13.07.2015 Views

MPhil thesis of Lo Chi Wa - Department of Electronic & Computer ...

MPhil thesis of Lo Chi Wa - Department of Electronic & Computer ...

MPhil thesis of Lo Chi Wa - Department of Electronic & Computer ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

The frequency diversity can be performed by frequency hopping. In a frequencyhopping system, the frequency for the wireless signal changes from time to time. In thiscase, the LO signal provided by the synthesizer is required to switch between differentfrequencies rapidly. The switching speed <strong>of</strong> the frequency depends on different systemsand purposes. In Bluetooth system 5 , the frequency changes around 1600 times persecond.frequency selective fadinginterferenceFig. 12 Frequency selective fading and narrowband interferencef<strong>Lo</strong>op bandwidthIn addition to generating the LO signals for up-conversion or down-conversion in areceiver. The frequency synthesizer can also be used as a frequency-shift-key (FSK)transmitter 6 . As shown in Fig. 13, by inputting different division ratio into the prescalar<strong>of</strong> the frequency synthesizer, the output frequency <strong>of</strong> the synthesizer will changedaccordingly. The output <strong>of</strong> the synthesizer can directly drive the power amplifier andthe antenna. In order to directly modulating the synthesizer and using it as a transmitter,the loop bandwidth has to be larger than the bandwidth <strong>of</strong> the transmitted signals orsome compensation is needed to provide a flat response for the transmitted signals 6 .17

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!