For example, Figure 5 shows a
dual-chain RF front-end module
(FEM) for 802.11 a/b/g/n designs
where designers were able to choose
a specific technology for each block
in order to optimize performance.
For instance, the 5 GHz PA is GaAs
HBT, the dual-band LNA and switch
are GaAS HEMT, the filters are implemented in a passive component
only process, and the 2.4 GHz PA
and logic are integrated in BiCMOS.
In this type of application, the SIP
approach allows a mix of technologies in a single package, allowing system designers to choose the best
technologies and then do a module
integration to deliver all of the
functions that a customer wants in
a short time. The advantage here
is a single package with the RF
front-end functionality that can be
dropped into a design to add wireless capability.
AVAILABLE TECHNOLOGIES
Despite its many advantages, the
use of a laminate substrate in SIP designs affects package height, assembly
complexity and cost, so package and
assembly are becoming important areas of research. One recent trend is
toward the use of multi-die QFN.
Figure 6 shows a multi-die 3× 3 mm
QFN that achieves the < 0.5 mm
height required for mobile phones.
The innovative package shown here
also includes a number of thru-die
vias, which are critical to reducing
size and the number of required wire
bonds.
In the latest state-of-the-art smartphones, the RF signal chain requires
a surprising 18 mm of board space.
2
In Figure 7, the RF chain is the area
surrounded by the dotted line. Note
the large footprint also required for
voltage regulators and enable functions. The addition of WLAN in mobile handsets is driving a need to integrate all of these components into a
3× 3 mm package.
To address this need, some designers using GaAs for power amplification are achieving good integration of
the PA with low-noise amplifiers
(LNA) and switches. These multi-function RFICs have only become
available recently, and foundry support for fabless RF design companies
planning to use these technologies is
still not mature. TriQuint Semiconductor recently announced GaAs
RFICs for the front-end with this level of integration. However, because it
is implemented in GaAs, the device
still requires external filtering and
control circuitry that needs to be implemented in silicon. In addition,
since the designs are transistor-based,
they cannot integrate CMOS-based
control logic.
Taking the RF functionality to the
next level of integration requires the
use of BiCMOS to address the addition of control logic. As a result, the
integration of SiGe bipolar RF performance with SiGe CMOS bias-and-control functionality onto a single,
small-footprint integrated circuit is a
key enabler for the rapid growth of
wireless connectivity for multimedia
services in mobile consumer electronics devices. The next generation
