Biomedical Engineering Reference
In-Depth Information
Fig. 5.16 Hardware
implementation of the
IR-UWB RF section
BPF
Mixer
VCO
LPF
AND
Table 5.2 Main components of the IR-UWB RF section
Functional block
Component
Manufacturer
Mixer
SIM-73L+
Mini circuits [
15
]
BPF
BFCN-4440+
Mini circuits [
15
]
LPF
LFCN-1400+
Mini circuits [
15
]
VCO
HMC391LP4
Hittite microwave [
16
]
AND gate
NC7SZ08M5
Fairchild semiconductor [
12
]
tuned to operate at 4 GHz, which is used as the center frequency for the UWB RF
transmission. It can operate at a peak output power of 7 dBm while consuming a
peak current of 30 mA. However, it is biased to operate at one third of its output
power in order to reduce the power consumption of the design. The mixer can
operate at a conversion loss of 6.2 dBm under these operating conditions.
This method of pulse generation has a distinct advantage in terms of power
consumption over the direct conversion UWB pulse generation technique, where
the lower amplitude frequency lobe within the 3.5-4.5 GHz band is directly fil-
tered out and amplified in order to transmit at a spectral amplitude closer to the
FCC spectral mask. It can be observed that the up-conversion UWB transmitter
can generate a pulse stream at a close spectral amplitude to the FCC spectral mask
without using an amplifier. Hence, this method offers an energy efficient solution
for IR-UWB transmission. The time domain RF IR-UWB pulses emitted by the
transmitter at a 40 MHz PRF is depicted in Fig.
5.17
together with its transmit
frequency spectrum in Fig.
5.18
.
5.2.5 The 433 MHz ISM Band Receiver
The receiver in the sensor node is a narrow band receiver that operates in the
433 MHz ISM band. RX5500 ISM band amplifier sequenced hybrid receiver chip
by RFM [
17
], which is an off-the-shelf narrow band receiver chip, is chosen due to
its low operating power, high electromagnetic interference rejection and small
size. It can operate using both On-Off Keying (OOK) and Amplitude Shift Keying
