CAN FD - Eye diagram analysis for CAN FD - Further refinement of analysis criteria

Oct 25, 2026

Uploaded by McGucket

CAN FD eye diagram analysis evaluates signal quality and helps identify corrupting influences in CAN networks. The method clarifies how bit transmission can be affected by bus topology, cable length, line and terminating resistors, and external electrical influences, enabling early detection and correction during configuration. Because CAN FD uses higher, flexible data-phase bit rates, separate eye diagrams for arbitration and data phases are recommended, supporting robust topology and termination decisions through visualized bit timing and voltage behavior.

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CategoryTechnology

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CAN FD

Eye diagram analysis purpose and influencing factors

Creation of a classical eye diagram

Further refinement of analysis criteria

Tool-based eye diagram analysis with CANoe/CANalyzer

CAN FD Eye diagram analysis for CAN FD (Photo: Vector Informatik) The eye diagram isan analysis method for evaluating the signal quality of transmission networks. Eye diagram analysis can help finding corrupting influences on CAN networks. CAN networks can transmit information bit by bit from sender to partly distant receivers. The information transfer can, however, be easily corrupted by the network topology, cable length between the participants, line and terminating resistors as well as external electric influences. Both eye diagram analysis and serial bit mask analysis allow these influences to be identified and corrected early during the configuration phase of the CAN network. Due to the higher and flexible bit-rate of the data phase, CAN FD is considerably more noise-sensitive than Classical CAN, which has a fixed bit-rate only for the entire frame. The transmission of CAN FD frames always begins with the lower bit-rate of the arbitration phase. A switch to the higher bit-rate of the data phase is made at the sampling point of the bit-rate switch (BRS) bit. At the sampling point of the cyclic redundancy check (CRC) delimiter bit, the bit-rate is switched back to the lower bit-rate. The shorter duration of the bits during the faster data phase has a negative effect on the signal quality, which can best be analyzed with an eye diagram. The signal quality is highly dependent on: X Design and complexity of the bus topology e.g. line or star topology, X Adversely selected cable routing and/or bus termination, X Susceptibility of the system to higher transmission rates typical in vehicle networks, X Cable properties, such as their impedances or shielding. Creation of a classical eye diagram During the network design, a configuration for the phase segments of the bit as well as their sampling points is created separately for the arbitration phase and the data phase. According to the CAN protocol, one bit is timedivided into four segments: a synchronization segment, a segment for compensating time delays, and two phase segments, which compensate the phase errors of the bit edges. The phase segments are often designated TSEG1 and TSEG2 . The TSEG 1 summarizes the first phase segment and the compensation segment. Figure 1 shows the time division of a bit into the mentioned segments. The sampling point lies between the phase segments. TSEG2, on the other hand, corresponds to the phase segment which begins after the sampling point. Since the grid of the superimposed bits is displayed directly in the eye diagram, it is immediately apparent how well the superimposed bits fit into this grid. The bit edges should ideally lie within the synchronization segment. The algorithm used here works like areal CAN controller. Due to the time delay of the bit edges, caused by the CAN transceiver delay and the jitter of the control units, CAN controllers must resynchronize at the transition from the recessive to the dominant bus level on the receiver side. This is a prerequisite for detecting the logic level of a bit at the set sampling point. With the adjustment of the phase segments, the robustness of the synchronization mechanism can be influenced. These 36 CAN Newsletter 4/2016 settings are usually checked using an eye diagram, which allows the user to visualize whether his controller settings are practical and meaningful. Due to the fact that CAN FD has two different bit-rates, it is advisable to create separate eye diagrams for the arbitration phase and the data phase. With the software tools CANoe and CANalyzer from Vector, the user is able to configure a CAN network and record voltage signals using the Option Scope. After measuring, the user can perform an eye diagram analysis, which analyzes all received frames bit by bit and superimposes them graphically in a fixed time window. In this example, the time window is a percentage of the bit duration (Figure 1) . The displayed bit segments show the configured

FAQs

What is the purpose of CAN FD eye diagram analysis?

It evaluates signal quality of CAN FD transmission networks and helps find corrupting influences. It also supports early identification and correction during the CAN network configuration phase.

Why is CAN FD more noise-sensitive than Classical CAN?

CAN FD has a higher and flexible data-phase bit rate, which increases sensitivity to noise. Bit edges also have shorter duration during the faster phase, reducing signal quality effectiveness.

How does the article suggest improving diagnosis accuracy?

Create eye diagrams from different aspects using filter options such as frame type, CAN channel number, control unit name, and defined bit sequences. This narrowing down helps locate likely error sources.

Oct 25, 2026

Uploaded by McGucket