New DigRFSM and RFFE Specifications Address Growing System Complexity
The DigRFSM Working Group released the first version of MIPI Alliance Specification for DigRFSM v4 in 2009, continuing a long history of developing interface specifications for baseband ICs and RF ICs in mobile devices. The DigRFSM v4 specification addresses 4G interfaces including LTE and WiMax, yet continues to support 3GPP air interfaces such as UMTS, HSPA and EGPRS. The latest version update of DigRFSM v4 v1.10 was released in December 2011.
Previously, the working group had issued DigRFSM 3G, a baseband IC to RF IC interface standard for dual mode 2.5G/3.5G
Specifications are available to MIPI members only. For more information on joining MIPI, please go to Join MIPI.
DigRFSM v4 is intended to be used in mobile terminals that support next generation mobile broadband technologies such as Long Term Evolution (LTE) and Mobile WiMax. It also supports existing 3GPP standards such as 2.5G and 3.5G (EGPRS, UMTS, HSPA, etc) and due to its large data rate and scalability it is suitable to cover other non 3GPP air interfaces. All the standards discussed are supported over a common interface.
Single-mode 2.5G terminals are covered by DigRF Baseband / RF Digital Interface Specification: Logical, Electrical and Timing Characteristics - EGRPS Version, Version 1.12. Dual mode 3GPP 2.5G/3.5G mobile terminals are covered by MIPI Alliance Specification for Dual Mode 2.5G/3G Baseband/RFIC Interface, Version 3.09.06.
The DigRFSM v4 Specification defines the interface between one or more Baseband ICs (BBICs) and Radio Frequency ICs (RFICs) in a single terminal. The interface is intended to be efficient, flexible, and extensible, accommodating many variations in the overlying system design, while providing interoperability at the interface level between compliant ICs. Additionally, the specification has been designed to allow the use of a common physical layer. This is of significant benefit given the increased complexity of performance requirements of next generation mobile terminals. The requirement to support increased functionality for such applications as camera, gaming, and video capture and playback has driven the need to support several high speed interfaces inside the terminal. The ability to design one common high speed interface that can be re-used for all of these applications will help to reduce design resource requirements and hence speed up the time to market for these terminals.
The key pillars for the design are to:
The MIPI Alliance Specification for DigRFSM v4 focuses on the protocol and the programming model as well as parts of the physical interface between the BBICs and RFICs. It does not prescribe anything within either IC, except for the minimum necessary to ensure compatibility at these layers. Additionally, it does not specify how multiple ICs, if available, should be used to support a particular standard. However, where necessary, additional text has been added to ensure there is a standardized interpretation of the specification. Details include definitions, timing diagrams, modes of operation, basic configurations and state diagrams. The intention is to leave designers the freedom to seek competitive advantage within the ICs, while ensuring that devices compliant with this specification can work together when correctly configured.
DigRFSM v4 is not a system design specification; it avoids defining anything inside either the BBICs or RFICs that does not need to be specified to ensure correct operation of the interface. However, some system aspects are needed to be considered when developing the specification in order to ensure correct functionality (e.g. EMI issues). The specification also includes sections covering a variety of supporting information necessary to ensure correct understanding and compliant operation of the interface. Such sections include: Architecture and Operation overview, applications which have been considered in the development of this specification, and supplementary information. The latter makes recommendations for best practices to be used in the chip and layout of designs. It is explicitly expected that RFICs from different vendors will require different driver software on the BBIC(s). Finally, DigRFSM v4 is not backwards-compatible with earlier DigRFSM versions (DigRFSM 3G), but is designed to ensure that existing standards can still be supported, whilst also meeting the pillars of a DigRFSM v4 design targeting advanced air interface standards.
A MIPI Alliance Application Note for DigRF℠ v4/M-PHY℠ v0.70.00 is also available.
The DigRFSM 3G Specification covers dual-mode 3GPP 3G / 2.5G (UMTS/EGPRS) mobile terminals where both modes of operation are supported over a common interface. The interface can also be used for single-mode 3G terminals. Single-mode 2.5G terminals are covered by DigRF Baseband / RF Digital Interface Specification: Logical, Electrical and Timing Characteristics - EGRPS Version, Version 1.12, but can also use the DigRFSM 3G specification. DigRFSM 3G Specification defines the interface between a baseband IC (BBIC) and one or more RFICs in a mobile terminal. The interface is intended to be efficient and flexible, accommodating many variations in the overlying system design, while providing interoperability at the interface level between compliant ICs. The key pillars for the design were to:
• Minimize interface pin count
• Minimize overall interface power consumption
• Provide a very reliable physical layer so error correction and detection are not needed
The purpose of the this specification is to describe the logical, electrical and timing characteristics of the DigRFSM 3G Digital BBIC/RFIC Interface with sufficient detail to allow physical implementation of the interface, and with sufficient rigor that implementations of the DigRFSM Interface from different suppliers are "plug and play" compatible at the physical level. This version of the document addresses dual-mode 3GPP-compatible 3G / 2.5G (UMTS/EGPRS) implementations; later versions of the document will extend the coverage to later versions of 3G and perhaps to other specifications.
Every effort has been made to retain flexibility where this does not compromise compatibility or cost, thus leaving many design choices within the BBIC and RFIC implementations.
The DigRFSM 3G specification confines its attention to the physical interface between the BBIC and RFIC and does not prescribe anything within either IC, except for the minimum necessary to ensure compatibility at the physical level. The intention is to leave designers the freedom to seek competitive advantage within the ICs, while ensuring that devices compliant with this specification can work together when correctly configured.
DigRFSM 3G also covers the electrical, logical and protocol aspects of the interface; it attempts to define all aspects of the interface that need to be specified to allow ICs from different vendors to interoperate, given suitable RFIC driver software on the baseband. The specification is not a system design specification; it avoids defining anything inside either the baseband or RFICs that does not need to be specified to ensure correct operation of the interface. It is explicitly expected that different RFICs will require different driver software on the BBIC. Finally, the DigRFSM 3G Specification is not backwards-compatible with earlier versions, but is designed to achieve a very efficient dual-mode design.