This document discusses architectural considerations for RF MEMS switching solutions in LTE wireless technology mobile platforms. It provides a high-level overview of the mobile platform and RF front end architecture, with a focus on the role of RF MEMS switching solutions in the RF front end. Specifically, it describes how RF MEMS switches are well-suited for implementing high-performance RF switching and discusses their benefits for improving antennas, filters and power amplifiers.

1. Application Note AN002
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Architectural Considerations for an RF
MEMS Switch
By: Igor Lalicevic, RF Director
Introduction
This application note focus is on architectural considerations for RF MEMS switching solutions in
LTE wireless technology mobile platforms, focusing on the RF platform subsystem.
RF MEMS benefits according to these architectural considerations will be observed through
different aspects of RF front end (RF FE) performance improvement and analyzed in subsequent
DelfMEMS application notes.
A short description of mobile platform and RF front end architecture will be included, while focus
will be on the RF MEMS switching solution role in RF front end.
Extensive work has already been performed on RF MEMS solutions in the RF front end and it
has been demonstrated that you can get better antennas, filters and power amplifiers by using
RF MEMS. Along with applications such as tunable antennas and filters, RF MEMS are deemed
to be an ideal choice to implement high performance RF switching.
Mobile Platform and RF Front End
The mobile platform is a very complex environment from a system perspective. On Picture 1,
major smartphone mobile platform components and their interconnection with peripherals are
presented in the functional block diagram. For easier understanding, we have divided the mobile
platform in two major subsystems: RF Platform and Application Processor subsystem.

2. Architectural Considerations for an RF
MEMS Switch
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MIMO
FEM
PAM
PA
Main
FEM
Add-on Tx & Rx
PA
Antenna
Tuner and
Coupler
RF Transceiver (RFIC)
Add-on
Rx
Rx
MIMO
Rx
Tx
PA PMU
Envelope
Modulator
SMPS
Tx Vctrl
Rx MIMO
Analog FE
Rx
Analog FE
Rx MIMO
Digital FE
Rx
Digital FE
Tx
Analog FE
Tx
Digital FE
DigRF
Interface
Measurement
Receiver
RFFE
Interface
PLLs
RFIC
Controller
Clock
Power
Management
DigRF
Clock
Modem Baseband Processor
D I G I T A L
B A S E B A N D
A N A L O G
B A S E B A N D
Power
Supply
Vbat
SIM LED SPI SDIO
GPS
Communication
Interfaces
Application Processor
Micro
SD
FLASH
SD/MMC
EMIF
C P U
I n t e r f a c e
S e n s o r s
M e d i a
e n g i n e
GeomagAccGyro
U S B
Audio Codec
...
XGA
QVGA
Sensors
Sensors
Sensors
Vbat
Picture 1. (Mobile platform example)
The RF platform may typically include following hardware components:
 Modem baseband processor (MBBP)
 2G/3G/4G RF transceiver (RFIC)
 RF Front End (RF FE)
 GPS & Wi-Fi
 Flash memory
The modem baseband processor is considered to be the central hardware unit in the RF platform
and it is optimized for high-speed mobile data. It hosts all the mobile platform software and
provides an interface to the modem and telephony functionality. Hardware and functional features
like core processors and memory interfaces, cellular access, communications support, security
and internal level shifting for power management and SIM level shifting are all integrated as part
of the MBBP
From a packaging point of view, the MBBP consists of the Digital Baseband (DBB) and Analog
Baseband (ABB) dies with the possibility to add an additional SDRAM die.
From the system point of view, the DBB can be divided into two subsystems: the cellular modem
subsystem, and the platform communication subsystem.
The cellular modem subsystem provides true multimode-multiband function of all of the 3GPP
Radio Access Technologies (RAT).
The platform communication subsystem provides different connectivity interfaces for the host
device to establish packet switched channels to network access. It also includes core processors
for high-speed data processing and speech audio support.

3. Architectural Considerations for an RF
MEMS Switch
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Page 3 of 7
The ABB, analog baseband is a mixed digital and analog subsystem and includes the main
power management unit. It provides telephony services, speech audio encoders and decoders
with echo cancellation and noise suppression audio enhancements features. The power
management unit, responsible for optimizing power and current consumption and henceforth
maximizing battery life, can be considered as a part of the ABB.
The Applications Processor is the chip responsible for general processing which includes the
CPU and may have several other functions built into it. One of the additional application
processor functions is to control and process information coming from existing MEMS solutions
like microphones, accelerometers, gyroscopes and geomagnetic sensors which have become the
key building blocks of a modern mobile phone architecture.
When the MBBP is paired with the application processor, the platform is called a cellular-modem
chip also known as a thin modem.
RF MEMS in RF platform
To clearly understand system value and the position of the RF MEMS switch in the modern RF
platform, all major RF components will be analyzed in this section.
Picture 2 is the block diagram focusing on the RF platform RF components.
MIMO
FEM
PAM
PA
Main
FEM
Add-on Tx & Rx
PA
Antenna
Tuner and
Coupler
RF Transceiver (RFIC)
Add-on
Rx
Rx
MIMO
Rx
Tx
PA PMU
Envelope
Modulator
SMPS
Tx Vctrl
Rx MIMO
Analog FE
Rx
Analog FE
Rx MIMO
Digital FE
Rx
Digital FE
Tx
Analog FE
Tx
Digital FE
DigRF
Interface
Measurement
Receiver
RFFE
Interface
PLLs
RFIC
Controller
Clock
Power
Management
DigRF
Clock
Picture 2. (RF FE and RFIC)

4. Architectural Considerations for an RF
MEMS Switch
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The RF subsystem shown in Picture 2, consists of two parts: RFIC with external power
management unit (PMU) for power amplifiers’ voltage supply control and RF front end.
A modern RFIC is an RF component that performs multiple top-level functions. AnRFIC’s receiver
and transmitter have to be capable of handling the multimode-multiband of all 2G/3G/4G 3GPP
Radio Access Technologies (RAT).
Modern RFICs have receivers designed according to the homodyne concept and use direct
conversion followed by an ADC and digital decimation and filtering. To ensure MIMO and
diversity options receivers use two Rx paths, main and MIMO, along with I/Q channel analog
baseband filtering and LNAs available for each receiver input. 3G/4G Rx MIMO technology
implemented by using multiple antennas in the receiver path, enables increased Rx data
throughput and down-link range without the need for additional channel bandwidth. Additional
increases in receiver data throughput is provided by receive carrier aggregation technology which
enables the simultaneous reception of two carriers.
Transmit data from the modem baseband is received by the RFIC over a MIPI DigRF interface
and depending on the RAT will be handled differently in the RFIC Tx digital and analog front end.
Another MIPI interface, MIPI RF front end, is used by the RFIC to control all RF FE components
(power amplifier modules, front end modules, RF switches and antenna tuners).
Together with an antenna tuner which is used in the RF front end to control RF peak currents, the
RFIC provides an integrated measurement receiver for additional Tx power control and
calibration. Another external component, the crystal oscillator (TCXO module), needs to be
connected to the RFIC to provide an external clock signal frequency that is fed to the RFIC VCO,
PLL and all RF functions.
A typical up-to-date PMU provides an envelope tracking (ET) function which is used to improve
the efficiency of the power amplifier (PA) carrying signals to achieve high data throughput for LTE
transmissions. Efficiency is vastly improved by varying the PA supply voltage in sync with the
envelope of the RF signal. If the signal is reduced, the supply voltage is reduced, hence there will
be no energy loss dissipated due to the heat and efficiency will be increased. Traditional fixed-
supply PAs would be highly inefficient under 4G transmit linearity requirements.
RF front end as the second part of an RF subsystem is a combination of modules (antenna tuner
module, front end module, diversity module, power amplifier module, power amplifier duplexer
modules, and possible switch modules) and discrete components (stand-alone filters, switches,
power amplifiers, tunable and decoupling capacitors and inductors and possible ferrite beads)
between two antenna (main and MIMO) ports and the RFIC.
4G technology specifications and a “high number of bands” environment that was introduced with
LTE-A carrier aggregation have made the list of needed RF FE components increasingly long
which results in increasingly complex design constraints on the RF FE. Picture 3 is an example of
an LTE-A RF FE architecture solution.

5. Architectural Considerations for an RF
MEMS Switch
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MIPI RFFE
Serial Control
Master
Diversity
RX LNAs
RFIC
Main
RX LNAs
RFIC
TX FE
RFFE
Control
Interface
Diversity
FEM
SPnT
SPnT
mipi RFFE
mipi RFFE
FEMid
mipi RFFE
mipi RFFE
Envelope Tracking
Modulator
VPA
...mipi RFFE
mipi RFFE
PA
mipi RFFE
VHF 4G PAM
SPnT
mipi RFFE
mipi RFFE
SPnT
mipi RFFE
PA
3G/4G
HB
mipi RFFE
SPnT
PA
3G/4G
LB
GSM
PA
PA
MMMB
PAM
SPnT
mipi RFFE
mipi RFFE
Antenna
Tuner
MIPI RFFE
SPnT
SPnT
Diversity
Antenna Switch
High Frequency
Bands
Antenna Switch
Antenna Switch
High Frequency
Band-Select
Switch
Band-Select
Switch
MIMO
Antenna Port
Main
Antenna Port
Picture 3. (RF FE example)
This complex RF environment introduces many challenges to RF FE components, which are
clearly visible as insertion loss, isolation and linearity performance degradations. Additional
complications are introduced with the inter-band carrier aggregation requirement, which requires
the use of multiple active Tx/Rx paths within a single RF FE, with the usual impact on cost,
performance and power. These supplemental complexities result from the requirements to reduce
signal intermodulation and cross modulation from the two or more receiver and transmitter paths.
In this environment, for all RF FE components and particularly for the RF antenna switch, linearity
performance is a crucial specification. Basic RF parameters, such as insertion loss, isolation,
linearity and power efficiency in LTE-A RF front ends have again become the crucial driver in
component selection and component technology development. DelfMEMS switching solutions are
targeting switching applications highlighted yellow in Picture 3.

6. Architectural Considerations for an RF
MEMS Switch
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sales or technical support, contact DelfMEMS at (+33) 320 05 05 45
Page 6 of 7
RF Front End Switching Applications
Antenna Switch
The main front end module with integrated duplexers (FEMiD) or antenna switch modules (ASM)
were the first front end modules (FEM) introduced.
The FEMiD is a highly integrated multiband module with dedicated Rx outputs and Tx inputs for
each band that is supported. It includes filters, antenna switches and a dual line bi-directional
coupler to measure both forward and reflected transmit power. It also includes auxiliary ports to
enable additional bands by adding external duplex or Rx filters.
The FEMs supporting LTE carrier aggregation or dual band HSPA have a dual feed antenna
interface and separate switches for high bands and low bands. These modules are using a dual
line power coupler. The RF subsystem is dimensioned so that an external diplexer can be added
when a single antenna feed is preferred.
An antenna switch, also called a Tx/Rx switch, is high throw count, low insertion loss, high
isolation and high linearity making this switch a perfect candidate for an RF MEMS switching
solution.
Diversity Switch
The diversity FEM (divFEM) is an integrated multi-band receive module that complements the
main FEM to offer Rx diversity and MIMO reception.
Additional low-band and high-band auxiliary ports can be available to enable additional bands by
adding Rx filters external to the module in the same way as for the main FEM.
All Rx ports are connected to a single antenna port through a diplexer and either the low band
multi-throw switch or the mid-band multi-throw switch.
The diversity switch, also called an Rx switch, is high throw count, low insertion loss, high
isolation and high linearity making this switch a perfect candidate for an RF MEMS switching
solution.
Band Select Switch
Band select Tx switches are placed in the power amplifier module (PAM), making the overall
architecture independent to the choice of PAM architecture. Band select switches are used
together with multimode multiband (MMMB) PAMs where all radio access technologies share the
same PA core and together with single mode multiband (SMMB) PAMs that have separate PA
cores for the GSM and WCDMA/LTE/TD-SCDMA application.
A band select switch, also called a TX switch, has a low throw count and is targeted as an RF
MEMS switch solution only for high frequency bands (2.7 & 3.5 GHz bands).

7. Architectural Considerations for an RF
MEMS Switch
AN002 DELFMEMS S.A.S. Hub Innovation, 11 rue de l'Harmonie 59650 Villeneuve d'Ascq, France. For
sales or technical support, contact DelfMEMS at (+33) 320 05 05 45
Page 7 of 7
Conclusion
LTE technology with its global roaming needs, carrier aggregation, MIMO design approach and
adoption of higher frequency bands have made RF front end architectures for high-end
smartphones exceptionally complex and a key bottleneck in achieving the market’s needed RF
performance. Mobile handset battery life, call quality, data throughput and higher network linearity
requirements are the most obvious victims of this excessive complexity. DelfMEMS simple yet
innovative approach to the problem is to replace specific switching components using SOI
technology with an enhanced solution utilizing RF MEMS technology.
Overall, the enhancements that DelfMEMS switching solution can provide to LTE systems and
beyond radically improve the major RF performance criteria of insertion loss, isolation and
linearity Furthermore, DelfMEMS switching solutions will allow system and architecture designers
to simplify and reduce the number of needed components in RF front ends reducing complexity
and which will be addressed in subsequent DelfMEMS application notes.