What are the practical differences between LVDS and MIPI?
A little background information:
I am attempting to build my own projector on the cheap and want to use a nexus 10 LCD panel (2560 X 1600 resolution) but I have been reading mixed information on its interface, some say it is LVDS and others say it is MIPI.
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asked Jul 7, 2014 at 15:05
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4 Answers
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I believe MIPI's DSI (Digital Serial Interface) specifications utilize LVDS (Low Voltage Differential Signaling). Thus, they are the same in that one utilizes the other in it's main specification. You can think of DSI as the protocol and it uses LVDS as the transmission method. In terms of building your own projector. I would say that using an LCD screen that large is going to result in chromatic aberrations as well as uneven light distribution.
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2\$\begingroup\$ It's actually a 10" screen which is why it is so appealing to me and hopefully worth the effort of building my own circuit. \$\endgroup\$ Commented Jul 7, 2014 at 15:57
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1\$\begingroup\$ Essentially placing the screen on an overhead projector? \$\endgroup\$– pjc50Commented Jul 7, 2014 at 16:02
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1\$\begingroup\$ Well, if you are talking about a projector where light will be transmitted through the screen, then it's actually better to have a smaller screen. The smaller the screen, the easier it is to have the whole screen in the optimal focal point of the lens. Though, I believe this does have a limitation in that if you want to go really small, you have to split up the RGB signals into 3 separate LCD's and adjust them all to converge. However, this is of course only a requirement for a consumer grade projector. If you're just messing around, it doesn't matter that much. \$\endgroup\$ Commented Jul 7, 2014 at 16:09
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3\$\begingroup\$ Actually MIPI DSI uses differential signaling as it's PHY but it is not LVDS. mipi.org/specifications/d-phy Also, I think the user actually meant FPD-Link instead of LVDS which are usually (but technically incorrect) used interchangeably. \$\endgroup\$– SilCommented Aug 20, 2019 at 15:56
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\$\begingroup\$ I think by now you should have a clearer understanding that MIPI isn't a 'kind of' LVDS. It is much more complex. And this doesn't really answer OP's question about what protocol their display uses. It could be DSI, or it could be raw pixel LVDS, or there may be versions that support each one. \$\endgroup\$ Commented Mar 16, 2022 at 4:09
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MIPI and LVDS panels are quite different. They are different ways of sending a RGB, DE, Hsync, VSync signal to a panel. Older (lower res) panels would accept these digital signals directly so RGB24 would have 27 signals, and they would toggle at the pixel rate.
LVDS is quite straight forward, and is just parallel data serialised 7:1. The RGB, DE, and syncs go in defined places. It is normally a clock pair, and 3 LVDS pairs for 18bpp, or 4 LVDS pairs for 24bpp, or 5 LVDS pairs for 30bpp. The LVDS clock tends to be ~75MHz max, and data lines tend to top out at 525MHz (7x75M). Because of this some larger res displays use even and odd groups. So a 24bpp 1080P display would likely have 2 clock pairs, and 8 data pairs - so 20 signal lines. Not a great saving over parallel RGB, but better signal integrity and lower emissions
MIPI on the other hand is a lot more complex. It is typlically a clock and 3 data pairs. The data pairs operate at ~1GHz. It has high voltage and low voltage signalling to conserve power. It has a messaging protocol in addition to raw video. This allows the controller to read data from the display (such as what it is). It allows the controller to control things like the gamma curve, colour calibration, adaptive brightness, etc if the panel supports it. It can be more painful getting a MIPI display to go if you don't know the settings to send it (And these are often poorly documented).
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3\$\begingroup\$ Actually this is the correct answer if by LVDS the user actually meant FPD-Link or OpenLDI (both of which use LVDS as their physical layer (PHY)). \$\endgroup\$– SilCommented Aug 20, 2019 at 15:54
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I'd like to clarify some things:
- LVDS standard describes a way to transmit 0s and 1s serially as voltage differences.
- FPD-Link (and OpenLDI) standard describe a way to use LVDS to transmit video data. Becaue FPD-Link is so tightly coupled with LVDS they are used synonymously. So when someone says LVDS they usually mean FPD-Link (even data sheets do this!)
- MIPI-DSI is another standard, which competes with FPD-Link, but uses a different physical layer, different from LVDS but still differential in nature.
- Now you can read Russel Hocken's answer which is actually the correct answer.
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LVDS -> Low Voltage Differential Signalling is the actual voltage and impedances on the physical wires. There are different voltage levels even within the MIPI standard, so pay attention to those.
MIPI is the format of the how the various bits are located relative to other bits and signalling and start and stop sequences inside the data stream. In some parts of the Mipi standard there is description tables for register locations (if my memory serves me).
So Mipi is a stream of formatted bits, and LVDS is the signals that push those bits in the real world.
answered Jul 7, 2014 at 15:45
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1\$\begingroup\$ I have never heard of MIPI, but I know that LVDS defines a physical layer. From this description, it sounds like MIPI defines a data link layer. If this is true, then the interface can (and probably does) support both as they each define non-overlapping sets of interface specifications. \$\endgroup\$ Commented Jul 7, 2014 at 15:52
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2\$\begingroup\$ Both are very helpful answers, the other was first so I chose it as best. So do LCD manufacturers that use LVDS just use their own proprietary protocol to communicate data versus using a unified standard such as MIPI? \$\endgroup\$ Commented Jul 7, 2014 at 15:56
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1\$\begingroup\$ @CraigPatrickLafferty yes ... and no. The standard is set by the driver chips that are mounted to the glass of the monitor and were defined by the first manufacturers of those chips. MIPI started as a camera/sensor interface standard and has expanded into the display space. \$\endgroup\$ Commented Jul 7, 2014 at 15:58
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2\$\begingroup\$ For what is it worth, The Display Serial Interface Specification MIPI-DSI defines protocols between a host processor and peripheral devices using a D-PHY physical interface/MIPI Physical Layers PDF ... however nowhere in the specs I have seen a reference to LVDS acronym and that "bothers" me a little. I figured that if it uses LVDS as physical layer, they'd mention it (?) D-PHY is not LVDS right? voltage diff. mentioned above? \$\endgroup\$– zabumbaCommented Mar 17, 2015 at 14:26