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RF Multiplexing
Transmitting and
Receiving Unit
EE413 Final Report
By
Adam Halstead and Michael Pfetsch
Problem and Solution
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Problem: There are a limited number of
frequency bands that can be allocated for
sending information over long distances
Solution: Devise a system that enables the
transmission of multiple sources of information
over a single RF carrier frequency
Description
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Digitize analog information from several sources
Multiplex multiple sources to form one source for
transmission
Transmit multiplexed source using frequency
modulation
Receive frequency modulated signal
Separate single source into its original sources
Convert signal back to analog and output to user
Finished Project
Op-amps
A/D
PLL
CPLD
FPGA
D/A
Demonstration
Results
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Successful multiplexing and de-multiplexing of 4 analog
audio sources
Successful construction of phase locked loop circuit
Successful construction of an FM transmitter
Could not synchronize transmitter and receiver using
phase lock loop
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Used direct clock connection for final demonstration
Tried several different line coding schemes
Bandwidth of transmitter/receiver limited to 75kHz
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inadequate for transmission rate of 330 kbps
Applications
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Surround sound radio/television streams:
eg.: Front-left, front-right, rear-left, rear-right
Multilingual broadcasts
eg.: Cantonese, Hindi, Arabic, English
Two stereo music streams of different genres:
eg.: Beethoven’s 9th Symphony and “I did it” by
Dave Matthews Band
Four simultaneous talk radio shows:
eg.: health, auto mechanics, poetry, politics
Cost
Transmission Protocol
Transmission Protocol
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A single unit of data transmission is 33 bits in length.
Reason: (4 signal sources) * (1 sample per source) * (8
data bits per sample) + 1 synchronizing bit = (32 + 1)
bits = 33 bits
The data for all four sources are interleaved at the bit
level.
Bytes are transmitted MSB first, with signal source 1
transmitted first
Baud rate: (33 bits/sample) * (10,000 samples/s)=
330,000 bits/s
Line coding
Clock Recovery
Phase locked loop circuit utilizing the NTE989, which is pin
equivalent to the LM565
Phase Locked Loop Demonstration
FM transmitter/receiver
performance
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Bandwidth: 10,000 Hz
Frequency response: 8 Hz – 10 kHz
FM Transmitter Circuit Diagram
Circuit design courtesy of Velleman-kit K1771
Advantage: Greater bandwidth due to high carrier frequency (around 100MHz)
Disadvantage: Difficult to replicate the transformer provided by printed circuit board.
System as implemented
Parts
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LF353 OpAmp – amplified incoming audio signals and output signal
of receiver
TLC0838 – 8 bit A/D converter to digitize audio signals to be
processed by FPGA
XC2S50 FPGA on Digilent Pegasus board with 50 MHz crystal
oscillator – controlling hardware (state machine with 132 states) for
the transmitting end
NTE989 Phase Lock Loop – used for clock recovery (pin equivalent
to LM565)
XC2C64 CPLD in Digilent CMOD package – controlling hardware
(state machine with 33 states) for the receiving end
TLC7524 – 8 bit parallel input D/A converter to convert digitized
signal to audio signal
LD1086V33 Voltage Regualtor – Provided 3.3V for CPLD
K1771 FM Transmitter Kit – Used to transmit signal
Challenges
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A/D converters utilized complicated configuration
scheme which required 5 configuration bits to be
sent before each conversion.
Positive and
negative clock
edges used at
various points
in each
conversion.
Designed a
state machine
with 132 states,
and
implemented
on the FPGA
Challenges
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Interfacing a 3.3V FPGA with 5V A/D
converters
FPGA is 5V Compliant
 Configured I/O pins for TTL signal standard
 Used high impedance state for logic 1
 Output pins of FPGA connected to 5V through
10kΩ pull up resistors
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Future Work
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Solve problem encountered in clock recovery with
phase locked loop, eliminating need for separate
clock connection.
Wireless transmission using TRF-24G transceiver
to provide enough bandwidth for higher quality
audio signal.
Increase the number of multiplexed signals, by
adding more A/D converters and changing the
programmable logic controller.
Utilize digital audio compression/decompression
References
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Clark, Jeremy and Mcneil, Kyle James. “Experiment to view T1
clock recovery”. Retrieved April 12, 2005, from
“http://www.picotech.com/experiments/t1_clock_recovery/”.
Liu, Pao-Lo. “Signal Generation and Conditioning” lecture notes.
Retrieved April 4, 2005, from
“http://www.ee.buffalo.edu/faculty/paololiu/413/sigen.ppt”.
Tomasi, Wayne. Electronic Communications Systems: Fundamentals
Through Advanced, Fifth Edition. Upper Saddle River, New Jersey:
Pearson Education, Inc., 2004.
Questions?
End of show
Extra Slides
Timeline
Example Verilog Code – mod128
counter
module counter( clock, counter );
input clock;
output [6:0] counter;
reg [6:0] counter;
always @ ( posedge clock )
begin
counter <= counter + 1;
end
endmodule
Programmable Logic Devices
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Complex Programmable Logic Devices (CPLD’s):
Typically have 32 to 512 macrocells, each containing
combinational logic and a flip flop.
Field Programmable Gate Arrays (FPGA’s): A more
recent technology, capable of realizing more
complicated designs than CPLD’s.
Verilog HDL: Hardware description language used to
abstractly define a digital system. Useful for
implementing a design on a CPLD or an FPGA,
although basic schematic design may still be used.
Work Plan
1.0 Project scope and approach
1.1 Define project goals
1.2 Develop specifications to achieve goal
1.3 Create block diagram of system
2.0 Design system
2.1 Design multiplexing/de-multiplexing circuits
2.2 Design A/D and D/A conversion circuits
2.3 Design transmitter/receiver circuits
3.0 Construction
3.1 Construct multiplexing/de-multiplexing circuits
3.2 Construct A/D and D/A conversion circuits
3.3 Implement transmitter/receiver circuits
Work Plan continued
4.0 Optimization
4.1 Optimize synchronization of system
4.2 Make adjustments for increased quality at output to
system
4.3 Fine tune system for maximum efficiency
5.0 Testing and Documentation
5.1 Test system for quality of output versus quality of
input
5.2 Document results