SerDes, growing importance as number of cameras mounted on cars increases
Image sensor and display resolution advancements, increased distribution of GMSL 2

As the number of cameras mounted on vehicles increases, analog devices' GMSL is attracting attention to supplement the problems in data transmission.

Jeong Woon-ho, FAE of Gilanix, explained the GMSL (Gigabit Multimedia Serial Link), an automotive SerDes product of Analog Devices ADI, at the e4ds webinar on the 20th.

GMSL is the name for ADI's SerDes products, and SerDes is a word that stands for serializer and deserializer.

Jeong Woon-ho, FAE, said that the reason for using SerDes is that a large number of wires are needed to transmit a large number of parallel data such as RGB888 and raw data.

The large number of wires used to transmit parallel data has disadvantages in terms of price, weight, and volume, and also has a negative impact on EMI.

By using SerDes, parallel data can be serialized and transmitted, so multiple wires can be transmitted as a single wire or two wires, thereby compensating for the above shortcomings.

A representative growth factor in the SerDes market is the increase in the number of cameras installed in automobiles.
> In modern vehicles, cameras are installed in rear-view cameras, surround-view monitors, lane departure prevention and parking assistance systems, cruise control, and side mirror cameras, and are also used to detect the status of drivers and passengers.

Cameras, which serve as vision sensors, are also an essential element in autonomous driving.

SerDes used in LCD displays have also increased significantly compared to the past.

In addition to the existing navigation and radio, an HVAC-controlled center display has also been added, and displays are also used for the cluster and side mirror screens, and are also installed in the head-up display.

The main functions of the analog device GMSL include: △video transmission, △audio signal transmission, △POC capable of power transmission, and △SerDes control through internal register control.

▲ ADI GMSL 1 architecture configuration (Image source: e4ds webinar)

GMSL 1 consists of a forward link for video transmission over the same link and a reverse link for control communications.

Forward link refers to the direction of transmission from the serializer to the deserializer, and reverse link refers to transmission in the opposite direction.

There are three bus-width modes: 24-bit, 30-bit, and high bandwidth, and the transmittable pixel clock range is from 6.25 MHz to 104 MHz.

In full-duplex mode, the control channel operates at a speed of up to 1 Mbps. Support.

“GMSL 2 has become more widespread due to advancements in image sensors and display resolution,” said Jeong Woon-ho, FAE. “The difference between GMSL 1 and 2 is bandwidth.”

GMSL 2, which doubles the 3 Gbps of GMSL 1, supports up to 6 Gbps, which can support 4k displays and 8 megapixel image sensors.

Features that have been improved compared to GMSL 1 include Adaptive Equalization, Automatic HDCP, and Sync functions.

The data interfaces supported by GMSL 2 devices include △MIPI CSI-2 △MIPI DSI △HDI △oLDI △eDP, etc., and there are no parallel products because they are not used in most APs or ISP image sensors.

GMSL 2, like GMSL 1, supports coax and STP and supports 4k displays.

Previously, to support Ethernet communication, Ethernet was configured separately from SerDes and cables were used.

GMSL 2 allows simultaneous transmission over a GMSL link using RGMII ports, which has many advantages in cost and structure.

Video multi-streaming splitting of GMSL 2 serializers is supported, enabling multi-display implementation.

“In the past, separate SerDes had to be configured to transmit images to the CID and IC in the SoC,” explained Jeong Woon-ho, FAE. “On the other hand, GMSL 2 devices allow splitting, allowing transmission to two deserializers through one serializer.”