Implementation of Ultra-Wideband (UWB) Sensor Nodes for WBAN Applications - Ultra-Wideband and 60 GHz Communications for Biomedical Applications - page 115

Fig. 9 Frequency spectrum of VCO-based sensor node at a UWB pulse generator output, b 1.4-GHz
low pass filter output, c mixer output, and d 3.5-4.5-GHz band pass filter output

Fig. 10 VCO-based UWB
sensor node

frequency lobe used in the amplifier-based design. It employs a low pass filter (LPF)
to filter out the 0-1.4-GHz section of the UWB pulse spectrum. As shown in Fig. 9 a,
9 b, this portion of the spectrum is of the highest power compared to the rest of the
spectrum. The filtered spectrum is then shifted using a mixer and a VCO operating
at 4 GHz (Fig. 9 c). A BPF is used at the output of the mixer in order to contain the
UWB signals within the 3.5-4.5-GHz band. The spectrum taken at various points of
this process is shown in Fig. 9 .
Figure 10 depicts the realization of this design in a PCB. This design is slightly
larger in dimension than the amplifier-based design due to the additional space re-
quired for the VCO and the mixer. Figure 11 shows the time domain waveforms
taken at various sections of the VCO-based design. This sensor node's dimensions
are 35 mm (L) × 27 mm (W) × 1.5 mm (H).