As more digital devices are adopted in vehicles, such as car navigation systems, information terminals, and image detection systems, the transmission of data between stringent in-vehicle automotive systems has become increasingly important. To ensure fast and accurate data transmission, high-speed logic and data path management must be implemented, utilizing data path signal conditioners, digital crosspoint switches, level translators, serializers/deserializers (SerDes), and selector multiplexers and track/hold amplifiers to meet the tight requirements of modern high-data-rate systems. This article will focus on the design essentials of SerDes and the related solutions introduced by ADI.
Design tips for long-distance high-data-rate transmission applications
Any application involving long-distance high-data-rate transmission requires testing to ensure good link quality. The MAX9259/MAX9260 Gigabit Multimedia Serial Link (GMSL) SerDes chipset from ADI can transmit audio/video data at payload rates of up to 2.5Gbps over a single twisted-pair cable up to 15 meters long.
One of the most straightforward tests for link quality is the Bit Error Rate (BER) test. The transmitter sends a known data pattern through the serial link, and the receiver checks the incoming data for any bit errors. Another test is the eye diagram, which graphically represents link quality. Both tests require generating a suitable pattern and transmitting it through the serial link. While there are various test patterns available, a common choice is the long pseudo-random bit sequence (PRBS).
The MAX9259/MAX9260 chipset features an internal PRBS generator and BER checker, simplifying the test process. Only a parallel clock and a UART port are needed to program the device. The MAX9259 sends a 230 -- 1 (in 32-bit mode) or a 222 -- 1 (in 24-bit mode) PRBS data pattern through the serial link, and the MAX9260 checks the received data and records the number of bit errors.
Generally, obtaining PRBS output from the serializer requires inputting data on all inputs to be serialized. For the MAX9259, this means inputting data on the video, audio, and UART inputs. Due to the significant differences in bit rates across these three interfaces, this can easily become very complex. The MAX9259 includes an internal PRBS generator that can be controlled via a single UART command.
To activate the PRBS mode for testing, you can run the quick-start procedure in the MAX9259EVKIT/MAX9260EVKIT to verify that the evaluation kit board, software, and drivers are correctly installed and running.
The BER test is a simple method to measure link quality. Another way to evaluate system performance is by analyzing the eye diagram opening. This provides a graphical representation of link quality and insights into the nature of channel imperfections. A high-bandwidth digital oscilloscope (in infinite persistence mode) can be used to capture the eye diagram of the serial link on the deserializer side of a 15-meter STP cable. Users can determine impedance mismatches, reflections, timing variations, and even frequency attenuation issues through eye diagram analysis.
Serializer/deserializer chipset for digital video devices
For in-vehicle data transmission applications, ADI has introduced the MAX9259/MAX9260 single-link serializer/deserializer chipset, which integrates a control channel and is ideal for digital video devices. These Gigabit Multimedia Serial Link (GMSL) chipsets offer spread spectrum functionality and a full-duplex control channel, utilizing Maxim's GMSL technology. The MAX9259 serializer works in conjunction with the MAX9260 deserializer to form a complete digital serial link, enabling high-speed video, audio, and control data transmission.
The MAX9259/MAX9260 allows a maximum serial payload data rate of 3.125Gbps when transmitting over a 15-meter shielded twisted-pair (STP) cable. The maximum bus clock for the 24-bit and 32-bit parallel interfaces can reach 104MHz and 78MHz, respectively. The serial link supports display panels ranging from QVGA (320 x 240) to XGA (1280 x 768) or dual-screen WVGA (2 x 854 x 480).
In 24-bit or 32-bit mode, it processes 21-bit or 29-bit data through I2S inputs supporting 4 to 32-bit audio word widths and sampling rates from 8kHz to 192kHz. The built-in control channel forms a full-duplex, 100kbps to 1Mbps differential UART link between the serializer and deserializer. The host electronic control unit (ECU) or microcontroller (µC) can be placed on the MAX9259 side (for video display) or on the MAX9260 side (for image detection). Additionally, the control channel enables ECU/µC control of remote peripherals via I2C (basic mode) or a user-defined full-duplex UART format (bypass mode).
The MAX9259 serializer's driver pre-emphasis and the MAX9260's channel equalization extend link length and improve link reliability. The MAX9259/MAX9260 also provides spread spectrum functionality to reduce EMI on serial and parallel output data signals. The differential link complies with ISO 10605 and IEC 61000-4-2 ESD protection standards.
The core supply voltage for the MAX9259/MAX9260 are 1.8V and 3.3V, respectively. Both devices operate with I/O supplies ranging from 1.8V to 3.3V. The MAX9259/MAX9260 are available in 64-pin TQFP (10mm x 10mm) and 56-pin TQFN (8mm x 8mm x 0.75mm) packages with an exposed pad. Their electrical performance is guaranteed over the automotive temperature range of -40°C to +105°C.
ADI also offers the MAX9259 evaluation kit—MAX9259EVKIT—and the MAX9260 evaluation kit—MAX9260EVKIT, providing proven designs for evaluating the MAX9259 and MAX9260 GMSL with spread spectrum and full-duplex control channels. The evaluation kit also includes Windows®-compatible software, offering a user-friendly graphical user interface (GUI) for evaluating the performance of the MAX9259 and MAX9260. The MAX9259GCB/V+ and MAX9260GCB/V+ are pre-installed on each board. To evaluate the complete GMSL, order the MAX9259 evaluation kit along with its companion board, the MAX9260 evaluation kit.
Single link serializer/deserializer chipset with HDCP support
On the other hand, ADI has also introduced the MAX9263/MAX9264 single-link serializer/deserializer chipset, which integrates a control channel and is ideal for digital video devices. These HDCP Gigabit Multimedia Serial Link (GMSL) serializer/deserializer chipsets extend Maxim's GMSL technology to support High-Bandwidth Digital Content Protection (HDCP) encryption for DVD and Blu-ray™ video and audio data protection. The MAX9263 serializer or any HDCP-GMSL serializer, paired with the MAX9264 deserializer or any HDCP-GMSL deserializer, forms a digital serial link for transmitting control data and HDCP-encrypted video and audio data. GMSL is a Digital Content Protection (DCP), LLC-certified HDCP technology.
The serial link signals are AC-coupled current-mode logic (CML) using 8b/10b coding. To drive longer cables, the serializer provides programmable pre-emphasis/de-emphasis, and the deserializer provides a programmable channel equalizer. GMSL devices offer programmable spread spectrum functionality on serial (serializer) and parallel (deserializer) outputs. The serial link inputs and outputs meet ISO 10605 and IEC 61000-4-2 ESD standards. The serializer's core supply voltage is 1.8V; the deserializer's core supply voltage is 3.3V; and the I/O supply is 1.8V to 3.3V. Both devices are available in 64-pin TQFP packages with an exposed pad and operate over the automotive temperature range of -40°C to +105°C.
Serial link serializer/deserializer with LVDS system interface
ADI's MAX9265/MAX9266 HDCP Gigabit Multimedia Serial Link (GMSL) serializer/deserializer with LVDS system interface integrates a control channel and is ideal for digital video systems. The MAX9265 GMSL serializer features an LVDS system interface and HDCP encryption for content protection of DVD and Blu-ray™ video and audio data. The serializer can be paired with any HDCP GMSL deserializer to form a digital serial link for transmitting control data and HDCP-encrypted video and audio data.
The serial link signals are AC-coupled CML using 8b/10b coding. To drive longer cables, the serializer provides programmable driver pre-emphasis/de-emphasis; to reduce EMI, it offers programmable spread spectrum functionality on the serial output. The serial output meets ISO 10605 and IEC 61000-4-2 ESD standards. The serializer/deserializer operates with a 1.8V core supply, 1.8V to 3.3V I/O supply, and 3.3V LVDS supply. The device is available in a 48-pin TQFP package with an exposed pad and operates over the automotive temperature range of -40°C to +105°C.
Serial link deserializer with LVDS system interface and integrated control channel
The MAX9268 is a Gigabit Multimedia Serial Link (GMSL) deserializer with an LVDS system interface and integrated control channel, ideal for digital video products. The MAX9268 deserializer utilizes Maxim's GMSL technology and features an LVDS system interface, effectively reducing pin count and package size. The device can be paired with any GMSL serializer to form a complete digital serial link, enabling high-speed video, audio, and bidirectional control data transmission.
The MAX9268 allows a maximum serial payload data rate of 2.5Gbps when transmitting over a 15-meter shielded twisted-pair (STP) cable. The deserializer's maximum output clock rate can reach 104MHz (3-channel LVDS) or 78MHz (4-channel LVDS). The serial link supports 24-bit color display panels ranging from QVGA (320 x 240) to WXGA (1280 x 800) and even higher resolutions.
In 3-channel mode, it outputs an LVDS clock signal and three lanes of signals consisting of LVDS data (21-bit), UART control signals, and one I2S audio channels. In 4-channel mode, it outputs an LVDS clock signal and four lanes of signals consisting of LVDS data (28-bit), UART control signals, an I2S audio channel, and auxiliary control output.
The standard I2S interface consists of three audio outputs, supporting sampling rates from 8kHz to 192kHz and audio word lengths from 4 to 32 bits. The built-in control channel forms a 100kbps to 1Mbps, full-duplex, differential UART link between the serializer and deserializer. The electronic control unit (ECU) or microcontroller (µC) can be placed on the serializer side of the link (typically for video display) or on the MAX9268 side (typically for image sensing), or on both sides.
Additionally, the control channel enables ECU/µC control of remote peripherals such as backlight control, grayscale gamma correction, camera modules, and touchscreens. Basic mode communication with peripherals uses I2C or GMSL UART format. Furthermore, the MAX9268 features a bypass mode that uses a custom UART format for full-duplex communication.
The GMSL serializer's driver pre-emphasis combined with the MAX9268's channel equalizer effectively extends link distance and improves link reliability. Spread spectrum functionality reduces EMI on the MAX9268's LVDS outputs and control outputs. The serial input complies with ISO 10605 and IEC 61000-4-2 ESD protection standards. The MAX9268's core supply is 3.3V, and the I/O supply ranges from 1.8V to 3.3V. The MAX9268 is available in a 48-pin TQFP package (7mm x 7mm) with an exposed pad and operates over the automotive temperature range of -40°C to +105°C.
Conclusion
The design of data transmission for in-vehicle automotive systems must balance high speed, low latency, stability, and security. As vehicles become more electronic and intelligent, ensuring fast and accurate data transmission is crucial. Faster and more secure data transmission solutions will drive smart vehicles further toward efficiency and connectivity. The ADI serializer/deserializer solutions introduced in this article meet the stringent requirements of modern high-data-rate systems, ensuring stable operation of in-vehicle systems.