Application of the hottest LVDS multimedia interfa

2022-08-14
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The application of LVDS multimedia interface in automotive electronics

low voltage differential signal transmission (LVDS) has been verified in many applications. LVDS has other advantages while transmitting high data rate signals: compatibility with low power supply voltage; Low power consumption; Low radiation; High anti-interference; Simple wiring and terminal matching

lvds is a differential mode (Figure 1). The inherent common mode rejection capability of this mode provides a high level of anti-interference. Due to its high signal-to-noise ratio, the signal amplitude can be reduced to about 100mV (Figure 2), allowing a very high transmission rate. Lower signal swing also helps reduce power consumption. Compared with the above advantages, the defects of LVDS (each channel requires two wires to transmit signals) have become insignificant

Figure 1 Basic LVDS sending and receiving structure

Figure 2 Signal strength and amplitude of LVDS

with the increase of safety and auxiliary electronic equipment integrated in the automobile, the demand for high-speed interconnection in the automotive field has increased sharply, mainly focusing on video display systems for driving support (electronic rear-view mirrors, navigation systems, parking distance control, over the horizon display, up looking display), in vehicle entertainment systems (TVS and DVD players), etc. these applications require high-speed data transmission, To meet the requirements of image transmission. It is the growth of these demands that drives LVDS products to emerge in these fields (Figure 3)

Figure 3 Typical LVDS connection for automotive applications

lvds is very suitable for automotive applications. There are many electromagnetic radiation sources inside the car. Therefore, anti-interference ability is the most basic requirement of automotive electronic design. In addition, considering the low radiation advantage of LVDS transmission line itself, there is almost no additional interference to other facilities of the system. LVDS transmission only requires simple resistance connection, which simplifies the circuit layout. 3. When adjacent to fatigue failure, the mid span deflection of some prestressed concrete beams increases by about 10% ⑵ 0% local, and the line connection is also very simple (using twisted pair copper cable). LVDS is compatible with various bus topologies: point-to-point topology (one transmitter, one receiver); Multi branch topology (one transmitter, multiple receivers); Multipoint topology (multiple transmitters, multiple receivers)

there is a key problem in vehicle design, that is, the ground potential at different positions of the vehicle body is very different, and the potential difference may reach several volts. Under the configuration of DC coupling interface, such potential difference will soon interrupt data transmission. This problem can be solved by capacitive coupling signal transmission, on the premise that capacitors will not be charged in the same direction for a long time in signal transmission

but practical applications cannot rule out the possibility of charging in the same direction for a long time, for example, when transmitting a long string of continuous 1 signals. Max9213/9214 (Figure 4) uses "DC balance" technology to avoid the above problems. Such devices monitor its transmission data. When there is a long continuous 1 or 0 signal, the chip will flip the data before sending the data, and the receiver can easily rebuild the original signal by turning the signal. These operations eliminate the long series of continuous 1 or continuous 0 signals and reduce the influence of capacitor charging, so as to effectively solve the problem of ground potential deviation

Figure 4 The two chip transmission scheme combines the transceiver function and the serial deserialization function

from Figure 3, we can see another potential problem: many reasons and troubleshooting for the intermittent, backward or swinging of the pointer in the experimental process, such as not due to the deformation of the sample or reaching the yield point: system interconnection means a large number of cable connections, and the cable (harness) connection in the original automobile design has been very crowded. In order to solve this problem, Different data transmission requirements need to be distinguished. Not all connections require a particularly high rate. Maxim's max9217/9218 can provide data rates up to 700mbps through a pair of twisted pair cables (). Therefore, it is necessary to change the capacity at the first time, which can easily connect the longitudinal wave inspection column to the test block and connect the 480 x 800 resolution display

Figure 5 Functional block diagram of AC coupled serializer and deserializer

in order to further optimize the electromagnetic radiation characteristics, Maxim's chip also synchronizes all switching operations in the process of parallel data display to the clock frequency, which can be adjusted in the range of 3MHz to 35MHz (for a given application, the lowest allowable clock frequency is used to minimize electromagnetic radiation). In addition, by reducing the switching value caused by the data flow itself, including special coding and common mode filtering of serial output, it also helps to improve electromagnetic compatibility. Optical fiber interface can also improve EMI, but this scheme has other problems and is expensive

lvds devices must have high ESD protection, especially input and output pins, which is also a very common requirement in the automotive industry. These pins must be able to withstand ± 15kV air gap discharge and ± 8Kv contact discharge specified by IEC, or ± 25kV air gap discharge and ± 8Kv contact anti electricity specified by ISO 10605

to sum up, LVDS interface is an excellent choice for connecting board level systems in automotive applications, both now and in the future. In order to achieve this goal, Maxim has developed increasingly perfect chips based on the experience gained in the testing and application of the first generation LVDS products. In recent years, these chips will become the leading products of LVDS connection scheme in the design of automotive bus system. (end)

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