Biomedical Engineering Reference
In-Depth Information
Triangular
pulse
generation
(a)
Triangular pulse
generator
/15
DLL
PA
/15
Balun
Triangular pulse
generator
(b)
Reconstruction
Filter
DAC
MUX
Data
Reconstructed
spectrum in the
RF domain
RF
f
sample
Reconstruction
filter mask
Fig. 4.4 Waveform synthesis UWB pulse generators a triangular pulse synthesis b DAC based
pulse synthesis
waveform synthesis techniques to directly synthesize UWB pulses such that they
directly fall within the target frequency range without using any filtering tech-
niques. Direct synthesis of the UWB pulses can be realized using several methods.
The methods shown in [
14
,
15
] generate triangular pulses in the RF domain. A
fully digital implementation of a triangular UWB pulse generator is described in
[
14
]. In this method, the triangular pulses are generated by combining the edges of
several square pulses created using a Delay Locked Loop (DLL) (Fig.
4.4
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 combined using a balun. This
method provides more controllability over the pulse generation at the cost of
increased hardware complexity.
A less complex, logic gate based triangular pulse generation technique is pre-
sented in [
15
]. In this method, the triangular pulses generated using a combination
of XOR gates are used to periodically switch a voltage controlled ring oscillator. In
this manner it is possible to generate the triangular UWB pulses in the RF domain.
Since the oscillator operates only during the presence of a pulse, this method
reduces the power wastage due to the continuous operation of local oscillators in
the other methods.
A Digital to Analog Converter (DAC) based direct UWB pulse synthesis
approach is demonstrated in [
16
] (Fig.
4.4
b). This technique uses a high speed
DAC in order to synthesize accurate UWB pulse in the RF domain. This method
