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3 · Patent applicant 4 · Agent 0160 [Phase] Japan Patent Office 0 JP-A-51-573030 Published
Japan. (1976) 6.29 specification Title of the invention Demodulation circuit of 4-channel stereo
composite signal 4-channel stereo signal is matrixed and the first subcarrier of a frequency
higher than the band is amplitude modulated with the second matrix signal The second channel
signal, the third channel signal obtained by amplitude-modulating the second subcarrier
orthogonal to the first subcarrier with the fifth matrix signal, and the third subcarrier having a
frequency twice that of the first subcarrier In the circuit for performing gold demodulation of the
above four channel stereo signal from a composite signal consisting of a fourth channel signal
amplitude-modulated by four 1 trix signals and a pilot signal of the rod frequency of the first
subcarrier frequency First to fourth switching circuits and fifth to eighth switching circuits, and
the first to fourth switching circuits are each provided with the first to fourth switching circuits.
The first to fourth switching signals repetitively and phase-shifted are sequentially supplied in a
cycle of the carrier wave, and the first to fourth switching signals are inverted in phase to be
supplied to the fifth to eighth switching circuits respectively The phase inversion circuit and
the accumulator are provided on the input side or the output side of the fifth to eighth switching
circuits, and the outputs of the first to fourth switching circuits and the fifth to eighth switching
circuits are The second, third, and fourth matrix IJ signals are obtained by combining the
outputs, and the first, second, and fourth matrix signals obtained from the combined signal are
matrixed. And a demodulation circuit for a 4-channel stereo Q composite signal adapted to obtain
the 4-channel stereo signal.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a demodulation
circuit for a four channel stereo composite signal. On the other hand, assuming that the signals
corresponding to the left rear, right front, and right rear sounds are respectively LFLBRFRB, the
4-channel stereo synthesized signal f '(t) is frequency multiplexed as shown by, for example, the
following equation EndPage: 1. The first, second, third and fourth matrix signals A-D are
represented by A = (LF + LB) + CRF + RB) B = (LF + LB)-(RF + RB) C = (LF). -LB) + (RF-RB) D "" (LFLB)-(RF-RB)? = 2? Ff ˜ The band of pilot signals A to D is 50 Hz to 15 kHz. The composite signal
to be cut is demodulated by the configuration shown in FIG. In FIG. 2, (1) shows the input
terminal to which the composite signal f (t) obtained by receiving and detecting the signal by the
FM receiver is supplied, and (2) shows the switching signal 51 (t) from the signal f (t). It is a
switching signal formation circuit which forms ˜ S4H>. Each of the switching signals 5l (t) to 54
(t) has a deity factor of 25 C%) as shown in (3) and FIG. 3, and a repetition period T of (1 #) It is a
pulse signal of amplitude wave which shifted sequentially. Therefore, the switching signals 4St (t)
to 54 (t) are as follows if expanded into Fourier series. 11, 11 51 (t) = -10-smωt +-cosωt +-3 [12
(1) t + ...-4ππI11. 5z (t) = = + 5ift omega i C-CclS omega 13112 (11t + "" 4 π π π 5s (t) =--8 tn
omega t--eO 3 omega t +-5 i II 2 omega t +---. -Smz ωt + · · · In FIG. 2, (19 to (I4) show a switching
circuit to which the combined signal f (t) is supplied, and the switching circuits (Ill to I each have
a switching signal 5t (t) to 54 (t). Is supplied. Q + to 15 indicates a switching circuit in which the
composite signal f '(t) is supplied via the phase inverting amplifier (3) and the attenuator (4). If
the attenuation ratio of the attenuator (4) is assumed to be α for simplicity of the phase
inversion amplifier (3) and the attenuation ratio of the attenuator (4) is α, (4) the human power
signal for the switching circuits a9 to + IEO is -αfD) Become. Further, in the switching circuit
151-Ge, as is clear from the switching signal form in which each of the switching signals 5l (t) to
54 (t) passes through the inverters (21) to e4, 5l (t) = 1-5x (T)
Assuming that the outputs of the above-described switching circuit αnS− 鵠 are 01 to e8, these
outputs are as follows. e1 = f (t) x5t (t) e2 = f (t) x5z (t) es = f (s * 謁 (1) e4 = f (t) 'x84 (1) es = -af
(seasonal xSt (t) ) =-Af (t) 'x (1-8t (t)) e6 = -ccf (t) x5z (t) =-ctf (t) l * (1-8s (t)) er = -czf (t) ) 'XSa (t)
=-. Alpha.r (t) x (1-8s (1) e'8 "-. Alpha.fCt>' X54 (t) xs: =-af (t) X (1-84 (t)). Then, the outputs e1
and e5 of the switching circuit are added (5). Arithmetic circuit 01) K is supplied, the outputs e2
and e6 are supplied to the adder circuit G2, the outputs e3 and e7 are supplied to the adder
circuit-, and the outputs e4 and @ $ are supplied to the adder circuit-. Among the outputs e9 to
e12 of the adding circuits (31) to 曽, the output e9 is supplied to the adding circuit (d), and the
output elloall 1512 is supplied to each of the adding circuits (6). In this case, the output eis @ 14
elB of the adding circuit (6)-(good) becomes the matrix signal BOD by selecting the attenuation
ratio α. This will be described by taking the signal B as an example, the output C9 of the adder
circuit ell) is es−e1 + e5−f (t) (51 (t) −CL (l−81 (t)) ′) = f (t) It becomes "L + alpha) 51 (t)alpha). Here, if (α = bar), e9−β (s + c + D) EndPage: 2. Similarly, the output elO of the adder
circuit C32 is elQ: β (B-0-D). Therefore, the addable output e13 becomes e13 = e9 + elo: 2β-B,
and only the second matrix signal B is obtained. The third matrix signal C and the fourth matrix
signal are also obtained in the same manner. Therefore, these second to fourth −f) +7 signals B
to D and the first matrix signal A separated from the combined signal f (t) by the low pass filter
(5) are formed into a matrix circuit (6) By supplying, four-channel stereo signals LF, LB, RB, RF
can be obtained at the output. FIG. 5 is one connection example of the portion forming the matrix
signal B in the embodiment of the present invention described above, and in FIG. 5-represents a
variable resistor corresponding to the attenuator (4), (2a) and (2b) are terminals to which the
switching signals 51 (t) and 82 (t) are given from the switching signal forming circuit (2). The
switching signal St (t) is applied to the base of the transistor ring (switching circuit αυ) and is
applied to the base of the transistor (switching circuit α9) after being phase-inverted by the
transistor (in). .
Similarly, the switching signal 8g (t) is provided to the base of the transistor t4 (switching circuit
(12), and is phase-inverted by the transistor .pi. The composite signal f '(t) from the input
terminal (1) is supplied to the emitter of the transistor Q (2) through the transistor (d) operation,
and the phase inversion amplification is applied to the emitter of the transistor (d) The combined
signal -.alpha.f (t) through the reservoir (3) and the variable resistor is supplied via the transistor
tI force. Then, the output terminals of the switching circuits are added to the output terminal (−)
by connecting the rector to the load resistor (d) of the transistor f4 (d) to t4 (4), and only the
matrix signal B is obtained. Be The circuits for forming the other matrix signals C and D can be
configured as in FIG. According to the present invention described above, since the matrix signals
81C and 81D of the subchannels (second, third and fourth channels) can be detected
independently, even if the level fluctuation of the subchannels occurs, It can be completely
corrected. In general, the switching demodulation method has the advantage that the circuit
configuration is simplified as compared to the frequency division rear cylinder method, but since
the matrix signal of the subchannel can not be detected, correction is made when the level
fluctuation of the subchannel occurs. There is a drawback that it is difficult to adjust the
separation. Therefore, according to the present invention, the level fluctuation of the sub-channel
can be easily and completely corrected by inserting the level adjusters between the adder circuits
(6) to (10) and the matrix circuit (6). Can. Also, when receiving 4-channel stereo broadcasting,
when weak antenna input, remove the sub-channels of the S / H bad matrix signal and obtain 4channel stereo signal from the matrix signals A, B and O to reproduce According to the invention,
the above-mentioned reception and reproduction is facilitated by providing a manual or
automatic switch circuit between the output side of the adder circuit and the matrix circuit (6)
and IQ). And there is no need to provide a filter for removing the signal DI) subchannel, thereby
avoiding degradation of the phase characteristic. The present invention is applicable not only to
the case where the channel of the matrix signal is DSB modulated but also to the case where it is
VSB or SOB modulated.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is the frequency spectrum of a 4-channel stereo
composite signal, FIG. 2 is a system diagram of an embodiment of the present invention, FIGS. 3
and 4 are waveform diagrams of switching signals, and FIG. , FIG. + Is a partial connection
diagram of FIG. (1) is an input terminal of the synthesized signal, (2) is a switching signal forming
circuit, (3) is a phase inversion amplifier, (4) is an attenuator, (6) is a matrix circuit, I to li sand is
a switching circuit It is. Patent applicant Sony Corporation Agent 9 Fujitsu nr @ EndPage: 3
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