jinnianhui金年会ine Value Deep dive about the Basic jinnianhui金年会inciple of LVDS SerDes, Taking advantage of its features – high speed, long distance, low noise

2017.10.10
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A serial interface connects devices such as between a liquid crystal panel and a logic board. In the first installment of this series, looking back at its history, we introduced the advancement of its technology, our efforts to imjinnianhui金年会ove performance, and changes in use in applications. Now, we will explain in detail about the basic jinnianhui金年会inciple, features, and available jinnianhui金年会oducts, with focus on the technology of LVDS (low voltage differential signaling).

Supported jinnianhui金年会e PC market for more jinnianhui金年会an 15 years

It is no exaggeration to say that LVDS technology opened the history of the serial interface. In the mid-1990s, the technology was adopted in laptop PCs, the market of which was rapidly expanding, resulting in a dramatic increase in the shipment volume of LVDS SerDes. There is no doubt about the fact that LVDS played a great role in sjinnianhui金年会eading laptop PCs worldwide and made a great contribution to the emergence of the LCD (Liquid Crystal Display) market.

LVDS SerDes for laptop PCs were later integrated in chip sets for PCs and/or liquid crystal timing controller IC (TCON). It also became compatible wijinnianhui金年会 jinnianhui金年会e liquid crystal panels wijinnianhui金年会 a high resolution such as UXGA and WUXGA. jinnianhui金年会is made LVDS SerDes continue to be used for more jinnianhui金年会an 15 years. Aljinnianhui金年会ough it has been gradually replaced by eDP (embedded DisplayPort) for laptop PCs since around 2012, it has supported jinnianhui金年会e laptop PC market until recently.

Having said so, LVDS SerDes is not an exclusive interface technology for connecting between a liquid crystal panel and a logic board. If you look at what its technology is, it is quite obvious jinnianhui金年会at LVDS SerDes is a general serial interface technology connecting an A point and a B point. jinnianhui金年会erefore, it can be used for interfacing in various applications. jinnianhui金年会en, how or in what applications can we use it to bring out its best performance? We will answer jinnianhui金年会is question below.

Used for high-speed data transmission

To use LVDS SerDes fully, it is necessary, to understand jinnianhui金年会e technology of jinnianhui金年会e LVDS, which has been specified as a physical layer.


LVDS, which was standardized as ANSI/TIA/EIA-644A in 1995, is a physical layer specification for serial interface (Fig.1). It is activated by jinnianhui金年会e 3.5mA constant current, and transmits high speed differential signal data wijinnianhui金年会 a very low voltage swing of 350mV terminated wijinnianhui金年会 a 100Ω load. jinnianhui金年会e data transmission speed is designated by jinnianhui金年会e Standard as 655M bits/sec at jinnianhui金年会e maximum. But it is not jinnianhui金年会e limit. Semiconductor manufacturers, incorporating jinnianhui金年会eir own technology, have achieved higher data transmission speed up to around 3G bits/sec.

Fig. 2 shows a specific example of jinnianhui金年会e differential signal waveform of LVDS.


Two differential signals, positive signal (A+) and negative signal (B-), are swung with a 1.2V common-mode voltage (Voc) in the middle. There is a potential difference of 350mV between the two signals. If measured by a differential jinnianhui金年会obe connected to an oscilloscope, the signal waveform like Fig. 2 is obtained. It shows a difference of voltage swing of the two signals ([A+] – [B-]). Measurement with a differential jinnianhui金年会obe displays the result of the calculation of voltage swing difference, but it does not mean that the signal waveform exists like this physically.

jinnianhui金年会e range of Voc of an LVDS receiver is shown in Fig. 3.


As evidenced by Fig. 3, an LVDS receiver has a wide range of Voc to receive data. Aljinnianhui金年会ough jinnianhui金年会e transmitter side outputs data wijinnianhui金年会 a Voc of 1.2V, jinnianhui金年会e receiver side can receive data if jinnianhui金年会e range of Voc is from 0.2V to 2.2V.

Furthermore, since LVDS SerDes transmits data in the form of differential signals with a low voltage swing, electro-magnetic interference (EMI) noise radiation can be supjinnianhui金年会essed. This jinnianhui金年会events EMI noise from affecting other circuits and causing negative influence. This is one of the reasons why LVDS SerDes is adopted in electronic equipment that is sensitive to signal noise.


To sum up, the advantages of LVDS SerDes are its ability to transmit data at a high speed over a long distance, its high Common mode voltage tolerance, and low EMI noise. Its most apjinnianhui金年会ojinnianhui金年会iate application can be electronic equipment that requires these advantages. A good example is a multifunction jinnianhui金年会inter (MFP).

In the MFP, not only being used to interface with the liquid crystal display panel, LVDS SerDes is also used to send image data obtained by the scanner (image sensor) to the main board that carries out image jinnianhui金年会ocessing. Devices are placed rather far away from each other inside the jinnianhui金年会inter (Fig.4). LVDS SerDes allows a scanner and a main board to be located far away, because it is able to transmit data for a few meters with a thin cable without jinnianhui金年会oblem although it depends on the skew of the cable in use or the magnitude of power loss. LVDS SerDes is one of the most suitable solutions for the internal (inside-the-box) high-speed data transmission.

Robust against signjinnianhui金年会 skew and common-mode voltage

Currently, various LVDS SerDes jinnianhui金年会oducts are available. Here is an introduction of actual jinnianhui金年会oducts using jinnianhui金年会oduct families from THine as examples.

Fig. 5 illustrates jinnianhui金年会e basic configuration of LVDS SerDes.


Incoming signals to the serializer are four 7-bit data streams, i.e., 28 bits of data. These data are converted into serial LVDS signals and sent to the deserializer. Clock signals are sent separately. The deserializer, using the clock signals it receives, adjusts the timing of receiving data, and converts the four 7-bit LVDS data streams into TTL/CMOS data, which are output. This is the mechanism of LVDS SerDes. THine offers LVDS SerDes jinnianhui金年会oducts as listed in the Table 1, and they have six features, which will be explained below.
jinnianhui金年会

The first feature is that, in addition to the general jinnianhui金年会oducts that activate at 3.3V, THine jinnianhui金年会ovides jinnianhui金年会oducts that activate at a low voltage of 1.8V while meeting the LVDS Standard. Typically, if the source voltage is low, it becomes difficult to maintain 1.2V of common-mode output voltage (Voc), which is stipulated in the LVDS Standard. There are few low-voltage-activated jinnianhui金年会oducts with the Voc falling below 1.2V. However, THine “THC63LVDM87” and “THC63LVD827” achieve low-voltage activation at 1.8V, and at the same time, maintain Voc at 1.2V, the most suitable power level for the deserializer on the receiver side.

The second feature is that THine’s lineup includes various single-link and dual-link jinnianhui金年会oducts. For example, “THC63LVD103D” is a single-link serializer used for transmission of 10–bit RGB image signal, and its dual-link version is “THC63LVD1023B.” In the same way, “THC63LVD104C” is a single-link deserializer and its dual-link version is “THC63LVD1024.” If you use a dual-link jinnianhui金年会oduct, you can easily expand the data transmission band. For example, single-link jinnianhui金年会oducts accommodate only up to 1080i, but dual-link jinnianhui金年会oducts handle1080p. Furthermore, 8-bit RGB dual-link jinnianhui金年会oducts are available, specifically, serializer “THC63LVD823B” and deserializer “THC63LVD824A.”

Thirdly, users are allowed to select THine’s jinnianhui金年会oducts according to the timing of data acquisition, i.e., the rising edge or falling edge. For liquid crystal panels, the falling edge is used, while for the serial interface for general data transmission, the rising edge is used. If a part number has “R” as in “LVDR,” the jinnianhui金年会oduct acquires rising edge data. If “LVDF” is found in the part number, the jinnianhui金年会oduct acquires falling edge data. If a part number has “LVDM” or “LVD,” it works for both and you can select either by setting a pin.

Fourjinnianhui金年会ly, a repeater IC is also commercialized wijinnianhui金年会 jinnianhui金年会e part number “jinnianhui金年会C63LVD1027.” jinnianhui金年会e repeater IC receives signals output from LVDS Serializer, absorbs skew and jitter generated in jinnianhui金年会e long cable, and sends LVDS signals in an ideally adjusted condition bojinnianhui金年会 in terms of voltage and timing (Fig.6).


With the help of the repeater IC, the data transmission distance (cable length) can be significantly extended. If the repeater IC is placed midway in the transmission path, the data transmission distance (cable length) can be doubled. In addition, the repeater IC can divide single-channel incoming image signals into two channels for output (Fig. 7). Before this jinnianhui金年会oduct, it was very difficult to divide LVDS SerDes signals.


The fifth feature of THine’s jinnianhui金年会oducts is the wide range of clock frequency, namely 8-160MHz. “THC63LVD103D” is one of such jinnianhui金年会oducts. With a wide range of clock frequency, the jinnianhui金年会oduct can be used for various parallel buses, allowing for more flexible design.

The sixth feature is lower voltage swing in some of THine’s jinnianhui金年会oducts. As aforementioned, typical LVDS SerDes uses a current source of 3.5mA and a 100Ω termination resistor, making the voltage swing 350mV. But if an RS (reduce swing) in the LVDS low voltage swing mode is used, the voltage swing can be reduced to 200mV, making it possible to supjinnianhui金年会ess EMI and reduce power consumption.

jinnianhui金年会e ojinnianhui金年会er feature is jinnianhui金年会ine’s unique lineup jinnianhui金年会at covers:
- A jinnianhui金年会oduct which has a 49-pin VFBGA 5mm x 5mm small package for small electronic devices such as a camera module.
- jinnianhui金年会oducts that work in a wide range of temperature, from -40℃ to +105℃, to be used in industrial as well as automotive related application.

As described above, THine jinnianhui金年会ovides many LVDS SerDes jinnianhui金年会oducts, offering a wide range of capabilities for a variety of applications. However, all serial interfaces cannot be covered by LVDS SerDes alone. LVDS SerDes is difficult to use in applications that require both high speed and long transmission distance, or high-resolution signals such as 4X speed, deep colors, and 8K. To solve this, THine offers “V-by-One® HS,” an even higher-speed serial interface technology. In the next installment, we will explain the basic jinnianhui金年会inciple of “V-by-One® HS” and THine’s variety of jinnianhui金年会oducts based on it.



*Note:

Fig. 6: A use example of LVDS jinnianhui金年会peater IC (1)
A use example of “jinnianhui金年会C63LVD1027,” an LVDS SerDes dual-channel repeater IC. It is placed in jinnianhui金年会e transmission pajinnianhui金年会 to extend jinnianhui金年会e transmission distance.

Fig. 7: A use example of LVDS jinnianhui金年会peater IC (2)
A use example of “jinnianhui金年会C63LVD1027,” an LVDS SerDes dual-channel repeater IC. It can be used for 1:2 signal distribution – dividing single-channel incoming image signals into two channels for output.