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

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

wikipedia.org

Different Modern Different Modern Communication SystemsCommunication Systems

InternetCellular phonesWi-FiTV broadcastRadiosAnd much more…

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

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

Schematic of Modulators Designed Schematic of Modulators Designed Using Visual Systems SimulatorUsing Visual Systems Simulator

QPSK Modulator

BPSK Modulator OOK Modulator

ASK-4 Modulator

Schematic of Modulators Designed Schematic of Modulators Designed Using Visual Systems SimulatorUsing Visual Systems Simulator

QPSK Modulator

BPSK Modulator OOK Modulator

ASK-4 Modulator

Part 1: Design and simulate modulators

Part 2: Test power amplifier, operating in saturation, using the different modulators

Part 1: Design and simulate modulators

Part 2: Test power amplifier, operating in saturation, using the different modulators

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)

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

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

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

Spectrum Plots of Pre-amplified and Spectrum Plots of Pre-amplified and Amplified SignalsAmplified Signals

dBm

dBm

dBm

dBm

Spectrum Plots of Pre-amplified and Spectrum Plots of Pre-amplified and Amplified SignalsAmplified SignalsAdded

harmonic tones

dBm

dBm

dBm

dBm

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

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.

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

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.