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[TONE SOUNDING]

[WHOOSH]

Hello. My name is Yaser Ibrahim. In this video, I will cover the basics of using Multipoint-Low Voltage Differential Signaling, or M-LVDS, in a backplane environment.

I will start with a quick overview of M-LVDS technology. Then I will address the question of how many devices can really be supported on a backplane with M-LVDS. I will then talk about the termination scheme for M-LVDS in a multipoint configuration. I will also address where to locate M-LVDS drivers on a backplane if you have a choice. And how to choose the right M-LVDS transceiver for your application.

M-LVDS is an industry standard that builds on the LVDS standard by adding enhancements to support multipoint and multidrop configurations. One of these enhancements is that M-LVDS increases driver current to 11.3 milliamps. This is needed to drive the increased load, which is due to the double termination used in M-LVDS, and also due to the loading from the multiple transceivers on the shared bus in multipoint environments.

This load can be 50 ohms or less, as low as 30 ohms, depending on how many transceivers are present on the bus. Other enhancements include increased receiver sensitivity and wider input common mode range. With these enhancements, M-LVDS can support up to 32 transceivers on the bus in total, including drivers, receivers, or transceivers.

While M-LVDS technology is geared toward multipoint environments, as mentioned earlier, where there are multiple drivers and multiple receivers as shown here, it can also be used for point to point communication where there is only one driver and one receiver. It is also suitable for multidrop or broadcast arrangements where there is only one driver and multiple receivers.

Why is M-LVDS suitable for backplane environments? One reason is that M-LVDS supports multipoint configurations as mentioned earlier, which is generally needed in a backplane environment. M-LVDS generates very little noise or EMI due to the fact that it utilizes a low voltage swing and uses differential signaling. The control drives and fall times also help reduced EMI.

M-LVDS also offers good noise immunity due to the use of differential signaling. Also, due to its wide input common mode range, M-LVDS offers good tolerance for ground shifts. The plug-in boards on the backplane creates stubs, which are basically unterminated transmission lines.

The controlled transition times of M-LVDS help reduce the effect of the stubs. The M-LVDS termination scheme is simple, as we will see later in this video. Additionally, power consumption of M-LVDS is low due to the low voltage swing.

How many devices can be supported on a single backplane using M-LVDS? Per the M-LVDS standard, a maximum of 32 devices can be connected on an M-LVDS bus. This includes transmitters, receivers, or transceivers.

But is there a lower practical limit? This really depends on how well the system is designed, including how good is the PCB layout and how closely it follows the recommended guidelines. It depends on the line impedance control, the proper terminations, the length of the stubs, and the rise and fall times of the drivers. It has been demonstrated that it is possible to run a well optimized M-LVDS backplane with 30 slots populated with plug-in boards at greater than 200 megabits per second.

In M-LVDS, double terminations are used-- one on each end of the bus. The intermediate plug-in boards on the backplane are not terminated, and therefore create stubs or unterminated transmission lines. These stubs create impedence mismatches in the bus, which can potentially cause reflections, which in turn degrades the signal integrity and can lead to errors on the communication link. To minimize the effects of the stubs, they should be as short as possible.

If in your system you have some specific plug-in boards that normally act as drivers and others that normally act as receivers, and you have freedom in terms of where to locate the different boards on the backplane, then locate the drivers toward the two ends of the backplane. This helps with signal integrity, because it results in longer signal path on average, which slows down the signal transitions, which makes the signal less affected by discontinuities and impedance mismatches that exist on the backplane due to the stubs, as was mentioned earlier.

When selecting an M-LVDS driver for your application, select one that has the slowest rise/fall times you can get by with. Check the M-LVDS transceivers datasheet for ones that satisfy the required data rate. Then from among those, select the M-LVDS transceiver whose driver has the slowest rise and fall times. Slower rise/fall times reduce the issues with reflections and signal integrity.

As an example, we have an application that requires supporting 200 megabits per second, and we have a list of M-LVDS transceivers, all of which support 200 megabits per second. And let's assume that they also satisfy other requirements for this particular application. From among these transceivers, we should take the SN65MLVD206B, which has the slowest rise/fall times.

TI offers a wide range of M-LVDS transceivers that are suitable for different applications. For full portfolio, please visit ti.com/mlvds. And if you have any specific questions about our products, please utilize our E2E forum. Thank you for watching this video.