This week on EYE ON NPI we’re eatin’ our Wheaties – it’s the Analog Devices MAX96714 Single GMSL2/GMSL1 to CSI-2 Deserializer, a way to send high resolution digital video over a coax wire without losing quality. These advanced serial-deserial sets – we’ll call them SerDes for short – let you minimize cabling, for reduced weight and complexity when passing high speed video from cameras or to displays over single flexible RG coax.

It’s easier than ever these days to add high quality video or camera sensing to your products: boards like the Raspberry Pi can do dual 4K HDMI and up to two DSI / CSI ports on the Compute Modules but the cables that they come with tend to be short, maxing out at 500mm long. That’s because the MIPI protocol used for data transfer is designed for ultra high speeds over low cost flex PCBs, from say a laptop motherboard to the laptop monitor or webcam.

Now, we do sell looooong cables that are 2 meters long but with the caveat that they are well outside the expected specification. They do work! But we wouldn’t put it in a product that goes to customers.

So what do you do if you have a car, where the seats and dashboard have monitors but the main processor is probably in the back of the car, far from the hot engine? That’s where Analog Devices got inspired from the Cable TV of our youth that would let kids of the 90’s watch dozens of channels using…only one cable! The cable, in this case, is a coaxial cable: one copper wire surrounded by a plastic dielectric, then a braided metal ground return.

Coax cables are flexible but rugged, and DigiKey stocks thousands of different types by the foot or reel. So they make an excellent physical transport layer for video in aggressive environments because they are shielded yet flexible.

With GMSL you need two chips: a serializer like the MAX96717 and a deserializer like the MAX96714. Between the two, connect said coax, then configure both sides for the data format you want and boom, you have a transparent video link! The serializer will take the digital data, then turn it into a serialized-packetized-data-packet on a single wire.

That thin wire can fit into spaces that would normally be a challenge such as cars / aerospace where weight is at a premium, robotics where the shielding will protect the signal integrity, and medical where high rez cameras have to fit in tiny spaces.

GMSL even supports ‘power over coax’ where a DC signal can be used as a carrier for the high frequency data – so you really can have one thin cable for everything.

Depending on which generation of GMSL you choose, you will get either 3 Gbps or 6. A small portion of that is ‘upstream’ communication, that’s used for IRQs, video/camera control and extra I2C or GPIO. If you need stereo or quad camera/video , you can use a quad deserializer: you will still get 4 coax cables in, but it’ll be smaller and perhaps better synchronized than having four separate deserializers.

This all sounds magical, and it is – once you’ve done the setup configuration! Config registers are set over I2C and there are a lot because of the wide variety of cameras available and the different resolutions/framerates/color depths. However, once that’s done, the routing is nice and clean, thanks to having QFN packaging with all the CSI pins on one side and the differential coax on the other. You could probably get away with a 4 layer or even 2 layer board! For the coax output, you can have a single wire or dual wire differential – that might give you longer distance and better noise immunity but you need dual-core coax.

To get started, we recommend picking up the MAX96714-BAK-EVK eval board, which is not inexpensive but does have everything you need to get started with the MAX96714.

Note you’ll also need the serializer!

One thing that’s nice is that if you want to get set up with a Raspberry Pi to start, you can order the Pi Cam Eval board which is an adapter for the eval to use off-the-shelf Pi camera modules, pick up at DigiKey.

Then to setup the configuration you can use the Linux driver to have automatic setup without a separate configuration program.

If you’d like to try out GSML for your next long-distance video product, you can pick up the Analog Devices MAX96714 Single GMSL2/GMSL1 to CSI-2 Deserializer today from DigiKey because it’s in stock for immediate shipment! Book now and you can be zipping along MIPI CSI data at 6Gbps by tomorrow afternoon.

See the video below: