JPH07283750A - Wireless audio equipment - Google Patents

Abstract

PURPOSE:To improve the substantial performance of a wireless headphone stereo set. CONSTITUTION:The modulation circuits 21L and 21R convert the received audio signals L and R into the modulated signals SL and SR respectively. A detection circuit 46 detects the presence or absence of the signals L 80d R supplied to the circuits 21L and 21R, and a circuit 42 produces a signal S42 outside an audible area. When the absence of both signals L and R is detected, the signal S42 is supplied to both circuits 21L and 21R as the modulation input. Meanwhile the signal S42 is not supplied to the circuits 21L and 21R when the presence of both signals L and R is detected. For this purpose, the modulation of both signals SL and SR is controlled by the detection output S46 of the circuit 46.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless audio device such as a so-called headphone stereo.

[0002]

2. Description of the Related Art As a headphone type stereo cassette player (hereinafter referred to as "player") such as Walkman (registered trademark), a wireless system between the player and the headphone is considered.

FIG. 6 is a perspective view showing the appearance of an example of the wireless cassette player, 1 is a player and 6 is a dedicated receiver for the headphones.

Then, in the player 1, during reproduction, stereo audio signals L and R of the left and right channels are reproduced from a tape cassette (not shown), and these signals L and R are FM signals SL of a predetermined carrier frequency, Converted to SR, the signals SL and SR are transmitted to the receiver 6.

Then, in the receiver 6, the player 1
When the FM signals SL, SR from the
Audio signals L and R are demodulated from L and SR, and the signals L and R are demodulated.
Are supplied to the left and right acoustic units 7L and 7R of the headphone 7, respectively.

In this case, the receiver 6 can be half or less than a business card. Also, the distance at which the receiver 6 can be used away from the player 1 is about 1.5 m in consideration of the Radio Law.

Therefore, according to this wireless type player, for example, when listening to a cassette on a commuter train, the player 1 is put in a bag, a bag, etc., and the receiver 6 is put in a chest pocket of a jacket. , The clip can be attached to a tie or the like by using the clip, and the cord of the headphone 7 does not get in the way.

[0008]

The transmission output of the FM signals SL and SR in the wireless player 1 is regulated by the Radio Law. When the Radio Law regulates the transmission output of this type of wireless device, it must be specified that the radio wave transmitted from the target wireless device must be received and that the received electric field strength must not exceed the limit value. Therefore, the transmission output is regulated. Therefore, also in the player 1, the transmission output is designed (or adjusted) so that the reception electric field strength of the FM signals SL and SR does not exceed the limit value.

However, when the player 1 is reproducing a new, silent tape, a silent section between songs, and a leader tape portion at the beginning and end of the tape, audio signals L and R are obtained. Therefore, the FM signals SL and SR are in a non-modulated state, and as shown in FIG. 5A, the transmitted signals SL and SR have only carrier components (fC is the carrier frequency of the signals SL or SR). Therefore, in the player 1, the transmission output is designed so that the received electric field strength of the carrier component does not exceed the limit value ES.

However, if the audio signals L and R are obtained from the tape and the FM signals SL and SR have sideband components by designing in this way, as shown in FIG. 5B,
The received electric field strength of the FM signals SL and SR is lowered by a level ΔE from the limit value ES, and as a result, the reach distance of the FM signals SL and SR is disadvantaged by a distance corresponding to the level ΔE. Alternatively, even within the reachable range, the reception electric field strength decreases, which causes disadvantages in the interference characteristics and the S / N ratio of the received audio signals L and R.

The present invention is intended to solve such a problem.

[0012]

Therefore, in the present invention, when the reference numerals of the respective parts correspond to the embodiments described later, in the audio device 1 which transmits the audio signals L and R by radio waves, Signal L, R
Is supplied as a modulation input and this audio signal L, R
Circuit 2 for converting modulated signals SL and SR that become radio waves
1L, 21R and a detection circuit 4 for detecting the presence / absence of audio signals L, R supplied to the modulation circuits 21L, 21R.
6, the modulated signals SL and SR are controlled by the detection output S46 of the detection circuit 46 so that the reception electric field strength of the radio wave becomes equal between when there is no audio signal L and R and when there is audio signal. It was done.

[0013]

In the reproduction mode, the effective transmission output is increased and the transmission signal reaches a longer distance.

[0014]

1 and 2 show an example of a signal system of a wireless cassette player 1 and a dedicated receiver 6 for headphones thereof. In the player 1, 2 is a magnetic tape of a cassette, 10 is a reproducing circuit, 20 is a transmitting circuit, 31 is a tape running mechanism, 32 is a microcomputer for system control, 33 is an operation key such as a reproduction key and a stop key. is there.

In this case, although not shown, the tape running mechanism 31 has a capstan, a pinch roller, a capstan motor, a plunger, etc., and a lever or the like is triggered by the plunger, and the trigger result and the rotation of the capstan motor. The force is used to control or maintain the mechanical state of the player 1 in a stop mode, a reproduction mode, or the like.

When the play key of the operation keys 33 is pressed, the running mechanism 31 is controlled by the microcomputer 32 to set the mechanical operation mode of the player 1 to the play mode and the tape 2 is run at a constant speed to play. Head 11L,
11R reproduces the audio signals L and R of the left and right channels from the tape 2. Then, the reproduction signals L and R are reproduced equalizer amplifiers 12L and 12R → pre-emphasis circuits 13L and 13R → addition circuits 14L and 1L.
FM modulation circuits 21L and 21L through the 4R signal line.
It is supplied to R and converted into FM signals SLO and SRO.

In this case, the frequency deviation of the FM signals SLO and SRO is set to 75 kHz at a modulation factor of 100%, and the carrier frequencies fLO and fRO of the FM signals SLO and SRO are set.
Is set to be considerably lower than the transmission frequencies (carrier frequencies) fL and fR of the actual transmission signals SL and SR, for example, fLO = 11.29 MHz fRO = 11.75 MHz.

The FM signals SLO and SRO are supplied to the mixer circuits 22L and 22R, and the local oscillation circuit 23 supplies the local oscillation signal S23 for beatup to the mixer circuits 22L and 22R. The signal S23
The frequency f23 of is, for example, f23 = 64.00 MHz.

Thus, the signals SLO and SRO are converted into FM signals SL and SR whose carrier frequencies fL and fR are, for example, fL = fLO + f23 = 75.29 MHz fR = fRO + f23 = 75.75 MHz by the signal S23 in the mixer circuits 22L and 22R. Frequency converted.

The FM signals SL, SR are converted into bandpass filters 24L, 24R and a power amplifier 25.
It is supplied to the antenna 26 through L and 25R, and the receiver 6
Sent to.

On the other hand, in the receiver 6, the FM signals SL and SR transmitted from the player 1 are received by the antenna 61, and these signals SL and SR are received by the antenna tuning circuit 6
2 and the high frequency amplifier 63 to the mixer circuit 64, and the local oscillator circuit 65 to the mixer circuit 6
4 is supplied with the local oscillation signal S65. In this case, the signal S
The frequency f65 of 65 is, for example, f65 = 65.05 MHz.

Thus, the FM signals SL and SR are supplied to the mixer circuit 64 by the signal S65 so that the frequencies fLI and fRI can be obtained.
Is converted into intermediate frequency signals SLI and SRI of fLI = fL-f65 = 10.24 MHz fRI = fR + f65 = 10.70 MHz, for example.

The signals SLI and SRI are supplied to the FM demodulation circuits 68L and 68R through the intermediate frequency filters 66L and 66R and the amplifiers 67L and 67R to demodulate the audio signals L and R, and the signals L and R are decoded. Emphasis circuits 69L and 69R and an output amplifier 71L,
71R acoustic units 7L, 7R of headphones 7
Is supplied to each.

Further, in order to set the received electric field strength in the reproducing mode of the player 1 to the limit value ES, the player 1 is configured as follows in this example.

That is, generally, the processing contents of the microcomputer 32 are not so complicated, and the processing speed is not required to be so high. The original oscillation frequency of a so-called digital timepiece is 32.768 kHz, but the crystal oscillator for oscillation is mass-produced at low cost. For these reasons, in the player 1, the clock frequency of the microcomputer 32 is 32.768 kHz.

Therefore, the clock signal SCK is taken out from the microcomputer 32, and the clock signal SCK is supplied to the multiplication circuit 42 through the buffer amplifier 41, and the clock signal SCK is, for example, 3
The signal S42 having the double frequency is multiplied, and this signal S42 is supplied to the switch circuit 43. In this case, the clock signal S
Since CK is a rectangular wave signal and has a harmonic component, the multiplier circuit 42 can be configured by a bandpass filter having a passband at the frequency of the signal S42 and an amplifier, and the characteristics of the bandpass filter. Need not be so strict.

Further, the reproduction equalizer amplifiers 12L, 1
The signals L and R from 2R are added to the adder circuit 44 and the amplifier 4
5 is supplied to the detection circuit 46, and a detection signal S46 indicating the presence or absence of the audio signals L and R is taken out. That is, the detection signal S46 which is "1" when at least one of the audio signals L and R is above a predetermined level and is "0" when both of the signals L and R are below a predetermined level is taken out.

In this case, the time constant capacitor 47 is connected to the detection circuit 46, and the detection signal S46 immediately becomes "1" when at least one of the signals L and R exceeds a predetermined level. When both the signals L and R fall below a predetermined level, the signal is set to "0" after a predetermined time.

The detection signal S46 is supplied to the switch circuit 43 as its control signal. When S46 = "0", the switch circuit 43 is turned on and the signal S42 is taken out and taken out from the switch circuit 43. Signal S42
Is supplied to the adder circuits 14L and 14R.

With such a configuration, when the player 1 is in the reproduction mode, the audio signals L and R are obtained, so that S46 = "1" and the switch circuit 43 is off. Therefore, as described above, the FM signals SL and SR are modulated by the audio signals L and R and transmitted to the receiver 6.

However, even when the player 1 is in the reproduction mode, an audio signal is generated as in the case where the tape 2 is silent, the silent section of the tape 2 is reproduced, or the leader tape portion is reproduced. When L and R cannot be obtained, S46 = "0" and the switch circuit 43 is turned on.

Therefore, in this case, the signal S42 is
Since it is supplied as the modulation signal to the FM modulation circuits 21L and 21R through the switch circuit 43 and the addition circuits 14L and 14R, the FM signals SL and SR are modulated by the signal S42 and transmitted, and the FM signals SL and SR
Has not only the carrier component but also the sideband component due to the signal S42 as shown in FIG. 3A, for example.

At this time, as shown in FIG. 3A,
The received electric field strength of the FM signals SL and SR in this state is
The transmission output can be designed (or adjusted) so as to be equal to the limit value ES.

Then, the audio signal L from the tape 2 is
When R is obtained, the FM signals SL and SR are similarly modulated by the audio signals L and R, and have sideband components in addition to the carrier components, as shown in FIG. 3B. The received electric field strengths of SL and SR are almost equal to the limit value ES.

That is, the FM signals SL, SR in the state where the audio signals L, R are not obtained and the FM signals SL, SR in the obtained state are the signals in the modulated state, and the audio signals L, R The received electric field strength of the FM signals SL and SR in the state that the
Since it is set to S, the received electric field strengths of the FM signals SL and SR in the state where the audio signals L and R are obtained are also
It is almost equal to the limit value ES.

In this way, according to the player 1, the actual received electric field strength in the reproduction mode can be set to the limit value ES, so that the reaching distance of the FM signals SL and SR can be lengthened. Alternatively, even within the reachable range, the received electric field strength becomes high, so that the interference characteristic and the S / N ratio of the received audio signals L and R are advantageous.

According to the experiment, the received electric field strength in the reproduction mode can be increased by about 5 to 6 dB, and thus the reach distance of the FM signals SL and SR can be doubled. In addition, even if the transmission output is set so that the reception electric field strength of the FM signals SL and SR is about 3 dB lower than the limit value ES when the audio signals L and R are not obtained, the audio signal Since the received electric field strength when L and R are obtained can be increased by about 3 dB, the reach distance of the FM signals SL and SR can be expanded by about 1.4 times.

Further, since the switch circuit 43 is controlled according to the presence or absence of the audio signals L and R, the received electric field strength of the FM signals SL and SR does not exceed the limit value ES. That is, a signal indicating the operation mode of the player 1 is taken out from the microcomputer 32, and in the case other than the reproduction mode by this signal, the switch circuit 43 is turned on and the signal S
42 can also be supplied to the modulation circuits 21L and 21R.

However, in such a case, when the ordinary tape 2 is reproduced, the sideband components are generated in the FM signals SL and SR by the audio signals L and R, and the received electric field strength exceeds the limit value ES. Even if there is no sound, the audio signals L and R cannot be obtained when playing a silent tape, a silent section of the tape 2, a leader tape portion, etc., so that the FM signals SL and SR are only carrier components and the received electric field strength Exceeds the limit value ES and violates the Radio Law.

However, in the above-mentioned player 1, the switch circuit 4 is used according to the presence / absence of the audio signals L and R.
Since 3 is controlled, by playing a silent tape, a silent section of tape 2, a leader tape part, etc.,
When the audio signals L and R cannot be obtained, the signal S42
Is supplied to the modulation circuits 21L and 21R instead, so that the received electric field strength of the FM signals SL and SR does not exceed the limit value ES.

FIG. 4 shows another example of the present invention. In this example, the reception electric field strength when the audio signals L and R are obtained by controlling the transmission output itself of the FM signals SL and SR. This is the case where the limit value ES is set.

That is, in this example, the audio signals L and R from the pre-emphasis circuits 13L and 13R are used.
However, the modulation circuits 21L and 21R without passing through the adding circuit
Is supplied to.

In the power amplifier 25L, Q21
Indicates the transistor of the output stage, and the transistor Q21 has its emitter grounded, and the resistor R21 is connected between its emitter and ground. The collector and emitter of the transistor Q22 are connected in parallel to the resistor R21, and the detection signal S46 of the detection circuit 46 is supplied to the base thereof. Further, although not shown, the power amplifier 25R is also configured similarly to the power amplifier 25L and is supplied with the signal S46.

According to this structure, when the audio signals L and R cannot be obtained, S46 = "0" and the transistor Q22 is off. Therefore, the transistor R21 is subjected to current negative feedback due to the resistor R21, and its gain is reduced, so that the transmission output of the FM signal SL is reduced to a predetermined value, and the reception electric field strength becomes the limit value ES. Similarly, the received electric field strength of the FM signal SR is also the limit value ES
Becomes

However, when the audio signals L and R are obtained, S46 = "1" and the transistor Q21 is turned on. Therefore, the transistor Q21 does not receive the current negative feedback by the resistor R21 and its gain increases, so that the transmission output of the FM signal SL increases to a predetermined value and the FM signal SL has a sideband component. Even
The received electric field strength increases to the limit value ES. Similarly, the received electric field strength of the FM signal SR also increases to the limit value ES.

Therefore, also in this example, the FM signals SL, SR when the audio signals L, R are obtained
Can reach longer distances. Alternatively, even within the reachable range, the received electric field strength becomes high, so that the interference characteristic and the S / N ratio of the received audio signals L and R are advantageous.

Further, since the size of the transmission output is controlled according to the presence / absence of the audio signals L and R, the audio signals L and R are reproduced by reproducing the silent tape, the silent section of the tape 2, the leader tape portion, and the like. Even when R is not obtained, the received electric field strength of the FM signals SL and SR does not exceed the limit value ES.

In the above description, the present invention is applied to a headphone type stereo cassette player, but the present invention is also applied to a player using a CD, MD, DAT, DCC or the like as a recording medium. Can be applied.

Further, in the above description, the signal 42 for modulation is used.
Was obtained by multiplying the clock signal SCK of the microcomputer 32, but the signal S42 can be formed by another circuit as long as it is a signal having a frequency outside the audible band.

[0050]

According to the present invention, since the actual received electric field strength in the reproduction mode can be set to the limit value ES, the reach distance of the FM signals SL and SR can be lengthened. Alternatively, even within the reachable range, the received electric field strength becomes high, so that the interference characteristic and the S / N ratio of the received audio signals L and R are advantageous. According to the experiment, the received electric field strength in the reproduction mode can be increased by about 5 to 6 dB, and thus the reach distance of the FM signals SL and SR can be doubled.

Further, when the audio signals L and R cannot be obtained by reproducing the silent tape, the silent section of the tape 2, the leader tape portion, etc., the signal S42 is supplied to the modulation circuits 21L and 21R instead. Because it is done, F
The received electric field strength of the M signals SL and SR does not exceed the limit value ES, and does not violate the Radio Law.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of the present invention.

FIG. 2 is a system diagram showing an example of a receiver that can be used in the player of FIG.

FIG. 3 is a diagram showing a frequency spectrum of a transmission signal of the player of FIG.

FIG. 4 is a system diagram showing another example of the present invention.

FIG. 5 is a diagram showing a frequency spectrum of a conventional example.

FIG. 6 is a perspective view for explaining the present invention.

[Explanation of symbols]

 1 headphone type stereo cassette player 2 magnetic tape 6 dedicated receiver 7 headphone 10 reproduction circuit 20 transmission circuit 21L, 21R FM demodulation circuit 22L, 22R mixer circuit 23 local oscillation circuit 24L, 24R bandpass filter 25L, 25R power amplifier 31 tape running Mechanism 32 Microcomputer 42 Multiplier circuit 43 Switch circuit 46 Detection circuit

Claims (5)

[Claims] 1. An audio device for transmitting an audio signal by radio waves, wherein the audio signal is supplied as a modulation input, and a modulation circuit for converting the audio signal into a modulated signal which becomes the radio wave, and the modulation circuit. A detection circuit for detecting the presence or absence of the audio signal supplied to the above, and by the detection output of the detection circuit so that the received electric field strength of the radio wave becomes equal when there is no audio signal and when there is. A wireless audio device that controls the modulated signal. 2. The wireless audio device according to claim 1, further comprising a circuit that forms a signal outside the audible band, and when the audio signal is absent, modulates the signal outside the audible band into the modulation circuit. When the audio signal is supplied as an input and the audio signal is present, the modulation of the modulated signal is controlled by the detection output of the detection circuit so that the signal outside the audible band is not supplied to the modulation circuit as the modulation input. Wireless audio equipment. 3. The wireless audio device according to claim 1, further comprising a circuit for controlling a transmission output of the modulated signal, wherein the electric field for receiving the radio wave is present when the audio signal is absent and when the audio signal is absent. A wireless audio device in which the transmission output of the modulated signal is controlled by the detection output of the detection circuit so that the intensities become equal. 4. The wireless audio device according to claim 1, 2, or 3, wherein the modulation circuit is an FM modulation circuit. 5. The wireless audio apparatus according to claim 1, 2, or 4, wherein the signal outside the audible band is formed from a clock signal of a microcomputer for system control. Audio equipment.