JPS62291277A - Mode discriminating device for recording medium reproducing device - Google Patents

Abstract

PURPOSE:To discriminate by which recording mode a recording is performed out of plural recording modes, by detecting a DC level difference according to difference in the carrier frequencies of the plural recording modes, from a reproducing video signal from a recording medium. CONSTITUTION:An FM demodulator 2, after demodulating an arriving reproducing video signal, eliminates a carrier at an LPF3, and furthermore, performs a level shift of prescribed share at a level shift circuit 4, and outputs it to an amplifier and LPF5. The amplifier and LPF5 amplifies a level-shifted reproducing luminance signal, and outputs a signal equivalent to an average DC level obtained by the elimination of a noise component, to a comparator 6. The comparator 6 compares it with a reference value set in advance, and outputs a mode discriminating signal.

Description

Detailed Description of the Invention a Detailed Description of the Invention Field of Industrial Application The present invention relates to a mode determination device for a recording medium reproducing device, and in particular whether a reproduced video signal from a recording medium is recorded in one of a plurality of recording modes. The present invention relates to a mode discriminating device for a recording medium reproducing apparatus that discriminates whether the medium is recorded in a mode.

Conventional technology In recent years, tape performance and head performance have improved, and magnetic recording and reproducing devices with high resolution and high image quality are required, and the carrier frequency has been shifted to a level sufficiently higher than that of current home VTRs. Various high-quality modes have been considered.

Problems to be Solved by the Invention However, as mentioned above, there is no compatibility between signals recorded in recording modes with different carrier frequencies, so a signal recorded in one recording mode cannot be reproduced in the other recording mode. The problem is that it cannot be done. In order to solve this problem, it is conceivable to provide a changeover switch, for example, and change the changeover switch according to the recording mode, but this would not only be very inconvenient to use, but also playback that is different from the recording mode. There were problems such as the user might mistake the device for failure if the device is played back in this mode.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a mode discriminating device for a recording medium reproducing apparatus that solves the above-mentioned problems by discriminating the mode based on the DC level difference of the FMlalJ reproduced video signal.

Means for Solving the Problems The mode discriminating device for a recording medium reproducing apparatus according to the present invention includes a detecting means for detecting a DC level difference from a reproduced video signal obtained by reproducing and demodulating a recording medium, and a detecting means for detecting a DC level difference from a reproduced video signal obtained by reproducing and demodulating a recording medium. It consists of a discriminating means.

Function: A video signal is recorded on the above-mentioned recording medium in one of a plurality of recording modes in which the four-way-seven frequencies of the frequency-modulated video signal are different from each other. The detection means is
From the reproduced video signal from this recording medium, the DC level difference accompanying the change in main 129 frequency of a plurality of recording modes is detected. Thereafter, the determining means determines in which of the plurality of recording modes the reproduced video signal was recorded based on the DC level difference.

Embodiment FIG. 1 shows a block system diagram of an embodiment of a mode discriminating device for a recording medium reproducing device 4 according to the present invention.

Before explaining this embodiment, the principle of the apparatus of the present invention will be explained with reference to FIG.

Frequency variation vA (FM modulation) is a modulation method that changes the amplitude level of a signal to each frequency, and this modulation method is generally used, for example, in magnetic recording of video signals.

Here, for example, the carrier frequency of A mode (standard mode) is a (Mllz), and the carrier frequency of B mode (high image quality mode) is b (MHz) (however, a<b, and b is about 2 MHz higher than a). Since there is generally a relationship between the input frequency and the output amplitude level in an FM demodulator, the waveforms of the demodulated video signals (demodulated luminance signals) in A mode and B mode are shown in Fig. 4 and (2). It becomes like this. Therefore, the carrier frequency difference between the two modes appears as a DC level difference in the demodulator output. In the present invention, the recording mode is determined by reading the difference between the average values of the DC levels.

Returning to FIG. 1 again, the device 1 of the present invention is an FM
It is composed of a demodulator 2, a low-pass filter (LPF) 3, a level shift circuit 4, an amplifier and low-pass filter (LPF) 5, and a comparator 6.

After the FMI modulator 2 demodulates the incoming reproduced video signal (that is, the reproduced frequency modulated luminance signal), the LPF 3 removes the carrier, and the level shift circuit 4 further shifts the level by a predetermined level and sends it to the amplifier and Output to LPF5.

The amplifier and PF5 amplify the incoming level-shifted reproduced luminance signal, remove noise components, etc., and output a signal corresponding to the average DC level of the reproduced luminance signal to the comparator 6.

The comparator 6 compares the output signal level values of the amplifier and LPF 5 with a preset reference value, and outputs a mode discrimination signal according to the comparison result.

Here, in this embodiment, the DC level difference of the output of the FM demodulator 2 between the standard mode and the high image quality mode is, for example, 0.
Since the DC level difference is as small as 1 VH, the level shift circuit 4, amplifier, and LPF 5 are used to reduce the DC level difference to, for example, about 2 mm.
Therefore, mode discrimination is sufficiently possible. Therefore, for example, even if the level shift circuit 4 in FIG. 1 is omitted, the principle remains the same.

FIG. 2 shows a detailed circuit diagram of this embodiment.

In the figure, the same components as in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted. Here, transistor Q1. and Q2 are level shift transistors constituting the level shift circuit 4, and a coaxial cable 7 is connected between the emitter of the transistor Q1 and the base of the transistor Q2.

The amplifier and LPF5 are an amplifier Δ1 and a capacitor C.
+, C2, variable resistor R1, and resistors R2 to R4, while comparator 6 includes operational amplifier A2, capacitor C3, and variable resistor R5.

A transistor Q+ is connected to the inverting input terminal of the operational amplifier A+.
, Qz, and the non-inverting input terminal is supplied with a DC voltage obtained by dividing the power supply voltage Vcc by a variable resistor R1.

Further, the resistor R4 and the capacitor C2 constitute an LPF. Therefore, a DC voltage Voc corresponding to the average DC level of the reproduced luminance signal is output from the output terminal of the operational amplifier A1.

The DC voltage Voc is supplied to the non-inverting input terminal of the operational amplifier A2. On the other hand, a reference voltage VR obtained by dividing the power supply voltage Vcc by a variable resistor R5 is supplied to the inverting input terminal of the operational amplifier A2. Therefore, operational amplifier A2
are the output DC voltage Voc of operational amplifier A1 and the reference voltage VR
For example, if the recording mode is high image quality mode, VDC>VR and the output will be at a high level.
On the other hand, when the recording mode is standard mode, Voc≦VR
The output becomes low level.

In this way, a mode discrimination signal that switches between high level and low level depending on the recording mode is obtained.

In this embodiment, since the average value of the entire output signal of the demodulator is taken, the DCln changes depending on the video.

Therefore, the amplification factor of the amplifier is the DC level difference between the amplifier output value when the signal is 100% black in the B mode and the amplifier output value when the signal is 100% white in the A mode, that is, the minimum DC level difference between the two modes. The values should be stable and have distinguishable differences.

Further, in order to enable stable discrimination even when the DC level difference between the two modes is the minimum value as described above, the reference voltage VR is set to an intermediate value between the amplifier output values in both modes.

However, when the video signal is greatly disturbed by noise etc., the average DC level value may fluctuate above or below the reference voltage [tVR], and so-called jitter occurs in which the output mode discrimination signal of the comparator 6 continues to switch at high speed. Unwatchable playback a! There is also a possibility that it will become a II image. In such a case, the comparator 6 may be configured to have a required hysteresis characteristic.

Next, a reproduction system of a VTR to which this embodiment is applied will be explained with reference to FIG. Here, the reproduced video signal reproduced from the magnetic tape 8 by the rotary heads H+ and H2 is transmitted to the terminal 11a of the switch circuit 11 via the preamplifier 9.10.
11b, respectively. Switch circuit 11 is connected to terminal 12
The head switching pulse is switched in accordance with the incoming head switching pulse, thereby obtaining a continuous reproduced video signal.

The output reproduced video signal of the switch circuit 11 is passed through a low-pass filter (
LPF) 13 and a high-pass filter (T1ρF) 14, respectively. The LPF 13 converts the incoming reproduced video signal into one wave of the low-frequency conversion carrier color signal and converts it into a color signal 51!1 logic circuit 15
Output to. The color signal processing circuit 15 frequency-converts the incoming low-pass converted carrier color signal into a carrier color signal in the original frequency band, and outputs the frequency-converted carrier color signal to the adder 16 .

On the other hand, the n-band filter (HPF) 14 outputs one frequency-modulated luminance signal from the incoming reproduced video signal and passes it through the equalizer circuit 17, 18 to the terminal 19a of the switch circuit 19.
, 19b, respectively. The output signal of the switch circuit 19 is supplied via an automatic gain control circuit (AGC circuit) 20 to a limiter 21 and a mode discrimination device 1 of this embodiment, respectively.

The output signal of the limiter 21 is sent to the FM demodulator 22, LPF 2
3. De-emphasis circuit 24 and FM demodulator 25, L
The signal is demodulated via the PF 26 and the de-emphasis circuit 27, respectively, and supplied to terminals 28a and 28b of the switch circuit 28.

The mode discrimination device 1 generates a mode discrimination signal according to the output signal of the AGC circuit 20 (covered wave 11 modulated luminance signal) and outputs it to the system controller 29 as described above.

The system controller 29 generates a mode switching signal in response to the incoming mode discrimination signal and outputs it to the switch circuits 19 and 28, respectively, to control switching between them.

Here, equalizer 17, FMIWA device 22, LPF 2
3 and de-emphasis circuit 24 are provided for video signal processing in the A mode (standard mode), and similarly, the equalizer 18, FM demodulator 25, LPF 26 and de-emphasis circuit 27 are provided for video signal processing in the A mode (standard mode). It is provided for video signal processing. Therefore, when the recording mode is determined to be A mode by the mode determining device 1, the switch circuits 19 and 28 are connected to the terminals 19a and 28a, respectively.
On the other hand, when the recording mode is determined to be 8 mode, switch circuits 19 and 28 are connected to terminals 19b and 2, respectively.
8b. As a result, demodulation according to the recording mode and imparting of equalizer characteristics and de-emphasis characteristics to the frequency modulated luminance 4 degree signal are performed.

Thereafter, the adder 16 adds the output carrier color signal of the color signal processing circuit 15 and the output luminance signal of the switch circuit 28 and outputs the obtained video signal to the output terminal 30.

Note that the FM demodulator 2 and LPF 3 in the mode discriminator 1
is omitted, the output n of the LPF 23 for high image quality mode is
The mode may be determined based on the degree signal. Further, the amplifier and LPF 5 are not limited to the configuration of this embodiment, but may be configured to detect the average DC level of the reproduced video signal. Furthermore, it goes without saying that the device of the present invention can also be applied to reproducing devices for recording media other than magnetic recording media.

Effects of the Invention As described above, according to the present invention, since the mode is determined based on the DC level of the FM demodulated reproduced video signal, the mode can be automatically and reliably determined. Therefore, the present invention has the advantage that it does not require a changeover operation of a changeover switch, is easy to use for the user, and can realize a mode discrimination device with an extremely simple circuit configuration.

[Brief explanation of the drawing]

1 and 2 are block diagrams and detailed circuit diagrams showing one embodiment of a mode discriminating device for a recording medium playback device according to the present invention, respectively, and FIG. 3 is a VTR to which the device of the present invention is applied. FIG. 4 is a block system diagram showing an example of a reproduction system of the present invention. 1... Mode discrimination device, 2... FM demodulator, 3...
・Low pass filter (LPF), 4...Level shift circuit, 5...Amplifier and low pass filter (LPF), 6...
・Comparator, 7...Coaxial cable, A+, A2
...Operation amplifier, C+~C3...Capacitor, Q+
, Q2...Transistor, R+, Rs...Variable resistor, R2-R4...Resistor.

Claims (2)

[Claims] (1) A reproduced video signal obtained by reproducing and demodulating a video signal recorded on a recording medium from the recording medium in one of a plurality of recording modes in which the carrier frequency of the frequency-modulated video signal is different from each other. a detection means for detecting a DC level difference due to a difference in carrier frequency between the plurality of recording modes; 1. A mode discriminating device for a recording medium reproducing device, characterized in that the mode discriminating device comprises discriminating means for discriminating whether the recording medium is a recording medium or not. (2) The detecting means detects the average DC level of the reproduced video signal, and the determining means compares the average DC level with a preset reference value, and determines the level of the reproduced video signal according to the comparison result. 2. A mode determining device for a recording medium reproducing device according to claim 1, wherein the mode determining device is configured to determine a recording mode of a recording medium.