patent introduces a test multiplexer as an intermediary component that selectively connects test ports to the FFE input and output. This multiplexer acts as a mediator that enables test signal injection and extraction without permanently altering the high-speed data path, thereby allowing individual FFE testing while minimizing degradation of signal quality and bandwidth during normal operation.
Solution Approach 2:
The patent implements dynamic switching capability through the test multiplexer, which can dynamically connect or disconnect test ports from the FFE based on whether testing or normal operation is required. This dynamic configuration allows the system to adapt its topology, enabling individual FFE testing when needed while maintaining optimal signal integrity during data transmission.
2Device complexity
If the FFE is integrated in the same integrated circuit as other electronic building blocks, then circuit integration is achieved, but it becomes difficult to test the FFE individually
Solution Approach 1:
The patent applies segmentation by functionally isolating the FFE within the integrated circuit through the test multiplexer. Although physically integrated with other building blocks, the FFE can be segmentally accessed for individual testing by routing test signals through the multiplexer to the FFE input and extracting outputs through the same mechanism, enabling independent characterization without physical separation.
Solution Approach 2:
The test multiplexer serves multiple functions: it acts as a signal router for normal data transmission, a test signal injector for individual FFE testing, and an output extractor for measuring FFE performance. This multi-functionality enables both integrated operation and individual FFE testing through the same circuit structure.
3Difficulty of detecting and measuring
If test multiplexers are inserted to enable FFE testing, then individual testing becomes possible, but signal quality degrades especially at high frequencies
Solution Approach 1:
The patent optimizes the test multiplexer parameters (such as switching speed, insertion loss characteristics, and impedance matching) to minimize signal degradation at high frequencies. By carefully selecting and tuning these parameters, the multiplexer can handle high-frequency test signals with minimal impact on signal quality, enabling accurate FFE testing even at elevated frequencies.
Data Source
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AI summary
Described herein is a feed forward equalizer (200) which operates in a normal operational mode and in a test operational mode. The feed forward equalizer (200) has an input port (201) and an output port (202) which is used for the normal operational mode. A test input port (203) and a test output port (204) are provided which are used for the test operational mode. Buffers (301, 302, 303, 304) are provided for matching the impedance of respective ones of the input, output, test input and test output ports. The feed forward equalizer (200) allows testing during development and once mounted in an integrated circuit without interfering with the normal operational mode.