Passive Equalization Circuit for USB Signal Integrity
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Solution Overview
Problem
High speed serial buses, such as USB, face challenges in signal integrity due to impedance discontinuities and reflections, which affect data transmission, especially at high frequencies, leading to signal degradation and failure to meet desired transmission capabilities.
Innovation Solution
The implementation of passive equalization circuits, including resistive-inductive (RL) and resistive-inductive-capacitive (RLC) configurations, which couple differential pairs via shunting circuits to flatten frequency responses and manage insertion loss, thereby improving signal fidelity and reducing jitter and voltage shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high speed serial bus operates at high frequencies, then data transmission speed is improved, but signal integrity deteriorates due to impedance discontinuities and reflections
Solution Approach 1:
The patent applies parameter changes by modifying the impedance characteristics of the transmission line through shunting circuits. The circuits present different impedances at different frequencies, specifically presenting a high impedance at a first frequency and a different high impedance at a second frequency, thereby changing the electrical parameters to compensate for signal degradation at high speeds
Solution Approach 2:
The shunting circuit acts as an intermediary element between the differential pair terminals. It mediates the signal transmission by introducing controlled impedance variations that counteract the harmful effects of impedance discontinuities and reflections in the transmission line, thereby protecting signal integrity while maintaining high speed operation
2Stability of the object's composition
If shunting circuit presents high impedance at multiple frequencies, then frequency response is flattened, but insertion loss increases
Solution Approach 1:
The shunting circuit changes its impedance parameters at different frequencies to flatten the frequency response. By presenting high impedance at specific frequencies, it prevents excessive signal attenuation at those frequencies, thereby equalizing the frequency response across the bandwidth while managing the trade-off with insertion loss
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
These passive equalization circuits enhance signal integrity by maintaining acceptable insertion loss at low frequencies while providing a flatter frequency response, improving timing and voltage margins, and increasing manufacturing yield, even at high speeds like USB High Speed operations.
Implementation Method 1
the shunting circuit is configured to present a high impedance between the positive and negative terminals at a first frequency
Implementation Method 2
The implementation of passive equalization circuits, including resistive-inductive (RL) and resistive-inductive-capacitive (RLC) configurations, which couple differential pairs via shunting circuits to flatten frequency responses and manage insertion loss
Data Source
AI summary
Methods and apparatus for equalization of a high speed serial bus. A well-tuned passive equalization circuit for use with high frequency differential signals suffer from e.g., impedance mismatches, impedance discontinuities (e.g., connectors, etc.). In one embodiment, a shunting circuit is inserted between the differential terminals of a Universal Serial Bus (USB) cable, connector, etc. The shunting circuit is configured to “open” at low frequencies to enable Full Speed (FS) enumeration, while also providing sufficiently high impedance at high frequencies to enable High Speed (HS) operation. In one such implementation, the shunting circuit includes a tuned resistor, capacitor, inductor, and switch element arranged in series.