JPH03122868A - Video tape recorder - Google Patents

Abstract

PURPOSE:To automatically adjust the level of a reproducing video signal by connecting the reproducing video signal to an AGC circuit at the time of reproducing, connecting an input video signal to the AGC circuit at the time of not reproducing and fixing the gain of an FM demodulation circuit. CONSTITUTION:At the time of reproducing, the reproducing video signal processed by a reproducing signal processing circuit 1 is inputted in the AGC circuit 11 through a switching means SW1 and its level is adjusted in the circuit 11. On the other hand, when not reproducing, the input video signal is inputted in the AGC circuit 11 through the switching means SW1 and transmitted to a recording signal processing circuit or an EE circuit after adjusting its level. Since the gain of the FM demodulation circuit 6 provided in the circuit 1 is fixed, the level of a demodulation signal which is FM demodulated is not adjusted in the circuit 6. Thus, the brightness of a reproduced video is appropriately adjusted and the adjustment of the level is automatized, thereby facilitating an operation.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention generally relates to an AGC that adjusts the level of an input video signal.
The present invention relates to a video tape recorder that uses a circuit to adjust the level of a reproduced video signal.

[Conventional technology]

As shown in FIG. 2, in the playback signal processing circuit 21 of the home video tape recorder, the playback signal of the video head 22 is amplified by the head amplifier 23, and then is separated into a low frequency conversion color signal and a playback FM signal. be done. The reproduced FM signal has its amplitude-frequency characteristics corrected by a reproduction equalizer 24, is further limited in two stages at high and low frequencies by a double limiter 25, and is FM demodulated by an FM demodulation circuit 26. In the FM demodulation circuit 26, the level of the demodulated signal is set to 2 by a volume 26a independent from other circuits.
It is adjusted so that it becomes Vp-p. The demodulated signal output from the FM demodulation circuit 26 is sent to the main de-emphasis circuit 2.
7, high frequencies are suppressed, noise components are removed by a noise canceller circuit 28, and then the signal is combined with a color signal restored by a color signal processing system (not shown) in a mixing circuit 29 to produce a reproduced video signal. This reproduced video signal is amplified by the reproduction amplifier 30 and sent to the switch SW2. The signal is input to the sub-clamp circuit 31 via the sub-clamp circuit 31, where it is clamped to a predetermined level, and then further amplified by the buffer amplifier 32 and output.

On the other hand, an input video signal inputted from outside the tuner or video tape recorder (not shown) is inputted to the AGC circuit 33 via the capacitor C21, where it is adjusted to an appropriate level. The input video signal output from the AGC circuit 33 is input to the sub-clamp circuit 31 via the switch SWzl, where it is clamped to a predetermined level and then sent to the recording signal processing circuit or the EEu path. Ru.

[Problem to be solved by the invention]

Incidentally, the level of the reproduced video signal output from the video tape recorder is determined by the frequency change range of the FM-modulated luminance signal, that is, the deviation. For example, P
In the AL system VH3 standard, the frequencies corresponding to the sync tip and white peak are 3.8 MHz and 4 MHz, respectively.
．． 8 MHz, and the above deviation corresponds to the difference in these frequencies. However, in the market, there are video tapes on which non-standard recording signals such as VH3 are recorded, and when such recording signals are played back, the reproduced image may be abnormally bright or dark, which may cause discomfort to the user. It will give you a sense of pleasure.

In contrast, in the conventional technology described above, the brightness and darkness of the reproduced video was adjusted by adjusting the level of the demodulated signal with the volume 26a of the FM demodulation circuit 26, but in order to solve the above problem, adjustment is required. was insufficient. Since the reproducing amplifier 30 has a fixed gain and does not have a level control function, it is not possible to adequately adjust the level at the output stage.
It has become difficult to appropriately adjust the brightness and darkness of the reproduced video.

Further, in the above conventional technology, the level of the input video signal is automatically adjusted by the AGC circuit 33, but in the case of a reproduced video signal, the level of the demodulated signal is adjusted by the FM demodulation circuit 26.
Since the volume 26a is delicately adjusted manually, this adjustment takes time and complicates the operation.

[Means to solve the problem]

In order to solve the above-mentioned problems, a video tape recorder according to the present invention includes an AGC circuit that adjusts the level of a video signal, and a playback video signal processed by a playback signal processing circuit when playing back, which is connected to the AGC circuit. On the other hand, it is provided with a switching means for switching the connection of the human video signal sent to the recording signal processing circuit or the EE circuit to the AGC circuit when no reproduction is performed, and the switching means is provided in the reproduction signal processing circuit. It is characterized in that the gain of the FM demodulation circuit used is fixed.

[Function] According to the above configuration, when performing reproduction, the reproduced video signal processed by the reproduced signal processing circuit is input to the 600 circuit via the switching means, and the level is adjusted there. On the other hand, when reproduction is not performed, the input video signal is input to the AGC circuit via the switching means, the level is adjusted here, and the signal is sent to the recording signal processing circuit or the EE circuit.

Therefore, when a non-standard recorded signal is played back, the played video signal is adjusted to an appropriate level by the AGC circuit in the same way as the input video signal, so the brightness is almost the same as when played back a within-standard recorded signal. You can play the video with

In addition, since the gain of the FM demodulation circuit provided in the reproduced signal processing circuit is fixed, the FM demodulation circuit
Level adjustment of the demodulated signal after M demodulation is not performed. Therefore, the reproduced video signal in which the demodulated signal and the color signal are mixed is
As described above, level adjustment is performed only in the AGC circuit, and level adjustment is also automated in the reproduced signal processing circuit.

〔Example〕

An embodiment of the present invention will be described below based on FIG.

As shown in FIG. 1, in the playback signal processing circuit 1, the playback signal with minute amplitude output from the video head 2 is amplified by the head amplifier 3, and then the low frequency conversion color signal is separated and the playback FM signal is generated. Only the signal is input to the FM demodulation circuit 6 via the reproduction equalizer 4 and the double limiter 5. The reproduction equalizer 4 is a circuit that corrects the amplitude-frequency characteristics to improve the high-frequency amplitude characteristics of the reproduced FM signal. In addition, the double limiter 5 is a circuit that limits the reproduced FM signal to a certain amplitude by applying a limiter in two stages to the low frequency component and the high frequency component, thereby preventing the reversal phenomenon and improving the S/N ratio. . The FM demodulation circuit 6 is a circuit that performs FM demodulation on the input reproduced FM signal to demodulate it into a video signal before FM modulation. This FM demodulation circuit 6 has a fixed gain and outputs the demodulated signal without level adjustment.

The demodulated signal output from the FM'Ii modulation circuit 6 is input to a mixing circuit 9 via a switch emphasis circuit 7 and a noise canceller circuit 8. The switch emphasis circuit 7 is a circuit that removes noise components generated during FM demodulation by suppressing high-frequency components enhanced by a pre-emphasis circuit (not shown) during recording. Further, the noise canceller circuit 8 is a circuit that removes minute high-frequency components that become noise components from the demodulated signal. The mixing circuit 9 is a circuit that mixes the demodulated signal with a color signal restored by a color signal processing system (not shown).

The reproduced video signal output from the mixing circuit 9 is sent to the switch S.
The input video signal is input to the AGC circuit 11 via the capacitor C1 mute circuit 10 and the switch SWI in the same way as the reproduced video signal. Switch S as a means
Wl is the mixing circuit 9 and the AGC circuit 11 when performing reproduction.
The mute circuit 10 and the AGC circuit 11 are connected when no reproduction is performed. Furthermore, the mute circuit 10 prevents interference between the reproduced video signal and the input video signal by blocking the output of the input video signal using a high-level control signal sent from a control circuit (not shown) during playback. It is a circuit.

The AGC circuit 11 includes an AGC amplifier 12 and a clamp circuit 1.
3. Consists of a synchronization separation circuit 14 and an AGC detection circuit 15. The AGC amplifier 12 is composed of, for example, a differential amplifier, and is configured to detect the AG output from the AGC detection circuit 15.
By controlling the gain with the C voltage, the level of the input video signal is adjusted. The clamp circuit 13 is a circuit that clamps the sync chimp of the video signal output from the AGC amplifier 12 to a constant potential. The synchronization separation circuit 14 is a circuit that separates a synchronization signal from a video signal. The AGC detection circuit 15 is the synchronization separation circuit 1
Detect the peak voltage of the synchronization signal separated by A
This is a circuit that outputs a GC voltage. This AGC detection circuit 1
The detection sensitivity of No. 5 is adjusted by a volume 15a. And an AG configured as above
The reproduced video signal output from the C circuit 11 is amplified to a level that can be output by the buffer amplifier 16 and output, while the input video signal output from the clamp circuit 13 is
The signal is sent to a recording signal processing circuit or an EE circuit.

In the above configuration, when performing playback, the video head 2
After the reproduced signal is amplified by the head amplifier 3, the reproduced FM signal separated from the low frequency conversion color signal has its amplitude-frequency characteristics corrected by the reproduced equalizer 4. This reproduced FM signal is limited to a constant amplitude by a double limiter 5, and the FM signal is
The demodulation circuit 6 performs FM demodulation. The demodulated signal demodulated by the FM demodulation circuit 6 has its high frequency band suppressed by the switch emphasis circuit 7, and the noise component is removed by the noise canceller circuit 8, and then the color is restored from the low frequency converted color signal by the mixing circuit 9. mixed with the signal. The reproduced video signal output from the mixing circuit 9 is adjusted to an appropriate level by the AGC circuit 11 via the switch SWI, and is amplified by the buffer amplifier 16 and output as an output video signal.

At this time, the mute circuit 10 and A are connected by the switch SW.
Since the GC amplifier 12 is not connected, the input video signal is not inputted to the AGC amplifier 12, but its output is blocked by the mute circuit 10, and a malfunction of the switch SW1 causes the mute circuit 10 and the AGC amplifier 1 to
2 is connected, the input video signal does not interfere with the reproduced video signal.

On the other hand, when no reproduction is performed, the mute circuit 10 and the AGC amplifier 12 are connected by the switch SW.
The input video signal input via the capacitor C1 is input to the AGC circuit 11 via the mute circuit 10. The input video signal is adjusted to an appropriate level by an AGC circuit 11, and then sent from a clamp circuit 13 to a recording signal processing circuit or an EE.
Sent open circuit.

In this way, the reproduced video signal is
Since the level is automatically adjusted by the C circuit 11, there is no need to manually adjust the level of the reproduced video signal during reproduction. In addition, the reproduced video signal is transmitted to the AGC circuit 1.
Since the level is adjusted to an appropriate level by 1, even a non-standard recorded signal can be reproduced with almost the same brightness as a non-standard recorded signal.

In this embodiment, the AGC circuit 11 uses the AGC voltage of the AGC circuit 11 as the detection voltage of the synchronization signal, but other types may be used.

〔Effect of the invention〕

As described above, the video tape recorder according to the present invention has the following features:
An AGC circuit that adjusts the level of the video signal, and a playback video signal processed by the playback signal processing circuit when playing back is connected to the AGC circuit, and a recording signal processing circuit or EE open circuit sending out when not playing back. The FM demodulation circuit provided in the reproduced signal processing circuit has a fixed gain.

As a result, when a non-standard recorded signal is played back, the played video signal is adjusted to an appropriate level by the AGC circuit in the same way as the input video signal, so the brightness is almost the same as when played back a within-standard recorded signal. You can play the video with Further, since the gain of the FM demodulation circuit provided in the reproduced signal processing circuit is fixed, the level of the demodulated signal is not adjusted in the FM demodulation circuit. Therefore, as described above, the AGC circuit can automate the level adjustment of the reproduced video signal, thereby improving operability.

[Brief explanation of drawings]

FIG. 1 shows one embodiment of the present invention, and is a block diagram showing a reproduced signal processing circuit. FIG. 2 shows a conventional example, and is a block diagram showing a reproduced signal processing circuit. ■ is a reproduction signal processing circuit, 6 is an FM demodulation circuit, 11 is an AG
In the C circuit, SWl is a switch (switching means). -40(

Claims (1)

[Claims] 1. An AGC circuit that adjusts the level of the video signal, and a reproduced video signal processed by the reproduced signal processing circuit when playing back is connected to the AGC circuit, while being sent to the recording signal processing circuit or EE circuit when not playing back. and switching means for switching the connection of the input video signal to be connected to the AGC circuit, and the gain of the FM demodulation circuit provided in the reproduced signal processing circuit is fixed. video tape recorder.