Biomedical Engineering Reference
In-Depth Information
Fig. 3
Block diagram of the impulse radio ultra-wideband (IR-UWB) transceiver system on
chip (SoC)
Both VCO and driving amplifier only consume power during the pulse generation. On
the RX side, the weak received signal from antenna is amplified by an LNA, followed
by a squarer as energy detector to recover the signals. A variable gain amplifier (VGA)
further boosts the signal level and finally the analog signal is digitized by a limiting
amplifier. Narrow band interference (NBI) is suppressed by embedded notch filter
in LNA and the frequency conversion characteristics of energy detector.
Digital baseband (DBB) provides synchronization, forward error correction
(FEC) coding/decoding, and data framing/de-framing for the TX and RX data respec-
tively. The media access control (MAC) layer is implemented in a Texas Instrument
(TI) low-power microcontroller MSP430 which communicates with transceiver SoC
through SPI and dedicated data lines.
In an IR-UWB system, the transmitted signal consists of a sequence of pulses,
modulated by information symbols. For the purpose of studying the mechanism of
NBI suppression, we focus on the signals in a single period in the interval (0,
t
p
),
where
t
p
is the pulse period. To simplify the analysis, the multipath effect and circuit
noise contribution are neglected. The LNA output signal is expressed as:
r
(
t
)
=
s
(
t
)
+
i
(
t
)
t
∈
(0,
t
p
),
(1)
where
s(t)
is the UWB signal and
i(t)
is the NBI signal.
The carrier-based UWB pulse signal
s(t)
can be approximated as a Gaussian pulse,
modulated by a carrier signal, which is expressed as:
A
s
e
−
π
t
−
t
0
2
τ
2
=
s
(
t
)
cos (2
πf
c
t
),
(2)
where
A
s
is the amplitude of the pulse,
2τ
represents the duration of the pulse,
t
0
is
the time delay and
f
c
is the carrier frequency.
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