Biomedical Engineering Reference
In-Depth Information
Fig. 3 Baseband pulse generation approach
Baseband UWB Pulse Generators
In this approach, a baseband pulse is generated initially in the form of a rectangular
pulse [ 24 - 26 ]. The square baseband pulse provides signal with a wide spectrum.
However, initial baseband pulse does not comply with the FCC spectrum require-
ments. Hence, a filtering stage is used in order to shape the pulse spectrum, such that
it complies with the FCC spectral mask. This approach is shown in Fig. 3 .
In this approach, the square pulse and its delayed version is passed through a XOR
gate, forming an edge combining circuit. The narrow square pulses formed by the
XOR output are then filtered using either a passive band pass filter (BPF) [ 24 , 26 ]
or a finite impulse response (FIR)- based filter [ 27 ]. The square pulses that form the
input to the XOR gate can be obtained either using the input data waveform itself
[ 5 ], through a flip-flop arrangement [ 26 ], or using a separate clock waveform [ 25 ].
This method provides advantages in terms of simplicity in design. It avoids the
complexities of directly generating the UWB pulses that comply with the FCC spec-
trum requirements. A significant portion of the power spectrum of the square wave
has to be filtered in order to bring the UWB pulse spectrum into the target frequency
range. This results in significant power loss. Often, the amplitude of the UWB pulse
spectrum after the BPF stage is lower than the FCC spectral mask. Hence, a power
amplification stage has to be followed after the BPF in order to use the maximum
allowable spectral amplitude. The use of a power amplifier further increases the
power consumption of the transmitter.
Up-Conversion UWB Pulse Generators
The difference between the baseband pulse generation technique and the up-
conversion method is that the up-conversion method uses a mixer to up-convert
the frequency of the baseband pulses into the target frequency range. Both rect-
angular [ 28 ] and triangular [ 29 ] pulses can be used as the baseband pulse stream.
Search WWH ::




Custom Search