Analog Single Sideband-Pulse Width Modulation Processor for Parametric Acoustic Arrays

<p>Parametric acoustic arrays are ultrasonic-based loudspeakers that produce highly directive audio. The audio must first be preprocessed and modulated into an ultrasonic carrier before being emitted into the air, where it will self-demodulate in the far field. The resulting audio wave is proportional to the double time-derivative of the square of the modulation envelope. This thesis presents a fully analog processor which encodes the audio into two Pulse Width Modulated (PWM) signals in quadrature phase and sums them together to produce a Single Sideband (SSB) spectrum around the fundamental frequency of the PWM signals. The two signals are modulated between 8% and 24% duty cycle to maintain a quasi-linear relationship between the duty cycle and the output signal level. This also allows the signals to sum without overlapping each other, maintaining a two-level output. The system drives a network of narrowband transducers with a center frequency equal to the PWM fundamental. Because the transducers are voltage driven, they have a bandpass frequency response which behaves as a first-order integrator on the SSB signal, eliminating the need for two integrators in the processor. Results show that the “SSB-PWM” output wave has a consistent 20-30dB difference in magnitude between the upper sideband and lower sideband. In simulation, a single tone test shows higher total harmonic distortion for lower frequencies and higher modulation depth. A two-tone test creates a 2^nd order intermodulation term that increases with the frequencies of the input signals.</p>

Name thesis:degree_name

MS in Electrical Engineering

Discipline thesis:degree_discipline

Electrical Engineering

Year dc:date.available

2019

Author dc:creator

• Marathe, Vikrant A

Contributors dc:contributor

• Vladimir Prodanov

• parametric loudspeaker
• Berktay’s equation
• amplitude modulation
• bandpass PWM
• polyphase networks
• Hilbert transform
• monostable multivibrator
• series resonance
• Electrical and Computer Engineering
• Electrical and Electronics
• Systems and Communications
• VLSI and Circuits, Embedded and Hardware Systems

Identifier

10.15368/theses.2019.91

OAI identifier oai:identifier

oai:digitalcommons.calpoly.edu:theses-3524