JPS60157705A - Muting signal generating circuit - Google Patents

Abstract

PURPOSE:To obtain a muting signal generating circuit which has simple constitution and also can be converted easily into an IC, by controlling the charge/ discharge of a charging/discharging circuit of a VTR by a dropout detecting signal, switching the discharge time constant with the output of a comparator and also using the output of the comparator as a muting signal. CONSTITUTION:A dropout detecting signal SD is supplied to a terminal 58. Connection switches 48 and 51 are controlled by the signal SD, and charge/discharge to a capacitor 52 is controlled. When the threshold level of a comparator 54 is set at Vth1, the signal obtained at the output side of the comparator 54 is changed to a high level ''1'' from a low level ''0'' at a time point t1 (Fig. G). Therefore the output of an AND circuit 57 is kept at level ''0'' with the switch 51 kept off. Under such conditions, the capacitor 52 is discharged via a resistor 53 only.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a VTR that reproduces a recorded signal in which, for example, an audio signal is FM modulated and frequency multiplexed with a video signal.
The present invention relates to a muting signal generation circuit for generating a muting signal of an audio signal type in a video tape recorder.

BACKGROUND TECHNOLOGY AND PROBLEMS In a VTR, the luminance signal in the video signal is FM-modulated in the fAJ region side, and the chroma signal is low-frequency converted to frequency interleave between adjacent tracks, which have different azimuth angles. Recording is performed using two rotating magnetic heads on an inclined trunk on a tape without a guard hand.

In such a VTR, audio signals are conventionally recorded using a fixed head on a trunk continuous in the tape transport direction in a manner similar to that of a so-called audio tape recorder.

By the way, in the above-mentioned VTR, if the tape transport speed is reduced in order to increase the recording density, the relative speed between the fixed head and the tape during audio signal recording becomes slow, making it difficult to record audio signals well.

Conventionally, an audio signal is FM-modulated between an FM-modulated luminance signal and a low-frequency converted chroma signal, frequency-multiplexed with a video signal, and recorded on a tilted trunk.

That is, in FIG. 1, a video signal Sv is supplied from the terminal (2) to the video signal recording circuit (1), from which a luminance signal YFM converted to FM and a chroma signal CD converted to low frequency are obtained (1). (see Figure 2), combiners (3A) and (3B), respectively.
supplied to

Moreover, the audio signal sA is supplied to the terminal (4), and this is supplied to the FM modulators (58) and (5B). and,
In each, the FM signal is subjected to 6 cycles at one general transmission frequency of frequencies f1 and f2 between the luminance signal Y FM and the chroma signal CD, and the modulated audio signals SAFM□ and SAFM2 are obtained from each, and the hand bus fill ( 6A and (6B)
is supplied to combiners (38) and (3B) via.

Signals obtained from synthesizers 38) and (38) are supplied to rotating magnetic heads HA and HB having different azimuth angles through recording amplifiers (7A) and (7B), respectively.

A and HB are arranged with an angular interval of approximately 180°, and are rotated once by an I frame, for example, so that the head H
and HB are sequentially scanned on the magnetic tape field by field.

- As mentioned above, the head I (8 is the signal [sAFM□
, CD%YFM), and the head H8 receives a signal (S
AFM2, CD, YFM) are supplied to the magnetic tape (Tadochi), and TEIs are alternately formed on the recording trunks T having different recording azimuths as shown in FIG.

In this way, ζ is recorded into the video signal SV and the audio signal S.

The signal thus recorded is then reproduced as shown in FIG.

That is, during playback, the heads HA and HB are made to scan the recording trunk T and TR, respectively. Therefore,
Head HΔ and HB signal (SAF□1, CD-YF
M) and (SAFM2.co%YF)l) are regenerated.

The reproduction signal of the head HA is supplied to the A side terminal of the switch circuit 00) via the reproduction amplifier (98).

In addition, the playback signal of head ■] 8 is supplied to the B side terminal of switch circuit 1pi (101) via a playback amplifier (9B). Depending on the rotational position of During one field period of scanning, it is connected to the terminal on the B side.The continuous signal obtained from this switch circuit 00) is fed to the video signal N4 generation circuit (12), from which the luminance signals Y and A chroma signal C is obtained.

Furthermore, the reproduced signal to the head [1] is supplied to a band pass filter (13A) whose center frequency is fl after being passed through a reproduction amplifier (9A). A modulated audio signal SAFM1 is obtained from this bandpass filter (13A),
This is supplied to the A-side terminal of the switch circuit (14). In addition, the playback signal of head I (B) is output from the playback amplifier (9B).
After passing through (j), it is fed to a bandpass filter (13B) whose center frequency is f2.

A modulated audio signal SAFM2 is obtained from this bandpass filter (13B>) and is supplied to a frequency converter (15).The converter (15) receives a conversion signal (frequency f2 fx) from an oscillator (16). is supplied, and on its output side is a modulated audio signal SAF whose carrier frequency is converted to fl.
M□ is obtained and is supplied to the B side terminal of the ζ switch circuit (14) via the band pass filter (17).

A switching pulse PSW is supplied from the terminal (11) to the switch circuit (14) to the head H and is obtained according to the rotational position of HB. It is connected to the B-side terminal during one field period when the head HB is scanning the track TB. This switch circuit (14
The continuous modulated audio signal SAFM1 obtained by SA is a low-pass filter (20
), sample and hold circuit values 21), are obtained at the output terminal (24) via the muting circuit (22) and the low-pass filter (23).

By the way, if there is a scratch or defect on the tape, a dropout will occur in the playback signal of head I (Δ, HB) at the location of the scratch or defect. When recording on the audio trunk, the width of the audio trunk is usually relatively large, and the scratches and defects do not cover the entire width of the audio trunk, so dropouts in the playback signal are hardly a problem. , the FM-modulated audio signal SA as described above.
When multiplexing FMi and SAFM2 into video signals and recording them using the rotating magnetic head 118 and HB on tracks that are inclined with respect to the running direction of the tape, the width of the trunk is small, so scratches and defects may occur. , a dropout occurs in the reproduced signals of the FM modulated audio signals SAFMi and SAFM2, and the output of the FM demodulator (19), that is, the reproduced audio signal S
8. Pulse noise occurs.

The above-mentioned sample and hold circuit (21) is for pre-holding the audio signal SΔ at such a dropout portion to avoid noise appearing in the audio signal SA due to the dropout.

Dropout detection is done using a bandpass filter (13^)
and (13B) the resulting signals SAFM1 and SA
FM2 is supplied to the dropout detection circuit (25), and this detection signal SD is sent to the sample and hold circuit (25).
21) as a control signal.

In this way, dropouts are detected and the reproduced audio signal S
The method of applying pre-bold to Δ to remove noise caused by dropouts is effective when the frequency of dropouts is low, but when the frequency of dropouts is high, the effect is weak and it is more likely that continuous dropouts will occur. It is better to mute some parts.

The above-mentioned muting circuit (22) is for muting the reproduced audio signal SA when the frequency of dropouts is high. The above-described dropout detection signal SD is supplied to a muting signal generation circuit (26), which generates a muting signal SMU when the frequency of dropouts is low, thereby applying muting.

By the way, the conventional muting signal generation circuit (26)
is configured as shown in FIG. 5, for example.

That is, it is composed of 2111iI signal generating circuits (27) and (28) having a charging/discharging circuit and a comparator.

In the figure, the power terminal (29) is connected to the connection switch (30
), current sources (31), (32) and connection switches (3
3), and the current height 1 (31) and (32)
The connection point P1 is grounded via a capacitor (34). This capacitor (34) is of relatively small capacity and has a small time constant. The voltage ■1 obtained at the connection point Pz is supplied to the comparator (35).

Further, a dropout detection signal SD is supplied to the terminal (36), which is directly and inverted by an inverter (37) and supplied as a control signal to the connection switches (30) and (33), respectively. Then, the detection signal SD is at a high level.
1” and low level “0”, the respective connection switches (3
0) and (33) are turned on.

Here, when the detection signal SD is as shown in FIG. 6A, the voltage 1 at the connection point P1 is as shown by the solid line in FIG. 6B. Therefore, if the threshold level in the comparator (35) is V thl, then the comparator (35)
From the output side of 5), a signal shown in C in the figure is obtained.

Further, the power terminal (29) is grounded via the connection switch (38), the current sources (39), (40), and the connection switch (41), and the connection point P of the current sources (39) and (40)
2 is grounded via a capacitor (42).

This capacitor (42) is of relatively large capacity and has a large time constant. Voltage obtained at connection point P2■
2 is supplied to a comparator (43). Further, the signal obtained from the above-mentioned comparator (35) (shown in FIG. 6C) is directly and inverted by the inverter (44) and supplied as a control signal to the connection switches (38) and (41), respectively. .

Then, this signal is the sieve level “1” and the low level “0”.
At this time, the connection switches (38) and (41) are turned on, respectively.

Here, the voltage (2) at the connection point P2 becomes as shown in the sixth diagram. Therefore, if the threshold level in the comparator (43) is Vtb2, then the comparator (43)
) can obtain the signal shown in the figure E.

Further, the signals obtained from the comparators (35) and (43) are respectively supplied to an OR circuit (45). Then, the signal shown in FIG. 6F is obtained from this OR circuit (45), and this is obtained as the muting signal SHO at the output terminal (46).

A muting signal generation circuit (2
According to 6), the outputs of the signal generation circuits (27) and (28) having charging/discharging circuits with different time constants are logically summed to generate the muting signal SHO. Muting can be repeatedly turned on and off in short cycles, impairing the hearing sense (avoided by the output of the T!i signal generation circuit (28)), or it takes time for muting to turn on (the output of the signal generation circuit (27) can be avoided). Good muting can be applied without the inconvenience of M).

However, according to this example, two signal generation circuits (27)
and (2 days), which is wasteful in terms of construction, and also has the drawback that, for example, when integrated into an IC, two pins are required for the capacitors (34) and (42).

OBJECTS OF THE INVENTION In view of these points, the present invention is designed to have a simple configuration and to be easily integrated into an IC.

Summary of the Invention In order to achieve the above object, the present invention comprises a charging/discharging circuit having first and second discharge time constants and a comparator to which the output of the charging/discharging circuit is supplied, and the charging/discharging circuit is configured to perform charging/discharging by a dropout detection signal. The charging and discharging of the circuit is controlled, the discharge time constant is switched by the output of the comparator, and the output of this comparator is used as a muting signal.

Therefore, the configuration is simple as it can consist of one charging/discharging circuit and one comparator, and since there is only one charging/discharging circuit, only one capacitor is required.For example, when integrated into an IC, only one pin is required for the capacitor. This makes it easy to integrate into an IC.

EXAMPLE Hereinafter, an example of the present invention will be explained with reference to FIG. 7.

In the figure, the power terminal (47) is connected to the connection switch (
4B) is grounded through the current sources (49), (50) and the connection switch (51), and the current sources (49) and (5
The connection point P'r of 0) is grounded via a capacitor (52). Further, this connection point P'1 is grounded via a resistor (53) having a relatively 1 (11) resistance.
The voltage V'1 obtained at r is supplied to a comparator (54).

Then, from the output side of this comparator (54), an output terminal (5
5) is derived, and the output of this comparator (54) is supplied to the AND circuit 1/& (57) via an inverter (56).

Further, a dropout detection signal SD is supplied to the terminal (58). This detection signal SD is connected to the connection switch (48)
is supplied as a control signal to the inverter (59
) is supplied to the AND circuit (57). and,
The output of this AND circuit (57) is connected to the connection switch (51)
is supplied as a control signal to The connection switches (48) and (51) face each other and are turned on when a signal of bell "1" is supplied.

This example is configured as described above, and the connection switches (48) and (51) are controlled by the detection signal sD, and the capacitor (
52) is controlled. In this example, when the detection signal SD is as shown in FIG. 6, the voltage V'1 at the connection point P't is as shown by the broken line in FIG.

That is, if the threshold level in the comparator (54) is V thl, the signal obtained at the output of the comparator (54) will be at a low level aO'' at time t1.
to a high level "1" (see Figure 6G). Therefore, the output of the AND circuit (57) is held at a low level "0", and the connection switch (51) remains off. If this connection switch (51) is left off, the capacitor (52) will be discharged only through the resistor (53). Since this resistor (53) has a high resistance, the discharge time constant is switched from small to large at this time. Therefore, the discharging time constant is larger than the charging time constant, so the pressure V'1 at the connection point P'1 becomes gentler, and this voltage V'1 is the same as the broken line in Figure 6B. It becomes as shown in .

As a result, the signal shown in FIG. 6G is obtained from the output side of the comparator 54), and this is supplied to the output terminal (55) as the muting signal 5) 10.

In this manner, in this example, a muting signal substantially similar to the muting signal shown in the above-mentioned example of FIG. 5 can be obtained, and it has the same function as the example of FIG. 5.

According to this example, the configuration is simple because it includes one charging/discharging circuit and one comparator. Also, the capacitor is 1
Therefore, the number of pins for the capacitor when integrated into an IC can be 1 (hard), which facilitates integration into an IC.

Although not mentioned in the above embodiment, a comparator (54
) is composed of, for example, one having hysteresis.

Effects of the Invention According to the present invention described above, the configuration is simple as it can consist of one charging/discharging circuit and one comparator, and since the charging/discharging circuit is 1 + 11d, the capacitor can only be 1111i1, and it can be integrated into an IC. It's easy.

[Brief explanation of drawings]

Figure 1 is a configuration diagram showing the recording system of a VTR, Figures 2 and 3
4 is a block diagram showing a reproduction system of a VTR, FIG. 5 is a block diagram showing a conventional muting signal generation circuit, and FIG. 6 is a waveform diagram for explaining the same. ,
FIG. 7 is a configuration diagram showing an embodiment of the present invention. (48) and (51) are connection switches, (49) and (50) are current sources, (52) are capacitors, (5
3) is a resistor, (54) is a comparator, and (55) is an output terminal.

Claims (1)

[Claims] A charging/discharging circuit having first and second discharge time constants and a charging/discharging circuit in which an FM-modulated audio signal reproduced by a magnetic head from a magnetic track is outputted via a demodulation circuit and a muting circuit. The charging and discharging of the charging and discharging circuit is controlled by the dropout detection signal detected from the FM modulated audio signal, and the output of the comparator controls the discharging time constant. A muting signal generating circuit characterized in that the output of the comparator is switched and the output of the comparator is used as a muting signal for controlling the muting circuit.