Transmitting and receiving apparatus for a radio headphone

A transmitter and receiving apparatus from a headphone, comprising a demodulating circuit for demodulating a received broadcasting signal into multi-channel data, a modulating circuit for frequency-modulating each channel of the multi-channel data with a different carrier frequency, said carrier frequencies being selectable by the user to avoid local interference, and a transmitting circuit for transmitting output data from said modulating circuit externally. There is also provided a receiver for a radio headphone, comprising a data receiving circuit for receiving data transmitted from an external transmitting circuit, a demodulator for dividing the data received by said data receiving circuit into separate frequency channels, an envelope detecting circuit for detecting envelopes of respective channel data, and an output circuit for outputting an output signal from said envelope detecting circuit as an analog sound signal so as to allow a user to listen to noiseless sound through a headphone.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates in general to a radio transmitting and 
receiving apparatus, and more particularly to a transmitting and receiving 
apparatus for a headphone of the digital type. 
2. Description of the Prior Art 
With reference to FIG. 1, there is shown a block diagram of a conventional 
transmitting apparatus for a headphone of the analog type. The illustrated 
transmitting apparatus comprises a first amplifying circuit 33 including 
amplifiers 31 and 32 for amplifying respectively a left sound signal L/S 
and a right sound signal R/S from a headphone output of a television set 
or a radio set by a predetermined amplification degree, a frequency 
modulating circuit 35 including frequency modulators 35a and 35b for 
frequency-modulating respective output signals from the amplifiers 31 and 
32 in the first amplifying circuit 33, a first band-pass filtering circuit 
36 including band-pass filters 36a and 36b for filtering respective output 
signals from the frequency modulators 35a and 35b in the frequency 
modulating circuit 35 to pass only frequency components of desired band 
width, and a transmitting circuit 37 including a transistor Q4 and a 
light-emitting diode D5, for transmitting output signals from the 
band-pass filters 36a and 36b in the first band-pas filtering circuit 36 
with infrared rays carrying the signals. 
With reference to FIG. 2, there is shown a block diagram of a conventional 
receiving apparatus for a headphone of the analog type. The illustrated 
transmitting apparatus comprises a circuit 38 including a transistor Q5 
and a light-receiving diode D8, for receiving light signals transmitted 
from the transmitting circuit 37 in the transmitting apparatus and 
amplifying the received signals by a predetermined amplification degree, a 
second band-pass filtering circuit 41 including band-pass filters 39 and 
40 for filtering respective output signals from the receiving circuit 38 
to pass only frequency components of desired band width, a demodulating 
circuit 44 including demodulators 42 and 43 for demodulating respective 
output signals from the band-pass filters 39 and 40 in the second 
band-pass filtering circuit 41, a second amplifying circuit 47 including 
amplifiers 45 and 46 for amplifying respective output signals from the 
demodulators 42 and 43 in the demodulating circuit 44 by a predetermined 
amplification degree, and a sound output circuit 52 including a switch 
SW1, resistors R3 and R4, power amplifiers 48 and 49 and headphone 
speakers 50 and 52, for outputting analog sound signals from the 
amplifiers 45 and 46 in the second amplifying circuit 47 as sound signals. 
The operation of the conventional transmitting and receiving apparatus for 
a headphone of the analog type which is constructed as mentioned above 
will be described. 
Generally, the left sound signal L/S and the right sound signal R/S through 
the headphone output of the television set or radio set are weak in level. 
For this reason, in the transmitting apparatus, the left sound signal L/S 
and the right sound signal R/S are amplified by a predetermined 
amplification degree, respectively, by the amplifiers 31 and 32 in the 
first amplifying circuit 33. These amplified signals from the amplifiers 
31 and 32 are frequency-modulated, respectively, by the frequency 
modulators 35a and 35b in the frequency-modulating circuit 35 and the 
frequency-modulated signals from the frequency modulators 35a and 35b are 
then applied to the band-pass filters 36a and 36b in the first band-pass 
filtering circuit 36. 
Upon receiving the frequency-modulated signals from the frequency 
modulators 35a and 35b, the band-pass filters 36a and 36b filter, 
respectively, the received signals to pass only frequency components of 
desired band width. Then, the output signals from the band-pass filters 
36a and 36b are transmitted to the light-receiving diode D8 in the 
receiving circuit 38 in the receiving apparatus through the light-emitting 
diode D5 in the transmitting circuit 37. 
At this time, a diode D7 emits a light signal which is indicative of signal 
transmission. An LED driver 34 functions to drive the diode D7. 
In the receiving apparatus, the signals inputted through the 
light-receiving diode D8 in the receiving circuit 38 are amplified, 
respectively, by a predetermined amplification degree by the transistor Q5 
in the receiving circuit 38. Then, the band-pass filters 39 and 40 in the 
second band-pass filtering circuit 41 filter the amplified signals, 
respectively, from the receiving circuit 38 to pass only frequency 
components of desired band width. In the demodulating circuit 44, the 
demodulators 42 and 43 demodulate the output signals from the band-pass 
filters 39 and 40, respectively. Then, the demodulated signals are 
amplified by the amplifiers 45 and 46 in the second amplifying circuit 47. 
In the second amplifying circuit 47, the resistor R1 and the capacitor C1, 
and the resistor R2 and the capacitor C2 operate, respectively, as 
low-pass filters. In the sound output circuit 52, the amplified left and 
right signals from the amplifiers 45 and 46 are inputted to the power 
amplifiers 48 and 49 in mono or stereo in accordance with a selection of 
the switch SW1. Upon receiving the amplified left and right signals from 
the amplifiers 45 and 46, the power amplifiers 48 and 49 amplify the 
received signals, respectively, by a given amount and output the amplified 
signals as sound signals through the headphone speakers 50 and 51. 
However, the conventional transmitting and receiving apparatus for a 
headphone of the analog type has a disadvantage, in that the apparatus is 
susceptible to noise. For this reason, when the apparatus transmits the 
signals utilizing an infrared ray, a malfunction thereof may occur 
according to a direction of the TV set or radio set. Also, there may occur 
interference due to an infrared ray signal from other systems. 
SUMMARY OF THE INVENTION 
Therefore, the present invention has been made in view of the above 
problem, and it is an object of the present invention to provide 
transmitting and receiving apparatus for a headphone of the digital type, 
which processes audio signals from a television set or radio set in a 
frequency modulation (FM) manner, transmits the FM processed audio signals 
by wireless in a digital transmission manner and receives the transmitted 
signals by wireless in a digital reception manner. 
In accordance with one aspect of the present invention, there is provided a 
transmitting and receiving apparatus for a headphone, comprising: 
transmitting means for demodulating a received broadcast audio signal into 
a digital signal, frequency-modulating the digital signal in accordance 
with predetermined carrier frequencies corresponding to contents of 
channel data, and transmitting the frequency-modulated digital signal with 
an infrared ray carrying the signal; and receiving means for receiving the 
signal transmitted from said transmitting means, demodulating the received 
signal into a digital signal, converting the demodulated digital signal 
into an analog signal, and transducing/outputting the analog signal as 
sound. 
In accordance with another aspect of the present invention, there is 
provided a transmitter for a headphone, comprising: demodulating means for 
demodulating a received broadcast audio signal into a digital signal, 
dividing the digital signal into three-channel data; namely, sound data, 
data for synchronization of the sound data, and data indicative of whether 
the sound data is in mono or in stereo; modulating means for 
frequency-modulating the three-channel data from said demodulating means 
in accordance with predetermined carrier frequencies corresponding to the 
three-channel data; and transmitting means for transmitting output data 
from said modulating means externally. 
In accordance with still another aspect of the present invention, there is 
provided a receiver for a headphone, comprising: data receiving means for 
receiving data transmitted from the transmitting means; envelope detecting 
means for dividing the data received by said data receiving means into 
data by channel and detecting envelopes of respective channel data; and 
output means for outputting an output signal from said envelope detecting 
means as an analog sound signal.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
First, a construction of transmitting and receiving apparatus for a 
headphone of the digital type in accordance with the present invention 
will be described with reference to FIGS. 3 through 5. 
With reference to FIG. 3, there is shown a block diagram of a transmitting 
apparatus for a headphone of the digital type in accordance with the 
present invention. As shown in this drawing, the transmitting apparatus of 
the present invention comprises: a demodulating circuit 21 including a 
quadrature phase shift keying (QPSK) demodulator 1 and a sound demodulator 
2, for receiving a broadcast sound signal transmitted in a QPSK 
transmission manner, demodulating the received broadcast signal into a 
digital signal and dividing the digital signal three-channel data, a first 
sound output circuit 22 including a D/A converter 3, a first amplifier 4 
and a speaker 5, respectively, for converting the three-channel data from 
the demodulating circuit 21 into an analog signal, amplifying the analog 
signal by a predetermined amplification degree and outputting the 
amplified signal through the speaker 5; a frequency modulating circuit 23 
including carrier modulators 6a through 6c and frequency oscillators F1 
through F3, for frequency-modulating, respectively, the three-channel data 
from the demodulating circuit 21; an amplifying circuit 24 including 
amplifiers 7a through 7c, for amplifying output signals from the frequency 
modulating circuit 23, respectively, to a predetermined transmission 
level; and a transmitting circuit 25 including infrared transmitters 8a 
through 8c having transistors Q1 to Q3 and light-emitting diodes D1 to D3, 
respectively, for transmitting output signals from the amplifying circuit 
24 with infrared rays carrying the signals. 
With reference to FIG. 4, there is shown a block diagram of a receiving 
apparatus for a headphone of the digital type in accordance with the 
present invention. As shown in this drawing, the receiving apparatus of 
the present invention comprises a receiving circuit 26 including a 
light-receiving diode D4 and a preamplifier 9, for receiving signals 
transmitted from the transmitting circuit 25 in the transmitting apparatus 
and amplifying the received signals by a predetermined amount, a band-pass 
filtering circuit 27 including band-pass filters 10a through 10c for 
filtering, respectively, output signals from the receiving circuit 26 to 
pass only frequency components of desired band width corresponding to 
respective channel data, an envelope detecting circuit 28 including 
envelope detectors 11a through 11c, for detecting envelopes of respective 
channel data from output signals from the band-pass filtering circuit 27, 
a D/A converting circuit 12 for converting output signals from the 
envelope detecting circuit 28 into analog sound signals, and a second 
sound output circuit 29 including power amplifiers 13a and 13b and 
speakers 14a and 14b, for amplifying analog signals from the D/A 
converting circuit 12, respectively, by a predetermined amount and 
outputting the amplified signals, respectively, through the speakers 14a 
and 14b. 
With reference to FIG. 5, there is shown a block diagram of the D/A 
converting circuit 12 in the receiving apparatus. The D/A converting 
circuit 12 includes a timing controller 15 for controlling timing of an 
output signal from the envelope detecting circuit 28, a digital data latch 
16 for latching an output signal from the timing controller 15, a right 
channel data latch 17 for latching right channel data of an output signal 
from the digital data latch 16, a left channel data latch 18 for latching 
left channel data of the output signal from the digital data latch 16, a 
D/A converter 12a for converting digital data from the left channel data 
latch 18 into the left analog sound signal, and a D/A converter 12b for 
converting digital data from the right channel data latch 17 into the 
right analog sound signal. 
Now, the operation of the transmitting and receiving apparatus for a 
headphone of the digital type with the above-mentioned construction in 
accordance with the present invention will be described in detail with 
reference to FIG. 6. 
First, when the television set receives a digital audio signal SO 
transmitted in the QPSK transmission manner (digital transmission manner) 
from a broadcasting station, the digital audio signal SO is demodulated 
into a digital signal by the QPSK demodulator 1 in the demodulating 
circuit 21. The digital signal from the QPSK demodulator 1 is demodulated 
into digital sound data S1, timing data S2 and digital channel information 
data S3 by the sound demodulator 2 in the demodulating circuit 21. 
In first sound output circuit 22, the D/A converter 3 converts the digital 
sound data S1, timing data S2 and digital channel information data S3 from 
the demodulating circuit 21 into an analog signal. Then, the analog signal 
from the D/A converter 3 is amplified to an aural sound level by the first 
amplifier 4 and the amplified signal is outputted as a sound signal 
through the speaker 5 in the television set. 
As shown in FIGS. 6a through 6c, the digital sound data S1 are sound data 
values transmitted from the broadcasting station, the timing data S2 is 
clock data for synchronization of the digital sound data S1, and the 
digital channel information data S3 indicates whether the digital sound 
data S1 is a mono signal or a stereo signal. 
Also, the digital sound data S1, timing data S2 and digital channel 
information data S3 from the demodulating circuit 21 are inputted to the 
frequency modulating circuit 23. In the frequency modulating circuit 23, 
the digital sound data S1, timing data S2 and digital channel information 
data S3 are frequency-modulated, respectively, by carrier modulators 6a 
through 6c in accordance with carrier frequencies from the frequency 
oscillators F1 through F3, as shown in FIG. 6d. Typically, in the carrier 
modulators, the user can directly adjust the frequency oscillators F1 
through F3 to vary the modulating frequencies. For this reason, there can 
be prevented interference due to infrared ray signals from other systems. 
Next, the digital sound data S1, timing data S2 and digital channel 
information data S3 from the frequency modulating circuit 23 are 
amplified, respectively, to a predetermined transmission level by the 
amplifiers 7a through 7c in the amplifying circuit 24. Then, the amplified 
data from the amplifying circuit 24 is transmitted to the receiving 
apparatus with infrared rays carrying the data by the infrared 
transmitters 8a through 8c in the transmitting circuit 25. 
In the receiving apparatus, the receiving circuit 26 receives the digital 
sound data S1, timing data S2 and digital channel information data S3 
transmitted from the transmitting circuit 25 in the transmitting apparatus 
by the light-receiving diode D4 therein and amplifies the received data by 
a predetermined amount by the preamplifier 9 therein. The amplified signal 
from the receiving circuit 26 is applied to the band-pass filtering 
circuit 27. 
Upon receiving the amplified signal from the receiving circuit 26, the 
band-pass filters 10a through 10c in the band-pass filtering circuit 27 
filter, respectively, the amplified signal from the receiving circuit 26 
to pass only frequency components of desired band width corresponding to 
the digital sound data S1, timing data S2 and digital channel information 
data S3. Then, the envelope detectors 11a through 11c in the envelope 
detecting circuit 28 detect envelopes of respective corresponding data, 
i.e., the digital sound data S1, timing data S2 and digital channel 
information data S3 from the output signals from the band-pass filtering 
circuit 27 and output the detected envelopes of respective data to the D/A 
converting circuit 12. 
The D/A converting circuit 12 converts the detected envelopes of the 
digital sound data S1, timing data S2 and digital channel information data 
S3 from the envelope detecting circuit 28 into analog sound signals and 
outputs the analog sound signals to the second sound output circuit 29. 
Then, in the second aural sound output circuit 29, the analog sound 
signals from the D/A converter 12 are amplified, respectively, to a sound 
level by the power amplifiers 13a and 13b and the amplified signals are 
outputted as sound signals through the speakers 14a and 14b. 
Referring again to FIG. 5, upon receiving the digital sound data S1 and the 
timing data S2, the timing controller 15 in the D/A converter 12 controls 
a timing of the digital sound data S1 synchronously with the timing data 
S2. Then, the digital sound data S1 from the timing controller 15 is 
latched into the digital data latch 16. The digital sound data S1 in the 
digital data latch 16 is then latched into the left channel data latch 18 
or the right channel data latch 17 or both of them in accordance with a 
content of the digital channel information data S3. Then, the D/A 
converter 12a converts the digital data from the left channel data latch 
18 into the left analog sound signal S4 and the D/A converter 12b converts 
the digital data from the right channel data latch 17 into the right 
analog sound signal S5. These analog sound signals S4 and S5 are applied 
to the second sound output circuit 29. 
As hereinbefore described, in accordance with the present invention, there 
is provided a transmitting and receiving apparatus for a headphone of the 
digital type, which processes audio signals from the television set or 
radio set in a frequency modulation (FM) manner, transmits the FM 
processed signals by wireless in a digital transmission manner and 
receives the signals by wireless in a digital reception manner. Therefore, 
the user can listen to noiseless sound through a headphone. Also, since 
the user can directly adjust the modulating frequencies, there can be 
prevented an interference due to infrared ray signals from other systems. 
Although the preferred embodiments of the present invention have been 
disclosed for illustrative purposes, those skilled in the art will 
appreciate that various modifications, additions and substitutions are 
possible, without departing from the scope and spirit of the invention as 
disclosed in the accompanying claims.