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■ Muting circuit (So) 45-59,459 [Phase] Application Akira 45 (1970) July 9 @ Inventor Ishigaki
Yukinobu 12 12th Victor Company of Moriya-cho, Kana city, Yokohama City Nobuaki Takahashi
Office 12 Assignee Nippon Victor Corporation Yokohama 12 Yokohama-shi Moriya-cho 3 [phase]
Agent patent attorney Tadahiko Ito
BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B respectively show a block system
diagram of a conventional circuit and an electric circuit diagram of the main part thereof, and
FIGS. 2A and 2B each show a block system diagram of one embodiment of the present invention
circuit and its key FIG. 3 is a circuit diagram of one embodiment of the electric circuit of the
circuit, FIG. 3 is a signal waveform diagram, and FIG.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a muting circuit,
and a carrier circuit is lowered or turned off in a demodulator of an FM (PM) transmission
system by an extremely simple circuit configuration by combining a class C amplifier with a
limiter circuit. It is an object of the present invention to provide a circuit that performs squelch
(also 5t muting) operation to remove the offensive noise component that may occur. In an FM
(PM) anti-spacing device such as 4-channel record and TV voice multiplex, remove AM
component (noise component generated from transistor and resistor etc. in circuit) generated
when carrier is turned off (as circuit Conventionally, a mute as shown in FIG. An ink circuit was
used. In order to explain the operation, in FIG. 1A, the FM (PM) wave coming from the input
terminal 1 passes through the equalizer circuit 2 while the bandpass circuit 3 passes through the
limiter circuit 4 and the [111111] muting circuit 6 are supplied to the amplifier 7. The
modulated wave having passed through the limiter circuit 4 is demodulated by the demodulation
circuit 5 to be an audio signal and supplied to the gate circuit 10. On the other hand, the
modulated wave supplied to the amplifier 7 is led to the rectifying and time constant circuit 8.
The output control voltage of the circuit 8 is sufficiently amplified by the amplifier 9 and then
applied to the gate circuit 10 to turn on / off the audio signal from the demodulation circuit 5.
That is, when the carrier level of the modulation wave is extremely lowered or turned off, the
control voltage level applied to the gate circuit 10 is lowered. The gate circuit 10 is turned off,
and the demodulated audio signal is not transmitted to the matrix circuit 12. Therefore, the
muting operation has been performed, and all noises are not generated from the output terminal
13 of the off-state of the carrier. Reference numeral 11 denotes a low pass filter and an amplifier
circuit. An example of the electric circuit of the amplifier 7, the rectifying and time constant
circuit 8, the amplifier 9 and the gate circuit 10 in the muting circuit 6 is shown in FIG. 1B.
According to this muting circuit 6, as apparent from the figure ((6 transistors Q1 to Q6.1 diodes
D1 are required). Thus, the conventional circuit with the above configuration has the
disadvantages that the circuit is complicated, the number of circuit components used is large, and
the response speed is slow due to the rectification and time constant circuit elements. The
present invention eliminates the above disadvantages and will be described with reference to FIG.
In FIG. 2A, the FM (PMJ wave coming from the input terminal 1 passes through the equalizer
circuit 2 and is supplied to the band pass amplifier 3, the low pass filter, and the amplifier circuit
The modulated wave passed through the band pass amplifier 3 is made constant in amplitude
through the limiter circuit 14 to remove AM, and then passed through the class 0 amplifier 15
and then demodulated by the demodulation circuit 16 and output from the circuit 11 Along with
the matrix circuit 12. [111111] EndPage: FIG. 2B shows a circuit diagram of an embodiment of
the electric circuit of the limiter circuit 14 and the sixth-class amplifier 15. The limiter circuit 14
is a transistor Q? , Q8, and the amplitude limited modulation wave appears at the collector of the
transistor Q3. The collector output of the transistor Q8 is applied to the base of the transistor Q9
of the sixth class amplifier 15 via the capacitor 17. The emitter output of transistor Q is
transmitted to demodulation circuit 16. In general, when playing back a 4-channel record
obtained by directly combining FM (PM) modulation wave with direct wave and recording a
signal of 4 channels on a 45-45 system groove, the pickup traces a groove. However, the
playback carrier component may fall to an extreme momentarily depending on the board quality
of the record board, and if the pickup does not trace the sound groove when the regenerator
(demodulator) is on, the regenerator (demodulation (demodulation) The entire carrier component
is not added to the container. In such a case, an AM component (noise component) generated
from a transistor, a resistor or the like used in the operating regenerator is disadvantageously
obtained as an output. This is shown in FIG. In the figure, C represents a carrier component
appearing at the collector of the transistor Q8, and N represents a noise (AM) component when
there is no light. Therefore, in the circuit of the present invention, when the carrier is off, the
operation is stopped in the circuit up to the demodulation circuit 16 to cut off the AM (noise)
component, which is performed by the sixth class amplifier 15. The resistance value of the
resistors is, is, and 20 is appropriately selected and the operating point is determined so that the
transistor Q9 of the sixth-class amplifier 15 conducts (amplifies) when the carrier component is
applied. An operation diagram of the transistor Q9 is shown in FIG. The operating point of the
transistor Q9 is set to the position P in the figure, and when the carrier C is present, the collector
current Ic flows and the carrier signal voltage appears at the emitter of the transistor Q9. On the
other hand, when the carrier component does not exist, the noise component N is generated, but
even if this noise component N is applied, the transistor Q9 is cut off and the output voltage does
not appear on the emitter side of the transistor Q9. Therefore, the sixth class amplifier 15
operates and amplifies only when the carrier component is applied, and becomes inactive when
there is no carrier component or when the carrier component becomes smaller than a
predetermined value, and does not produce an output.
Therefore, the noise component generated in the absence of the carrier component is cut off by
the sixth class amplifier 15, and only the necessary modulation wave component is transmitted
to the demodulation circuit 16 and demodulated and extracted as an audio signal. (As described
above, according to the muting circuit of the present invention, means for separating a signal
reproduced from a multi-channel record provided at the rear stage of the limiter circuit into a
direct wave signal component and an FM (PM) signal component In a reproduction system
comprising: means for demodulating the separated FM (PM) signal component; and means for
matrixing the demodulated signal and the direct wave signal component to obtain each other
channel signal A C class amplifier is provided in the latter stage, and the operating point of the C
class amplifier is appropriately selected (in this way, it is necessary to provide a conventional
muting circuit with a complicated circuit configuration (pass only the carrier component A
squelch or muting operation may be performed that does not pass noise components when the
carrier component is turned off or falls below a predetermined level, and the class C amplifier As
a whole, the circuit is extremely simple and the number of parts used is small (it can be
configured inexpensively and has a high degree of stability (as well as the response speed of the
time constant circuit as in the conventional circuit). It has features such as not causing problems.
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