JPS588636B2 - SECAM Irosingou Fukuchiyou Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a SECAM color signal demodulation circuit used in a SECAM type color television receiver, and is particularly designed to prevent abnormal voltages occurring during the horizontal planking period using a simple method. be.

In general, the color television signal of the SECAM system (hereinafter referred to as SECAM color signal) is the red difference signal (ER-E).
Carrier color that transmits the red difference signal (ER-EY) by frequency modulating the color carrier wave with the blue difference signal (EB-EY) and the blue difference signal (EB-EY) (ER is the red signal, EB is the blue signal, and EY is the luminance signal) signal (hereinafter abbreviated as FM signal a) and blue difference signal (
A carrier color signal (hereinafter abbreviated as FM signal b) that transmits the
As shown in Figure A, the data is transmitted line-sequentially.

When this SECAM color signal is supplied to a SECAM color television receiver, the F of this SECAM color signal is
The M signals a and b are electrically switched line by line by a switching signal obtained from the color burst signal C existing in the horizontal blanking period H to generate a red difference signal (ER
-EY) and an FM demodulator that reproduces the blue difference signal (EB-
However, in this case, since FM signals a and b are interrupted during the horizontal blanking period H, the FM signals
The input signal of the demodulator is also interrupted, and a pulse-like abnormal voltage as shown in FIG.
ER from the blue difference signal (EB-EY) and the blue difference signal (EB-EY).
, EG, and EB (however, EG is a green color signal). The level of the color signal also fluctuates, making it impossible to obtain a predetermined level, resulting in a disadvantage that the white balance deteriorates.

Therefore, in order to solve this problem, conventional S
An ECAM color signal demodulation circuit has been proposed.

In this FIG. 2, one of the SECAM color signal supply sources 1 supplying the SECAM color signals as shown in FIG. The other side of this SECAM color signal supply source 1 is connected to the movable contact 2a of the changeover switch 2 that is connected to the SECAM color signal source 1, and the changeover switch 2 is
The FM signal a that transmits the red difference signal (EF-EY) from the CAM color signal supply source 1 is connected to the movable contact 2 of this changeover switch 2.
While being supplied to the switch 2, the movable contact 2a is a switching signal obtained from the color burst signal C.
F which further transmits the blue difference signal (EB-EY) from the SECAM color signal supply source 1.
While the M signal b is supplied to the movable contact 2a of the changeover switch 2, the switching signal causes the movable contact 2a to switch to the other fixed contact 2c of the changeover switch 2,
Further, one fixed contact 2b of the changeover switch 2 is directly connected to one fixed contact 5b of the changeover switch 5, and also connected to this fixed contact 5b via a delay circuit 3a, and the other fixed contact 2c of the changeover switch 2 is connected directly to one fixed contact 5b of the changeover switch 5. It is directly connected to one fixed contact 6b of the changeover switch 6, and is also connected to this fixed contact 6b via a delay circuit 4a.

In this case, the delay times of the delay circuits 3a and 4a are set to one horizontal period, and the continuous FM signal a is applied to the fixed contact 5b of the changeover switch 5 and the fixed contact 6b of the changeover switch 6, respectively.
and b are obtained.

That is, the FM signals a and b transmitted line-sequentially are converted into continuous signals here, and the FM signals a and b are simultaneously supplied to their respective demodulators.

Further, the other fixed contact 5c of the changeover switch 5 receives the FM signal a.
The movable contact 5a of the changeover switch 5 is connected to the output terminal of an oscillator 7 having an oscillation frequency corresponding to the center frequency of An output terminal 9 is led out from which a red color difference signal (ER-EY) can be obtained from the FM demodulator 3.

The other fixed contact 6c of the changeover switch 6 is connected to the FM signal b.
The movable contact 6a of the changeover switch 6 is connected to the output terminal of an oscillator 8 having an oscillation frequency corresponding to the center frequency of An output terminal 10 from which a blue color difference signal (EB-EY) can be obtained is led out from the FM demodulator 4.

Moreover, the movable contact 5a of the changeover switch 5 and the changeover switch 6
The movable contacts 6a are configured to interlock with each other, and during the horizontal blanking period H, the horizontal blanking signal (
(not shown) electrically controlled by the movable contact 5a.
and 6a are connected to the fixed contact 5c of the changeover switch 5 and the fixed contact 6c of the changeover switch 6, respectively.Therefore, during this horizontal blanking period H, oscillation signals of a predetermined frequency are sent from the oscillators 7 and 8 to the FM demodulators 3 and 4, respectively. Also, during the unblanking period K, the movable contacts 5a and 6a are connected to the fixed contact 5b of the changeover switch 5 and the fixed contact 6b of the changeover 1 switch 6, respectively, so that the FM can be supplied during the unblanking period K. It is configured such that signals a and b can be supplied to FM demodulators 3 and 4, respectively.

Therefore, the red difference signal (ER) is supplied from the SECAM color signal supply source 1.
-EY) When the movable contact 2a of the changeover switch 2 is switched to the fixed contact 2b side, the movable contact 5a of the changeover switch 5 and the movable contact 6a of the changeover switch 6 are also switched. Since the fixed contacts 5b and 6b are switched in conjunction with each other, the FM signal a is directly supplied to the FM demodulator 3 via the switch 5 and the limiter 14a, while the FM signal a is delayed by one horizontal period by the delay circuit 4a.
At this time, the M signal b is activated by the changeover switch 6 and the limiter 14b.
are supplied to the FM demodulator 4 through the FM demodulators 3 and 4 to obtain a red difference signal (ER-EY) and a blue difference signal (EB-EY) at the output terminals 9 of the FM demodulators 3 and 4, respectively, and After this, during the horizontal blanking period H, the movable contact 5a of the changeover switch 5 and the movable contact 6a of the changeover switch 6 are interlocked and switched to the fixed contacts 5c and 6c of the changeover switches 5 and 6, respectively, and the oscillators 7 and 8 oscillation signals with oscillation frequencies corresponding to the center frequencies of the FM signals a and b are supplied to the FM demodulators 3 and 4 via limiters 14a and 14b, respectively, and the output terminals 9 and 4 of the FM demodulators 3 and 4 are 1
It is possible to obtain a DC signal with a reference potential that is 0 and wide relative to the center frequency of the FM signals a and b, respectively, thereby making it possible to prevent abnormal voltages occurring during the horizontal blanking period H.

Furthermore, after this, a blue difference signal (
When the FM signal b transmitting EB-EY) is supplied, the movable contact 2a of the changeover switch 2 is switched to the fixed contact 2c side, and at this time, the movable contact 5a of the changeover switch 5 and the movable contact 6a of the changeover switch 6 are switched to the fixed contact 2c side. The fixed contacts 5 are also interlocked with each other.
b and 6b side, the FM signal b is directly introduced to the FM demodulator 4 via the changeover switch 6 and the limiter 14b, while the FM signal a delayed by one horizontal period by the delay circuit 3a is fed to this side. The red difference signal (ER-EY) is supplied to the FM demodulator 3 via the selector switch 5 and the limiter 14a, and is output to the output terminals 9 of the FM demodulators 3 and 4.
and a blue color difference signal (EB-EY).

As described above, according to the conventional SECAM color signal demodulation circuit, the oscillators 7 and 8 having oscillation frequencies corresponding to the center station wave numbers of the FM signals a and b are provided, and the horizontal blanking period H of the SECAM color signal is Since oscillation signals of predetermined frequencies can be supplied from the oscillators 7 and 8 to the FM demodulators 3 and 4 via the changeover switches 5 and 6, respectively, the input signals of the FM demodulators 3 and 4 are interrupted during the horizontal blanking period H. Therefore, the same FM demodulators 3 and 4
As a result, deterioration of the white balance of the color television receiver can be prevented, but the demodulation of oscillators 7 and By inserting it into the circuit, the entire demodulation circuit becomes complicated, and the oscillation frequencies of oscillators 7 and 8 must be adjusted to correspond to the center frequencies of FM signals a and b, respectively. The work was cumbersome.

In view of this point, the present invention provides an SEC that can prevent abnormal voltages that occur particularly during the horizontal blanking period by a simple method.
The present invention aims to provide an AM color signal demodulation circuit.

SE according to the present invention with reference to FIGS. 3 and 4 below.
An example of a CAM color signal demodulation circuit will be described.

In FIG. 3, parts corresponding to those in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this example, for the sake of simplicity, only the case where a red color difference signal (ER-EY) is demodulated will be described.

In FIG. 3, reference numeral 11 indicates an FM signal supply source, and this FM signal supply source 11 supplies a continuous signal of FM signal a.

One end of this FM signal supply source 11 is connected to one fixed contact 12b of the changeover switch 12, and this FM signal supply source 11
Ground the other end.

Further, the other fixed contact 12c of the changeover switch 12 is connected to the collector of an NPN transistor 13 for taking out current, and the movable contact 12a of this changeover switch 12 is connected to the input terminal of the limiter 14.

In this case, the movable contact 12a of the changeover switch 12 is electrically controlled by a horizontal blanking signal (not shown) present during the horizontal blanking period H, so that the movable contact 12a is on the side of the fixed contact 12c during the horizontal blanking period H. FM signal a is also output from the FM signal supply source 11 as shown in FIG.
During the period when the movable contact 12a is supplied with the fixed contact 12
so that it switches to side b.

Further, the output terminal of the limiter 14 is connected to the base of the transistor 13 and also to one input terminal of the multiplier 15.

In this case, when the movable contact 12a of the changeover switch 12 is switched to the fixed contact 12c side during the horizontal blanking period H, the phase difference between the input and output signals of this limiter 14 is converted into the FM signal a supplied from the FM signal supply source 11. The limiter 14 is made to oscillate at this time so that the center frequency becomes zero.

On the other hand, the emitter of the transistor 13 is grounded through a series resonant circuit consisting of a resistor 16, a capacitor 17, and a coil 18, and the midpoint between the capacitor 17 and the coil 18 is connected to the other input terminal of the multiplier 15. .

Furthermore, an output terminal 19 is derived from the multiplier 15.

In this case, the series resonant circuit consisting of the multiplier 15, resistor 16, capacitor 17 and coil 18 is Quadratu.
It constitutes a re-type demodulator, and in this demodulator, F
When the M signal is supplied, this FM signal is connected to the resistor 16,
The series resonant circuit consisting of the capacitor 17 and the coil 18 performs phase modulation and converts it into a phase modulation signal (hereinafter abbreviated as PM signal), and then this PM signal is input to two input terminals of the multiplier 15 at a position of 90 degrees at the center frequency. The FM signal is demodulated by supplying the signals so as to have a phase difference.

Therefore, by selecting the resistance, capacitance, and inductance values of the resistor 16, capacitor 17, and coil 18 that constitute the series resonant circuit, the phase difference between the PM signals supplied to the two input terminals of the multiplier 15 is centered. The frequency should be 90 degrees.

Since the SECAM color signal demodulation circuit according to the present invention is configured as described above, when the FM signal a is supplied from the FM signal supply source 11, the movable contact 12a of the changeover switch 12 is switched to the fixed contact 12b side, and the FM The signal a is supplied to the limiter 14 through the changeover switch 12, and the FM signal a is supplied to one input terminal of the multiplier 15 and is also transmitted through the base-emitter of the transistor 13, the resistor 16, and the capacitor 17. and is supplied to the other input terminal of the multiplier 15.

In this case, the FM signal a is phase modulated by a series resonant circuit consisting of a resistor 16, a capacitor 17, and a coil 18 and converted into a PM signal, and the two inputs of the multiplier 15 are inputted with a phase difference of approximately 90 degrees at the center frequency. Supplied to the terminal.

Therefore, the output terminal 19 of this multiplier 15 has a red difference signal (
ER-EY) can be obtained.

Also, during the horizontal blanking period H, the movable contact 12a of the changeover switch 12 switches to the fixed contact 12c side, and at this time, the phase difference between the input and output signals of the limiter 14 becomes zero degrees at the center frequency, so the limiter 14 Oscillation begins at this center frequency.

For this reason, an oscillation signal is supplied from the limiter 14, and this oscillation signal is supplied to one input terminal of the multiplier 15, and the base-emitter of the transistor 13 and the resistor 16.
and is supplied to the other input terminal of the multiplier 15 via the capacitor 17.

In this case, since the oscillation signal supplied to the multiplier 15 via the resistor 16 and the capacitor 17 has a phase difference of approximately 90 degrees due to the terminal voltage of the coil 18, the oscillation signal is supplied to the multiplier 15 with a phase difference of approximately 90 degrees. is supplied to the two input terminals of

Therefore, an output voltage corresponding to the oscillation frequency, that is, the center frequency, of the oscillation signal can be obtained at the output terminal 19 of the multiplier 15. If this output voltage is pulse-clamped in the subsequent stage, this output voltage can be set to a reference potential, for example, zero potential. Can be set to .

Therefore, by supplying the oscillation signal to the input terminal of the multiplier 15 during the horizontal blanking period H, the output voltage obtained at the output terminal 19 of the multiplier 15 will not adversely affect the operation of other circuits.

This makes it possible to prevent abnormal voltages occurring during the horizontal blanking period H.

Moreover, FIG. 4 shows the specific circuit of the example in FIG.
This will be explained with reference to the diagram.

However, in FIG. 4, parts corresponding to those in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted.

As described above, one end of the FM signal source 11 is connected to the fixed contact 12b of the changeover switch 12, and this FM signal source 1 is connected to the fixed contact 12b of the changeover switch 12.
Ground the other end of 1.

Further, the fixed contact 12c of the changeover switch 12 is connected to the collector of the transistor 13, and the movable contact 12a of the changeover switch 12 is connected to the base of the npn type transistor 20 and the base of the npn type transistor 21.

Furthermore, the emitters of transistors 20 and 21 are grounded via a constant current circuit 22, and the collectors of transistors 20 and 21 are connected to the emitters of npn type transistor 23 and npn type transistor 24, respectively.

On the other hand, the bases of the npn type transistor 25 and the npn type transistor 26 are connected to each other, and the midpoint of this connection is grounded via the DC power supply 27.

Furthermore, the emitters of transistors 25 and 26 are grounded via constant current circuit 22, and the collectors of transistors 25 and 26 are connected to the emitters of npn type transistor 28 and npn type transistor 29, respectively.

In this case, transistors 20, 21, 25 and 26 constitute limiter 14.

On the other hand, the bases of the transistors 23 and 28 are connected to each other, the collector of the transistor 23 is connected to the power supply terminal 30 to which a positive voltage is supplied, and the transistor 24
Connect to the collector of

Further, the collector of the transistor 28 is connected to the power supply terminal 30 via a resistor 31 and also to the base of the transistor 13.

Furthermore, the bases of the transistors 24 and 29 are connected to each other, and the midpoint of this connection is grounded via the DC power supply 32.

Further, the collector of the transistor 24 is connected to the power supply terminal 30, and the collector of the transistor 29 is connected to the power supply terminal 30 via a resistor 31 and to the base of the transistor 13.

In this case, transistors 23, 24, 28 and 29 constitute multiplier 15.

Further, the collector of the transistor 13 is connected to the power supply terminal 30 via the resistor 33, and the emitter of this transistor 13 is grounded via the series circuit of the resistor 16, the capacitor 17, and the coil 18 as described above.
The midpoint between the base of the transistor 23 and the base of the transistor 28 is connected to the midpoint between the base of the transistor 23 and the base of the transistor 28 .

Also, the midpoint of the connection between the collector of the transistor 20 and the emitter of the transistor 23 is connected to the base of the npn transistor 34, and the midpoint of the connection between the collector of the transistor 25 and the emitter of the transistor 28 is connected to the base of the npn transistor 35. Connect and further such transistor 3
Connect the emitters 4 and 35 to each other and connect the middle point to the constant current circuit 3.
6 to ground.

Also, the midpoint of the connection between the collector of the transistor 21 and the emitter of the transistor 24 is connected to the base of the npn transistor 37, and the midpoint of the connection between the collector of the transistor 26 and the emitter of the transistor 29 is connected to the base of the npn transistor 38. Connect and further such transistor 3
Emitters 7 and 38 are connected to each other, and the midpoint of this connection is grounded via a constant current circuit 36.

In this case transistors 34 and 35 and transistor 37
and 38 constitute differential amplifiers 39 and 40.

Furthermore, the collectors of the transistors 34 and 38 are connected to each other, and the midpoint of this connection is connected to the power supply terminal 30 via a resistor 41a.
At the same time, the output terminal 41 for obtaining the first output level of the differential amplifiers 39 and 40 is derived from the midpoint of this connection, and the collectors of the transistors 35 and 37 are connected to each other and the midpoint of this connection is connected to to the power supply terminal 3 via the resistor 42a.
0 and the differential amplifier 39 from this connection midpoint.
and an output terminal 42 for obtaining a second output level of 40.

Therefore, as mentioned above, the FM signal a is supplied from the FM signal supply source 11.
is supplied, the movable contact 12a of the changeover switch 12
is switched to the fixed contact 12b side, and the FM signal a is supplied to the input terminal of the limiter 14, that is, the bases of transistors 20 and 21, through this changeover switch 12, and the transistors 20 and 21 amplify the FM signal a. From the collectors of transistors 20 and 21, F is connected to one input terminal of multiplier 15, that is, the emitters of transistors 23 and 24.
The M signal a is supplied, and the transistors 25 and 26 constituting the limiter 14 amplify the FM signal a in reverse phase. a
is supplied to the base of transistor 13, and at this time, this transistor 13 becomes an emitter follower amplifier,
FM amplified by transistors 26, 29 and 25, 28
Signal a is applied via the base-emitter of transistor 13, resistor 16 and capacitor 17 to the other input terminal of multiplier 15, ie to the bases of transistors 23 and 28.

In this case, the FM signal a is phase-modulated by the series resonant circuit consisting of the resistor 16, capacitor 17, and coil 18 as described above and converted into a PM signal, and the multiplier 15 is outputted with a phase difference of approximately 90 degrees at the center frequency. supplied to the other input terminal.

For this purpose, transistors 23 and 28 forming the multiplier 15
operates alternately every f cycles of the signal, and the multiplier 15
, i.e., the output terminals 41 of the differential amplifiers 39 and 40
and 42, the red difference signal (ER-E
Y) can be obtained respectively.

Furthermore, as described above during the horizontal blanking period H, the movable contact 12a of the changeover switch 12 is switched to the fixed contact 12c, and at this time, the phase difference between the input and output signals of the limiter 14, that is, the transistors 20 and 21 constituting the limiter 14, is changed. The phase difference between the base input signal of the transistors 20 and 21 and the collector output signals of the transistors 25 and 26 is zero degrees at the center frequency.
5 and 26 are repeatedly turned on and off, that is, the limiter 14 starts oscillating, and the oscillation signal from the limiter 14 is sent to one input terminal of the multiplier 15, that is, the transistor 23.
and 24 emitters and transistor 1
3 base-emitter, resistor 16 and capacitor 17
to the other input terminal of multiplier 15, ie, the bases of transistors 23 and 28.

In this case, as described above, the oscillation signals are supplied to the two input terminals of the multiplier 15 with a phase difference of approximately 90 degrees, so the output terminal 19 of the multiplier 15, that is, the output terminal 41 of the differential amplifiers 39 and 40. From 42 and 42, output voltages with different output levels corresponding to the center frequency can be obtained, and as described above, if this output voltage is pulse-clamped in the subsequent stage, this output voltage can be set to a reference potential, for example, zero potential. Therefore, abnormal voltage occurring during the horizontal blanking period H can be prevented.

Also, in this example, only the case where the red difference signal (ER-EY) is demodulated is described, but the case of the blue difference signal (EB-EY) is also demodulated in the same manner as the case of the red difference signal (ER-EY). Therefore, the red difference signal (ER-
EY) and a blue color difference signal (EB-EY).

As described above, according to the present invention, the horizontal blanking period H
Since it is possible to obtain an oscillation signal of a predetermined frequency from the limiter 14 without particularly providing an oscillator, even if the FM signals a and b are interrupted during this horizontal blanking period H, this oscillation signal can be used to adjust the frequency, etc. Therefore, the abnormal voltage generated during the horizontal blanking period H can be prevented by a simpler method than the conventional method.

Further, even when this demodulation circuit is integrated, there is no need for an oscillator or the like, so there is no need for external components, which has the advantage of reducing costs.

Further, FIG. 5 shows another embodiment of the present invention, and the example of FIG. 5 will be explained below.

In FIG. 5, parts corresponding to those in FIG. 3 are designated by the same reference numerals, and detailed explanation will be omitted.

As mentioned above, one end of the FM signal supply source 11 is connected to the selector switch 1.
2, and the other end of this FM signal supply source 11 is grounded.

Further, the other fixed contact 12c of the changeover switch 12 is connected to the collector of the transistor 13, and this changeover switch 12
The movable contact 12a of the limiter 14 is connected to the input terminal of the limiter 14, and the output terminal of the limiter 14 is connected to one input terminal of the multiplier 15. 13, and the base of this transistor 13 is grounded.

In this case, as described above, when the movable contact 12a of the changeover switch 12 is switched to the fixed contact 12c during the horizontal blanking period H, the phase difference between the input and output signals of the limiter 14 is supplied from the FM signal supply source 11. At this time, this limiter 14
make it oscillate.

Furthermore, the midpoint of the connection between the capacitor 17 and the coil 18 is connected to the other input terminal of the multiplier 15, and the output terminal 19 is derived from the multiplier 15.

In this case, as described above, the series resonant circuit consisting of the multiplier 15, the resistor 16, the capacitor 17, and the coil 18 is Qu
It constitutes an adrature type demodulator, and by selecting the resistance, capacitance, and inductance values of the resistor 16, capacitor 17, and coil 18, the voltage is supplied to the two input terminals of the multiplier 15. Therefore, when the FM signal a is supplied from the FM signal supply source 11, the movable contact 12a of the changeover switch 12 is set so that the phase difference of the PM signal is 90 degrees at the center frequency.
is switched to the fixed contact 12b side, and the FM signal a is supplied to the limiter 14 via this changeover switch 12. Furthermore, this FM signal a is supplied to one input terminal of the multiplier 15, and the resistor 16 and It is supplied to the other input terminal of multiplier 15 via capacitor 17.

In this case, as described above, the FM signal a is phase-modulated by the series resonant circuit consisting of the resistor 16, capacitor 17, and coil 18 and converted into a PM signal, and the multiplier 15 is output with a phase difference of about 90 degrees at the center frequency. Since it is supplied to two input terminals, a red difference signal (ER-EY) can be obtained at the output terminal 19 of this multiplier 15.

Also, as mentioned above during the horizontal blanking period H, the movable contact 12a of the changeover switch 12 switches to the fixed contact 12c side, and at this time, the phase difference between the input and output signals of the limiter 14 becomes zero degrees at the center frequency. The limiter 14 starts oscillating at this center frequency, and an oscillation signal is supplied from the limiter 14. This oscillation signal is supplied to one input terminal of a multiplier 15, and is also supplied to a resistor 16 and a capacitor 1.
7 to the other input terminal of the multiplier 15.

In this case, since the oscillation signal supplied to the other input terminal of the multiplier 15 has a phase difference of approximately 90 degrees due to the terminal voltage of the coil 18, the oscillation signal is supplied to the multiplier 1 with a phase difference of approximately 90 degrees.
5, and therefore this multiplier 15
An output voltage corresponding to the oscillation frequency, that is, the center frequency, of the oscillation signal can be obtained at the output terminal 19 of the oscillation signal, and if this output voltage is pulse-clamped in the subsequent stage as described above, this output voltage can be set to a reference potential, for example, zero potential. be able to.

Therefore, abnormal voltage occurring during the horizontal blanking period H can be prevented.

Therefore, in the example shown in FIG. 5, the same effects as in the example shown in FIG. 3 can be obtained.

Further, FIG. 6 also shows another embodiment of the present invention, and parts in FIG. 5 that correspond to those in FIG. 3 are given the same reference numerals and detailed explanations will be omitted.

In the example shown in FIG. 6, the movable contact 12a of the changeover switch 12 is connected to the input terminal of the limiter 14 and also connected to one input terminal of the multiplier 15, so that the movable contact 12a of the changeover switch 12 is connected to one input terminal of the multiplier 15 without going through the limiter 14. A predetermined signal is supplied to the

The rest of the structure is the same as that shown in FIG.

Therefore, when the FM signal a is supplied from the FM signal supply source 11, the movable contact 12a of the changeover switch 12
is switched to the fixed contact 12b side, and the FM signal a is supplied to the limiter 14 via this changeover switch 12 and is also supplied to one input terminal of the multiplier 15, while the FM signal a supplied to the limiter 14 is further transistor 13
is supplied to the other input terminal of the multiplier 15 via the base-emitter, resistor 16 and capacitor 17.

Therefore, the red color difference signal (ER-EY) can be obtained at the output terminal 19 of the multiplier 15 as described above.

Also, during the horizontal blanking period H, the movable contact 12a of the changeover switch 12 switches to the fixed contact 12c, and at this time, the phase difference between the input and output signals of the limiter 14 becomes zero degrees at the center frequency as described above. The limiter 14 starts oscillating at this center frequency.

For this reason, an oscillation signal is supplied from the limiter 14, and this oscillation signal is sent to one input terminal of the multiplier 15 via the base-collector of the transistor 13 and the switch 12.
Also, since it is supplied to the other input terminal of the multiplier 15 via the base-emitter of the transistor 13, the resistor 16, and the capacitor 17, the output terminal 19 of the multiplier 15 has an output corresponding to the center frequency as described above. Therefore, an abnormal voltage occurring during the horizontal blanking period H can be prevented.

Therefore, the same effect as the example in FIG. 3 can be obtained in the example in FIG. 6 as well.

Further, FIG. 7 also shows another embodiment of the present invention, and in FIG. 7, parts corresponding to those in FIG. 3 are given the same reference numerals, and detailed explanation will be omitted.

The example in FIG. 7 shows the FM signal supplied from the FM signal supply source 11.
This device can be used when the signal a is relatively large. Therefore, a relatively large FM signal a is supplied from this FM signal supply source 11, and one end of this FM signal supply source 11 is connected to the input terminal of the limiter 14. It is connected to the collector of the transistor 13, and the other end of the FM signal supply source 11 is grounded.

Further, the output terminal of the limiter 14 is connected to one input terminal of the multiplier 15, and is also connected to the emitter of the transistor 13 via a series resonant circuit of the resistor 16, the capacitor 17, and the coil 18, and the base of the transistor 13 is connected to the emitter of the transistor 13. Ground.

In this case, limiter 14, resistor 16, capacitor 17,
The coil 18 and the emitter-collector of the transistor 13 are successively connected in series to form an oscillation loop with closed and open circuits.
When the signal a is supplied, the limiter 14 that makes up this oscillation loop oscillates in synchronization with the frequency of the FM signal a, and when no signal is supplied to this oscillation loop, the limiter 14 that makes up this oscillation loop oscillates in synchronization with the frequency of the FM signal a. Make it oscillate at its own center frequency.

Furthermore, the midpoint of the connection between the capacitor 17 and the coil 18 is connected to the other input terminal of the multiplier 15, and the output terminal 19 is derived from the multiplier 15.

Therefore, the FM signal a is relatively larger than the FM signal source 11.
is supplied, the FM signal a is also supplied to the above-mentioned oscillation loop, and at this time, the limiter 14 oscillates in synchronization with the frequency of the FM signal a, so the two input terminals of the multiplier 15 receive the PM signal as described above. Signals can be supplied with a phase difference of approximately 90 degrees,
Therefore, the output terminal 19 of the multiplier 15 has a red difference signal (ER
-EY) can be obtained.

Furthermore, when the supply of the FM signal a from the FM signal supply source 11 is interrupted during the horizontal blanking period H, no signal is supplied to the oscillation loop, and at this time the limiter 14 oscillates at its own center frequency, so the multiplier As mentioned above, the oscillation signal can be supplied to the two input terminals of the multiplier 15 with a phase difference of approximately 90 degrees, and the output terminal of the multiplier 15 can obtain an output voltage corresponding to the oscillation frequency of the oscillation signal. Therefore, abnormal voltage occurring during the horizontal blanking period H can be prevented.

Therefore, when the FM signal a supplied from the FM signal supply source 11 is large, the same effect as described above can be obtained even without providing the changeover switch 12.

Further, FIG. 8 also shows another embodiment of the present invention, and in this FIG. 8, parts corresponding to those in FIG. 3 are given the same reference numerals, and detailed explanation will be omitted.

As described above, one end of the FM signal supply source 11 is connected to one fixed contact 12b of the changeover switch 12, and the other end of the FM signal supply source 11 is grounded.

Further, the movable contact 12a of the changeover switch 12 is connected to one end of a series circuit of a coil 44 and a capacitor 45 via an amplifier 43, and the other end of this series circuit is connected to the other fixed contact 12c of the changeover switch 12. At the same time, it is grounded via the resistor 46.

In this case, the amplifier 43, coil 44, capacitor 45, and resistor 46 constitute a bell filter 47, and when the movable contact 12a of the changeover switch 12 is switched to the fixed contact 12c side during the horizontal blanking period H, this bell filter 4
7 starts oscillation.

Further, the other end of the series circuit of the coil 44 and the capacitor 45 is connected to one fixed contact 48b of the changeover switch 48, and also connected to the emitter of the transistor 13 via the series resonant circuit of the resistor 16, the capacitor 17, and the coil 18. , the base of this transistor 13 is grounded.

In addition, the collector of this transistor 13 is connected to the selector switch 4.
8, and the movable contact 48a of this changeover switch 48 is connected to one input terminal of the multiplier 15.

In this case, the mover 48a of the changeover switch 48 is made to interlock with the mover 12a of the changeover switch 12.

That is, the movable contact 12a of the changeover switch 12 receives a horizontal blanking signal (not shown) during the horizontal blanking period H.
When the movable contact 12a is electrically controlled to switch to the fixed contact 12c side during the horizontal blanking period H, the movable element 48a of the changeover switch 48 also switches to the fixed contact 48c.
Also, the FM color signal source 11
When the movable contact 12a is switched to the fixed contact 12b side during the period when the signal a is supplied, the movable element 48a of the changeover switch 48 is also switched to the fixed contact 48b side.

On the other hand, the midpoint of the connection between the capacitor 17 and the coil 18 is connected to the other input terminal of the multiplier 15, and the output terminal 19 is derived from the multiplier 15.

In the demodulation circuit configured as above, the FM signal supply source 1
When the FM signal a is supplied from 1, the movable contact 12a of the changeover switch 12 and the movable contact 48a of the changeover switch 48
are interlocked and switched to the fixed contacts 12b and 48b side,
The FM signal a is supplied to one input terminal of the multiplier 15 via a bell filter 47, and the FM signal a is supplied to the other input terminal of the multiplier 15 via a bell filter 48, a resistor 16, and a capacitor 17. is also supplied, so multiplier 1
As mentioned above, the PM signal is approximately 90
The output terminal 1 of the multiplier 15 is therefore supplied with a phase difference of degrees
9, a red color difference signal (ER-EY) can be obtained.

Further, during the horizontal blanking period H, the movable contact 12a of the changeover switch 12 and the movable contact 48a of the changeover switch 48 are switched to the fixed contacts 12c and 48c in conjunction, and at this time, the bell filter 47 starts oscillating. The output terminal of this bell filter 48, that is, the capacitor 45 and the resistor 4
6, an oscillating signal is supplied to one input terminal of the multiplier 15 via the resistor 16, the capacitor 17, the coil 18 and the emitter-collector of the transistor 13; It is also supplied to the other input terminal of multiplier 15 via capacitor 17 .

In this case, since the two input terminals of the multiplier 15 are supplied with the current component flowing through the coil 18 and the terminal voltage component of the coil 18, the oscillation signal from the bell filter 47 is always at approximately 90 degrees regardless of the oscillation frequency. It will be supplied to the two input terminals of the multiplier 15 with a phase difference, and therefore the multiplier 15
A DC voltage can always be obtained at the output terminal 19 of the controller, and by pulse-clamping this DC voltage at a subsequent stage, this DC voltage can be set to a reference potential, for example, zero potential.

This makes it possible to prevent abnormal voltages occurring during the horizontal blanking period H.

Therefore, even if the bell filter 47 is used instead of the limiter 14 as in the example in FIG. 8, the same effect as in the example in FIG. 3 can be obtained.

Further, FIG. 9 also shows another embodiment of the present invention, and in FIG. 9, parts corresponding to those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the example shown in FIG. 9, one end of the FM signal supply source 11 is connected to the base of the npn transistor 49, and the other end of the FM signal supply source 11 is grounded.

Further, the collector of the transistor 49 is connected to a power supply terminal 51 that supplies a positive voltage via a resistor 50, and the emitter of this transistor 49 is grounded via a constant current circuit 52, and a capacitor 53, a coil 54, and a resistor 55 are connected. Grounded through a series resonant circuit consisting of:

In this case, the transistor 49, constant current circuit 52, capacitor 53, coil 54, and resistor 55 constitute a bell filter 56.

Further, the midpoint of the connection between the coil 54 and the resistor 55 is connected to the collector of an NPN transistor 57, and the emitter of this transistor 57 is grounded, while the base of this transistor 57 is connected to an input terminal to which a horizontal blanking signal is supplied. 5
Connect to 8.

In this case, this transistor 57 is used as a switching element, and when a horizontal blanking signal is supplied to the input terminal 58, this transistor 57 is turned on.

On the other hand, the collector of the transistor 49 constituting the bell filter 56 is connected to one fixed contact 48b of the changeover switch 48, and is also connected to the emitter of the transistor 13 via a series resonant circuit consisting of the resistor 16, the capacitor 17, and the coil 18. , the base of this transistor 13 is grounded.

In addition, the collector of this transistor 13 is connected to the selector switch 4.
8, and the movable contact 48a of this changeover switch 48 is connected to one input terminal of the multiplier 15.

In this case, the movable element 48a of the changeover switch 48 is made to operate in conjunction with the on/off operation of the transistor 57.

That is, when the transistor 57 is controlled by the horizontal blanking signal present in the horizontal blanking period H and the transistor 57 is turned on during the horizontal blanking period H, the mover 48a of the changeover switch 48 is switched to the fixed contact 48c side. Further, when the transistor 57 is turned off, that is, during the period when the FM signal a is supplied from the FM signal supply source 11, the movable element 48a of the changeover switch 48 is switched to the fixed contact 48b side.

On the other hand, the midpoint of the connection between the capacitor 17 and the coil 18 is connected to the other input terminal of the multiplier 15, and the output terminal 19 is derived from the multiplier 15.

Therefore, when the FM signal a is supplied from the FM signal supply source 11, the FM signal a is also supplied to the base of the transistor 49, and the collector of the transistor 49 receives the FM signal a.

Also, at this time, the movable contact 48a of the changeover switch 48 has been switched to the fixed contact 48b side, so this FM signal a
is supplied to one input terminal of the multiplier 15, while this F
Since the M signal a is supplied to the other input terminal of the multiplier 15 via the resistor 16 and the capacitor 17, the multiplier 15
As mentioned above, the PM signal is supplied to the two input terminals with a phase difference of approximately 90 degrees, and therefore the output terminal 19 of the multiplier 15
A red color difference signal (ER-BY) can be obtained.

Furthermore, when a horizontal blanking signal is supplied to the input terminal 58 during the horizontal blanking period H, the transistor 57 is turned on, so that the coil 54 forming the series resonant circuit is directly grounded without going through the resistor 55. Therefore, the Q value of the series resonant circuit becomes infinite and the series resonant circuit oscillates, and an oscillation signal can be obtained at the output terminal of the bell filter 56, that is, the collector of the transistor 49, and at this time, Since the movable contact 48a of the changeover switch 48 is switched to the fixed contact 48c, this oscillation signal is sent to one input of the multiplier 15 via the resistor 16, capacitor 17, coil 18, and emitter-collector of the transistor 13. terminal, while this oscillating signal is supplied to the resistor 16
It is also supplied to the other input terminal of the multiplier 15 via the capacitor 17.

In this case, as described above, the two input terminals of the multiplier 15 are supplied with the current component flowing through the coil 18 and the terminal voltage component of the coil 18, so that the oscillation signal from the bell filter 56 is always approximately The signals are supplied to the two input terminals of the multiplier 15 with a phase difference of 90 degrees, so that a DC voltage can always be obtained at the output terminal 19 of the multiplier 15, and therefore during the horizontal blanking period H. It is possible to prevent abnormal voltages that occur in

Therefore, in the example shown in FIG. 9, the same effects as in the example shown in FIG. 8 can be obtained.

Further, the present invention is not limited to the above-described embodiments, and various other configurations may be adopted without departing from the spirit of the present invention.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the present invention, Fig. 2 is a diagram of the conventional S
Schematic block diagram showing an example of an ECAM color signal demodulation circuit, No. 3
The figure is a schematic configuration diagram showing one embodiment of the SECAM color signal demodulation circuit of the present invention, and FIG. 4 is a connection diagram showing a specific example of FIG. 3.
5 to 9 are schematic diagrams showing other embodiments of the present invention. 11 is an FM signal supply source, 12 is a changeover switch, 13 is a transistor, 14 is a limiter, 15 is a multiplier, 16 is a resistor, 17 is a capacitor, 18 is a coil, and 19 is an output terminal.

Claims (1)

[Claims] 1. A SECAM color signal is processed through a limiter circuit, an output signal from the limiter circuit is phase-shifted through a resonant circuit, and an output signal from the resonant circuit and an output from the limiter circuit are output from the limiter circuit. In a color signal demodulation circuit which adds a signal to two input terminals of a multiplier and obtains an FM-demodulated color difference signal from an output terminal of the multiplier, a signal is applied to the limiter circuit during the horizontal blanking period. Feedback is applied so that the circuit composed of the limiter circuit and the resonant circuit operates as an oscillation circuit during the horizontal blanking period, and the oscillation signal of the oscillation circuit is sent to one of the multipliers via the resonant circuit. The oscillation signal is supplied to the input terminal of the multiplier, and the oscillation signal is supplied to the other input terminal of the multiplier.
ECAM color signal demodulation circuit. 2 Process the SECAM color signal through a bell filter circuit, phase shift the output signal from the bell filter circuit through a resonant circuit, and combine the output signal from the resonant circuit with the output signal from the bell filter circuit. In a color signal demodulation circuit which obtains an FM demodulated color difference signal from the output terminal of the multiplier in addition to the two input terminals of the multiplier, positive feedback is provided to the bell filter circuit during the horizontal blanking period. hang,
During the horizontal blanking period, the bell filter circuit operates as an oscillation circuit, and the oscillation signal of the oscillation circuit is supplied to one input terminal of the multiplier via the resonance circuit, and the oscillation signal is A SECAM color signal demodulation circuit characterized in that the signal is supplied to the other input terminal of a multiplier.