An Ultra-Wideband Sensor Node Development with Dual-Frequency Band for Medical Signal Monitoring - Ultra Wideband Wireless Body Area Networks - page 95

P rogrammable
resistor

Reconfigurable square wave oscillator
Signal tracks to the buffers

Buffer 2 Buffer 1

Biasing resistors
of Buffer 2 Signal tracks to the XOR

XOR

Fig. 5.12 PCB implementation of the pulse generator

identical. This is necessary to make sure that the delay in each signal propagation
path is only affected by the voltage-controlled delay introduced by the buffers. The
propagation delay for the transmission lines are calculated using ( 5.7 )[ 13 ].

p

e r

;

t p ¼ B r :

ns
mm 300

B r ¼ 0 : 8566 þ 0 : 0294 ln ðÞþ 0 : 00239 h þ 0 : 0101e r ð 5 : 7 Þ

where e r is the dielectric constant of the PCB substrate, w is the width of the
transmission line in mils and h is the height from the nearest ground plane to the
transmission line in mils. The pulse generator implemented on the sensor node
PCB is shown in Fig. 5.12 .
The relationship between signal bandwidth, pulse width and center frequency
for an IR-UWB pulse stream generated using the up-conversion method is given
by ( 5.8 )[ 14 ].

B t w ¼ 2 ð 1 b Þ a ð 5 : 8 Þ

where B is the signal bandwidth, t w is the pulse width and a and b are dimen-
sionless scalar values given by:

b ¼ 1 B
2f c

ð 5 : 9 Þ

sinc p ð ð 1 þ b Þ a Þ sinc p ð ð 1 b Þ a Þ

¼ 0 : 3162 ð 5 : 10 Þ

sinc 2p a ð Þ 1