An Ultra-Wideband Sensor Node Development with Dual-Frequency Band for Medical Signal Monitoring - Ultra Wideband Wireless Body Area Networks - page 85

• Narrow band RF and base band section:
It is designed to communicate with the coordinator node using the 433 MHz ISM
band and interprets the data to the micro-controller.
• Micro-controller:
The micro-controller works as the central controlling unit that coordinates the
operation of all the operational blocks of the sensor node. This includes reading
both analog and digital data from the respective inputs, reading data from the
narrow band receiver, setting the PRF of the IR-UWB pulse generator, generating
the data bits that should be transmitted using the IR-UWB transmitter and con-
trolling the power to various sections of the sensor node in order to enable the
sleep mode operation. In addition, micro-controller handles all the functions
related to the operation of Medium Access Control (MAC) protocol at the sensor
node.
• Analog front-end:
This section interfaces the analog input signals, such as Electrocardiography
(ECG) with the Analog to Digital Converter (ADC) of the micro-controller.
• Power management unit:
The responsibility of the power management unit is to supply and control power to
all operational parts of the circuit. All the RF related circuits of the sensor nodes,
such as IR-UWB transmitter components and narrow band receiver module are
powered with a 3 V supply while rest of the hardware uses a 3.3 V power supply.
Each of these main operational blocks of the dual band sensor node are
described in detail in the following sub sections.
5.2.1 Pulse Generation Techniques
IR-UWB pulse generator lies at the core of the IR-UWB transmitter. An up-
conversion pulse generation technique is utilized in this design considering the
advantages offered by this technique that are discussed in Chap. 4 . The up-con-
version pulse generation technique uses a mixer to up-convert the base band pulses
generated by a pulse generator, and filters the up-converted pulses so that the pulse
spectrum falls within the intended bandwidth (3.5-4.5 GHz for the sensor node
described in this chapter) before transmission. This technique offers the highest
power efficiency for a UWB transmitter developed using off-the-shelf components.
In the sensor node design described in this chapter, IR-UWB pulses are generated
by passing a periodic square wave signal and its time-delayed version through a
XOR gate as shown in Fig. 5.4 . Two sets of buffers with different supply voltages
are used to introduce different delay levels to the signal [ 7 , 8 ]. The work presented in
[ 9 ] shows that the delay between the input and the output of a buffer depends on the
applied supply voltage to the buffer. This relationship is given by ( 5.1 ):