M-PHY benefits and challenges

EMI mitigation
Another critical parameter for operation in a mobile environment is EMI. Minimal EMI is needed to insure proper operation of sensitive RF receivers. To meet this challenge the M-PHY employs many EMI mitigation techniques. They are:  

• Dual data rates for each HS gear: Each of the HS gears supports two different data rates, A and B, as shown in Table 1. This feature allows moving common mode M-PHY signal away from sensitive RF LNAs signals such as GPS LNA or when handset has to support different geographical regions.
• Programmable slew rate: Implementation specific but always monotonic
• Minimize signal amplitude, by using programmable amplitude
• Limit common-mode noise by using 8b10b coding

All those mitigation strategies results in reduced common mode Power Spectrum Density (PSD) of the driver under -110 to-140 dBm/Hz range, as shown in Figure 8


Figure 8: Common mode PSD / Source: MIPI Alliance

Link variability
To be able to support a wide range of applications and multiple generations of mobile devices, a flexible aggregate BW is required. To meet this challenge, the M-PHY supports a variable number of links, sub-links, and data lanes as shown in Figure 9.


Figure 9: Architecture of the M-PHY LINK, showing sub-links and lanes / Source: MIPI Alliance

A multitude of use-cases, a wide range of bandwidth, and various interconnect media support under one umbrella
This is where M-PHY versatility pays off. Although the initial intent of the MIPI Alliance was to use the M-PHY for traditional mobile applications such as connecting cameras and displays to a host processor, the M-PHY versatility made it an attractive PHY in other applications that were not initially anticipated.

First there was DigRF protocol that is used for chip-to-chip communication between the baseband processor and the RF IC. Next there was the Universal Flash Storage (UFS), which is a JEDEC standard, and then Low-Latency-Interface (LLI) which is also used for chip-to-chip protocol and targets low latency in the magnitude of 80ns. Those different applications use a combination of TYPE I, TYPE II and HS Gears as shown in Table 2 (For a webinar on the new specifications, head here.)


Table 2: Multiple M-PHY use-cases / Source: Mixel

Additionally the M-PHY specifications support both electric and optical media, by using an optional optical media converter (OMC), which does not require any dedicated protocol layer.  By allowing for an optical option as shown in Figure 10, the M-PHY can extend its reach to longer distances, without consuming excessive power in implementing pre-emphasis or complex equalization schemes, and allow for adoption of complex, multi-axis, mechanical joints, while reducing EMI even further.


Figure 10: MIPI’s Optical Media Converter Module defines an electrical-optical interface for Mobile Devices / Source: MIPI Alliance

Although the absolute dates might have to be adjusted to reflect the reality of the standardization process, the current M-PHY road map, depicted in Figure 11, provides the ecosystem with a time line that enables stakeholders to plan for the long term.

 
Figure 11: M-PHY roadmap / Source: STE (Click figure for larger image)

Both ST-Ericsson and Mixel have a wide portfolio of MIPI products, lead the development of the M-PHY specifications and products, and make a significant investment in supporting M-PHY ecosystem.

Conclusion
Due to its unprecedented versatility, the M-PHY is enjoying a wide adoption rate in many applications, some beyond the traditional mobile domain. With this versatility come a large number of benefits and challenges.  The M-PHY ecosystem stakeholders, such as semiconductor companies and intellectual property providers, will need to overcome the significant challenges that are inherent to this exciting technology, and they are bound to reap the many benefits that it offers. This is paving the way for the system vendors to easily deploy this technology in exciting new products that keeps the end customer captivated, wanting to come back for more.

For more information:
http://www.stericsson.com
http://www.mixel.com

About the Authors
Ashraf Takla is President and CEO of Mixel Inc., which he founded in 1998. Mixel is the leading provider of MIPI PHY and high-performance mixed-signal IP, and its MIPI PHY IP has been licensed by many customers around the world. Before Mixel, Mr. Takla was Director of Mixed-Signal Design at Hitachi Micro Systems, and also worked at AMI and Sierra Semiconductors. Mr. Takla has over 30 years of experience in analog and mixed signal design, and holds 5 patents. Mr. Takla received his BSEE & MSEE degrees from San Diego State University.

Cedric BERTHOLOM is physical layer manager of Standards and Industry Alliances, CTO, ST-Ericsson. Mr. BERTHOLOM is also MIPI PHY WG vice chair and MIPI PHY Electrical SG chair. Mr. BERTHOLOM worked in STMicroelectronics as Technical leader of MIPI physical layer IP solutions before moving to ST-Ericsson. ST-Ericsson is a world leader in developing advanced high speed serial link solutions which are integrated into many of its products. Mr. BERTHOLOM has 11 years of experience in analog and mixed signal design. Mr. BERTHOLOM received his Master's degree in Micro-Electronic Engineering from ISEB, Brest France