Modulator-amplifier

• US 20070015473A1
• Filed: 09/18/2006
• Published: 01/18/2007
• Est. Priority Date: 01/18/2002
• Status: Active Grant

• Current Assignee: Turtle Beach Corporation
• Original Assignee: American Technology Incorporated (Emerson Electric Company)
• Inventors: Spencer, Michael
• Granted Patent: US 7,224,219 B2
• Time in Patent Office: Days
• US Class Current: 455/102
• CPC Class Codes: H03F 2200/331 Sigma delta modulation being used in an amplifying circuit
• CPC Class Codes: H03F 3/2171 with field-effect devices H03F3/2173 - H03F3/2178 take precedence
• CPC Class Codes: H03F 3/66 Amplifiers simultaneously generating oscillations of one frequency and amplifying signals of another frequency
• CPC Class Codes: H04B 11/00 Transmission systems employing sonic, ultrasonic or infrasonic waves

Abstract

A method and device for frequency shifting and amplifying an audio signal for use in a parametric loudspeaker system is disclosed. The method includes the operation of receiving an input audio signal and creating a reference signal. The audio signal is compared with the reference signal to derive a compared product signal. The compared product signal is sent to a switching power stage. Nonlinear preprocessing is performed with respect to the input audio signal, and/or a non-triangle wave is created as the reference signal. The input audio signal is shifted and amplified by modulating the reference signal in the switching power stage.

Claims

1. A modulator/amplifier (ModAmp) comprising:

a carrier reference generator for generating a carrier signal;

an event generator configured for comparing an audio input signal to the carrier signal, and generating event trigger signals based on said comparing;

an AM modulator configured for receiving the event trigger signals and generating double sideband modulation of the carrier signal;

an SSB modulator configured for receiving the event trigger signals and generating SSB modulation of the carrier signal; and

an output driver configured for receiving AM modulated or SSB modulated carrier signals and outputting a drive signal based thereon suitable for driving an ultrasonic transducer in a parametric sound reproduction system;

wherein event trigger signals are related to the audio input signal by a non-linear function and modulation is switch-mode modulation based on the event trigger signals.

2. The ModAmp according to claim 1, further comprising:

a power supply configured for powering the ModAmp; and

a power supply rejection circuit.

3. The ModAmp according to claim 1, further comprising an audio preprocessor for generating a preprocessed audio input to generate in-phase and quadrature audio input signals.

4. The ModAmp according to claim 3, further comprising an audio preprocessor configured to dynamically control a level of the carrier signal based upon the preprocessed audio input.

5. The ModAmp according to claim 1, wherein the ModAmp is configured for one of bi-level, tri-level, 4-level, and 5-level steady states in switching modulation/amplification.

6. The ModAmp according to claim 1, configured to perform at least one of SSB and DSB modulation.

7. The ModAmp according to claim 1, wherein the ModAmp is configured for modulation each with reduced third harmonic.

8. The ModAmp according to claim 1, wherein switching occurs at one of 2, 3 or 4 times a frequency of the carrier signal.

9. The ModAmp according to claim 1, wherein the ModAmp is configured for bi-level SSB modulation based on a staggered drive.

10. A method for frequency shifting and amplifying an audio signal for use in a parametric loudspeaker system, including the steps of,

i) receiving at least one input audio signal,

ii) creating at least one reference signal,

iii) comparing the at least one input audio signal with the at least one reference signal to derive at least one compared product signal,

iv) delivering the at least one compared product signal to a switching power stage wherein at least one operation is performed selected from the following:

a) performing nonlinear preprocessing with respect to the input audio signal, and,

b) creating a non-triangle wave as the at least one reference signal; and

v) frequency shifting and amplifying the input audio signal by modulating the reference signal in the switching power stage.

11. A method as set forth in claim 10, wherein there is a non-linear relationship between the input audio signal and timing of state changes in the switching power stage.

12. A method as set forth in claim 10, wherein the non-linear preprocessing of the audio input signal is based on an arcsine function.

13. A method as set forth in claim 10, wherein the non-triangle wave is a sinusoidal wave.

14. A method as set forth in claim 10, wherein the at least one reference signal is modulated in one of a lower sideband, upper sideband, or both upper and lower sidebands.

15. A method as set forth in claim 10, wherein switching in the switching power stage occurs at one of 2,3,4,5, and 6 times the reference frequency.

16. A method as set forth in claim 10, wherein the step of creating at least one reference signal comprises providing a power supply rejection circuit and controlling a frequency of the reference signal to within a selected range.

17. A method as set forth in claim 10, further comprising at least one of the steps of:

performing frequency modulation;

performing quadrature phase shift keying; and

performing quadrature amplitude modulation.

18. A modulator-amplifier operable for use in a parametric sound reproduction system for reproducing audio information in a medium, comprising:

an input configured for receiving at least one input signal including audio information;

at least one reference signal generator configured for generating at least one carrier signal;

a switch mode modulator configured to modulate the at least one carrier signal, configured so that there is a non-linear relationship between the at least one input signal and state transitions of a switching output waveform; and

wherein the modulator-amplifier is configured to generate an output signal that has been shifted in frequency relative to a frequency of the at least one input signal and wherein the output signal includes at least one sideband.

19. A modulator-amplifier as set forth in claim 18, wherein the output signal comprises two sidebands and satisfies at least one condition of a) the audio information being divided between the two sidebands unevenly and b) a strength of the output signal is divided between the two sidebands unevenly.

20. A system for generating an acoustic output reproducing an audio signal in an acoustic parametric array in an acoustic wave-transmitting medium, comprising:

a) a modulator-amplifier which produces a modulated carrier wave output which comprises a carrier waveform at an ultrasonic frequency modulated so as to include a processed audio signal, the modulated carrier wave output is operable for driving a transducer to reproduce the audio signal from the acoustic parametric array;

the modulator-amplifier including an event generator for generating a timing signal based on comparison of the audio signal and a carrier signal;

the modulator-amplifier further comprising a switching output stage coupled to the event generator for signaling the switching output stage, wherein timing of switching state transitions in the switching output stage is related to the audio signal by a non-linear function; and

b) an ultrasonic transducer coupled to the modulator-amplifier which converts the modulated carrier wave output into an ultrasonic waveform for producing an audio wave in a medium, whereby a pre-processed audio source signal is amplified and reproduced from the parametric array in the medium.