JPH05103299A - Reproduction equalizing circuit - Google Patents

Abstract

PURPOSE:To provide a reproduction equalizing circuit which permits the deterioration of S/N in a video signal and the decrease of an inversion mergin to be min. by considering that the increase of S/N change and an inversion phenomenon gives more influence to visual picture quality deterioration than the change of the frequency characteristic of the video signal does in a same screen arid adaptively changing the reproduction equalizing characteristic even in a case when a reproduction output is unstable or reduced. CONSTITUTION:The two equalizing circuits for a normal output and for a low output 3 and 21 which have the different equalizing characteristics, a switch circuit 5 changing-over the outputs of the two equalizing circuits in accordance with an input signal level and a reproduction output level detecting circuit 6 generating a control signal for changing over the switch circuit in accordance with the input signal level are provided and these outputs are changed-over in accordance with the reproduction output level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproduction equalizing circuit in a recording / reproducing apparatus such as a video tape recorder or a video disc.

[0002]

2. Description of the Related Art In a video tape recorder for FM-recording a video signal, an equalizing circuit corrects the frequency characteristic of amplitude for a reproduced FM signal. this is,
This is to correct the sideband level that has changed due to the lower sideband enhancement effect in the recording / reproducing process and the high frequency output reduction characteristic. At this time, even if the demodulated signals have the same frequency characteristics, the equalization characteristics change the margins for the S / N and the inversion phenomenon. This correction has no phase distortion at all, and the frequency characteristic of the amplitude correction is generally called the cosine characteristic (for example, VTR technology, Japan Broadcasting Corporation pp47-50).

FIG. 4 is a block diagram of an equalizing circuit,
FIG. 8 shows the relationship between the equalizing characteristic and the input / output carriers and side waves. In FIG. 4, the reproduced FM signal input to the input terminal 30 is the matching resistor 31 for the delay element.
To the delay element 32, and the other is supplied to the high input impedance amplifier 34. The output of the delay element 32 is supplied to the high input impedance amplifier 33. On the other hand, the output of the high input impedance amplifier 34 is supplied to the subtraction amount adjustment circuit 35. Then, the output of the high input impedance amplifier 33 and the subtraction amount adjustment circuit 3
After being added by the adder circuit 36, the output of 5 is supplied to the output terminal 38 via the amplitude adjusting circuit 37. Adder circuit 36
Is for inverting and adding the output of the subtraction amount adjusting circuit 35 to the output of the high input impedance amplifier 33. Further, the amplitude adjusting circuit 37 adjusts the output of the adding circuit 36 to the optimum amplitude for the FM demodulating circuit in the subsequent stage.

FIG. 8 shows the relationship between the equalizing characteristic and the carrier and side waves at the input / output at this time. Input terminal 30
The relationship between the carrier and the side wave of the reproduced FM signal input to
Normally (FIG. 8) becomes as shown in (a). That is, due to the lower sideband enhancement effect and the high frequency output lowering characteristic, the relationship of lower side wave J-1> carrier J0 and carrier J0> upper side wave J + 1 is established. If correction is performed using the equalizing characteristics shown in FIGS. 8B and 8B, the data is output to the output terminal 38 in a relationship close to that before recording as shown in FIGS.
Demodulation is possible.

[0005]

However, the conventional equalizer circuit has the above-mentioned input / output relation in the case of a relatively stable normal reproduction output (reproduction envelope) as shown in FIG. However, if the playback output becomes unstable or the playback output drops for some reason,
The input / output relationship as described above may not be achieved.

That is, the reproduction output may be unstable or lowered due to burn-in, spacing, tracking error during VTR recording / reproduction, or linearity during compatibility. This reproduction output reduction phenomenon has two characteristics, one with and without frequency characteristics when the output is reduced.
Classified into one. That is, since the tracking error and the linearity have no frequency characteristic, the relative relationship between the carrier and the sideband is almost the same as usual. On the other hand, with regard to burn-in and spacing, the high-frequency output is further reduced than usual, so that the relative output of the carrier with respect to the lower side wave and the relative output of the upper side wave with respect to the carrier are reduced as compared with the usual case.
However, regardless of the presence / absence of the frequency characteristic, the final S / N is inevitably deteriorated due to the decrease in C / N due to the decrease in reproduction output.

FIG. 5 shows a normal reproduction output (reproduction envelope), and FIG. 6 shows an unstable reproduction envelope including a reduction in reproduction output. In the case of the reproduction envelope as shown in FIG. 6, in the low output period shown in B, the S / N is deteriorated and the margin for the inversion phenomenon is decreased. Since the S / N deterioration and the decrease of the inversion margin occur in the same field (frame), the S / N of a part of the screen is significantly deteriorated, or the inversion phenomenon is remarkable only in a part of the screen. There was a problem that

When the reproduction output is reduced due to burn-in or spacing that further lowers the high-frequency output, the conventional equalize characteristic and the relationship between the carrier and the side wave at the input / output are shown in (a) and (b) of FIG. ), (C). (Figure 7)
As is clear from (a), when the high frequency component is further reduced in addition to the reduction of the reproduction output, according to the conventional equalization shown in (FIG. 7) (b), the carrier is further suppressed and Due to the significant reduction in the reproduction output of the wave, the situation becomes similar to the lower side wave and the one side wave only of the carrier even after equalization, as shown in FIG. 7C. In addition, the lower side wave and the carrier level are close to each other. Therefore, the demodulated signal is S
Along with deterioration of / N and reduction of inversion margin.

The present invention considers that, within the same screen, a change in the S / N ratio and an increase in the inversion phenomenon affect the visual quality deterioration rather than the change in the frequency characteristic of the video signal. By providing a reproduction equalization circuit that adaptively changes the reproduction equalization characteristic even when the reproduction output is unstable or drops, the reproduction signal equalization circuit and the reduction of the inversion margin are minimized. To do.

[0010]

According to the present invention, the equalizing characteristic is adaptively changed according to the input signal level. The n equalizing circuits having different equalizing characteristics and the n equalizing circuits are provided. A switch circuit for switching the output of the equalizer circuit according to the input signal level and a reproduction output level detection circuit for generating a control signal for switching the switch circuit according to the input signal level are configured.

[0011]

According to the present invention, with the above-described structure, the S / N ratio is better than the change of the frequency characteristic of the video signal in the same screen.
In consideration of the fact that the change and the reversal phenomenon affect the visual image quality deterioration, by adaptively changing the reproduction equalization characteristic even when the reproduction output is unstable or lowered, The S / N deterioration of the video signal and the reduction of the inversion margin are minimized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a reproduction equalizing circuit according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a reproduction equalizing circuit according to the first embodiment of the present invention. (FIG. 5) shows a normal reproduction output (reproduction envelope), and (FIG. 6) shows an unstable reproduction envelope including a reduction in reproduction output.
(FIG. 7) (a), (d), and (e) show an example of the relationship between the equalizing characteristic at low output and the carrier and side waves at input / output. (FIG. 8) shows an example of the relationship between the equalization characteristic at the time of normal output and the carrier and side waves at the input / output.

In FIG. 1, the reproduction output signal (reproduction FM signal) supplied to the input terminal 1 is divided into three systems of a normalization equalizing circuit 3, a low output equalizing circuit 4 and a reproduction output level detecting circuit 6. Is supplied to. The output of the normalizing equalizer circuit 3 and the output of the low-output equalizing circuit 4 are supplied to the switch circuit 5, and either one of the two equalizing circuits is switched within the synchronizing signal period according to the reproduction output level. , To the output terminal 7. The reproduction output level detection circuit 6 detects the level of the reproduction output signal and supplies a control signal for switching the output of the switch circuit 5 to the switch circuit 5 within the synchronization signal period supplied from the input terminal 2. The switch circuit 5 switches the output according to the control signal supplied from the reproduction output level detection circuit 6.

The normalizing equalizer circuit 3 has the structure shown in FIG.
As shown in (b), it has an equalizing characteristic having a peak in the frequency region of a white clip or higher, and it is due to a normal reproduction envelope shown in (FIG. 5) or a normal output period shown in A of (FIG. 6). Is an equalizing circuit. An example of the relationship between the equalization characteristic and the carrier and side wave at the input / output at this time is shown in FIG. The relationship between the carrier and the side wave of the reproduced FM signal input to the input terminal 1 is normally as shown in (a) of FIG. That is, due to the lower sideband enhancement effect and the high frequency output lowering characteristic, the relationship of lower side wave J-1> carrier J0 and carrier J0> upper side wave J + 1 is established. When correction is performed with equalization characteristics as shown in (FIG. 8) and (b), it is output to the output terminal 7 in a relationship close to that before recording as shown in (FIG. 8) and (c), and faithful FM demodulation is performed. Is possible.

On the other hand, the low output equalizing circuit 4 has an equalizing characteristic having a peak at the carrier frequency as shown in (FIG. 7) (d), and when the reproduction output is lowered or (FIG. 6). It is an equalizer circuit for the low output period shown in B. An example of the relationship between the equalization characteristic and the carrier and side wave at the input / output at this time (FIG. 7) (a),
Shown in (d) and (e). Playback F input to input terminal 1
When the relationship between the carrier and the side wave of the M signal is as shown in (FIG. 7) (a), that is, when the high frequency component is further reduced in addition to the reduction in the reproduction output, (FIG. 7) ( When the correction is performed with the equalizing characteristic as shown in (d), (FIG. 7)
It is output to the output terminal 7 in the relationship as shown in (e). Compared with (FIG. 8) (c), this means that the frequency characteristic after demodulation deteriorates, but the deterioration of S / N and the decrease of the inversion margin can be minimized.

In the normalizing equalizer circuit and the low output equalizing circuit of this embodiment, the delay element of the low output equalizing circuit is the normal equalizing circuit, as can be seen from the peak frequency of the equalizing characteristic. The delay time is longer than that of the delay element. Therefore, as in the second embodiment shown in FIG. 2, two equalizing characteristics are realized by switching between the normal delay element 12 and the low output delay element 13 by the switch circuits 11 and 14. May be. In this case, the delay element matching resistor 10, the high input impedance amplifiers 15 and 16, the subtraction amount adjusting circuit 17, the adder circuit 18, and the amplitude adjusting circuit 20 are each required to be one, so that the circuit scale and cost can be significantly reduced. Is. The operation of the second embodiment will be described. The reproduced FM signal input to the input terminal 8 is divided into two systems through the delay element matching resistor 10 and one of them is delayed by the switch circuit 11 for normal use. It is supplied to the element 12 and the low output delay element 13, and the other is supplied to the high input impedance amplifier 16. The outputs of the normal delay element 12 and the low output delay element 13 are supplied to the high input impedance amplifier 15 via the switch circuit 14. On the other hand, the output of the high input impedance amplifier 16 is supplied to the subtraction amount adjustment circuit 17. Then, after the output of the high input impedance amplifier 15 and the output of the subtraction amount adjustment circuit 17 are added by the adder circuit 18,
It is supplied to the output terminal 21 through the amplitude adjusting circuit 20.

The adder circuit 18 inversely adds the output of the subtraction amount adjusting circuit 17 to the output of the high input impedance amplifier 15. Further, the amplitude adjusting circuit 20 includes the adding circuit 1
The output of No. 8 has the optimum amplitude for the FM demodulation circuit in the subsequent stage. The reproduction output level detection circuit 19 switches the switch circuits 11 and 14 according to the input reproduction FM signal level.
Is generated during the synchronizing signal period of the synchronizing signal input from the synchronizing signal input terminal 9. The circuit size and cost can be further reduced by sharing the reproduction output level detecting circuit of this embodiment with the dropout pulse generating circuit.

FIG. 3 is a block diagram of the third embodiment of the invention. FIG. 9 shows an example of the relationship between the equalization characteristic at low output and the carrier and side waves at input / output, and FIG. 10 shows the equalization characteristic at normal output and carrier and side at input / output. An example of the relationship of waves is shown.

In FIG. 3, the reproduction output signal (reproduction FM signal) supplied to the input terminal 22 is supplied to two systems of a first equalizing circuit 23 and a second equalizing circuit 24. The output of the second equalizer circuit 24 is the limiter circuit 25.
After the amplitude is limited by, it is supplied to the addition amount adjusting circuit 26. The outputs of the first equalizing circuit 23 and the addition amount adjusting circuit 26 are added by the adding circuit 27 and then supplied to the output terminal 29 via the amplitude adjusting circuit 28. The adding circuit 27 includes a first equalizing circuit 23 and an adding amount adjusting circuit 26.
Is added in the positive phase. The amplitude adjusting circuit 28 adjusts the output of the adding circuit 27 to the optimum amplitude for the FM demodulating circuit in the subsequent stage.

In this embodiment, the equalizing characteristics are continuously changed from the characteristics close to the normalizing equalizing circuit in the first embodiment to the characteristics close to the low output equalizing circuit according to the reproduction output level without a switch circuit. It is variable. The first equalizer circuit 23 has characteristics close to those of the normal equalizer circuit of the first embodiment, and the second equalizer circuit 24 has characteristics close to those of the low output equalizer circuit of the first embodiment. ing.

FIG. 10 shows an example of the relationship between the carrier and the side wave at the equalizing characteristic and the input / output during the normal reproduction output. (FIG. 10) (a) and (e) show the relationship between input and output carriers and side waves, (b) shows the characteristics of the first equalizing circuit system, and (c) shows the second equalizing circuit system (limiter). The characteristics (including the addition amount adjusting circuit) and the total characteristics are shown in (d). As is apparent from the figure, the first equalizing circuit system has characteristics close to those of the normalizing equalizing circuit in the first embodiment. On the other hand, with respect to the second equalizing circuit system, the second equalizing circuit 24 has characteristics close to those of the low output equalizing circuit of the first embodiment, but the amplitude is limited by the limiter circuit 25 to obtain a constant output. Become. As a result, the total characteristics are close to those of the normalizing equalizer circuit in the first embodiment,
The relationship between the carrier and the side wave is also corrected from the input (a) to the output (e), and is output to the output terminal 29 in a relationship close to that before recording,
It enables faithful FM demodulation.

FIG. 9 shows an example of the relationship between the equalizing characteristic and the carrier and side wave at the input / output at low output. (FIG. 9) (a) and (e) show the relationship between input and output carriers and side waves, and (b) shows the characteristics of the first equalizing circuit system.
Further, (c) shows the characteristic of the second equalizing circuit system (including the limiter and the addition amount adjusting circuit), and (d) shows the total characteristic. As is apparent from the figure, the first equalizing circuit system has characteristics close to those of the normalizing equalizing circuit in the first embodiment. On the other hand, in the second equalizing circuit system, the second equalizing circuit 24 has characteristics close to those of the low output equalizing circuit in the first embodiment, and since the output is low, the amplitude is not limited by the limiter circuit 25. , The characteristics of the second equalizing circuit 24 appear as they are.
As a result, the total characteristics are close to those of the low output equalizer circuit in the first embodiment, and the relationship between the carrier and the side wave is corrected from the input (a) to the output (e).
It is output to the output terminal 29. This is the above (Figure 10)
Compared to (e), although the frequency characteristic after demodulation deteriorates, the deterioration of S / N and the decrease of the inversion margin can be minimized.

As the actual equalizing characteristic, since the equalizing characteristics of the above two examples are continuously changed, the visual image quality change at the characteristic change point can be minimized.

[0025]

According to the present invention, in the same screen, a change in S / N and an increase in inversion phenomenon have a greater effect on visual image quality deterioration than a change in frequency characteristic of a video signal. Considering this, even when the reproduction output is unstable or lowered, the reproduction equalization circuit adaptively changes the reproduction equalization characteristic to minimize the S / N deterioration of the video signal and the decrease of the inversion margin. Can be configured, and its effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of a reproduction equalizing circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a reproduction equalizing circuit according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a reproduction equalizing circuit according to a third embodiment of the present invention.

FIG. 4 is a block diagram of a conventional reproduction equalization circuit.

FIG. 5 is a waveform diagram of a normal stable reproduction output signal (reproduction envelope).

FIG. 6 is a waveform diagram of an unstable reproduction output signal (reproduction envelope) including a decrease in reproduction output.

FIG. 7A is a characteristic diagram showing a relationship between a carrier and a side wave when a reproduction output is reduced. FIG. 7B is an equalizing characteristic diagram of the same. FIG. 7C is a characteristic showing an example of a relationship between a carrier and a side wave after the correction. Figure (d) Characteristic diagram showing equalizing characteristics at low output (e) Characteristic diagram showing the relationship between the carrier and side waves after the same correction

FIG. 8A is a characteristic diagram showing an example of a relationship between a carrier and a side wave of a normal stable reproduction output. FIG. 8B is a characteristic diagram showing an equalization characteristic of the same carrier.

9A is a characteristic diagram showing a relationship between a carrier and a side wave when a reproduction output is reduced. FIG. 9B is an equalizing characteristic diagram showing characteristics of a first equalizing circuit system. FIG. 9C is a characteristic of a second equalizing circuit system. (D) Equalization characteristic diagram showing total characteristics (e) Characteristic diagram showing the relationship between the carrier and side waves after the correction

10A is a characteristic diagram showing a relationship between a carrier and a side wave at the time of normal stable reproduction output. FIG. 10B is an equalizing characteristic diagram showing characteristics of the first equalizing circuit system. FIG. 10C is a second equalizing circuit system. (D) Equalize characteristic diagram showing the total characteristic (e) Characteristic diagram showing the relationship between the corrected carrier and side wave

[Explanation of symbols]

 1 Input Terminal 2 Input Terminal 3 Normal Equalizing Circuit 4 Low Output Equalizing Circuit 5 Switch Circuit 6 Reproduction Output Level Detection Circuit 7 Output Terminal 8 Input Terminal 9 Input Terminal 10 Delay Element Matching Resistor 11 Switch Circuit 12 Normal Delay Element 13 Low output delay element 14 Switch circuit 15 High input impedance amplifier 16 High input impedance amplifier 17 Subtraction amount adjustment circuit 18 Addition circuit 19 Reproduction output level detection circuit 20 Amplitude adjustment circuit 21 Output terminal 22 Input terminal 23 First equalization circuit 24 Second Equalizer circuit 25 Limiter 26 Addition amount adjustment circuit 27 Addition circuit 28 Amplitude adjustment circuit 29 Output terminal

Claims (5)

[Claims] 1. A reproduction equalizing circuit, which adaptively changes the equalizing characteristic according to an input signal level. 2. N equalizer circuits having different equalize characteristics, a switch circuit for switching outputs of the n equalizer circuits according to an input signal level, and control for switching the switch circuit according to the input signal level. And a reproduction output level detecting circuit for generating a signal. 3. N equalizing circuits having different equalizing characteristics, a switch circuit for switching outputs of the n equalizing circuits according to an input signal level within a sync signal period, and the switch circuit for the input signal level. And a reproduction output level detecting circuit for generating a control signal to be switched within the synchronizing signal period according to the above. 4. A dropout pulse generation circuit is shared with the reproduction output level detection circuit.
Alternatively, the reproduction equalizing circuit described in 3. 5. A first equalizing circuit, a second equalizing circuit having an equalizing characteristic different from that of the first equalizing circuit, a limiter circuit for limiting the amplitude of the output of the second equalizing circuit, and the limiter. An addition amount adjusting circuit for adjusting the output amplitude of the circuit; an adding circuit for adding the output of the first equalizing circuit and the output of the adding amount adjusting circuit; and an amplitude adjusting circuit for adjusting the output amplitude of the adding circuit. A reproduction equalizing circuit having.