In recent years, more and more electronic devices are introduced in vehicle compare to traditional ones because driving safety is getting important for drivers. The AVM 360° around view monitor of ADAS (advances driving assistance system) is able to greatly improve driver's blind zone to avoid potential hazard in driving. The around view monitor uses 4 cameras to capture images which are composed by display chip around the vehicle to increase driver's range of field of view in the vehicle to reduce blind zone of lower obstacles. The around view monitor cameras can be switched to display a specific area of view to improve driving safety. After all, blind zone can easily cause probability of traffic accidents. The 360° around view monitor assists driver in expanding field of view when reversing, driving in narrow roads and in turning motion to reduce traffic accidents caused by blind zone.
GMSL（Gigabit Multimedia Serial Links）
GMSL is a high speed serial port which is suitable for transmission of video, audio and control signals. It uses 50Ω coaxial cable or 100Ω twisted wire (STP), the length of which can be used in the range of 15 meters. Its signal output is within 1.7V ~ 3.3V with 1.5Gbps transmission speed. It only needs to be equipped with a GMSL deserializer to receive video signals from 4 cameras simultaneously. GMSL supports PoC (Power-over-Coax) which transmits power while transmitting video data and control signal; and has higher requirements on stability during system operation. The ESD test requirements is more strict due to quality requirements. This purpose of this article is to recommend ESD protection unit for AVM 360° around view monitor under GMSL structure.
The GMSL supports two modes: ①single-end mode and ② differencing mode.
The single-end mode uses a coaxial cable to transmit power video signal to reduce cable cost and is suitable for on-board camera application.
Differencing mode consists of two pairs of differential lines and is used for transmission of HD video. Because of high transmission speed requirement, it is mainly used on center console display of vehicle for short distance image transmission.
Figure 1: AVM360° around view monitor system GMSL Block Diagram
Under the complex electromagnetic environment inside vehicle, it is important to ensure the un-interfered transmitted data and stable power. As stability of on-board electronic system is getting higher, the requirements for ESD has become stricter. The international standards for on-board system ESD protection is ISO10605, which is quite different from IEC61000-4-2 standards for consumer electronics. Mainly because ISO10605 includes 150pF/2000Ω, 330pF/330Ω and 330pF/2000Ω test modules. It also include 150pF/330Ω test requirement of IEC61000-4-2 standards for consumer electronics. The protective components must be selected with AEC-Q101 certified TVS to meet the high reliability standards of on-board systems. Amazing on-board TVS provides excellent protection performance and has been certified by AEC-Q101, we have been focused on needs of the automotive market to launch new products.
For GMSL single-end mode ESD protection, we recommend AZ9565-01F with about 0.45pF (Typ.) capacitance characteristic. It reduces impact on high speed signal transmission and is able to show that the system maintains a stable 17A clamping voltage at 17V during ESD testing. (The clamp voltage characteristic curve is shown in Figure 2) At the same time, the package of AZ9565-01F is only DFN1006 (0402), which can save PCB area.
Figure 2: AZ9565-01F ESD clamp voltage characteristic curve
For differencing mode application of GMSL, an ultra-low capacitance TVS must be used. We recommend integrated TVS for such application. The part number is AZ9143-04F with DFN2510P10E package which uses through-the-hole layout and is suitable for planning of differential pair signals. The AZ9143-04F has 0.45pF (Typ.) capacitance characteristic with excellent clamping effect (9V at 17A) (as shown in Figure 3). Even when encountering external ESD energy, it can still protect the back-end chip from damage.
Figure 3: AZ9143-04F ESD clamp voltage characteristic curve