ELEC5180: RF/Microwave Circuit Design and Measurement Course ...

RF Front-end (Transceiver)
Architecture: General
considerations
Limited bandwidth allocated to
each user (200 KHz in GSM)
leads to the limited rate of
information --- sophisticated
techniques such as coding,
compression, and bandwidthefficient
modulation are needed.
Transmitter --- Narrowband
modulation, amplification, and
filtering to avoid leakage to
adjacent channel
Receiver --- process the desired channel while sufficiently
rejecting strong neighboring interferers.
ELEC5180, Kevin Chen, HKUST 13
High-Q (quality factor) filters are
required for front-end bandpass
filters
The choice of the BPF is governed
by both the out-of-band rejection
and the in-band loss, with the latter
being the more critical parameter.
Rejection required of a hypothetical
front-end filter
channel width: 30 KHz
attenuation at 45 KHz from the
center: 60 dB
Q for a second-order LC filter: 10 4
difficult to achieve
ELEC5180, Kevin Chen, HKUST 14
Difference between the band and the channel
Band includes the entire spectrum in which the users of a
particular standard are allowed to communicate (e.g. the GSM
receive band spans 935MHz to 960MHz).
Channel refers to the signal bandwidth of only one user in the
system (e.g. 200 KHz in GSM).
Due to the high-Q required for channel filtering at RF
frequencies, a practical front-end BPF can only select the band
of interest, postponing the task of channel selection to some other
point in the receiver.
Typical duplexer characteristic
Effect of nonlinearity in the front end
Third-order
intermodulation
ELEC5180, Kevin Chen, HKUST 15
ELEC5180, Kevin Chen, HKUST 16