JPS59160806A - Dropout compensating circuit - Google Patents

Abstract

PURPOSE:To compensate a dropout sufficiently by utilizing the charging and discharging of a capacitor by inserting an analog switch into part of a de-emphasis circuit having the capacitor connected between a reference potential and a signal path where the 1st resistance is connected in series. CONSTITUTION:When the waveform at the input terminal (a) of the analog switch 7 reaches a point (f), the analog switch 7 is opened and the integration of the de-emphasis circuit is stopped, so that the output waveform of a low-pass filter appears. Consequently, the waveform changes from the point (f) to a point (g) to obtain a waveform tracing points (b), (c), and (d). When a dropout detection signal goes down from a high level to a low level again, the analog switch 7 is closed to make a connection between the input terminals (a) and (b), so the potential at the output terminal where the potential at the point (f) is held so far varies to the potential at the point (d). Thus, the waveform obtained at the output terminal (b) of the analog switch 7 becomes faithfully a waveform which has no dropout as shown by a dotted-line part. The signal with this waveform is outputted through an output amplifier 6 to obtain sufficient dropout compensation effect.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dropout compensation circuit, and particularly to a dropout compensation circuit for compensating for dropouts in a reproduced audio signal in a video disk device or video tape recorder device that records or reproduces an audio signal by FM modulating it. This invention relates to improvements in such dropout compensation circuits.

FIG. 1 is a block diagram showing an example of a conventional dropout compensation circuit. First, the sub-fine dropout compensation circuit will be explained with reference to FIG. 1. 3.
;F! j;'F5, a video record whose signal is FM modulated and recorded on a recording medium such as a disk or magnetic tape.
In a disc device or a video tape recorder device, an FM signal of audio reproduced from a recording medium is supplied to an FM demodulator 1, subjected to FMI modulation, and returned to an audio signal. FM revenge
In addition to the TLL articulation multiple signal, the output of the quadrupler 1 also contains an FM carrier wave component generally in a frequency band sufficiently higher than the voice band.

- For example, in the case of optical video discs, the audio band is DC to 20 kHz, while the audio carrier frequency is approximately 2.3 MHz or approximately 2.8 MHz. The aforementioned audio carrier wave frequency component is unnecessary for the demodulated audio signal, and this audio carrier wave frequency component is removed by the low-pass filter 2.

The output signal of the low-pass filter 2 is input to a pre-hold circuit 3. The pre-hold circuit 3 receives the reproduced audio F.
The dropout detection signal outputted from the dropout detector 4 to which the M signal is applied is compensated for the dropout by holding the value of the audio signal before the dropout occurs during the dropout occurrence period. There is.

By the way, when transmitting a signal by FM modulation, FM
In order to suppress triangular noise generated by modulation and demodulation, the recording side performs so-called pre-emphasis, which expands the high frequency components of the audio signal, and then performs FM modulation. On the reproduction side, in contrast to the recording side, it is common to perform so-called de-emphasis, which suppresses the high frequency components of the FM*II audio signal. The output of the pre-hold circuit 3 is in a state in which the high frequency components of the audio signal are expanded, so after the high frequency components are suppressed by the de-emphasis circuit 5, it is output as an audio signal via the output amplifier 6. Output.

FIG. 2 is a waveform diagram for explaining the operation of the dropout compensation circuit shown in diagram mi. Next, the operation will be explained. The dropout detector 4 is well known to be of an envelope detection type, which detects the envelope of the FM audio signal as shown in Figure 2 (A) and detects the input FM audio signal as shown in Figure 2 (B). Obtain a waveform that corresponds to the signal envelope.

When this waveform drops below an arbitrary set level v1, it is regarded as a dropout, and a dropout detection signal shown in 2nd vA(C> is output. On the other hand, the input of the pre-hold circuit 3 is supplied with The output signal of the low-pass filter 2 with the waveform shown in FIG. 2(D) is input.
In the waveform ↑, an abnormality in the waveform due to dropout occurs from point a to point b and then to point 0. The pre-hold circuit 3 detects the waveform (second
The potential shown in Figure (D)), that is, the potential at point e, is held and held until the dropout detection signal becomes low level again. Then, in pre-hold circuit 3, at the moment when the dropout detection signal changes from high level to low level, the potential at point d of the original waveform ←, ! !
I'm supposed to go home. Therefore, prefix hold times! ! The output of i3 has the waveform shown in FIG. 2(E). The output signal of the pre-hold circuit 3 is input to a de-emphasis circuit 5 consisting of a resistor R1 and a capacitor C1, and this de-emphasis circuit 5 is a type of integrating circuit. For this reason, the output waveform of the integrating circuit 5 is integrated as shown in FIG. 2(E), resulting in a dropout-compensated waveform as shown in FIG. 2(F). Then, the dropout-compensated output signal is outputted via the output amplifier 6 having a sufficiently high input resistance so as not to disturb the characteristics of the differential circuit 5.

However, in the dropout compensation circuit described above, the dropout detector 4 detects dropout and detects the dropout. Since some delay time occurs before the aS pulse is output, the waveform after the delay time when dropout occurs is held. For this reason, 1. The waveform shown in the second m1 (F) after dropout compensation becomes considerably different from the original waveform shown by the dotted line, and there is a drawback that the effect of the dropout and bulgeout compensation is considerably reduced.

As an example of a conventional device devised to eliminate such drawbacks, a delay is provided to compensate for the delay time required until a dropout detection pulse is generated between the low-pass filter 2 and the pre-hold circuit 3. A device with a circuit inserted has been devised.

Such a method, as shown by the attack shape in Figure 2 (G),
The output waveform of the low-pass filter 2 is delayed by Δτ using a delay element. By pre-bolding the waveform before dropout occurs, the output of the pre-hold circuit 5 has the waveform shown in FIG. 2(H). When this waveform is passed through the de-emphasis circuit 5, it becomes a dropout-compensated waveform as shown in FIG. 2(1). The waveform shown in FIG. 2 (1) is
Compared to the waveform shown in FIG. 2(F), this waveform is much more faithful to the original waveform, and a sufficient dropout compensation effect can be obtained. The delay element used in such a device is BB.
D (Bucket Br1oade Device
) or a delay line using a capacitor and a coil. However, such a delay element is expensive, and its implementation requires a complicated circuit configuration.

Therefore, the main object of the present invention is to provide a dropout compensation circuit which can overcome the above-mentioned drawbacks and can obtain a sufficient dropout compensation effect with a simple configuration.

FIG. 3 is a schematic block diagram showing one embodiment of the present invention. The example shown in FIG. 3 is the same as j1 described above except for the following points.
It is the same as the block diagram shown in FIG. That is, the first
An analog switch 7 is provided in place of the pre-hold circuit 3 shown in the figure. This analog switch 7 is for turning on or off the FM signal given from the low pass filter 2 to the output amplifier 6 according to the detection signal from the dropout detector 4. In the signal path between one input terminal a of the
resistors R1 are connected in series. Further, the output terminal of the analog switch 7 is connected to the output amplifier 6, and a first capacitor C forming part of a de-emphasis circuit is connected between this output terminal and a reference potential (earth potential).
1 are connected in parallel.

FIG. 4 is a waveform diagram for explaining the operation of the embodiment shown in FIG. 3. Next, the operation of the embodiment shown in FIG. 3 will be explained with reference to FIG. When the dropout detection signal shown in FIG. 4A is at a low level, the analog switch 7 is closed, and when the dropout detection signal is at a high level, the analog switch is opened.

By the way, in the waveform shown in FIG. 4(B), when an abnormality occurs in the waveform that passes through points a and b on the waveform and reaches point 0 due to dropout, if the analog switch 7 remains closed, , the abnormal portion is integrated by the differential circuit consisting of the first resistor R1 and the first capacitor C1, and the waveform shown by the dashed line in FIG. 4(C) is output to the output terminal of the analog switch 7. be done.

By the way, when the analog switch 7 is controlled by the dropout detection signal, the dropout detection signal shown in FIG. Then analog switch 7 is opened.

Then, the waveform at the output terminal of the analog switch 7 stops being integrated by the de-emphasis circuit i at point f shown in FIG. 4(C). At this time, the potential at point f charged in the capacitor C1 starts discharging toward the output amplifier 6, but since the input resistance of the output amplifier is sufficiently large, the potential at the output terminal 6 is lower than the dropout detection signal. The potential at one point is held until it becomes low level again.

However, when the waveform at the input terminal a of the analog switch 7 reaches point f, the analog switch 7 is opened, the integration by the de-emphasis circuit is stopped, and the output waveform of the low-pass filter '.2' appears. The waveform shown in FIG. 4(C) moves from point f to point 9, and then reaches point b, point 0, and point d. When the dropout detection signal shown in FIG. 4(A) returns from high level to low level again, analog switch 7 closes and input terminal a and output terminal A are connected. The held potential of the output terminal becomes the potential of point d. In this way,
Figure 4 (D) obtained at the output terminal of analog switch 7
) The waveform shown in ) is quite faithful to the waveform shown in the spotting section without dropout.

A signal with this waveform is outputted via the output amplifier 6, and a sufficient dropout compensation effect can be obtained.

Incidentally, in the above-described embodiment, a de-emphasis circuit including the first resistor R1 and the first capacitor C1 is used, but it goes without saying that other de-emphasis circuits can also be applied. Next, such an embodiment will be described.

FIGS. 5A and 5B are circuit diagrams showing other examples of de-emphasis circuits, and FIGS. 6A and 6B are electrical circuit diagrams of the Deen 7292 circuit included in other embodiments of the present invention.

First, the de-emphasis circuit shown in FIG. 5A is one in which a series circuit of a second resistor R2 and a capacitor C1 is connected in parallel between a signal path and a ground potential, that is, a reference potential. In order to apply such a de-emphasis circuit to the present invention, as shown in FIG. 6A, the analog switch 7 described above is connected in series between the connection point of the first resistor R1 and the second resistor R2. All you have to do is intervene.

Further, the de-emphasis circuit shown in FIG. 5B is
In place of the second resistor R2 shown in the figure, a third resistor R3 is connected in series between the capacitor C1 and the reference potential. In order to apply the de-emphasis circuit shown in FIG. 5B to this invention, the resistor R1 and the capacitor C1 are
The analog switch 7 may be inserted in series between the two.

As described above, according to the present invention, an analog switch is inserted in a part of a de-emphasis circuit in which at least a JIL resistor is connected in series in the signal path and a capacitor is connected between the signal path and the reference potential. With a relatively simple configuration, a sufficient dropout compensation effect can be obtained by utilizing the charging and discharging of the capacitor.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing an example of a conventional dropout compensation circuit. FIG. 2 is a waveform diagram for explaining the operation of a conventional dropout compensation circuit. FIG. 3 is a schematic block diagram of one embodiment of the present invention. FIG. 4 is a waveform diagram for explaining the operation of the embodiment shown in FIG. 3. FIG. 5 is a waveform diagram for explaining the operation of an embodiment of the present invention. 5A and 5b are electrical circuit diagrams showing other examples of the de-emphasis circuit. 6A and 6B are electrical circuit diagrams of de-emphasis circuits included in other embodiments of the invention. In the figure, 1 is an FM demodulator, 2 is a low-pass filter,
4 is a dropout detector, 6 is an output amplifier, 7 is an analog switch, R1, R2, and R3 are resistors, and C1 is a capacitor. Figure 2 (,'l) Feng Toku Rekimei Figure 4 Figure 58 Figure 6A ↓c7 '- Figure 5B Figure 6BIXJ

Claims (3)

[Claims] (1) FMS that records an FM modulated audio signal on a recording medium and reproduces it from the recording medium! The audio signal received by W is 1! ! a de-emphasis circuit including at least a first resistor connected in series with a signal path and a first capacitor connected in parallel between the signal path and a reference potential; An analog switch is inserted between the resistor and the first capacitor in series with the signal path, and the analog switch is opened and closed by a dropout detection signal. out compensation circuit. □ (2) The de-emphasis circuit includes a second capacitor connected in series to the negative path side with respect to the first capacitor.
2. The dropout compensation circuit according to claim 1, further comprising a resistor, wherein the analog switch is inserted in the signal path and connected between the first resistor and the second resistor. . (3) The de-emphasis circuit number includes a third resistor connected in series with respect to the reference potential side of the first capacitor, and the analog switch is inserted in the signal path and connected to the reference potential side of the first capacitor. The dropout compensation circuit according to claim 1, wherein the dropout compensation circuit is connected between a resistor of 1'F and the first capacitor.