KR19990032494A - Wireless audio signal transmission system - Google Patents

Abstract

The present invention relates to a wireless audio signal transmission system for wirelessly transmitting an audio signal in a local transmission region to a portable receiver.

The transmitter 30 of the wireless audio signal transmission system according to the present invention receives an input audio signal and automatically adjusts the signal to an optimal modulation level. It consists of a multiplexing encoder 306 for output, a radio frequency oscillator 310 composed of a phase-locked loop, a frequency modulator 308 composed of an amplifier, a varactor diode and a crystal resonator, a transmission amplifier 312 and a transmission antenna 314. do.

The receiver 40 of the wireless audio signal transmission system of FIG. 4 includes a reception antenna 402 for receiving a radio signal, a low noise amplifier 404 for increasing a signal-to-noise ratio for a radio frequency signal, and a reference frequency generation. Local oscillator 408 composed of a phase-locked loop using a crystal crystal for the purpose, a mixing unit 406 for converting the received radio frequency signal into an intermediate frequency signal, a buffer 410 for receiving the intermediate frequency signal to obtain impedance matching ), An FM receiver 414 for receiving the intermediate frequency signal through the single pole double switch 412 and outputting left and right channel audio signals, and a preamplifier 416 for receiving and amplifying the left and right channel audio signals and outputting the same. And an output jack 418 connected to the output of the preamplifier 416.

The present invention can automatically adjust the audio signals input to the transmitter to an optimal modulation level, and the use of the overmodulation detector and the low pass filter is unnecessary by the transmitter having an automatic level adjuster which prevents distortion caused by a wide range of input signals. Therefore, the cost can be reduced, and the carrier frequency can be easily changed by the transmitter having a carrier oscillator configured with a phase-locked loop using a commercially available crystal crystal as a reference frequency, and the amplifier, the varactor diode, and the crystal resonator The frequency modulator associated with the oscillating part includes a linear compensation and an ideal frequency deviation, and can reduce distortion caused by the modulation.

In addition, the oscillation frequency can be easily changed by the local oscillation section of the receiver composed of a phase-locked loop using a commercially available crystal crystal as the reference frequency, and other intermediate frequency signals can be generated. The receiving unit can receive FM broadcast signals of 88 MHz to 108 MHz.

Description

Wireless audio signal transmission system

The present invention relates to a wireless audio signal transmission system, and more particularly, to a wireless audio signal transmission system for wirelessly transmitting an audio signal in a local transmission area to a portable receiver.

1 and 2 are block diagrams of a transmitter and a receiver of a conventional wireless audio signal transmission system.

The configuration and operation of the transmitter 10 of the conventional wireless audio signal transmission system of FIG. 1 are as follows.

The pair of input terminals 100 for receiving a stereo audio signal include a first input terminal L for receiving a stereo audio signal from a left channel and a second input terminal R for receiving a stereo audio signal from a right channel. It consists of.

The volume control unit 102 may adjust a stereo audio signal input to the pair of input terminals 100 to obtain a better modulation level and prevent signal distortion caused by overmodulation by a wide range of input signals. have. Since the volume control 102 is manually adjusted, the overmodulation detection unit 104 is required to identify the formation of the overmodulation. When over-modulation occurs, the light emitting diode (LED) 106 obtains energy and emits light, so that a user can identify whether over-modulation is formed.

Low pass filter 110 cancels high frequency interference of about 15 kHz of audio signals from a television receiver. The audio signals of the compact disk player are input to the next stage pre-amplifier 112 without passing through the low pass filter 110 by the switch 108.

Pre-Amphasis 112 improves the level of high frequency components of audio signals to improve the signal-to-noise ratio (S / N ratio).

The stereo multiplexer 114 includes a Suppressed Subcarrier Signal that is a baseband audio component that is the sum of the left and right channel audio signals (L + R) and a difference LR between the left and right channel audio signals. The stereo multiplexer outputs a signal, and the stereo multiplexer 114 also outputs a pilot signal having a frequency that is 1/2 of the frequency of the suppressor carrier signal.

The radio frequency transmitter 116 is a stereo multiplexer 114 modulates a fixed carrier with a stereo multi-modulation signal, and transmits the modulated signal to a transmission antenna 118 carried in a local transmission area (Local Transmission Area). Supply. An oscillator circuit that generates a fixed carrier is composed of a varactor diode, a capacitance, and a ceramic resonator to form a resonant circuit, and a capacitor of the varactor diode is used to linearly vary the oscillation frequency. Frequency modulation is possible by using a modulating signal that changes.

The voltage regulator 130 supplies a DC voltage to the power switching unit 132 by outputting a constant DC voltage from an AC / DC converter that converts AC into DC. The power switching unit 132 supplies an operating voltage to the overmodulation detector 104, the stereo multiplexer 114, and the radio frequency transmitter 116, and supplies power to the battery charger 134. The battery charger 134 supplies a charging voltage to charge the rechargeable battery 252 of the receiver 20 of the wireless audio signal transmission system of FIG. 2.

The configuration and operation of the receiver 20 of the conventional wireless audio signal transmission system of FIG. 2 are as follows.

The impedance matching unit 202 matches the impedance between the receiving antenna 200 and the radio frequency amplifier 204. The radio frequency amplifier 204 amplifies a radio signal from the transmitter 10 of the radio audio signal transmission system of FIG. 1 and outputs an amplified signal.

The mixing unit 206 mixes the local oscillation signal which is the output of the local oscillator 208 composed of the surface acoustic wave resonator of the amplified signal which is the output of the radio frequency amplifying unit 204, and generates a constant intermediate frequency signal. Output Frequency Signal). The FM receiver 220 receives an intermediate frequency signal by the switch 210 or is directly connected to the reception antenna 200. By the switching unit 222 associated with the potentiometer 224, the FM receiver 220 selects the intermediate frequency signal or selects the FM broadcast signals of 88 MHz to 108 MHz directly from the receiving antenna 200 to the left and right channel audio. The signals are separated and output. The headphone driver 230 amplifies the separated left and right channel audio signals and outputs them to the stereo headphone 230.

The charging voltage from the battery charger 134 of the transmitter 10 of FIG. 1 is connected to an anode of the diode 250 and charges the rechargeable battery 252 through a cathode of the diode 250. Let's do it. The rechargeable battery 252 supplies a voltage to the receiver 20 of FIG. 2.

In the conventional wireless audio signal transmission system, the volume control unit, which must be controlled manually, causes inconvenience in operation, and the overmodulation detection unit is necessary due to the volume control unit, thereby increasing the cost and a low pass filter for preventing high frequency interference. Due to the increase in cost, the ceramic resonator used in the radio frequency transmission unit cannot obtain the ideal drift property and modulation frequency deviation, and the radio frequency transmission unit outputting only a constant carrier is not easy to match the operation of the receiver. Since the constant voltage unit, the power switching unit, and the battery charging unit are necessary, the cost increases.

In addition, the receiving surface of the conventional wireless audio signal transmission system is a surface acoustic wave resonator used in the local oscillator can not obtain the ideal drift characteristics, it is not easy to match the operation of the FM receiver and the switching unit due to the mixing part generating a constant intermediate frequency In addition, since the length of the receiving antenna and the wave length of the FM broadcasting signals do not coincide, the receiving antenna has problems in that it cannot receive FM broadcasting signals of 88 MHz to 108 MHz.

It is an object of the present invention to eliminate the need for use of an overmodulation detector and a low pass filter by a transmitter having an automatic level adjuster that automatically adjusts audio signals input to the transmitter to an optimal modulation level and prevents distortion from a wide range of input signals. Therefore, the present invention provides a wireless audio signal transmission system with reduced cost.

It is another object of the present invention to easily change the carrier frequency by a transmitter having a carrier oscillator configured with a phase-locked loop using a commercially available crystal crystal as a reference frequency, comprising an amplifier, a varactor diode and a crystal resonator. The present invention provides a wireless audio signal transmission system capable of obtaining linearity compensation and an ideal frequency deviation by a frequency modulator associated with an oscillator and reducing distortion caused by modulation.

It is still another object of the present invention to provide a wireless audio signal transmission system which reduces costs because the constant voltage unit, the power switching unit, and the battery charging unit are not required since the power is directly supplied from the outside.

It is yet another object of the present invention to provide a wireless audio capable of easily changing the oscillation frequency and generating other intermediate frequency signals by a local oscillation section of a receiver composed of a phase-locked loop using a commercially available crystal crystal as a reference frequency It is to provide a signal transmission system.

It is still another object of the present invention to provide a wireless audio signal transmission system capable of receiving FM broadcast signals of 88 MHz to 108 MHz by a receiver having a tank and an additional antenna.

1 is a block diagram of a transmitter of a conventional wireless audio signal transmission system,

2 is a block diagram of a receiver of a conventional wireless audio signal transmission system,

3 is a block diagram of a transmitter of the wireless audio signal transmission system of the present invention;

4 is a block diagram of a receiver of a wireless audio signal transmission system of the present invention;

5 and 6 are detailed views of a transmitter of the wireless audio signal transmission system of the present invention of FIG.

7 and 8 are detailed views of a receiver of the wireless audio signal transmission system of the present invention of FIG.

In order to achieve the above objects, the wireless audio signal transmission system of the present invention includes a radio frequency oscillator configured as a phase-locked loop and a frequency modulator configured by an amplifier, a varactor diode, and a crystal resonator. And a transmitter for frequency modulating the radio frequency of the high frequency band together with the audio signals to form a signal, and a receiver for receiving radio frequency signals transmitted wirelessly and reproducing the audio signals. It is characterized by having a Q value characteristic that causes a small capacitance change and is opposite to the resonant frequency curve formed by the crystal resonator connected in parallel with the varactor diode.

The transmitter further includes an automatic lever adjusting unit for automatically adjusting the input audio signals to an optimal modulation level, and the phase locked loop uses a crystal crystal as a reference frequency having a frequency range of 28 MHz to 86 MHz.

The receiver comprises a low noise amplifier for increasing the signal-to-noise ratio for the radio frequency signal, a local oscillator composed of a phase-locked loop using a crystal crystal for generating the reference frequency, and an intermediate frequency having a frequency range of 78 MHz to 86 MHz. Mixing unit for converting to a frequency signal, tank unit for passing FM broadcast signals of 88MHz to 108MHz without passing the received radio frequency signal, receiving antenna for receiving a radio signal, to receive FM broadcasting signals of 88MHz to 108MHz And an additional antenna unit for matching the receiving antenna.

Hereinafter, a wireless audio signal transmission system of the present invention will be described in detail with reference to the accompanying drawings.

3 is a block diagram of a transmitter of the wireless audio signal transmission system of the present invention, and FIGS. 5 and 6 are detailed views of the transmitter of the wireless audio signal transmission system of FIG. 4 is a block diagram of a receiver of the wireless audio signal transmission system of the present invention, and FIGS. 7 and 8 are detailed views of the receiver of the wireless audio signal transmission system of FIG.

The wireless audio signal transmission system of the present invention includes a transmitter 30 of FIG. 3 and a receiver 40 of FIG.

3, the transmitter 30 of the wireless audio signal transmission system of the present invention receives the input audio signals and automatically adjusts the signal to an optimal modulation level. Frequency consists of a multiplexing encoder 306 for outputting a modulated signal, a radio frequency oscillator 310 composed of a phase-locked loop (PLL), an amplifier, a varactor diode, and a quartz resonator It consists of a modulator 308, a transmit amplifier 312 and a transmit antenna 314.

The receiver 40 of the wireless audio signal transmission system according to the present invention of FIG. 4 is for receiving radio frequency signals transmitted wirelessly and reproducing audio signals. The receiving antenna 402 for receiving radio signals, A low noise amplifier 404 for increasing the signal-to-noise ratio (S / N ratio), a local oscillator 408 composed of a phase-locked loop using a quartz crystal to generate a reference frequency, and a received radio frequency Mixing unit 406 for converting a signal into an intermediate frequency signal having a frequency range of 78 MHz to 86 MHz, a tank unit 420 for passing FM radio signals of 88 MHz to 108 MHz without passing the received radio frequency signal, and 108 MHz to 88 MHz Additional antenna unit 422 for matching the receiving antenna to receive the FM broadcast signals of the, for receiving the intermediate frequency signal to obtain impedance matching FM receiver 414 which receives the intermediate frequency signal through the fur 410 and the single pole double switch 412 and outputs the left and right channel audio signals, and transposes it to receive and amplify the left and right channel audio signals. It consists of an output jack 418 connected to the output of the pre-amplifier 416 and the preamplifier 416.

Operation of the wireless audio signal transmission system of the present invention according to the above configuration is as follows.

The transmitter 30 of the wireless audio signal transmission system of FIG. 3 receives stereo audio signals from the left channel R and the right channel L of the input terminal 302. The automatic level adjuster 304 automatically adjusts the received stereo audio signals to an optimal modulation level in order to prevent distortion caused by the input signals for the wide range. The multiplexing encoder 306 receives the adjusted audio signals and includes a suppressed subcarrier signal and a pilot signal indicating a difference between the audio signal of the left channel R and the audio signal of the right channel L. Outputs a stereo multiplex modulated signal. The frequency modulator 308 receives the stereo multiplex modulated signal and frequency modulates a carrier, which is an output of the radio frequency oscillator 310 configured as a phase-locked loop. The frequency modulator 308 is composed of an amplifier, a varactor didde, a quartz resonator, and the like, and the varactor diode is applied with a high DC voltage to obtain a small capacitance change. It is possible to obtain a Q value characteristic opposite to the resonant frequency curve formed by the connected crystal resonator, improve the linearity of the circuit, detect the distortion caused by the modulation, and obtain an ideal frequency deviation.

The radio frequency oscillator 310 uses a commercially available quartz crystal for the reference frequency. The present invention is adapted for use in the band from 900 MHz to 2.7 GHz and the crystal crystal has a frequency range from 28 MHz (900 MHz / 32) to 86 MHz (2.7 GHz / 32). The transmit amplifier 312 receives the frequency modulated carrier signal and amplifies it, and the amplified signal is broadcast through the transmit antenna 314 into the local transmission region.

5 and 6 are detailed views of the transmitter 30 of the wireless audio signal transmission system of the present invention of FIG. The automatic level adjusting unit U1 configured as BA3308 receives stereo audio signals from the left channel L-CH and the right channel R-CH, and outputs audio signals to the OUT1 and OUT2 terminals of U1. The multiplexing encoder (U2) composed of BA1404 receives audio signals output from OUT1 and OUT2 of U1 and outputs a stereo multiplex modulated signal to the MPXO and PILO terminals of U2. A frequency modulator comprising an amplifier (U3), varactor diodes (D1, D2), and a crystal resonator (X1) receives a radio multiplexing modulated signal from the MPXO and PILO terminals of U2 and is configured as a phase-synchronized loop. The carrier wave generated by U4 is frequency modulated. The wireless signal output from the output terminals OUT1 and OUT2 of the transmission antenna radio frequency oscillator U4 is received.

Operation of the receiver 40 of the wireless audio signal transmission system of FIG. 4 is as follows.

The reception antenna 402 receives a radio signal broadcast by the transmission antenna 314. The low noise amplifier 404 amplifies the radio signal by the reception antenna 402 to increase the signal-to-noise (S / N ratio). The mixing unit 406 forms a subheterodyne by combining with the oscillation frequency generated by the local oscillation unit 408 controlled by the phase-locked loop to receive an amplified radio signal and form an intermediate frequency signal. Similar to the radio frequency oscillator 310 controlled by the phase seed loop of FIG. 3, the local oscillator 408 controlled by the phase locked loop is commercially used as a reference frequency so that the intermediate frequency signal can have a frequency range of 78 MHz to 86 MHz. Use the crystal crystal available. The buffer 410 receives the intermediate frequency signal and performs impedance matching. The FM receiver 414 composed of inductance and capacitors receives the intermediate frequency signal through the single pole double switch 412 and outputs left and right channel audio signals. The preamplifier 416 receives the left and right channel audio signals and amplifies and outputs the amplified outputs to the output jack 418.

The receiver 40 of the wireless audio signal transmission system of FIG. 4 further includes a tank 420 and a receiver antenna 422 directly connected to the receiver antenna 402, so that the FM receiver 414 is 108 MHz to 88 MHz. FM broadcast signals can be received. The tank unit 420 shows a higher impedance than the band signals of 900 MHz to 2.7 GHz but is designed to be shorter than the FM broadcasting signals of 88 MHz to 108 MHz, so that the receiving antenna 402 connected to the additional receiving antenna unit 422 is FM broadcast signals of 88MHz to 108MHz can be received, and the FM receiver 414 receives the FM broadcast signals received through the switch 412.

7 and 8 are detailed views of the receiver 40 of the wireless audio signal transmission system of the present invention of FIG. The low noise amplifier 404 composed of Q2 amplifies the radio signal received by the reception antenna, and the mixer 406 composed of Q3 receives the amplified radio signal to form an intermediate frequency signal. The local oscillation section controlled by the phase-locked loop is composed of U5, and the buffer is composed of Q4. The intermediate frequency signal is transmitted to the FM receiver composed of U6. The left and right channel audio signals output from LO and RO, the output terminals of U6, are fed to a preamplifier consisting of U7A and U7B and connected to the output jacks.

The present invention can automatically adjust the audio signals input to the transmitter to an optimal modulation level, and the use of the overmodulation detector and the low pass filter is unnecessary by the transmitter having an automatic level adjuster which prevents distortion caused by a wide range of input signals. Therefore, the cost can be reduced, and the carrier frequency can be easily changed by the transmitter having a carrier oscillator configured with a phase-locked loop using a commercially available crystal crystal as a reference frequency, and the amplifier, the varactor diode, and the crystal resonator The frequency modulator associated with the oscillating part includes a linear compensation and an ideal frequency deviation, and can reduce distortion caused by the modulation.

In addition, the oscillation frequency can be easily changed by the local oscillation section of the receiver composed of a phase-locked loop using a commercially available crystal crystal as the reference frequency, and other intermediate frequency signals can be generated. The receiving unit can receive FM broadcast signals of 88 MHz to 108 MHz.

Claims (17)

In a wireless audio signal transmission system for transmitting audio signals wirelessly in a local transmission region, A radio frequency oscillator composed of a phase-locked loop and a frequency modulator composed of an amplifier, a varactor diode, and a crystal resonator are provided to convert the radio frequency of the high frequency band to form a radio signal transmitted wirelessly in the local transmission region. Transmission means for frequency modulation with the signals; And Receiving means for receiving radio frequency signals transmitted wirelessly and reproducing audio signals, The varactor diode is controlled by a high DC voltage and causes a small capacitance change, and has a Q value characteristic opposite to the resonance frequency curve formed by the crystal resonator connected in parallel with the varactor diode. Wireless audio signal transmission system. 2. The wireless audio signal transmission system according to claim 1, wherein said transmission means further comprises automatic level adjustment means for automatically and optimally adjusting input audio signals to a modulation level. The wireless audio signal transmission system according to claim 1, wherein the phase-locked loop uses a crystal crystal as a reference frequency. The wireless audio signal transmission system according to claim 3, wherein the crystal crystal has a frequency range of 28 MHz to 86 MHz. The wireless audio signal transmission system according to claim 1, wherein said receiving means further comprises low noise amplifying means for increasing a signal to noise ratio with respect to said radio frequency signal. The wireless audio signal transmission system according to claim 1, wherein said receiving means further comprises a local oscillating means composed of a phase-locked loop. The wireless audio signal transmission system according to claim 6, wherein the phase-locked loop uses a crystal crystal for generating a reference frequency. The wireless audio signal transmission system according to claim 1, wherein said receiving means includes mixing means for converting the received radio frequency signal into an intermediate frequency signal. The wireless audio signal transmission system according to claim 8, wherein the intermediate frequency signal has a frequency range of 78 MHz to 86 MHz. 10. The system of claim 8, wherein converting the received radio frequency signal into an intermediate frequency signal is accomplished by a subheterodyne. The wireless audio signal transmission system according to claim 1, wherein said receiving means includes tank means for passing FM broadcast signals of 88 MHz to 108 MHz without passing said received radio frequency signal. The wireless audio signal transmission system according to claim 1, wherein said receiving means has a receiving antenna for receiving a wireless signal. 13. The wireless audio signal transmission system according to claim 12, wherein the receiving means has an additional antenna unit for matching the reception antenna to receive FM broadcast signals of 88 MHz to 108 MHz. A transmission apparatus for frequency modulating a radio frequency together with audio signals in a high frequency region to form a radio signal transmitted wirelessly in a local transmission region, Wireless oscillation means composed of a phase-locked loop; Resonator is composed of an amplifier, a varactor diode and a crystal resonator, wherein the varactor diode is controlled by a high DC voltage to cause a small capacitance change, and is formed by the crystal resonator connected in parallel with the varactor diode. And a Q value characteristic opposite to the frequency curve. 15. The transmission apparatus according to claim 14, further comprising automatic level adjusting means for automatically adjusting the input audio signals to an optimal modulation level. 15. The transmission apparatus according to claim 14, wherein the phase locked loop uses a crystal crystal as a reference frequency. 17. The transmission apparatus according to claim 16, wherein the quartz crystal has a frequency range of 28 MHz to 86 MHz.