Biomedical Engineering Reference
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Fig. 5 Direct frequency ultra-wideband (UWB) pulse generators. a Triangular pulse synthesis.
b Digital-to-analog converter (DAC)-based pulse synthesis
The up-conversion pulse generation technique has the same advantages as the
baseband pulse generation technique. Additionally, the spectral shape of the final
pulse can be determined in the baseband domain in this method. Consequently,
baseband pulse-shaping techniques can be applied to this method rather than shaping
the pulses at high frequencies. Hence, this approach minimizes the use of the power
hungry RF components. However, this method also suffers from the relatively high
power consumption in the mixer and the oscillator.
Direct Frequency UWB Pulse Generators
In this method, the UWB pulses are directly synthesized in the targeted frequency
range without the use of an intermediate stage. Direct synthesis of the UWB pulses
can be realized using several methods. The methods shown in [ 31 , 32 ] generate
triangular pulses in the RF domain. A fully digital implementation of a triangular
UWB pulse generator is described in [ 31 ]. In this method, the triangular pulses are
generated by combining the edges of several square pulses created using a delay
locked loop (DLL) (Fig. 5 a). The pulse shape can be digitally controlled by varying
the delay of the original square pulses; hence, it is preferred over the analog pulse
generation techniques for low-power applications. Power amplification is applied
for the negative and positive triangular pulses separately. Finally, the pulses are
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