An Ultra-Wideband Sensor Node Development with Dual-Frequency Band for Medical Signal Monitoring - Ultra Wideband Wireless Body Area Networks - page 107

To UWB antenna

(a) (b)

To Narrow
band antenna

Micro-controller

Analog front
end

Power

Narrow band RF
and IF

UWB pulse
generator

UWB RF

Fig. 5.25 Various sections of the dual band sensor node. a Bottom side, b Top side

5.3.1 IR-UWB Receiver Front-End

Direct-conversion receiver architecture is utilized for the IR-UWB receiver front-
end described herein. Main advantages of using a direct-conversion architecture
are the ease of implementation using off-the-shelf components, ability to operate
without the use of any timing control and resetting signals as compared to energy
detection receivers and small power consumption.
The block diagram of the UWB receiver front-end circuit is shown in Fig. 5.27 .
UWB signals entering the receiver antenna pass through a BPF with a pass band of
3.5-4.5 GHz in order to eliminate unwanted out-of-band interfering signals. The
filtered signal is then amplified by 48 dB using three wideband Low Noise
Amplifiers (LNA) before down converting to a baseband signal using a mixer and
a VCO operating at 4 GHz. The baseband signal is passed through a LPF with
100 MHz cut-off frequency before going through an analog amplification stage.
The LPF acts as a partial integrator and stretches the pulses so that they are easily
detectable using the ADC.
Two implementations of the UWB RF front-end are developed based on the
receiver architecture shown in Fig. 5.28 . The first implementation is realized using
plug-in RF components as seen in Fig. 5.28 a. The second generation IR-UWB
front-end is realized with a PCB using off-the-shelf components (Fig. 5.28 b).
Table 5.4 depicts major components used in each design.
The LNAs in the first design introduce a gain of 17.27 dB each with a Noise
Figure (NF) of 5.44 dB while the LNAs in the second design produce a gain of 16 dB
each with a NF of 1.45 dB. Both analog amplifiers produce a gain of 10 dB while the
NF for the analog amplifier in first design is 19.2 dB and that of the second design is
16.6 dB. The overall NF for the first design calculated from the Fris formula [ 26 ]is
3.55 dB while the second design has an overall NF of 1.41 dB. The mixer in the first
design has a conversion loss of 7.22 dB while that of the second design is 7.16 dB.
All the band pass filters have an insertion loss of 1 dB while the low pass filters have