Page 178 - System on Package_ Miniaturization of the Entire System

Mixed-Signal (SOP) Design 153

With the convergence in communication, computing, and biomedical applications,
future devices are expected to become more and more mixed-signal in nature. For
example, Intel Corp., the largest microprocessor manufacturer in the world, announced
a “Radio Free Intel” initiative, adding communication capability to high-performance
computing by the merger of CMOS wireless radios and microprocessor chipsets [3].
Intel envisages a future where a user with a mobile computer can seamlessly move
between different wireless networks (long distance as well as short distance), achieving
“ubiquitous wireless connectivity” for a computing device. Similarly, Nokia Corp., the
world’s largest manufacturer of cell phones, has announced the “N-Gage” gaming
device platform where customers all over the world can compete with each other
wirelessly [4]. With the processing power in these gaming consoles expected to be equal
to or more than a consumer laptop, this would represent an unprecedented increase in
the computing power of a commercial wireless communication device.

4.1.1 Mixed-Signal Devices and Systems
The term “mixed signal” represents the integration of multiple signal domains. For
example, the cellular phone or wireless handset represents a mixed-signal system that
supports RF and digital signals. In a handset, the RF section receives the analog signal,
which is then down-converted and digitized for processing the data. Another example
of a mixed-signal device is an analog-to-digital converter that supports both analog and
digital signals. In a nutshell, the processing of data is best done digitally. However,
since we live in an analog world, the signals that are transmitted and received are
analog in nature. Hence, integration of multiple signal domains is required to enable
the convergence of communication and computing, which is the driving force behind
the emergence of mixed-signal devices.
In the context of handsets, as the convergence trend continues, next-generation mixed-
signal devices and systems will be expected to provide high-performance computing and
wireless connectivity to a mobile user. With a proliferation of communication standards
geared toward different applications, these computing-communicating hybrids will need
to support multiple communication protocols at multiple frequency bands [5] to achieve
this goal of ubiquitous connectivity. For example, a mobile user engaging in a video-
conference via cell phone can expect the call to be routed over a Wideband Code Division
Multiple Access (WCDMA) network as the person walks across the parking lot, with a
seamless handoff to a wireless LAN (WLAN) based network as the person enters the office.
At the same time, GPS signals from satellites continuously communicate location based
information to the phone, while the Bluetooth protocol is used to synchronise the contents
of the phone-based calendar with the one on the office computer.
In parallel, the computing industry has been following Moore’s law where the
number of transistors on the IC has continued to double every 18 months for the last
15 years. However, the scaling beyond the 90-nm node is causing significant challenges
associated with leakage and latency causing engineers to develop new architectures.
With the trend toward multicore processors and the need for significant memory content
with reduced latency in systems, the package is becoming more critical for the
functioning of the system. The package now has to support high-speed I/Os containing
serial and parallel links with speeds in excess of 3 Gbytes per second (Gbytes/s). With
the convergence of computing and communication capabilities, the need for integrating
the high-speed microprocessor, memory, and wireless ICs in a single package, with the
antenna and RF front-end passives integrated in the package, is becoming very critical.