![](bg5.png)
shown in Figure 12 while the constellation diagram
of the demodulated signal is presented in Figure 13.
Figure 12: The Rx- BPSK signal spectrum at 12.5 MHz
carrier (data rate 2Mbps).
Figure 13: The constellation diagram of BPSK at
Demodulator using Agilent digital demodulator (E8048A).
5 CONCLUSIONS
We implemented a new simple BPSK digital
modulator model in the Simulink MATLAB
environment. This has been successfully
implemented using hardware description language
VHDL code by the Altera UP2 development board.
The modulator generates the BPSK signal directly
from the binary data in order to control the carrier
signal. The output producing a modulated digital
signal was filtered to transmit through a miniature
BPF. Experimentally measurements are presented at
carrier frequency 12.50 MHz, and data rate 2Mbps,
which present good performance with high data rate
and carrier suppression >35dB. The filter is a critical
part of the design. For this work we designed and
simulated different types of analogue filter and
compared them to choose the best filter
performance. The simulation results were that the
Chebyshev I & II, appeared optimum at BPFs
compared to the others, and optimum LPF
performance was form the Butterworth type. Digital
filters could be implemented to allow integration
with the digital modulator device. However the
disadvantage of digital filter is that they need
clocking at high multiples of the sampling frequency
which increases the power consumption and size. As
future work, it is still necessary to investigate other
methods to improve the harmonic rejection
performance of the analogue output filters by digital
synthesis of alternative waveforms at the modulator.
It is also an intention to up-convert the signal into an
ISM unlicensed frequency band (e.g. 402~405 MHz)
for biomedical telemetry purposes.
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EXPERIMENTAL DIGITAL BPSK MODULATOR DESIGN WITH VHDL CODE FOR BIODIVECES
APPLICATIONS
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