CHAOTIC SIGNAL GENERATOR




ALVARO GURROLA


ALEJANDRO SALAZAR


MARIANE FERNANDEZ

OBJECTIVE

Design and build a chaotic signal generator with a 1 GHz center frequency and a 200 MHz bandwidth.

ABSTRACT

A chaotic signal generator will be built to produce chaotic signals at ultra high frequencies (~1 GHz) with a wide bandwidth (~200 MHz). The generator will consist of five circuits and frequency modulation. The user will have the option to select initial conditions and these selections will be interfaced with the generator through programming and switching. The final product will be utilized in current Ground Penetrating Radar (GPR) Systems to increase image resolution.

BLOCK DIAGRAM


METHOD OF COMPLETION

In order to meet the given specifications, building and testing a chaotic signal generator will require hardware and software to be implemented. The final design will consist of two stages, a computer interface, and the chaotic function generator.

Alvaro Gurrola is responsible for the LabVIEW programming and Mariane Fernandez is responsible for the interfacing, power supply, and the frequency modulation. Alejandro Salazar is responsible for the five circuits found in the function generator. The computer interface will include Lab View application software and the data acquisition board (DAQ). The generator will include five different circuits that will each produce a distinct chaotic signal and a frequency modulation circuit. The two stages will combine to control and view the chaotic output.

In the first stage, LabVIEW will be used to choose a circuit design, set its initial condition, and route information through a switching scheme according to the set initial conditions. In addition, LabVIEW software has a virtual instrumentation (VI) panel window, in which a virtual switch can be configured so that the initial conditions can be set via the computer. The VI panel will also enable a user to decide which circuit design in the generator to use. This software also enables plots to be displayed on the VI panel. This will be useful to show the attractor. The attractor is a plot of the chaotic signal versus the derivative of the signal with respect to time. The attractor is actually a set of points such that all trajectories nearby converge to it. Producing an attractor will confirm the deterministic qualities of the chaotic signal. All the information will be routed through a data acquisition board from and to the computer.

A National Instruments DAQPad 6020E data acquisition board (DAQ) will process and route all the information needed by the computer and the generator, respectively. The switching scheme is shown in the schematic below. The DAQ lines that will be used are: eight digital input/output (I/O) lines, and one analog input lines. The DAQ will interface the software with the hardware through its various lines. The eight digital I/O lines will be used to select one of the five circuits through the use of analog switches and an analog multiplexer. The analog input line will be used to send the chaotic signal from the generator to the DAQ, which will be displayed on the computer. The second stage will consist of the hardware, which will modulate the frequency of the chaotic signal from one of the five circuits to a 1GHz signal using a voltage-controlled oscillator. The hardware consists of the actual circuits used to generate a chaotic signal shown in Schematics 1-5. They are piecewise linear. Once the circuit generates the desired signal, the output of that stage will have two lines. One line will be routed back to the analog line of the DAQ and the second output signal will be directed to the voltage-controlled oscillator through an analog multiplexer.

For the frequency modulation, the chaotic signal specified through the interface will be generated and modulated using a POS 1400-A voltage-controlled oscillator (VCO). The VCO will serve to superimpose the chaotic signal onto the carrier signal. The carrier signal of the VCO will be set to a frequency of 1 GHz to produce an ultra high frequency modulated signal with a bandwidth of 200 MHz by adjusting the voltage of each chaotic circuit through the utilization of the amplifier circuit mentioned above.

ISSUES

The issue we faced was obtaining a 200 MHz bandwidth. This was resolved by building an amplifier stage for all the chaotic circuits.

SCHEMATICS

CIRCUIT 1
CIRCUIT 2
CIRCUIT 3
CIRCUIT 4
CIRCUIT 5
SWITCHING SCHEME

RESULTS

Project has been completely integrated and is working to produce a 1 Ghz, 200 Mhz bandwidth chaotic signal.

ACKNOWLEDGEMENTS

Dr. Benjamin Flores

Robert Rubio

Tony Woo

Rex Velasquez

Franz Kuhlmann

Ralph Loya