JP2979556B2 - No signal detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the above order.

A. Industrial application fields B. Summary of the invention C. Prior art D. Problems to be solved by the invention E. Means to solve the problems F. Function G. Embodiment G _1. Comb-type filter block One configuration example (FIG. 1) Another configuration example of G ₂ .comb filter block (FIG. 2) One embodiment of G ₃ .no-signal detection device (FIG. 3, FIG. 4, FIG. 5, FIG. Fig. 6) H. Effects of the Invention A. Industrial Field of the Invention The present invention is a comb filter processing of a VTR or the like, which starts up a processing operation when switching from a non-signal portion to a normal signal reproduction during tape reproduction or the like. The present invention relates to a no-signal detection device that can be suitably used to improve the noise reduction.

B. Summary of the Invention The present invention controls the amplification of a variable gain amplifier for applying AGC to a delay element output in a non-signal detection device that can be used for controlling comb filter processing in VTR tape reproduction or the like. The control signal is detected by the integrating means and the comparator, and the signal having a predetermined width or more inputted to the comb filter device to be suppressed to the voltage of the voltage holding means by the switch means, and further held by the output holding means for a predetermined period, By detecting the no-signal in a state where the held output is not present, the no-signal can be reliably detected, and at the time of the no-signal detection, the amplification of the variable gain amplifier is controlled by the control of the switch means at the time of the normal signal. It is possible to maintain the gain close to the amplification degree and improve the rise of comb filter processing when switching from processing of no-signal part to normal processing. In order, it is obtained by the control of the switch means of the comb filter apparatus to be able to use a detection output of the no-signal.

C. Conventional technology Conventionally, in order to widen the bandwidth of 8 mm video, chroma signals and luminance signals in a video signal are separated and processed independently.
Comb filtering is included. FIG. 7 shows a comb filter block of a conventional comb filter device in chroma signal processing, and FIG. 8 shows a comb filter block of a conventional comb filter device in luminance signal processing.

In FIG. 7, 1 is a delay (delay) element, 2 is a variable gain amplifier (VCA), 3 is a clamp circuit, 4 is an AGC detector, 5 is a pseudo sync generation circuit, and 6 is a mix circuit. When the chroma signal is subjected to the comb filter processing, the delay element 1 is required, and since the delay element 1 has a gain loss, it is necessary to manage the level to match the gain with the signal that does not pass through the delay element 1. By the way, since the chrominance signal does not include a sync (synchronization signal) like a luminance signal, the pseudo sync of the pseudo sync generation circuit 5 is inserted into the color signal by the mix circuit 6 and input to the delay element 1. AGC (Auto Gain Control) works to control the level. This level management is performed by controlling the amplification degree by the VCA 2 and clamping the clamp circuit 3. The VCA 2 is an AGC detector that receives the output signal from the clamp circuit 3 to the next stage and the signal from the mix circuit 6 as inputs. 4 (control voltage) is connected to its control input terminal to be controlled. This output of the AGC detector 4, a capacitor C ₁ to maintain the control voltage over the period of the pseudo sync is connected to ground. A clamp pulse for operating the clamp circuit 3 is created from a composite sync in an I / O (input / output) block (not shown), and the pseudo sync is generated by the pseudo sync generation circuit 5 in synchronization with the clamp pulse.

In FIG. 8, 11 is a 1H delay element, 12 is a VCA, 1
3 is a clamp circuit, 14 is an AGC detector, 15 is a delay element 1 that outputs an output signal to the next stage for each field during still reproduction.
A switch for switching between the signal side and the main signal (luminance signal) side. Also in the comb filter block of the luminance signal, in order to match the gain of this signal and the signal passed through the delay element 11, the VCA 12 is inserted in the delay element 11 side to control the level as in FIG. The luminance signal is input to the delay element 11 and the AGC detector 14, and the delayed output of the delay element 11 is input to one of the switches 15 through the VCA 12 and the clamp circuit 13, and is also input to the AGC detector 14. The output of the AGC detector 14 is connected to a control input terminal of the VCA 12 as a control voltage. Using the signal of the delay element 11 side (hereinafter referred to as delay side), 8m
In the still playback in the standard playback (SP) mode of the m3 head unit, the signal on the delay side and the main signal are reproduced for each field using the changing pulse of the dash chan head. In order to hold the control voltage during the period of the sink included in the luminance signal, the output of the AGC detector 14 is
Capacitor C ₂ is connected between the ground.

D. Problems to be Solved by the Invention However, each of the comb filter blocks of the comb filter device in the above-described conventional technology has the following problems.

(1) In the comb filter block in the chroma signal processing shown in FIG. 7, the pseudo sync inserted into the color signal is I / O
Since the O-block is created from the composite sync, during playback of the unrecorded tape portion or the no-signal (DC recording) tape portion where no composite sync is output, no pseudo sync is inserted, and VCA2 becomes full gain and the signal level Is greatly shifted. This occurs because the control voltage of the VCA from the AGC detector 4 deviates from the original operating voltage. The output of the AGC detector 4 has a large capacitor C _1.
Is connected, the time constant becomes longer, the rise of the AGC detector 4 becomes slow, and it takes a long time until the operation is stabilized. Therefore, when the reproduction state of the above-mentioned non-signal or the like is switched to the reproduction state of the normal signal (color bar or the like), the AGC detector 4 rises from the full gain control state, so that it takes a long time until the AGC operates on the color signal. ,
During this time, the image was disturbed.

(2) In the comb filter block in the luminance signal processing shown in FIG. 8, if the clamp pulse is held during the reproduction of the unrecorded tape portion or the non-signal tape portion, the clamp pulse is not transmitted, and the clamp circuit 13 Does not work properly, an error occurs in the operation of the AGC detector 14, and the VCA 12 has a full gain. By the way, AGC detector 14
In each case, be connected is large capacitor C ₂ to the output, the operation takes a long time to stabilize. For this reason, even if the normal signal enters the reproduction state of the non-signal tape portion or the like, the rise of the AGC operation is delayed because the gain is from the full gain, and the rise of the delay side signal to the normal level is delayed. Therefore, if the still playback mode is set immediately after switching to the normal signal playback mode, the image is distorted because the delay side signal has not risen.

The present invention, in order to solve the above-mentioned problems, performs a comb-shaped filter process for preventing image disturbance or the like from occurring when switching from a reproduction state of an unrecorded tape portion or a non-signal tape portion to reproduction of a normal signal. It is an object of the present invention to provide a no-signal detection device for reliably detecting a no-signal state of a video signal used for performing the operation.

E. Means for Solving the Problems In order to achieve the above object, the configuration of the no-signal detection device of the present invention is as follows. Integrating means for outputting a peak value, a comparator for comparing the output of the integrating means with a threshold value exceeding the predetermined value, and output holding means for holding the output of the comparator over a signal interval of a signal having the predetermined width or more Wherein the presence / absence of the output held by the output holding means is a detection output of the presence / absence of a signal having the predetermined width or more.

F. Action The present invention takes out a signal having a predetermined width or more by the integrating means and the comparator, holds the signal by the output holding means over the signal interval of the signal, and reliably eliminates the no signal by eliminating the held output. To detect. For example, by using this no-signal detection output in a comb filter device, a control signal for controlling the amplification of a variable gain amplifier for applying AGC to the delay element output can be suppressed to the voltage of the voltage holding means. By controlling the switch means of the comb filter device, by holding the amplification of the variable gain amplifier near the amplification at the time of a normal signal when no signal is detected,
This makes it possible to improve the rise of comb filter processing when switching from processing of a no-signal portion to processing of a normal signal.

G. Examples Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

G _1. One configuration example of comb filter block (FIG. 1) FIG. 1 is a block diagram showing one configuration example of a comb filter block using the detection output of the no-signal detection device of the present invention. This configuration example is an example in which it is used in the chroma signal processing of a VTR, and is an example in which the conventional example shown in FIG. 7 is improved. In FIG. 1, the same members as those in FIG. 7 are denoted by the same reference numerals. 1 is a delay (delay) element, 2 is a VCA (variable gain amplifier) for compensating the gain loss of the delay element and matching the gain with this signal (color signal not passing through the delay element 1), and 3 is clamping the output of VCA2. A clamp circuit for outputting an output signal to the next stage, an AGC detector for inputting the output signal and the present signal, controlling an amplification degree of VCA2 and applying an AGC to an output of the delay element 1, and a pseudo sync generator 5. The circuit 6 is a mix circuit for inserting the pseudo sync generated by the pseudo sync generating circuit 5 into the color signal which does not originally include the sync. This pseudo sink is
The clamp pulse is generated based on a clamp pulse used in the clamp circuit 3, and the clamp pulse is generated from a composite sync by an I / O block (not shown). The output of the mix circuit 6 is input to the delay element 1 and the AGC detector 4 described above.

The output of AGC detector 4 is connected to the control input of VCA2 as a control voltage, over the period of the pseudo sync, connected between the capacitor C ₁ and the ground GND in order to maintain the control voltage. In the present embodiment, the constant voltage source 8 can be connected via the switch 7 between the output of the AGC detector 4 connected in this way and the ground GND.
The potential V ₁ of the constant voltage source 8 is substantially set to the same potential as operating voltage for normal signal reproduction. The switch 7 is configured to be turned on when reproducing an unrecorded tape portion or a DC (direct current) recorded (non-signal) tape portion.

In the comb filter block configured as described above, when the unrecorded tape portion or the non-signal tape portion is reproduced, the switch 7 is turned on, and as a result, the AGC detector 4 is turned off.
Output is forcibly hold the potential V ₁ of the constant voltage source 8. Accordingly, the control voltage of VCA2 is maintained at substantially the operating voltage of the normal signal, and the amplification of VCA2 is maintained substantially the same as the amplification during reproduction of the normal signal. Here, when the reproduction state of the unrecorded tape portion or the non-signal tape portion is switched to the reproduction of the normal signal (color bar or the like), the AGC detector 4 and the like start up from the almost same amplification degree as the normal signal reproduction. the difference between the control signal and the previous potential V ₁ of the AGC detector 4 which switch 7 is output from the turned off is reduced, the earlier rise of the color signals.

G _2. Another configuration example of comb filter block (FIG. 2) FIG. 2 is a block diagram showing another configuration example of the comb filter block using the detection output of the no-signal detection device of the present invention. This configuration example is an example in which it is used in the luminance signal processing of a VTR, and is an example in which the conventional example shown in FIG. 8 is improved. In FIG. 2, the same members as those in FIG. 8 are denoted by the same reference numerals. 11 is a 1H delay element, 12 is a VCA for compensating the gain loss of the delay element 11 and matching the gain with this signal (a luminance signal that does not pass through the delay element 11), and 13 is a delay side signal that clamps the output of the VCA 12 (A signal on the delay element 11 side), a clamp circuit 14 receives the signal on the delay side and this signal and
AG that controls the amplification of A12 and applies AGC to the signal on the delay side
A C detector 15 is a switch for switching the output signal to the next stage between the delay side signal and the main signal (luminance signal) for each field during still reproduction.

The luminance signal is input to the delay element 11 and the AGC detector 14, and the delay output of the delay element 11 is VCA12, clamp circuit 13
And input to one of the switches 15 and to the AGC detector 14. The output of the AGC detector 14 is connected to a control input terminal of the VGC 12 as a control voltage of the VCA 12. In the still reproduction in the standard reproduction (SP) mode of the 8 mm3 head machine using the signal on the delay side, the signal on the delay side and the main signal are reproduced for each field using the changing pulse of the dash chan head. AGC detector 1
The output of 4 during the period of the sync included in the luminance signal,
To maintain the control voltage, ground GN capacitor C ₂
Connect between D. Also in this configuration example, the constant voltage source 18 can be connected via the switch 17 between the output of the AGC detector 14 connected in this way and the ground GND. The potential V ₂ of the constant voltage source 18 is approximately set to the same potential as operating voltage for normal signal reproduction. The switch 17 is configured to be turned on when reproducing an unrecorded tape portion or a DC (direct current) recorded (no signal) tape portion.

In the comb filter block configured as described above, when the unrecorded tape portion or the non-signal tape portion is reproduced, the switch 17 is controlled to be turned on, so that the AGC detector 14 is turned on.
Output is forcibly held at the potential V ₂ of the constant voltage source 18. Accordingly, the control voltage of the VCA 12 is maintained at substantially the operating voltage of the normal signal, and the amplification of the VCA 12 is maintained at substantially the same as the amplification during reproduction of the normal signal. Here, when switching from the playback state of the unrecorded tape portion or the non-signal tape portion to the still playback of the normal signal (color bar, etc.), the AGC detector 14 and the like start up from almost the same amplification degree as in the normal signal playback. , the difference between the control signal and the previous potential V ₂ of the AGC detector 14 which switch 17 is output from the turned off is reduced, accelerated rising of the delay side of the signal, the switch 15 is present signal side Even when switching from (normal) to the delay side, image disturbance can be prevented.

G _3. One embodiment of the no-signal detection device (FIGS. 3, 4 and 5)
(FIG. 6, FIG. 6) FIG. 3 is a block diagram showing one embodiment of the no-signal detecting device of the present invention. In this embodiment, the unrecorded tape portion and the DC
An example is given in which the reproduction of a recorded (non-signal) tape portion and the reproduction of a normal signal are discriminated, and the reproduction of an unrecorded tape portion or the like is detected. In the present embodiment, three comparators 21, 22, 23
They were connected in series, between (B point) between the first comparator 21 and the second comparator 22, one end is connected to the capacitor C ₃ connected in parallel to ground GND and a current source I ₁ as an integral unit It is composed. The first comparator 21 is connected with a voltage source 24 which gives the-threshold level V ₁ to the comparison voltage input, the second comparator 22 is connected with a voltage source 25 which gives the-threshold level V ₂ to the comparison voltage input, Third
The comparator 23 connects the voltage source 26 to provide a-threshold level V ₃ to the comparison voltage input. Further the second comparator 22 during the third comparator 23 (C point), the predetermined period of time, in order to maintain the output above a predetermined level, connected between the ground GND of the capacitor C _4. A composite sync is connected to the input point (point A) of the comparator 21, and a no-signal detection output is obtained from the output point D (point D) of the comparator 23. This detection output is a low level (L) detection output when there is no signal (no composite sync), and becomes a high level (H) when a normal signal (with composite sync) is input. By utilizing this detection output, the switch 7 in one embodiment of the comb filter block shown in FIG. 1 and the switch 17 in another embodiment of the comb filter block shown in FIG.
Can be turned on.

The operation and operation of the embodiment of the no-signal detection device configured as described above will be described. FIGS. 4 (a), (b) and (c) and FIGS. 5 and 6 are explanatory diagrams for that purpose. FIGS. 4 (a), (b), and (c) are explanatory diagrams of the potential relationship between the input and output points in FIG. 3, and FIGS. 5 and 6 are operation waveform diagrams over a long span. 4A shows the operation when it is assumed that the signal is a continuous signal of H (horizontal) sync without the composite sync V (vertical) sync inputted to the first comparator 21, and FIG. (C) shows the operation in the case where a noise that occurs randomly during reproduction of an unrecorded tape is input, and each of A, B, and
C and D indicate waveforms or potentials at points A, B, C and D in FIG. Comparator 21,-threshold level V ₁ is set so as to be able to detect a composite sync, to charge the capacitor C ₃ by the detection output. On the other hand, the current source I ₁ is the detection output of the comparator 21 is eliminated, to discharge the capacitor C _3. (A) H sink width shown in -A is 5μ
S, and the noise width shown in (c) -A is about the same or less. Therefore, at the point B, the charging time is short, and the potential is low. Since the V sink width shown in (b) -A is 32 μS and the charging time is long, the charge / discharge voltage becomes a triangular wave of a high potential as shown in (b) -B. Where the second comparator
22 of the-threshold level V ₂ detected only when the (b) -B, (a) -B, (c) -B is be set to not detect the value, the capacitor only when the point C (b) C ₄ and the threshold level V ₃ of the third comparator 23
And a high level (H) is output at the point D. Otherwise (a), (b) in the potential of the point B is lower than-threshold level V _2, lower than-threshold level V ₃ at point C, D points becomes a low level (L).

As shown in FIG. 5, in a normal signal V sync pulses of the composite sync is continuously input at a constant period to the point A, the potential of the point C is higher than the potential of the always V ₃ by the action of the capacitor C ₄ While point D is at a high level, it can be determined that normal signal reproduction is performed. That is, the capacitor C ₄ and the comparator 23 has a means for holding the detection output over the period of the V sync. On the other hand, in the reproduction of such non-recorded tape portions, the pulse width narrow for composite sink but come out randomly, lower than-threshold level V ₂ is the potential at the point B in order to be narrow, The detection output at point D becomes low level (L). That is,
In the case of normal signal reproduction, the detection output of the comparator 23 is H
(L in reverse logic), when playing back unrecorded tape, etc.
The detection output of the comparator 23 becomes L (H in reverse logic) indicating no signal. Therefore, the switch 7 in FIG. 1 and the switch 17 in FIG. 2 are turned on when the detected output of the comparator 23 is L (H in reverse logic) (when no signal is detected). This makes it possible to hold the control voltage of each VCA2, 12 during playback of unrecorded tape parts, etc., thereby speeding up the rise of the image and preventing image disturbance as described above. it can.
The no-signal detection device according to the present embodiment can suppress the capacitors C ₃ and C ₄ to be small, can be built in the IC, and can reduce external components.

As in the variable speed reproduction mode 2 head machine, when the V sync comes off in each frame, it is coped with by setting a low-threshold level V ₃ of the comparator 23 as shown in FIG. 6 It is possible. As described above, the present invention can be variously applied according to the gist and can take various embodiments.

H. Effects of the Invention As is clear from the above description, according to the no-signal detection device of the present invention, a no-signal is reliably detected by the presence or absence of a signal having a predetermined width or more, such as a vertical synchronization signal (V sync) of a video signal. Can be detected. By using this detection output and holding the control voltage of the variable gain amplifier when the AGC is performed at the time of reproducing the unrecorded tape portion or the non-signal tape portion almost to the control voltage at the time of normal signal reproduction, the unrecorded tape portion or the non-signal tape portion can be held. It is possible to improve the rise of the color signal when switching from the reproduction of the signal tape portion to the normal signal reproduction, and it is possible to prevent image disturbance when switching to the still reproduction in the above.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of a comb filter block using a detection output of a no-signal detection device according to the present invention;
FIG. 2 is a block diagram showing another configuration example of the comb filter block using the detection output of the no-signal detection device of the present invention, and FIG. 3 is a block diagram showing one embodiment of the no-signal detection device of the present invention. 4 (a), (b), (c), FIG. 5,
FIG. 6 is an explanatory diagram of the operation and operation of the above-described no-signal detecting device, and FIGS. 7 and 8 are explanatory diagrams of a conventional comb filter block. 1,11… Delay element, 2,12… VCA, 3,13… Clamp circuit, 4,14… AGC detector, 7,17… Switch, 8,18
…… Constant voltage source, 21,22,23 …… Comparator, 24,25,26…
... voltage _{source, C 1, C 2, C} 3, C 4 ...... capacitors, I ₁ ...... current source.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 9/79-9/898 H04N 5/91-5/956 G11B 20/06

Claims (1)

(57) [Claims] 1. Integrating means for outputting a signal having a width not less than a predetermined width of a signal having a width not less than a predetermined width with a peak value not more than a predetermined value, and a threshold value exceeding an output of the integrating means. And an output holding means for holding the output of the comparator over a signal interval of a signal having the predetermined width or more, the presence or absence of the output held by the output holding means being the presence or absence of a signal having the predetermined width or more. A non-signal detection device, characterized in that the detection output is a detection output.