JP2010136121A - Wireless microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless microphone that stably operates without changing sound volume according to a channel to be used. <P>SOLUTION: The wireless microphone includes: a first oscillation circuit (13) for oscillating a first frequency for modulating a sound signal; a second oscillation circuit (14) for oscillating a second frequency for changing a transmission frequency of a radio medium; a mixing circuit (15) for mixing the first frequency and the second frequency and outputting the mixed frequency; and a filter circuit (17) for filtering a predetermined frequency from an output of the mixing circuit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wireless microphone that can be used by switching a plurality of channels, and more particularly to a wireless microphone that can be stably operated without changing the volume depending on the channel to be used.

  As a wireless microphone that converts sound into an electric signal and modulates and transmits the electric signal, a wireless microphone that can select and use an arbitrary transmission channel from a plurality of transmission channels is known (for example, , See Patent Document 1). Such a multi-channel wireless microphone has an oscillation circuit capable of switching the oscillation frequency, and can change the frequency within a predetermined range from the basic frequency, and can output an audio signal using the selected frequency. It is configured to be able to transmit.

JP 09-107296 A

  In the oscillation circuit, the range in which the oscillation frequency can be varied is from several percent to several tens of percent of the reference frequency. Therefore, if the reference frequency is not high, a band for distinguishing a plurality of transmission channels cannot be secured. In order to use a large number of transmission channels, it is necessary to increase the reference frequency. Therefore, using two oscillation circuits that oscillate at a frequency higher than the transmission frequency, the first high frequency is modulated with the audio signal, the second high frequency and the modulated first high frequency are mixed, and the filter circuit is A method of transmitting a predetermined transmission frequency by using a known method is known.

  In the conventional method, the first high frequency is varied to change the transmission frequency. For example, when the first high frequency is varied from 65 MHz to 67 MHz, the second high frequency is fixed at 62.5 MHz, and the first high frequency and the second high frequency are input to the mixing circuit, the frequency of the output signal is , 4.5 MHz (67 MHz-62.5 MHz) to 2.5 MHz (65 MHz-62.5 MHz). As described above, compared with the case of using one oscillator, the variable range of the frequency can be expanded, so that a plurality of transmission channels can be used.

  The oscillation circuit is a circuit that oscillates at a predetermined frequency in accordance with the input voltage, and ideal characteristics are so-called linear characteristics in which the oscillation frequency is proportional to the input voltage. However, the actual oscillation circuit characteristics are not linear characteristics. For example, when the input voltage is low, the oscillation frequency is lower than the ideal characteristic, and when the input voltage is high, the oscillation frequency is higher than the ideal characteristic. An error occurs that becomes higher.

  In the conventional method described above, since the transmission channel is varied by the first high frequency to be modulated, the modulation degree characteristic varies depending on the selected transmission frequency (transmission channel). Even if the audio signal is input, variations such as different output levels occur. As described above, the conventional wireless microphone has a characteristic that varies depending on the transmission channel to be used. In order to perform stable operation, it is necessary to provide an adjustment circuit for each transmission channel. .

  The present invention has been made in view of the above problems, and is a wireless microphone that can be used by switching a plurality of transmission channels, and can be stably operated without being affected by the characteristics of the oscillation circuit. The purpose is to provide a wireless microphone.

  The present invention is a wireless microphone that converts a sound wave into an electrical sound signal and transmits the sound signal via a wireless medium, and includes a first oscillation circuit that oscillates a first frequency that modulates the sound signal, and a transmission frequency of the wireless medium. A second oscillation circuit that oscillates the second frequency to be changed; a mixing circuit that mixes and outputs the first frequency and the second frequency; and a filter circuit that filters a predetermined frequency from the output of the mixing circuit. Features.

  Further, according to the present invention, in the wireless microphone, the first oscillation circuit is a fixed oscillation circuit that oscillates a preset frequency, and the second oscillation circuit is a variable that can vary the oscillation frequency within a predetermined range. It is an oscillation circuit, and the mixing circuit is a circuit that outputs a variable frequency by subtracting a fixed frequency.

  According to the present invention, in a multi-channel switching type wireless microphone, a change in volume due to a difference in channels to be used is reduced, and stable operation can be performed without having a volume adjustment function for each channel. Become. Further, according to the present invention, it becomes possible to prevent fluctuations in the modulation frequency characteristic.

  Embodiments of a wireless microphone according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a wireless microphone according to the present invention. In FIG. 1, a wireless microphone 1 includes a microphone 11 that converts sound into an electric signal, an amplifier 12 that amplifies the converted electric signal (hereinafter referred to as “audio signal”) to a predetermined level, and a reference modulated by the audio signal. A first oscillation circuit 13 that supplies a signal at a predetermined frequency and outputs a first frequency signal obtained by modulating the reference signal with an audio signal, and has a predetermined frequency for converting the frequency of the first frequency signal into a transmission frequency A signal output from a second oscillation circuit 14 for supplying a second frequency signal, a mixing circuit 15 for mixing and outputting the first frequency signal and the second frequency signal, and a signal output from a filter circuit 16 for extracting a necessary frequency are set to a predetermined level. An amplifier 17 for amplifying and an antenna 18 for transmitting the output signal are provided.

  In the wireless microphone 1, the sound input to the microphone 11 is converted into an audio signal that is an electrical signal and output, and is amplified to a predetermined level by the amplifier 12. The first oscillation circuit 13 is a fixed frequency oscillation circuit that oscillates a predetermined frequency, and is a crystal oscillation circuit, for example. In the first oscillation circuit 13, the reference signal having the fixed frequency is modulated by the audio signal input from the amplifier 12 to generate a first frequency signal, which is output to the mixing circuit 15.

  The second oscillation circuit 14 is a variable oscillation circuit that can vary the oscillation frequency within a predetermined range in order to vary the transmission frequency. For example, the second oscillation circuit 14 is a PLL oscillation circuit. The second oscillation circuit 14 can vary the frequency within a predetermined range by a transmission channel selection switch (not shown) in FIG. 1 and a control circuit that sets the second oscillation frequency by detecting the state of the selection switch. it can.

  The mixing circuit 15 mixes and outputs the first frequency signal output from the first oscillation circuit and the second frequency signal supplied from the second oscillation circuit. For example, when the first frequency is 62.5 MHz and the second frequency is variable between 65 MHz and 67 MHz, the frequency (transmission frequency) of the signal output from the mixing circuit 15 is 2.5 MHz ( A frequency variable between 65 MHz-62.5 MHz and 4.5 MHz (67 MHz-62.5 MHz) is output.

  The signal output from the mixing circuit 15 is filtered by the filter circuit 16 to obtain a signal having a predetermined frequency, amplified by the amplifier 17 and transmitted from the antenna 18, thereby operating as a wireless microphone using a predetermined transmission channel. Can be made.

According to the wireless microphone 1 having the above configuration, the frequency of the reference signal modulated by the audio signal is fixed by the first oscillation circuit, so that the modulation degree does not change depending on the transmission frequency. It is possible to obtain a wireless microphone that eliminates the disadvantages of the conventional system, such as the volume varies depending on the channel.
Note that, by using an infrared LED instead of the antenna 18, the wireless microphone according to the present invention can be an infrared wireless microphone.

It is a block diagram which shows the Example of the wireless microphone which concerns on this invention.

Explanation of symbols

11 Antenna 13 First Oscillator 14 Second Oscillator 15 Mixing Circuit 16 Filter Circuit

Claims (5)

A wireless microphone that converts sound waves into electrical audio signals and transmits them over a wireless medium,
A first oscillation circuit that oscillates a first frequency modulated by the audio signal;
A second oscillation circuit for oscillating a second frequency for changing the transmission frequency of the wireless medium;
A mixing circuit for mixing and outputting the first frequency and the second frequency;
And a filter circuit that filters a predetermined frequency from the output of the mixing circuit. The first oscillation circuit is a fixed oscillation circuit that oscillates a preset frequency.
The second oscillation circuit is a variable oscillation circuit capable of varying the oscillation frequency within a predetermined range,
The wireless microphone according to claim 1, wherein the mixing circuit is a circuit that outputs a variable frequency by subtracting a fixed frequency. The first oscillation circuit is a crystal oscillator,
2. The wireless microphone according to claim 1, wherein the second oscillation circuit is a PLL type oscillator.   The wireless microphone according to any one of claims 1 to 3, wherein the wireless medium is infrared rays.   The wireless microphone according to claim 1, wherein the wireless medium is a radio wave.

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