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The objective of this project is to develop improved circuit and system
topologies for 3rd generation wireless handset power amplifiers. A variety of
"digitally oriented" techniques will be developed, which rely on the increasing
sophistication of digital technology to improve the performance of analog and RF
components.
The cellular telephones that we routinely use today are technological marvels,
and even more amazing features for these devices are on the horizon. These new
features will include full screen real-time video, web browsing, and a variety
of downloadable applications. However, these new features require much more
power from the battery than existing cellular phones, and the resulting battery
life will be unacceptable in most cases. Although cellular phones are capable of
greater features all the time, the batteries that power the phones do not
improve nearly as rapidly.
The purpose of this project is to significantly reduce the battery drain, and
increase the battery life, of next generation cellular telephones by developing
innovative power amplifiers for these devices. Power amplifiers are the
electronic circuits that transmit the signal to the antenna in a cellular
telephone. Remarkably, in todays cellular telephones, over 90% of the power used
to transmit the signal is wasted in the form of heat that stays inside the
phone! If we could significantly reduce this waste, we will increase the
"talk-time" of the phones, and dramatically improve the adoption of next
generation wireless services.
Our goal in this project is to develop innovative transmitter architectures and
designs for 3rd-generation CDMA wireless linear handset power amplifiers. These
systems are characterized by relatively high peak-average power ratios and
extreme dynamic range variations due to the power control loop. Our objective is
to develop improved circuit and system topologies for 3rd generation wireless
handset power amplifiers. A variety of "digitally oriented" techniques will be
developed, which rely on the increasing sophistication of digital technology to
improve the performance of analog and RF components.
Starting with the baseband signal and moving forward, a novel low-power digital
IF transmitter approach is proposed, that exhibits essentially perfect I/Q
matching, as well as very low power consumption. Implemented in a Si/SiGe BiCMOS
technology, the transmitter IC is expected to consume 60% of the power of
competing approaches, and exhibit much better EVM performance. Next, a Si/SiGe
BiCMOS dynamically biased power amplifier is proposed, where both the voltage
and current are adjusted on an "as-needed" basis to minimize power consumption
and distortion simultaneously. This circuit utilizes several novel approaches to
keep the power amplifier gain nearly constant as the dc power is varied. It is
expected that this approach will be utilized most effectively for a WCDMA
application.
Several other novel power amplifier approaches are also being investigated on
this program. Switching-mode power amplifiers have a long history of promise for
non-linear applications, but exhibit undesirable nonlinearities when linear
modulations are applied. We are developing a "delta-sigma" approach to
switching-mode power amplifiers that spectrally shapes the nonlinear spectral
components well away from the band of interest. At the same time, we are
investigating the injection of low-level pseudo-random sequences into the
baseband digital data, whose resulting distortion can be easily detected using
correlation techniques. These resulting detected distortion products can then be
used as a guide for compensation of the distortion in the baseband signal.
The following CWC faculty are participating in this research project: Larry Larson(lead PI),
and Peter Asbeck.
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Affiliated Faculty
CoRe Research Projects