Biomedical Engineering Reference
In-Depth Information
Fig. 4.9
Amplifier based UWB sensor node design and transmit spectrum
(PCB). This sensor node is not fully integrated for independent operation as the
data and the control signals have to be generated using an external FPGA.
A UWB transmitter developed using off-the-shelf components is presented in
[
30
]. In this method, narrow square pulses are generated in the base band domain
using a series of comparators. The RF pulses are generated by mixing these narrow
pulses with a high frequency signal generated using a phase locked loop. The
power consumption of this circuit is 660 mW; hence it is not suitable for power
stringent UWB applications.
A transmit-only UWB sensor node design is presented in [
31
,
32
] (Fig.
4.9
). Its
main operational blocks are depicted in Fig.
4.10
. The sensor nodes are assembled
on a four layer PCB with dimensions of 27 mm (L) 9 25 mm (W) 9 1.5 mm (H),
which is sufficiently compact for the use in a wearable WBAN node. This sensor
node is designed using an amplifier based hardware architecture. In this design, the
narrow base band pulses are filtered using a BPF with a pass-band of 3.5-4.5 GHz.
The UWB pulses are then amplified using a wideband low noise amplifier (LNA)
to meet the -41.3 dBm transmission power level. This amplifier has been included
to guarantee that the amplitudes of the UWB pulses are sufficient to provide a
targeted coverage by a WBAN application.
The power spectrum of the UWB pulses generated using this sensor node is
shown in Fig.
4.11
. This power spectrum consists of several frequency lobes
spread throughout the UWB bandwidth. The amplitudes of these frequency lobes
decrease towards the upper part of the UWB spectrum. The UWB sensor node is
designed to transmit UWB signals in the band of 3.5-4.5 GHz. As shown in
Fig.
4.11
a, the amplitude of the frequency lobe within the 3.5-4.5 GHz band is
well below the maximum allowable power level by the FCC (-41.3 dBm/MHz).
This sensor node design employs two amplifier stages in order to boost the power
level of the transmitted UWB signal within the band of 3.5-4.5 GHz (as marked in
Fig.
4.11
) while containing the power level within the FCC spectral mask.
