JPH0481185A - Characteristic changeover circuit - Google Patents

Abstract

PURPOSE:To improve the deterioration in picture quality being a problem in the case of compatible reproduction by providing a discrimination means whether the mode is the self recording and reproduction or the compatible reproduction and revising the characteristic of a video processing circuit based on the output of the discrimination means. CONSTITUTION:A microcomputer 11 discriminates whether the mode is the self recording and reproduction or the compatible reproduction based one output of a detection circuit 10. That is, in the case of the self recording and reproduction, when the state of tracking is changed, the envelope is almost flat and only the level is changed. On the other hand, in the case of the compatible reproduction, the level of the first half, the latter half or the middle of the envelope is especially reduced. When the self recording and reproduction or the compatible reproduction is discriminated, the characteristic changeover is executed in response to the result. For example, when the mode is discriminated to be the self recording and reproduction mode and the tracking value is within a prescribed range from the tracking center value, the tracking value is forcibly set to the tracking center.

Description

[Detailed description of the invention] (b) Industrial application fields The present invention relates to a characteristic switching circuit.

(b) Conventional technology For example, Utility Model Application No. 60-705 (G11B51027)
shows a device for switching the characteristics of a video processing circuit in a video tape recorder according to the playback output level. This improves the reproduced image quality.

(c) Problems to be Solved by the Invention The present invention aims to reduce the effects of increased crosstalk from adjacent tracks, mechanical noise, etc. caused by the inability of the magnetic head to completely trace a track during compatible playback. purpose.

(d) Means for Solving the Problems The present invention is provided with means for determining whether self-recording or compatible playback is being performed, and the characteristics of the video processing circuit are changed based on the output of this determining means.

(E) Effect: Since the characteristics of the video processing circuit are changed depending on whether self-recording/playback or compatible playback is being used, it is possible to improve the deterioration in image quality that occurs during compatible playback.

(f) Example Hereinafter, the present invention will be described in detail with reference to the drawings.

Figure 1 is a block diagram of a VTR playback system, Figure 2 is a circuit diagram of an equalizer circuit, Figure 3 is a circuit diagram of a de-emphasis circuit, Figure 4 is a block diagram of an IH noise canceller, and Figure 5 is a high-verse diagram. FIG. 2 is a block diagram of a filter type noise canceller.

In the figure, 1 is a magnetic head, 2 is a preamplifier, and 3 is an F
M equalizer, 4 is an FM demodulator, 5 is a de-emphasis circuit, 6 is an IH (H is one horizontal period) delay line, 7 is a line noise canceller, 8 is a /\path type noise canceler, 9 is an addition circuit, 10 is a The envelope detection circuit 11 is a microcomputer, and performs automatic tracking/king operations and self-recording/compatible playback. 12 is a chroma processing circuit.

The microcomputer 11 sets the trunking to the longest point based on the output of the detection circuit 10, discriminates between self-recording/'compatible playback, and sends the result to the luminance signal processing circuit. Then, based on this discrimination output, the characteristics are changed using any one or a combination of the equalizer circuit 3, de-emphasis circuit 5, line noise cancel 7, and bypass noise cancel 8.

Next, the specific configurations of each will be explained according to FIGS. 2 to 5.

In FIG. 2, a CR resonant circuit is provided on the collector of the transistor Tri to compensate for the drop in the high frequency range of the reproduced FM signal. The LC resonant circuit on the emitter side is provided for a tranoa of 629 KHz (the frequency of the low-frequency chroma signal).

An LCR series resonant circuit 20 is further connected to the emitter side of the transistor Tri, and this resonant circuit 20 is controlled by a transistor switch Tr2. A determination signal from the microcomputer 11 is applied to the base of the transistor Tr2, and when it is determined that compatible reproduction is performed, the resonant circuit 20 becomes operational. This emphasizes the resonant frequency of the resonant circuit 20 in the FM reproduction signal. By selecting the frequency to be emphasized as the reproduction F~1 carrier center frequency, side hand is suppressed and the S/N ratio is improved.

In FIG. 3, the de-emphasis characteristic is determined by the element connected to the collector of the transistor Tr4. Therefore, when the switch transistor Tr5 is turned on, the capacitor and resistor become meaningful. That is, when compatible playback is determined, the high frequency components are further suppressed, and the S/N ratio is improved.

In FIG. 4, 21 and 24 are subtracters, 22 is a limiter, and 23 is a doubler circuit, in which signals with small amplitude among signals without IH correlation are canceled as noise. In this circuit, when compatible reproduction is determined, the level applied by the limiter and/or the constant K are made larger than in the normal case, and the characteristics are changed in the direction of increasing the amount of noise cancellation.

In FIG. 5, 25 is a filter for extracting noise components, 26 is a limiter, 27 is a doubler circuit, and 28 is a subtraction circuit, in which high-frequency components and low-level signals are regarded as noise and canceled.

Even in this configuration, when it is determined that compatible playback is being performed, the level applied by the limiter and/or the constant K are made larger than usual, and the amount of noise cancellation is changed in the direction of increasing.

Next, a method for determining self-recording and compatible playback based on the shape of the envelope will be explained. In other words, in the case of self-recording and playback, when the tracking state changes, the envelope is almost flat and only the level changes;
In the case of compatible playback, the envelope shape changes because the first half, second half, or middle level of the envelope is particularly lowered due to the linearity of the track.

That is, when the tracking state changes as shown in FIG. 6 - ■ (■ is the best state), the shape of the envelope changes as shown in FIG. 7, for example.

FIG. 8 shows a flowchart when this discrimination method is used. Auto tracking (AT
R) Operation is initiated. In auto tracking operation,
First, the tracking value (the amount of delay given to the playback control signal) is set to the value (tracking center value) for self-recording/playback. In this state, the envelope level for one frame is sampled at an interval of 1 msec, and is summed (integrated) to obtain a value indicating the envelope level.

At the start of ATR, in order to determine the shape of the envelope,
Out of 15 samplings for one field, the sum of the first and second sampling values representing the first half, and the sum of the seventh and eighth sampling values representing the center. , the sum of the 14th and 15th sampling values representing the latter half is calculated and stored.

These are the three numerical values representing the envelope shape at the start of ATR, and will be used later.

Next, a comparison of envelope levels is made. This is to find the point where the envelope is maximum, and compares the previous level and the level obtained this time. The operation is controlled based on this result.

After the level comparison is completed, conditional branching is performed depending on the comparison result and past actions. If the ATR operation has ended, the process proceeds to the next step, which is determination of self-recording/playback/compatible playback.

At the start of ATR, there is no value to compare, so next the tracking value is changed by a predetermined amount. The direction of tracking value change is determined in advance, and first, as shown in Figure 7, the direction of increasing the delay amount (from ■ to ■)
Change to After the change, the playback envelope will be sampled again. This loop is then repeatedly executed until the ATR operation is completed.

Changes in tracking values are subsequently carried out as usual. If the current level is greater than the previous envelope level, the direction of the change remains the same. When the current level becomes smaller than the previous level a predetermined number of times (for example, three times) in succession, the direction of change is changed to a direction that reduces the amount of delay. In other words, it is determined that point (2) in FIG. 8 has been reached. However, the tracking value that starts after the change is a value that is a predetermined number of values (three values before) the current value. This shortens the time required to complete ATR as much as possible.

Even after reversing the change direction, if the current level is large, the change continues in the same direction. When the current level becomes smaller consecutively a predetermined number of times (for example, three times), the direction is reversed again. In other words, it is determined that the point shown in Figure 8 (■) has been reached. The starting point after the change is the same as point ■ (3 points).
) is the previous value. Thereafter, the level comparison is performed again, and when the current level becomes smaller a predetermined number of times (for example, three times) in succession, it is assumed that the envelope becomes the maximum at the tracking value from the predetermined number of times before. By setting this value, the ATR operation ends.

Data collection for determining the shape of the envelope is also performed at points ■ and ■ in FIG. In other words, the shape of the envelope is checked at three locations. Next, a method for determining self-recording/playback/compatible playback will be explained. Mazu, ATR
It is determined whether the level D of the envelope at the end of the operation is greater than a predetermined reference level Z. If it is small, it is immediately determined that compatible playback is being performed. If it is larger, proceed to the next condition. In the next step, envelope shape determination is performed.

The envelope shape is determined as shown in FIG. At each check point, values representing the first half, middle, and second half levels are stored, and these values are used. Let A be the level difference between the first half and the center, and B be the level difference between the second half and the center. If the value of A or B is larger than the predetermined value X, it is determined that the shape is not flat. For example, if it is down by 25% or more, it may be determined that it is not flat.

If it is determined that the data is not flat at two or more of the three check points, it is determined that compatible playback is being performed. On the other hand, if there are two or three flat points, proceed to the next step.

In the next step, self-recording/compatible playback is determined depending on how far apart the standard tracking value (delay amount in the case of self-recording/playback) and the tracking value after ATR are. That is, if the tracking value after ATR does not fall within a predetermined range centered around the standard tracking value, it is determined that compatible playback is being performed. If it is within the range, it is judged as self-recording. In the embodiment, this predetermined range is changed depending on the result of shape discrimination.

In other words, in this step, it is checked whether the difference C between the tracking center value and the tracking value after ATR is smaller than a predetermined value).
is changed depending on the case where the flat state occurs twice and the case where it occurs three times. If it becomes flat all three times, the value of Y is increased to widen the range in which it is determined that self-recording/reproduction is occurring.

This is because if the flat state does not occur two out of three times, there is a risk of misjudgment unless the range for determining self-recording is made narrower.

When self-recording/playback/compatible playback is determined, the characteristics are switched as described above in accordance with the result. For example, the 8th
In the case of the embodiment shown in the figure, when it is determined that self-recording/reproduction is being performed by the operation in the flowchart, and the tracking value after ATR is within a predetermined range from the tracking center value, the operation of forcibly setting the tracking value to the tracking center is performed. Let's do it. Note that the predetermined range in this case is set narrower than the predetermined range in FIG. 9.

(G) Effects of the Invention As described above, according to the present invention, when compatible playback is determined, the characteristics of the video processing circuit are changed.
S/N and image quality have been improved and are effective.

[Brief explanation of drawings]

1, 2, 3, 4, and 5 are circuit diagrams showing the configuration of the embodiment; FIGS. 6, 7, and 8;
FIG. 9 is an explanatory diagram of a method for determining self-recording/playback/compatible playback. 3... Equalizer, 5... De-emphasis, 78
...Noise canceller, 11...Microcomputer.

Claims (1)

[Claims] (1) A characteristic switching circuit comprising means for determining self-recording/compatible reproduction based on playback output, and means for changing characteristics of a video processing circuit based on this determining means.