SER-DES Communication Technology

In recent years, the number of in-vehicle cameras and DISPLAY installed in automobiles has rapidly increased as safety and comfort have improved. In order for these devices to work together and display high-definition images in real time, communication technology that can transmit large volumes of data with low latency is essential. This is where SER-DES communication technology has attracted attention. This article explains how SER-DES communication works, why it is necessary, and its benefits in development.

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What is SER-DES?

Overview of SER-DES communication technology and its necessity

In recent years, the number of in-vehicle cameras has increased, and the number of DISPLAY has grown, leading to advances in resolution. SER-DES communication technology is used for these. SER-DES communication technology uses signal conversion and signal decoding functions called serializers (SER) and deserializers (DES) to enable long-distance transmission of video, audio, and control signal data over a single shielded twisted pair (STP) CABLES or coaxial (COAX) CABLES. Compared to conventional complex, multiple wiring configurations, this technology allows for a simpler ECU (electronic control unit) architecture, providing greater design flexibility, reducing CABLES costs, and improving reliability.
For example, when high-definition video captured by an in-vehicle camera is processed and displayed on multiple DISPLAY in real time, SER-DES communication enables transmission with low latency and high image quality.Furthermore, since it can handle audio and control signals simultaneously, it makes it easier to integrate the entire in-vehicle system.

Common communication specifications for SER and DES

Three types of signals are mainly exchanged between SER-DES: video, audio, and control. Each signal will be explained in turn.

Video signal

The video signal is input on the SER side and sent to the DES side.
Video signals are the data with the largest bandwidth, containing FRAMES /synchronization information, etc. Since more detailed control requires maintaining high resolution and a high FRAMES rate, transmission with high throughput and low latency is essential.

Audio Signal

The audio signal is input on the SER side and sent to the DES side.
It can also handle audio signals synchronized with video, such as warning sounds for the driver, navigation, in-car entertainment, etc. Since it can be transmitted simultaneously with video, there is no need to add a separate CABLES, keeping the system configuration simple.

Control Signal

Control signals such as I²C, SPI, UART, and GPIO can also be superimposed on video and audio signals and transmitted bidirectionally. For example, bidirectional communication such as camera setting/control signals and ECU status acquisition can be achieved without additional wiring. This makes it easy to remotely configure and diagnose systems configured with SER-DES from the camera to the ECU and DISPLAY.

SER and DES communication contents

As mentioned above, SER-DES communication is a two-way data communication.
The roles and bandwidth usage differ between communication from SER to DES (downstream) and communication from DES to SER (upstream).

Downstream

The downstream signal is a high-bandwidth channel that carries mainly video signals from the SER to the DES direction, in an example application, from the camera to the ECU and then to DISPLAY.
It is configured through AC coupling and is configured according to CABLES length and frequency characteristics.

Upstream communication (Upstream)

The upstream signal is a low to medium bandwidth channel that travels from DES to SER, and is primarily used for control/diagnosis purposes, such as from the ECU to the camera or from DISPLAY to the ECU.
This is also configured through AC coupling, and is composed of a path with low-pass (LPF) characteristics that differ from the upstream communication path.

Common hardware configurations for SER and DES

Example of an element on a communication line (STP)
Generally, the configuration is as follows:

Communication lines carrying large video images have a high bandwidth, so AC coupling CAPACITORS are used to block the DC component.
Additionally, common mode FILTERS (CMF) and FERRITE BEADS (FB) can be inserted as needed to suppress noise on the communication lines.
In addition, the constants of CAPACITORS on the communication line are set according to the characteristics of the HPF, which passes only video images, and the LPF, which passes only relatively slow upstream communications.
For example, in HPF design, the frequency characteristics of the waveform that passes through will change depending on CAPACITORS multiplier, so it is necessary to set the constants while determining which frequencies you want to pass and which frequencies you want to FILTERS.

EMC performance

Automotive ECUs must pass noise tests (EMC tests) that comply with international standards.
To minimize noise, both radiated noise and susceptibility can be improved by reducing the wiring loop area and ensuring a return path. Performance changes depending on the element values, positions, and constants, so to optimize these, it is necessary to check noise performance through simulations and evaluations as you build in the device.

(For an overview of EMC test standards, please refer to the NEXTY technical column "Explanation of EMC test standards/measurement methods for automobiles.")

Characteristic impedance of communication lines

Because communication lines are high-frequency communication lines, it is important to achieve impedance matching over the entire transmission path (CONNECTORS, CABLES, and circuit board patterns).
If signal reflection increases due to a steep impedance step (via, pad, CONNECTORS shape), performance will be reduced, such as the communication margin will decrease, the possible transmission length will become shorter, and communication errors will become more likely to occur. Therefore, it is necessary to check through simulations and evaluations that the characteristics of the communication line are secured during development.

Key points for selecting SER and DES

When selecting a SER-DES in the ECU design field, keeping the following four points in mind will reduce confusion in the initial stages.

1. CABLES type and length
Considering harness routing and existing CONNECTORS assets, choose STP (100 Ω differential) or COAX (50 Ω single). Check CABLES length and error rate (BER) guarantee conditions.

2. Required Bandwidth and System Feasibility
We calculate the required bandwidth based on video conditions such as resolution, FRAMES rate, and color depth, and estimate the feasibility of the entire video architecture and system.
We check whether the overall system meets requirements, including image processing time and delays.

3. EMC immunity
This is done to ensure consistency with the EMC design of the entire vehicle, including the state of the ECU and circuit board (shielding, termination state, ECU grounding, etc.). If the result is NG in the latter stages of the evaluation and a review is required, this will mean going back to the drawing board, so it is important to check the design using simulations at the design stage and early confirmation tests using evaluation jigs.

4. Diagnostic and redundancy functions
We make a list in advance of the information necessary for failure analysis, such as communication stability between SER-DES, error detection, temperature and POWER SUPPLIES monitoring, and confirm what information needs to be exchanged.
Furthermore, by considering post-production troubleshooting and field analysis, exchanging control information in advance will also lead to early troubleshooting.

Summary

SER-DES communication technology not only delivers high-definition video with low latency, but also simplifies wiring, improves EMC performance, and integrates control and diagnostics.
In ECU development, by focusing on four aspects -CABLES selection, bandwidth and overall system estimation, EMC design, and diagnostic functions - you can reduce risks from initial consideration to mass production, and speed up the response and resolution of problems after mass production.
NEXTY Electronics handles multiple SER-DES to meet customer needs and has extensive experience in providing design support.
If you have any questions about specific product selection, evaluation boards, system configuration, or feasibility, please feel free to Inquiry Nexty Electronics.