C-PHY Transmitter Jitter Reduction via Phase-Shifted Clocks
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Solution Overview
Problem
High-speed data communication interfaces, such as the C-PHY interface, face challenges in reducing jitter due to channel bandwidth limitations and inter-symbol interference, which affects the ability to recover clock information and limits communication link speed.
Innovation Solution
The method involves providing multiple launch clock signals with different phase-shifts to control symbol transmission on a 3-wire interface, determining the type of signaling state transition, and selecting an appropriate launch clock signal to initiate transitions, ensuring that signals on each wire are out-of-phase with others, thereby reducing differences in arrival times of signaling state transitions at the receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pre-emphasis is employed at the transmitter to compensate for high frequency attenuation, then signal quality is improved, but it has limited effect on multi-wire interfaces and cannot sufficiently reduce jitter
Solution Approach 1:
The patent segments the clock signal into multiple phase-shifted versions (e.g., three phases for a 3-wire interface) and assigns different launch clocks to different wires based on their transition requirements. This segmentation allows each wire to be optimized independently, overcoming the limitation of conventional pre-emphasis that treats all signals uniformly.
Solution Approach 2:
The patent dynamically selects which launch clock to use for each wire based on the current signaling state transitions. The system adaptively adjusts the launch clock selection in real-time according to the transition type (e.g., driven-to-undriven vs. undriven-to-driven), making the system flexible and highly effective for multi-wire interfaces.
2Device complexity
If a single clock signal is used to control symbol transmission on all wires, then device complexity is reduced, but differences in arrival times of signaling state transitions increase, causing jitter
Solution Approach 1:
The patent divides a single clock signal into multiple phase-shifted segments (e.g., three phases for three wires). Each segment is specifically timed to compensate for the unique propagation characteristics of its associated wire, thereby reducing arrival time differences without significantly increasing overall system complexity.
Solution Approach 2:
The patent applies different launch clock phases to different wires based on their individual characteristics and transition requirements. This local optimization ensures that each wire's signal arrivals are synchronized at the receiver, improving precision while maintaining a relatively simple overall clock structure.
3Device complexity
If transitions on all wires are synchronized to occur at the same time, then device complexity is reduced, but maximum symbol transmission rate is limited by the slowest wire transition
Solution Approach 1:
The patent dynamically adjusts the launch timing for each wire by selecting from multiple phase-shifted clock options. This allows faster wires to be launched at optimal times without waiting for slower wires, thereby increasing the overall symbol transmission rate while maintaining manageable transition control complexity.
Solution Approach 2:
The patent uses preliminary phase-shifted clock signals to pre-position the launch timing for each wire. By preparing multiple clock phases in advance and selecting the appropriate one for each wire's transition type, the system optimizes transmission speed without requiring complex real-time adjustment mechanisms.
4Reliability
If multiple phase-shifted launch clock signals are provided to control symbol transmission, then transmitter encoding jitter is reduced and signal integrity is improved, but device complexity increases
Solution Approach 1:
The patent segments the clock generation function into multiple fixed phase-shifted versions, which can be generated using standard phase-locked loop (PLL) techniques. This segmentation approach reduces jitter and improves signal integrity while keeping the generation mechanism relatively simple and well-understood.
Solution Approach 2:
The patent introduces dynamic clock selection logic that adapts the launch clock choice based on the current signaling state transitions. This dynamic selection improves signal integrity by matching the right clock phase to each wire's needs, while the selection logic itself remains a manageable complexity level through systematic design.
Data Source
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AI summary
Apparatus, systems and methods for error detection in transmissions on a multi-wire interface are disclosed. One method includes providing a plurality of launch clock signals, including launch clock signals having a different phase shifts, determining a type of transition in signaling state that will occur on each wire of the 3-wire interface at a boundary between two consecutively transmitted symbols, and selecting one of the plurality of launch clock signals to initiate the transition of signaling state on each wire of the 3-phase interface. Selecting one of the plurality of launch clock signals may include selecting a first launch clock signal when the transition in signaling state terminates at an undriven state, and selecting a second launch clock signal when the transition in signaling state begins at an undriven state. An edge in the first launch clock signal may occur before a corresponding edge in the second launch clock signal.