Abstract:
A 900 MHz wireless speaker system having a tuning system that is features a variable down conversion scheme provided by a phase lock loop system controlled by a microprocessor and an automatic frequency control circuit. The speaker system utilizes either a battery and/or AC power source and provides remote control of features on the speaker.

Description:
This application claims priority to U.S. Provisional Application Ser. No. 60/015,428, filed Apr. 15, 1996. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention generally relates to wireless speaker systems; and, more particularly, it relates to a 900 MHz Wireless Speaker System. 
     Traditional wireless speaker systems have problems associated with tuning systems that cause drift, and are not truly wireless in that they use hardwired AC power sources to drive speakers in the system. Further, prior art speaker systems have the drawback of using fixed frequency downconverters. Hence, there exists a need for a wireless speaker system that eliminates or reduces the problems in the prior art speaker systems and does not utilize fixed frequency downconverters. Exemplary speaker systems having the drawbacks described above are illustrated in the U.S. Pat. Nos. 5,272,525 and 5,410,735. It is an object of the present invention to solve the problems in the art. 
     SUMMARY OF THE INVENTION 
     The present invention provides a 900 MHz wireless speaker system that uses a phase lock loop system in conjunction with a microprocessor to perform a variable fequency down conversion scheme that locks onto the carrier frequency eliminating problems associated with drift of the carrier frequency. The present invention include a phase lock loop control circuitry, local oscillation frequency of the variable frequency downconverter, and downconversion beat frequency that is not fixed (but variable). Tuning of the present invention is accomplished in the variable setting on the phase lock loop system by a variable downconversion beat frequency. The design has the advantage of not requiring any tuning system on another circuit area. 
     The wireless speaker system of the present invention further utilizes a battery power source and/or alternating current power source, and provides for a remote control to control the various features on the speaker. Other features of the invention include a wireless transmitter, an antenna, and a wireless frequency modulated receiver. 
     The objects and features of the present invention, other than those specifically set forth above, will become apparent in the detailed description of the invention set forth below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 a  through  1   d  are block diagrams of components of the present invention; 
     FIGS. 2 a  and  2   b  is a parts list for the schematic of FIG. 1; 
     FIGS. 3 a  thru  3   d  are electrical schematics of a circuit for a stereo transmitter board of the present invention; 
     FIGS. 4 a  and  4   b  are a parts list for the schematic of FIGS. 1 a  through  1   d ; 
     FIG. 5 is a 900 MHz speaker receiver board and circuit diagram of the present invention; 
     FIG. 6 is a parts list for the schematic of FIG. 3; 
     FIG. 7 is an audio board and control board of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a circuit approach used in the present invention. The variable frequency oscillator in the present invention includes a microprocessor, a variable control oscillator, pre-scaler, phase detector, low pass filter, and a mixer. This circuit uses, one microprocessor, one phase locked loop IC, one pre-scaler IC, two crystals, one VC module, a few transistors and a pair of speakers. FIGS. 2 a  and  2   b  show in particularity a feedback loop from the Automatic Frequency Control. 
     FIG. 1 shows in particularity a feedback loop from the Automatic Frequency Control (AFC) to the PLL circuit in the initial IF stage variable frequency down conversion. It is found that the clock generator of the PLL can be fine adjusted up to 30 KHz by the AFC feedback signal, which can compensate a 240 KHz drift in the transmitter carrier frequency. The channel select coarsely tunes the variable frequency down conversion and the AFC feedback signal self adjusts the fine tuning of the variable frequency down conversion. 
     Variable down conversion is a novel feature of the current invention. Fixed frequency down conversion offsets the carrier frequency by a specified frequency, where tuning must be accomplished by a second stage. The current invention uses variable frequency down conversion which self adjusts offseting the received signal by a variable frequency, down converting to a specified frequency. Variable frequency down conversion on the first intermediate frequency (“IF”) stage eliminates the need to tune the circuit in a subsequent stage. Tuning the circuit in the first IF stage increases the signal to noise ratio of the over all system because the signal strength of the received signal is maximized, thereby decreasing the neccessary gain of the system to acheive a given output. Tuning in the first IF stage also lowers the distortion and coloration of the audio signal by a subsequent stage that filters the audio signal from the intermediate frequency thereby providing improved signal quality and frequency response. 
     The speaker system of the present invention further includes a double conversion feature whereby signals are first downconverted to the first IF (intermediate frequency), and then to the 2nd IF, but on the second IF AFC (auto frequency control) is implemented by Phase Lock Loop that feeds a control signal back to the first IF stage thereby eliminating any significant drift and performs the tuning of the circuit. 
     A wireless speaker system utilizing a carrier frequency which may vary with time comprising: means for transmitting an audio signal modulated on said carrier frequency, means for receiving said audio signal modulated on said carrier frequency, means for variably down converting the carrier frequency to an intermediate frequency, means for separating said audio signal from said intermediate frequency; and, means for transducing the audio signal into accoustical energy (FIG.  9 ). Said means for variably down converting said carrier frequency is self adjusting to said carrier frequency. 
     FIG. 3 illustrates the 900 MHz stereo transmitter board. The accompanying bill of materials or parts list in FIG. 2 lists and references all of the parts that comprise the 900 MHz stereo transmitter board of FIG.  1 . All components are to be at least suitable for use in the commercial temperature range. Item  1  comprises a high band width quad-buffer. Suitable equivalents are well known in the art. Item  2  is an antenna connector that is suitable for use with a 900 MHz signal. Many equivalent connectors are known in the art. Item  3  is a modulator used to combine the left and right audio signals. Item  4  is a 6 volt battery used to supply power to the 900 MHZ transmitter board. Item  5  is a BU2419, which tracks the carrier signal, is well know by those skilled in the art. Item  6  through Item  15  comprise capacitors. Item  17  is an RCA jack, several equivalents such as ¼th inch or ⅛th inch jacks may be used for example. Item  18  is a standard D.C. jack suitable for use with a 12 volt D.C. supply. Item  19  is a diode, many equivalents are well known in the art. Item  20  is a Zener diode having a threshold voltage of 3.3 volts. Item  21  through Item  26  comprise electrolytic capacitors of standard commercial tolerance. Item  27  is a voltage controlled oscillator, functioning to up modulate the signal for transmitting at approximately 914 MHz. Item  28  is a light emitting diode of any color. Item  29  is a PMB2306, a component well known in the art, supplying the carrier frequency to Item  27 . Item  30  is a PMB2312 that controls Item  29  supplying the carrier frequency. Item  31  through Item  53  comprise resistors of standard commercial tolerance, equivalents are well known in the art. Item  54  are four-pole-double-throw switches rated for use with 12 volts D.C. Item  55  is a variable resistor of 50 Kilo-ohms and of standard commercial tolerance. Item  59  through Item  61  comprise crystal oscillators, non-crystal equivalents are well known in the art for use as a clock signal. 
     As illustrated in FIG. 1, IC 1 BA1404, IC 2 PMB 2312, IC 3 PMB 2306, IC 4 BU 2419/BU 2459, are commercially available. A description of BA 1404 and other ICs (“integrated circuits”) can be found in the  Master IC Cookbook  published by Tab Books Blue Ridge Summit, Pa. (1991). FIG. 3 illustrates a 900 MHz speaker receiver board, being the receiver circuit of the mhz modulated signal transmitted from the MHZ stereo transmitter board of FIG.  1 . The bill of materials in FIG. 4 lists and references all of the parts that comprise the 900 MHz speaker receiver board of FIG.  3 . All components are to be at least suitable for use in the commercial temperature range. Item  1  is an antenna suitable to receive a 900 MHz carrier signal with a bandwidth of at least the essential audio spectrum. Item  2  through Item  20  comprise capacitors of standard tolerance, the designation “/C” denotes ceramic capacitors, this is well known in the art. Item  21  through Item  28  comprise electrolytic capacitors of standard commercial tolerance. Item  29  is an tuning coil, comprising an inductor of 0.68 Milli-Henrys. Item  30  is a tuner to filter the modulated audio signal from the carrier signal. Item  31  comprises diodes, many equivalents are known to those skilled in the art. Item  32  comprises transformers. Item  33  comprises a voltage controlled oscillator capable of tracking a 914 MHz control signal. Item  34  is a two color light emitting diode, of any color combination, which is well known in the art. Item  35  and Item  36  function to track the carrier frequency. Item  37  through Item  56  are resistors of standard commercial tolerance. Item  57  is an 8 pin connector, of which many equivalent connectors are well known to those skilled in the art. Item  59  comprises variable capacitors used to tune the circuit for optimal reception. Item  60  through Item  63  comprise diodes. Item  63  and Item  64  are variable resistors of standard commercial tolerances. Item  65  and Item  66  are 10.7 kilohertz notch filters. Item  67  is a crystal oscillator, many non-crystal clocks are also available and are well known in the art. As illustrated in FIG. 3, IC 1 PMB 2306, and IC 2 PWB 2312, are commercially available. 
     FIG. 7 illustrates the Audio Board and Control Board of the present invention. The bill of materials in FIG. 6 lists and references all of the parts that comprise the Audio Board and Control Board. All components are suitable for use in the commercial temperature range. Item  1  is a demultiplexer used in selecting a frequency range for the system to operate in performing the down conversion of a received signal. Item  2  is a buffer which may be implemented as four separate buffers or as a quad-pack minimizing layout area on the circuit board and also minimizing cost. Items  3  and  4  are diodes. Item  5  through Item  12  are connections to the 900 MHz speaker receiver board. Item  13  comprises two 6 volt batteries supplying power to the Audio Board and Control Board and the 900 MHz speaker receiver board. Item  14  is also a battery supplying power to the Audio Board and Control Board and the 900 MHz speaker receiver board. Item  15  is a BU2458 of which its function and equivalents are well known in the art. Item  16  through Item  43  are capacitors the designation (M) meaning mylar, of which is well known to those skilled in the art. Item  44  comprises two inductor coils. Item  45  comprises two D.C. jacks rated for use with a 12 volt D.C supply. Item  46  comprises diodes. Item  47  comprises a zener diode. Item  48  is a Light Emitting Diode of any color. Item  49  is a dual pack operational amplifier for use in the commercial temperature range, any suitable equivalent may also be used. Item  50  through Item  79  are resistors, with standard commercial tolerance. Item  80  comprises two speakers suitable for use with music listening applications and preferably with high efficiency drivers that are capable of handling the power supplied by the power amplifier used to supply program power the speakers. Item  81  through Item  84  are switches rated for low power D.C. applications. Item  85  is a power amplifier supplied by a 12 volt supply suitable to power the speakers of Item  80 . Item  86  through Item  89  are transistors. Item  90  and Item  91  comprise variable resistors of standard commercial tolerance. Item  92  is a crystal oscillator, suitable equivalents are well known to those skilled in the art. 
     While only a few preferred embodiments of the invention have been described hereinabove, those of ordinary skill in the art will recognize that the embodiment may be modified and altered without departing from the central spirit and scope of the invention. Thus, the preferred embodiment described hereinabove is to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than by the foregoing description, and all ranges which come within the meaning and range of equivalency of the claims are intended to be embraced herein.