M-PHY is a high speed data communications
physical layer
In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer: the layer most closely associated with the physical connection between devices. The physical layer provides an electrical, mechani ...
protocol standard developed by the
MIPI Alliance, PHY Working group, and targeted at the needs of mobile multimedia devices. 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,
Universal Flash Storage, and as the physical layer for
SuperSpeed InterChip USB.
To support high speed, M-PHY is generally transmitted using
differential signaling
Differential signalling is a method for electrically transmitting information using two complementary signals. The technique sends the same electrical signal as a differential pair of signals, each in its own conductor. The pair of conduc ...
over
impedance controlled traces between components. When use on a single
circuit card, the use of
electrical termination
In electronics, electrical termination is the practice of ending a transmission line with a device that matches the characteristic impedance of the line. Termination prevents signals from Signal reflection, reflecting off the end of the transmi ...
may be optional. Options to extend its range could include operation over a short
flexible flat cable, and M-PHY was designed to support optical media converters allowing extended distance between transmitters and receivers, and reducing concerns with electromagnetic interference.
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 Interface
The Camera Serial Interface (CSI) is a specification of the Mobile Industry Processor Interface (MIPI) Alliance. It defines an interface between a camera
A camera is an instrument used to capture and store images and videos, either digit ...
s. 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 the
UniPro protocol stack.
Signaling speed and gears
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
PWM) mode and high speed (using
8b10b). 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.
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.
References
Serial buses
Computer standards
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Physical layer protocols
MIPI Alliance standards