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Analyzing the Effects of a Class AB Power Analyzing the Effects of a Class AB Power Amplifier Using Different RF Modulation Amplifier Using Different RF Modulation
SchemesSchemes
Maui Akamai InternshipSymposium
July, 22, 2008
Kenneth EstoresTrex Enterprises
Mentor: Hien Do
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OutlineOutline Different Modern Communication Systems
– Impacts to Society Basic Definitions for RF Communication Systems
– Modulation– Amplification
My Project– Design and Simulate Four Modulators: BPSK, QPSK, OOK, ASK-4– Advantages and Disadvantages of Operating Class AB Amplifier in Saturation
– Effects of Using Power Amplifier with Modulators– Comparison of Amplitude Shift Keying vs. Phase Shift Keying
Conclusion Future Goals Acknowledgments
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wikipedia.org
Different Modern Different Modern Communication SystemsCommunication Systems
InternetCellular phonesWi-FiTV broadcastRadiosAnd much more…
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Basic Definitions for RF Basic Definitions for RF Communication Systems: Communication Systems:
Modulation and AmplificationModulation and AmplificationModulation: The process in which a low frequency signal is
converted into a high frequency signal in order to propagate through a medium
Amplification: The process in which a low power signal is increased to a high power signal
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Four Common Digital ModulatorsFour Common Digital Modulators
Amplitude Shift Keying (ASK) Class– On Off Keying (OOK)
Uses two different waveforms with different amplitudes to transmit 0 or 1– Amplitude Shift Keying-4 (ASK-4)
Uses four different waveforms with different amplitudes to transmit 00, 01, 10 or 11
Phase Shift Keying (PSK) Class– Binary Phase Shift Keying (BPSK)
Uses two different waveforms with different phases to transmit 0 or 1– Quadrature Phase Shift Keying (QPSK)
Uses four different waveforms with different phases to transmit 00, 01, 10 or 11
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Schematic of Modulators Designed Schematic of Modulators Designed Using Visual Systems SimulatorUsing Visual Systems Simulator
QPSK Modulator
BPSK Modulator OOK Modulator
ASK-4 Modulator
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Schematic of Modulators Designed Schematic of Modulators Designed Using Visual Systems SimulatorUsing Visual Systems Simulator
QPSK Modulator
BPSK Modulator OOK Modulator
ASK-4 Modulator
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Part 1: Design and simulate modulators
Part 2: Test power amplifier, operating in saturation, using the different modulators
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Part 1: Design and simulate modulators
Part 2: Test power amplifier, operating in saturation, using the different modulators
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Trex Enterprises Corporation
Characteristic Curve and Power Characteristic Curve and Power Added Efficiency Plots of AmplifierAdded Efficiency Plots of Amplifier
Linear to non-linear region (~ 30dBm)
Maximum efficiency region (~ 37dBm)
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Advantages and Disadvantages of Advantages and Disadvantages of Operating Amplifier in SaturationOperating Amplifier in Saturation
Advantages– Region where
maximum power efficiency occurs
– Larger range of transmission
Disadvantages– Creates excess
harmonic tones to modulated signal
– Causes amplitude distortion in signals
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Effects of Using Power Amplifier with Effects of Using Power Amplifier with Amplitude Shift Keying ModulatorsAmplitude Shift Keying Modulators
OOK Modulator– Both signals are
synchronized with each other
ASK-4 Modulator– Amplitudes are distorted
Decision circuit at receiver won’t be able to decipher transmitted data
Amplitudes distorted
Wat
tsW
atts
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Effects of Using Power Amplifier with Effects of Using Power Amplifier with Phase Shift Keying ModulatorsPhase Shift Keying Modulators
For both modulators, the pre-amplified and amplified signals are synchronized with each other– Minimum effects of
amplifier distortion
– Phase transitions are recognizable
Phase transitions
Phase transition
Wat
tsW
atts
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Spectrum Plots of Pre-amplified and Spectrum Plots of Pre-amplified and Amplified SignalsAmplified Signals
dBm
dBm
dBm
dBm
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Spectrum Plots of Pre-amplified and Spectrum Plots of Pre-amplified and Amplified SignalsAmplified SignalsAdded
harmonic tones
dBm
dBm
dBm
dBm
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Amplitude Shift Keying vs. Phase Amplitude Shift Keying vs. Phase Shift Keying Using Class AB Power Shift Keying Using Class AB Power
AmplifierAmplifierPSK can operate in saturated region of amplifier
– PSK can operate at maximum power efficiency level– PSK modulated signals can transmit farther than ASK
modulated signalsPSK is less prone to amplifier distortionASK has a better signal quality vs. PSK when
operating in linear region of amplifier– ASK is more robust against noisy mediums
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ConclusionConclusion
There is no “optimum” modulation scheme!– Modulation schemes are decided based on
specific application and needs.All modulators have positive and negative
drawbacks associated with them.In the case of this amplifier, I observed that
the phase shift keying modulators performed better.
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Future GoalsFuture Goals
Design and build demodulators– Obtain quantitative results
Bit error rate
Design more “complex” modulators – Quadrature Amplitude Modulators
– Differential Phase Shift Keying Modulators
Incorporate encoders and decoders to communication system
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AcknowledgementsAcknowledgements
Hien Do, Ned Davis, Daron Nishimoto
Lynne Raschke, Scott Seagroves, Lisa Hunter, Lani LeBron
The Akamai Internship Program is funded by the Center for Adaptive Optics through its National Science Foundation Science and Technology Center grant (#AST-987683) and by grants to the Akamai Workforce Initiative from the National Science Foundation and Air Force Office of Scientific Research (both administered by NSF, #AST-0710699) and from the University of Hawaii.