Design of Ultra-Wideband RF Front-End

breezerlxd

PhD thesis, UC berkeley

Stanley Bo-Ting Wang, 2005PhD Thesis

Advisor: Professor Robert W.Brodersen

As opposed to traditional narrowband radios, ULtra-Wideband (UWB) is a wireless digital
communication system exchanging data using short duration pulses. Based on large signal
bandwidth it possesses, UWB promises low-power implementation with fine time resolution
and high throughput at short distances without interfering with other existing wireless com-
munication systems. However, the wideband nature of the front-end architecture leads to a
totally different design methodology from traditional narrow-band systems. For example,
in narrow-band systems, phase response is not crucial and the communication link budget
can be calculated based on single values like power level and gain. But for UWB systems,
waveform dispersion needs to be characterized to ensure an accurate data correlation at
the receiver, which implies the necessity of deriving the frequency dependent transfer
function from the transmitter to receiver. The most difficult part falls in the antenna/circuit
interface due to the lack of research in this area.

The focus of this research is to determine the methodology for characterizing the transfer
function at the RF front-end, and seek for a way to optimally co-design an antenna
with the analog circuits that achieves efficient pulse generation and reception. Electro-
magnetic wave simulation is used to characterize the antenna. After some investigations,
small antennas are found to be suitable for UWB applications. Based on their omnidirec-
tional property, a modeling technique that transforms the antennas into circuit networks
and relates the far-zone E-fields to the voltage across the radiation resistor is proposed.
This enables co-simulation of the antennas and front-end circuits in circuit simulators. It
saves a lot of time on simulation, and a low-power pulse generator can be designed by
embedding the antenna model at its output. Other challenges at the UWB RF front-end
include ultra-low power < 1GHz LNA design and low-voltage 3 - 10GHz LNA design.
Novel circuit topologies fulfilling the required specifications are proposed in this research.

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