Wireless microphone apparatus and transmitter device for a wireless microphone

• US 6,778,814 B2
• Filed: 12/20/2000
• Issued: 08/17/2004
• Est. Priority Date: 12/28/1999
• Status: Expired due to Fees

• Current Assignee: Circuit Design, Inc.
• Original Assignee: Circuit Design, Inc.
• Inventors: Koike, Yukinaga
• Primary Examiner(s): Vo, Nguyen T.
• Assistant Examiner(s): Le, Nhan T.
• Application Number:
  US09/746,338
• Publication Number:
  US 20010034214A1
• Time in Patent Office: 1,336 Days
• Field of Search: 455/72, 455/91, 455/95, 455/127.1, 381/26, 381/91, 381/92, 381/122, 389/362, 389/381
• US Class Current: 455/95
• CPC Class Codes: H04B 1/04 Circuits
• CPC Class Codes: H04R 2420/07 Applications of wireless loudspeakers or wireless microphones

Abstract

A compact and lightweight wireless microphone and transmitter. The transmitter is connected to the microphone using a standard connector. The transmitter includes a low-frequency amplifier for amplifying a received voice signal and a surface acoustic wave oscillator providing a high-frequency oscillation signal. A modulator combines the amplified voice signal and the high frequency oscillation signal into a modulated signal. The modulated signal is amplified using a high-frequency amplifier to create a high-frequency modulated signal. The high-frequency modulated signal is output as radio waves through an antenna. A power supply is included for powering the transmitter. To improve sound quality, the transmitter additionally includes a compander circuit for improving signal-to-noise ratio and increasing a dynamic range through a logarithmic compression algorithm. Also, a pre-emphasis circuit which reduces noise by providing higher gain in the high frequency amplification than in the low frequency amplification.

Claims

1. A transmitter device for a wireless microphone, comprising:

a connector operable to transfer a voice signal from a microphone to a circuit;

wherein the circuit comprises;

a low-frequency amplifier for amplifying the voice signal;

a surface acoustic wave oscillator providing a high-frequency oscillation signal,

a modulator for modulating the high-frequency oscillation signal by the amplified voice signal, wherein a modulated high frequency signal is created, wherein the modulator includes an oscillation element, a modulation and oscillation circuit, and a buffer amplification circuit, and wherein the voice signal is superimposed on a bias voltage created by a variable diode, the superimposed voice signal being applied to the oscillation element and being modulated by changing a load of the surface acoustic wave oscillator;

a high-frequency amplifier for amplifying the modulated high frequency signal;

an antenna for radiating the amplified and modulated high-frequency signal as radio waves, and

a power supply for powering the circuit.

2. A transmitter device for a wireless microphone as defined in claim 1, further comprising:

a compander circuit for improving a signal-to-noise ratio and increasing a dynamic range, wherein the dynamic range is increased by logarithmic compression of the voice signal, and

a pre-emphasis circuit for reducing a signal noise, wherein the signal noise is reduced by providing a greater gain in the high frequency amplifier than in the low frequency amplifier.

3. A transmitter device for a wireless microphone as defined in claim 2, wherein the compander circuit performs ½

logarithm compression.

4. A transmitter device for a wireless microphone as defined in claim 2, wherein the surface acoustic wave oscillator outputs the high-frequency oscillation signal with a band of about 800 MHz directly without multiplication.

5. A transmitter device for a wireless microphone as defined in claim 1, wherein the surface acoustic wave oscillator outputs the high-frequency oscillation signal with a band of about 800 MHz directly without multiplication.

6. A transmitter device for a wireless microphone as defined in claim 1, wherein the high-frequency amplifier amplifies oscillation power of a band of about 800 MHz outputted from the modulator to +10 dBm with transmission output power at the antenna end of the antenna means.

7. A transmitter device for a wireless microphone as defined in claim 6, wherein a band-pass filter circuit for eliminating a harmonic noise of the high-frequency oscillation signal and matching the impedance to the antenna connected to a backend stage of the high-frequency amplifier.

8. A transmitter device for a wireless microphone as defined in claim 7, wherein a body case of the transmitter device serves as the antenna and the body case has a size with about ¼

the wavelength of the high-frequency oscillation signal.

9. A transmitter device for a wireless microphone as defined in claim 1, wherein the power supply comprises a battery and a direct current to direct current converter for increasing an output voltage of said battery, and wherein each element of the circuit operates at the voltage provided by the direct current to direct current converter.

10. A transmitter device for a wireless microphone as defined in claim 9, wherein the battery is one AAA size dry cell battery providing greater than 10 hours of continuous operation.

11. A wireless microphone apparatus comprising:

a microphone for receiving a voice signal, and a wireless transmitter connected to said microphone by a connector, the wireless transmitter comprising;

a low-frequency amplifier for amplifying the voice signal,

a surface acoustic wave oscillator for outputting a high-frequency oscillation signal;

a modulator for combining the high-frequency oscillation signal and the amplified voice signal to form a modulated signal, wherein the modulator includes an oscillation element and a buffer amplification circuit, wherein the voice signal is superimposed on a bias voltage and applied to the oscillation element, and wherein the voice signal is modulated by changing a load of the surface acoustic wave oscillator which is inserted into a base terminal of the oscillation element;

a high-frequency amplifier for amplifying the modulated signal to create a high frequency modulated signal;

an antenna means for radiating the high frequency modulated signal as radio waves, and

a power supply, wherein power from the power supply is distributed to the transmitter.

12. A wireless microphone apparatus as defined in claim 11, the apparatus further comprising:

a compander circuit for improving a signal-to-noise ratio and increasing a dynamic range of the voice signal, wherein the dynamic range is increased by logarithmic compression of the voice signal; and

a pre-emphasis circuit for reducing a noise by making an amplification degree of a high-pass frequency in the voice signal larger than that of other frequency regions.

13. A wireless microphone apparatus as defined in claim 12, wherein the surface acoustic wave oscillation means outputs the high-frequency oscillation signal with a band of about 800 MHz directly without multiplication.

14. A wireless microphone apparatus as defined in claim 12, wherein the compander circuit performs ½

logarithm compression.

15. A wireless microphone apparatus as defined in claim 11, wherein the high-frequency amplification means amplifies oscillation power of a band of 800 MHz outputted from the modulation means to +10 dBm with transmission output power at the antenna end of the antenna.

16. A wireless microphone apparatus as defined in claim 15, further comprising a band-pass filter circuit for eliminating a harmonic noise of the high-frequency oscillation signal and for matching the impedance to the antenna connected to a backend stage of the high-frequency amplification means.

17. A wireless microphone apparatus as defined in claim 16, wherein a body case of said transmitter device serves as the antenna, the body case having a length of about ¼

the wavelength of the high-frequency oscillation signal.

18. A wireless microphone apparatus as defined in claim 11, wherein the surface acoustic wave oscillator outputs the high-frequency oscillation signal with a band of about 800 MHz directly without multiplication.

19. A wireless microphone apparatus as defined in claim 11, wherein the power supply comprises a battery and a DC—

DC converter for increasing an output voltage of said battery, and wherein each of the elements of the transmitter operate at the same voltage.

20. A wireless microphone apparatus as defined in claim 19, wherein the battery is a AAA dry battery providing 10 hours or longer of continuous operation of the transmitter.

21. A wireless microphone apparatus as defined in claim 11, wherein the microphone is fitted and connected to the wireless transmitter through a non-conductive elastic member, wherein the elastic member maintains electrical and mechanical connections between the connector and the transmitter.