JPS6159594B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color signal processing circuit for a VTR that enables switching of recording/playback time by changing tape running speed.

Conventional VHS VTRs have short-time (2 hours) mode and long-time (4 hours) mode.For example, like the short-time mode, H-aligned αH
is 1.5H (IH is one horizontal period), and when adjacent video tracks are lined up in H, burst emphasis (burst level emphasis) is applied during recording.
During playback, burst de-emphasis (burst level suppression) is usually performed, and such a mode will be referred to herein as A mode. However, when αH is 1.0H and adjacent video tracks are not lined up in H, such as in long-time mode, burst signal crosstalk components from adjacent video tracks may interfere with the chroma signal of the main track. , In order to reduce this, it is preferable not to perform burst emphasis during recording and burst de-emphasis during playback. Such a mode will be referred to as B mode here.

Conventional color signal processing circuits that can be implemented as ICs only have one dedicated to A mode, such as the 2-hour mode, and in A mode, they can perform burst emphasis during recording and burst de-emphasis during playback. For example, 4
When switching to B mode such as time mode, neither burst emphasis nor burst de-emphasis is performed during recording or playback.
An IC-based color signal processing circuit has not yet been realized.

An object of the present invention is to provide a color signal processing circuit capable of switching the recording time mode, which can be used for both recording and playback modes, and in A mode, performs burst emphasis during recording and burst de-emphasis during playback. On the other hand, in B mode, we provide a color signal processing circuit that has a function that does not perform burst emphasis or de-emphasis during recording and playback, and that suppresses fluctuations in dynamic range due to each mode switch, making it easy to integrate into an IC. It's about doing.

The present invention provides burst level detection using a burst signal extracted through a burst gate amplifier from a color signal before passing through a burst emphasis circuit and a frequency converter so that the burst level of the gain control circuit output is constant in recording mode. The color signal is extracted from the color signal after passing through the burst de-emphasis circuit, 1H delay line and frequency converter through the burst gate amplifier so that the burst level of the reproduced color signal output is constant in the reproduction mode. The present invention is characterized in that burst level detection is performed using the burst signal, and the gain control circuit is controlled based on this.

An embodiment of the present invention is shown in FIG.

In FIG. 1, the switch circuit 3 performs a switching operation according to the recording mode or the reproduction mode, and in the recording mode, it outputs the color signal (chroma signal and burst signal) from the recording color signal input terminal 1, and in the reproduction mode, it outputs the color signal (chroma signal and burst signal) from the recording color signal input terminal 1, and in the reproduction mode, it outputs the reproduction color signal. The color signal from the signal input terminal 2 is led to an automatic gain control (AGC) circuit 4. The automatic gain control circuit 4 is
In order to suppress fluctuations in the input color signal level, it works to control and output the burst signal level in the color signal so that it always has an appropriate value.

In the recording mode, the frequency converter 5
Converts the color signal input at 3.58MHz to 629KHz, and also converts the color signal input at 3.58MHz to 629KHz in playback mode.
Converts the input color signal to 3.58MHz. 6 is a 1.2MHz low pass filter. The burst emphasis circuit 7 emphasizes the burst signal with respect to the chroma signal during A-mode recording, but does not emphasize the burst signal during B-mode recording. That is, during B-mode recording, the burst emphasis circuit 7 is bypassed or its function is stopped. The color killer circuits 8 and 13 function to suppress output signals to the recording color signal output terminal and the reproduction color signal output terminal 20 when a monochrome signal is input. 9 is a 3.58MHz bandpass filter. The 1H delay line 11 has the function of passing only the 3.58 MHz color signal component, and consists of a parallel connection circuit of the 1H delay line and a circuit that passes it straight, and eliminates crosstalk components from adjacent tracks in playback mode. It acts to remove.

The burst de-emphasis circuit 12 suppresses the burst signal by the amount emphasized during recording during reproduction in A mode, and does not perform this suppression effect in B mode. In other words, in B mode, burst
Is the de-emphasis circuit 12 bypassed?
Or its functions will be stopped. switch circuit 1
4 selects the input signal to the amplifier 15 according to each mode. The switch 16 selects the input signal to the burst gate amplifier 17 according to the recording mode or the playback mode, and the burst gate amplifier extracts only the burst signal from the color signal. The burst level detection circuit 18 generates a control signal to the automatic control gain circuit 4 based on the input burst signal level. 21 is a phase detection signal output terminal.

An embodiment of the present invention shown in FIG.
6 and filters 6 and 9 determine the circuit configuration for each mode. 2 shows a recording circuit in A and B modes, FIG. 3 shows a reproducing circuit in A mode, and FIG. 4 shows a reproducing circuit in B mode. The operation of each mode will be explained below with reference to FIGS. 2 to 4.

As shown in FIG. 2, in the A and B mode recording circuits, the 3.58MHz color signal (burst signal and chroma signal) extracted from the video signal is supplied to the recording color signal input terminal 1, and the switch circuit 3
The burst signal is inputted to the automatic gain control circuit 4 through the circuit 4, and gain control is performed so that the burst signal level is constant. That is, the output of the automatic gain control circuit 4 is inputted to the burst gate amplifier 17 through the switch circuit 16, where only the burst signal is extracted from the color signal and inputted to the burst level detection circuit 18, and the burst level is compared. A control signal obtained from the control signal is fed back to the automatic gain control circuit 4.

When the burst level of the input signal of the automatic gain control circuit 4 is large, the gain is lowered, and when the burst level is small, the gain is increased, so that the burst level at the output of the automatic gain control circuit 4 is adjusted to the input color signal. remains constant regardless of its size. The feedback circuit described above does not include the burst emphasis circuit 7 and is not affected by the burst emphasis effect in the A mode, so the output burst level of the automatic gain control circuit 4 is kept constant regardless of the A mode or the B mode. It is possible to do so.

The color signal whose burst level is kept constant is input to the frequency converter 5, where it undergoes frequency conversion, passes through the low-pass filter 6, and is extracted as a low-frequency converted color signal of 629KHz. It is input to circuit 7. As aforementioned,
The burst emphasis circuit 7 is bypassed or its function is stopped in the B mode.

Therefore, the color signal passes through the color killer circuit 8 and is output from the recording color signal output terminal 19 with its burst signal emphasized only in the A mode, and with the burst signal not emphasized in the B mode. Therefore, although the burst level of the output color signal differs depending on the A and B modes during recording, it is possible to keep the chroma level constant. In addition,
In this specification, "constant chroma level" means that the chroma level is constant when there is no change in level, such as in a color bar signal.

Also, the color signal from the automatic gain control circuit 4 is
After passing through the switch circuit 14 as 3.58MHz and being amplified by the amplifier 15, it is output from the phase detection signal output terminal 21 as a color signal with a constant burst level regardless of A or B mode, and is used as an input for phase detection. It becomes a signal.

As described above, in the recording mode, the chroma level in the color signal output to the recording color signal output terminal 19 and the burst level at the phase detection signal output terminal 21 are kept constant regardless of the A or B mode. becomes possible.

In the playback mode A shown in FIG. is input. Therefore, the input color signal is subjected to gain control so that the burst signal level remains constant with respect to fluctuations in the input signal level, as in the case of the recording mode. However, gain control in the A mode of reproduction is different from that in the recording mode, and operates so that the burst level in the output of the de-emphasis circuit 12 is kept constant by feeding back the output of the de-emphasis circuit 12.

The color signal from the automatic gain control circuit 4 undergoes frequency conversion in the frequency converter 5, passes through the 3.58MHz bandpass filter 9, becomes a color signal whose frequency is converted to 3.58MHz, and passes through the amplifier 10 to the 1H delay line. 11. The 3.58MHz color signal from which crosstalk components from adjacent tracks have been removed by the 1H delay line 11 is input to the burst de-emphasis circuit 12, where it is suppressed by the amount emphasized during recording and restored. Thereafter, the signal is outputted to the reproduced color signal output terminal 20 through the color killer circuit 13.

Further, the color signal from the 3.58MHz bandpass filter 9 passes through the switch circuit 14, is amplified by the amplifier 15, and then is output to the phase detection signal output terminal 21. In the circuit shown in FIG. 3, since the burst signal is subjected to automatic gain control as described above, the burst level of the output color signal of the burst de-emphasis circuit 12, that is, the output color signal of the reproduced color signal output terminal 20, is equal to the reproduced color input. It is kept constant regardless of the magnitude of the signal, and fluctuations in the burst signal level of the color signal at the phase detection signal output terminal 21 are also suppressed.

In the B mode of reproduction shown in FIG. 4, the 629KHz color signal input from the reproduction color signal input terminal 2 has no burst emphasis;
As in A mode, the 3.58MHz color signal with crosstalk removed is the 1H delay line 1.
Output from 1. And this color signal is
The signal is outputted to the reproduced color signal output terminal 20 through the color killer circuit 13 without being subjected to the burst signal suppression effect. However, the feedback circuit that performs gain control acts to maintain the burst level at the input of the color killer circuit 13 at a predetermined level, as in the case of the A mode, so that the burst level of the output color signal from the reproduced color signal output terminal 20 It is possible to keep the level constant regardless of A mode and B mode.

Also, as the color signal to the phase detection signal output terminal 21, the one that has passed through the 1H delay line 11 - that is, the input color signal of the color killer circuit 13 is used, so regardless of the playback mode, A or B mode. It becomes possible to keep the burst level of the output color signal at the phase detection signal output terminal 21 constant.

In the embodiment of the present invention described above, since a 3.58 MHz color signal is used as the color signal input to the burst gate amplifier 17 in both recording and playback modes, the burst level detection circuit 18 and automatic gain control The circuit 4 can easily be used for both recording and reproducing modes.

As is clear from the above description, according to the present invention, the recording color signal output terminal 19 and the reproduction color signal output terminal 20 can be used regardless of the presence or absence of burst emphasis and burst de-emphasis by switching between A and B modes. It is possible to keep the chroma signal level constant. Furthermore, it is also possible to make the burst signal level at the output terminal of the automatic gain control circuit 4 constant regardless of each mode, thereby making it possible to maintain the burst signal level at the output terminal of the automatic gain control circuit 4 at the output terminal 21 for phase detection.
Recording and reproducing the burst signal level of A and B
It is possible to keep it constant regardless of the mode.

Furthermore, the features of the present invention can be further demonstrated by implementing it into an IC. Figure 5 shows the present invention.
A specific example of the case where it is implemented as an IC will be shown.

In Figure 5, the part surrounded by dotted lines is the IC circuit, and each terminal 1, 2, 19-21, etc.
Corresponds to the pin legs of an IC. As is clear from the figure, a low-pass filter 6, a bandpass filter 9, an amplifier 10,
The 1H delay line 11 is an external circuit, and the automatic gain control circuit 4 and frequency converter 5 are connected by an external capacitor 26 to cut off the DC connection. The external electrolytic capacitor 27 is charged by a charging current that varies depending on the burst level from the burst level detection circuit 18, and the automatic gain control circuit 4
Generates a control signal to the Also, the switch circuit 22
is switched according to the recording/reproducing mode, and the switch circuit 23 is switched depending on whether the A mode of reproduction is any other mode.

In this way, in the IC circuit shown in Figure 5, the frequency of the automatic gain control circuit 4 and frequency conversion carrier is
By using the 4.21MHz frequency converter 5, burst gate amplifier 17, and burst level detection circuit 18 for both recording and playback modes, the number of elements and pins can be significantly reduced, and the advantages as an IC circuit are as follows. It is remarkable.

As described above, according to the present invention, the chroma level of the recorded color signal output and the reproduced color signal output can be made constant regardless of the presence or absence of burst emphasis and de-emphasis. Further, it is possible to suppress fluctuations in the burst level in the recorded color signal output and the reproduced color signal output, and also to suppress fluctuations in the dynamic range due to differences in color signal processing for switching recording/playback modes and switching recording time.

Further, when the color signal processing circuit of a VTR is integrated into an IC, the number of pins can be reduced by using the present invention, and the circuit can be housed in a low-cost package, thereby reducing the cost of the entire device.

It should be noted that, as is obvious to those skilled in the art, the connection order of the circuit blocks illustrated and described above can be changed as appropriate. That is, for example, the burst emphasis circuit 7 and frequency converter 5 in the recording mode, and the burst de-emphasis circuit 12 in the reproduction mode,
Even if the order of the 1H delay line 11, frequency converter 5, etc. is changed, there is no change in circuit operation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a color signal processing circuit which is an embodiment of the present invention, FIG. 2 is a block diagram of a color signal processing circuit when the circuit of FIG. 1 is switched to recording mode, and FIG. Figure 4 is a block diagram of the color signal processing circuit when switching to B mode reproduction, and Figure 5 is the IC of the color signal processing circuit of the present invention.
The converted block diagram is shown. 1...Record color signal input terminal, 2...Reproduction color signal input terminal, 3...Switch circuit, 4...
Automatic gain control circuit, 5... Frequency converter, 6...
Low-pass filter, 7...burst emphasis circuit,
8...Color killer circuit, 9...Band filter, 1
0...Amplifier, 11...1H delay line, 1
2...Burst de-emphasis circuit, 13...
...Color killer circuit, 14...Switch circuit, 1
5...Amplifier, 16...Switch circuit, 17...
Burst gate amplifier, 18... Burst level detection circuit, 19... Recording color signal output terminal, 2
0... Reproduction color signal output terminal, 21... Phase detection signal output terminal, 22, 23... Switch circuit, 28... Automatic gain control circuit output terminal, 29...
...Frequency converter input terminal, 30...Frequency conversion carrier input terminal, 31...Frequency converter output terminal, 32...Burst de-emphasis circuit input terminal, 33...Burst de-emphasis circuit input terminal, 34...Phase detection signal input terminal for
35...Burst level detection terminal.

Claims (1)

[Claims] 1. Has the function of switching recording/playback and switching between two or more recording/playback times by changing the tape running speed, and in A mode, emphasizes the burst signal level during recording, suppresses the burst signal level during playback, On the other hand, in B mode, the VTR's color signal processing circuit, which does not emphasize or suppress the burst signal level during recording or playback, has a gain control circuit that keeps the output level of the burst signal constant, and a gain control circuit that controls the output level of the burst signal. burst level detection means for supplying a signal, wherein the input signal to the burst level detection means is taken from the color signal before being processed by the burst emphasis circuit and the frequency conversion circuit in the recording mode, and in the playback mode. The burst de-emphasis circuit and the burst de-emphasis circuit are bypassed or their functions are taken from the color signal after being processed by the burst de-emphasis circuit, the 1H delay line and the frequency converter, respectively, and in B mode the burst de-emphasis circuit and the burst de-emphasis circuit are bypassed or their functions are A color signal processing circuit characterized in that: