M-PHY

M-PHY is a high speed data communications physical layer standard developed by the MIPI Alliance, PHY Working group, and targeted at the needs of mobile multimedia devices..^[1] The specification's details are proprietary to MIPI member organizations, but a substantial body of knowledge can be assembled from open sources. A number of industry standard settings bodies have incorporated M-PHY into their specifications including Mobile PCI Express,^{[2][3][4][5][6][7][8]} Universal Flash Storage,^[9][10][11] and as the physical layer for SuperSpeed Inter-Chip USB.^{[12][13][13][14][15][15][16][17]}

M-PHY is generally transmitted using low-voltage differential signaling (LVDS) over impedance controlled traces between two components within one circuit card, or over a short flexible flat cable, however M-PHY was designed to support optical media converters allowing extended distance between transmitters and receivers, and reducing concerns with electromagnetic interference.^[15]

Applications

M-PHY (like its predecessor D-PHY) is intended to be used in high-speed point-to-point communications, for example video Camera Serial Interfaces. The CSI-2 interface was based on D-PHY (or C-PHY), while the newer CSI-3 interface is based on M-PHY. M-PHY was designed to supplant D-PHY in many applications, but this is expected to take a number of years.

The M-PHY the physical layer is also used in a number of different high-speed emergent industry standards, DigRF (High speed radio interface), MIPI LLI (Low latency memory interconnect for multi-processors systems), and one possible physical layer for UniPro (UniPort-M.)

Signaling speed

M-PHY supports a scalable variety of signaling speeds, ranging from 10 kbit/s to over 11.6 Gbit/s per lane. This is accomplished using two different major signaling/speed modes, a simple low-speed (using NRZ) mode and high speed (using Pulse-width modulation).^[18] Communications goes on in bursts, and the design of both high-speed and low-speed forms allows for extended periods of idle communications at low-power, making the design particularly suitable for mobile devices.

Gears

Within each signaling method, a number of standard speeds, known as "gears", is defined, with the expectation that additional gears will be defined in future versions of the standard.^[19]

Termination

M-PHY is flexible with regard to bus termination impedance.

References