Today, the MIPI Alliance announced new DigRF and RFFE specifications, and yesterday, I had the opportunity to speak with Jim Ross, of Skyworks, and Dr. Dietmar Wenzel, of Intel about the changes. Both men are part of the MIPI Alliance.
The DigRF v4 v1.10 specification released today still defines the interface between the baseband and the RFIC, but it addresses the increased bandwidth handled by HSPA+ and LTE architectures in one common high-speed interface. Specifically, DigRF v4 v1.10:
- supports LTE, HSPA+, WiMAX, 3.5G, 2.5G
- features multiple speed modes, fast cycling
- PHY uses MIPI M-PHY technology which provides a single link between baseband and RFIC
"In order to fit different bandwidth requirements, the speed of the physical interface is scalable and can be done quickly with fast cycling," notes Wenzel. He reports that the spec allows the system to be tailored to a lower current consuming mode, optimizing for power. "It reduces time to market and speeds up designs for customers," he adds.
The companies working on the DigRF specification include Arasan Chip Systems Inc., Cadence Design Systems, Inc, Fujitsu Limited, Intel Corporation, Motorola Mobility, Inc.,Nokia Corporation, Panasonic Corporation, Research In Motion, ST-Ericsson, Synopsys, Inc., and Texas Instruments, Inc.
Introduced about a year ago, the RFFE standard aims to provide a consistent method to control RF front end devices, minimizing the need for package pins and routes on the board. RFFE v1.10 highlights include:
- control for all types of RF front ends
- support for point-to-multi-point connectivity
- multi-mode/multi-band multiple antennas
- up to 15 slaves per bus
- common control interface
According to Ross, in the RFFE standard, the RFIC is the master for the interface, then up to 15 slave devices, such as antenna tuners, antenna switches, LNAs, PAs, and filters, attach to this interface. "It only requires a very select number of pins to control anywhere from 1 to 15 devices, and it doesn't grow in required pins for the number of devices," says Ross.
The primary contributors to the new RFFE spec include Analog Devices Inc., Fujitsu Limited, National Semiconductor, Nokia Corporation, NXP Semiconductors, Panasonic Corporation, Peregrine Semiconductor, Qualcomm Incorporated, RF Micro Devices, Skyworks Solutions, Inc., ST-Ericsson and WiSpry Inc. Are they worried about LTE-Advanced?
By all accounts, there is great industry uptake of the MIPI Alliance recommendations, but what's next? LTE-A is a hot topic, so you can bet that the MIPI Alliance is already working on it. Wenzel notes that part of the challenge is that the LTE-A topologies are still being defined. He expects that the MIPI Alliance will be able to formally address LTE-A with DigRF in the next one to two years. Technical discussions are ongoing within the organization in order to identify clear requirements. Right now they expect that there will be different versions of RF transceiver topologies, and that needs to be addressed by the spec.
As for RFFE, Ross says that for now the group has identified some "nice to have" features, but haven't identified any show stoppers for LTE-A. The group is still looking at the evolving requirements. "We should satisfy LTE-A given what we know, but we are still investigating what might be a must have in the near future," says Ross. Given that this is still a fairly new specification (only a year and a half old), he notes that the group is still working with the user community to see what new features they could use to help their devices. For more on the MIPI Alliance:
MIPI Alliance website M-PHY benefits and challengesMIPI M-PHY takes center stage
Unification in the RF front-end : the new MIPI standard