JPS6335086A - Information signal reproducing device - Google Patents

Abstract

PURPOSE:To make it possible to switch a demodulator circuit automatically in each mode by extracting plural bands corresponding to record spectrum arrangement from pulse signals, detecting each of them, and comparing their level and discriminating which record spectrum arrangement made the modulated information signals. CONSTITUTION:A limiter 2, a delay circuit 3, an exclusive OR gate 4 and low pass filters 91, 92 are demodulating means, and band-pass filters 51, 52, detector circuits 61, 62 and a level comparator 7 are discriminating means. By extracting plural kinds of bands from pulse output (d), detect in each of them and comparing level, the mode in which the signals are recorded is discriminated. By changing a switch 10 according to the result of discrimination, it is made possible to switch to respective mode and reproduce automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an information signal reproducing apparatus, and more particularly, to an information signal reproducing apparatus that discriminates and reproduces information signals recorded in two modes having different recording spectrum arrangements.

2. Description of the Related Art Conventionally, as shown in FIG. 9A, VTRs and the like have recorded a frequency-modulated luminance signal YA and a low frequency-converted color signal C on the lower frequency side thereof.

However, recent advances in recording media have been remarkable, and as shown in FIG. 3B, it has been considered to improve the horizontal resolution by increasing the FM carrier frequency of the luminance signal Ys for recording. Here, performing recording and reproducing using the spectrum arrangement shown in FIG. 12A will be referred to as A mode, and performing recording and reproducing using the spectrum arrangement shown in FIG. 10B will be referred to as 8 mode. .

Problems to be Solved by the Invention However, in a reproducing device that reproduces a recording medium recorded with such a plurality of recording spectrum arrangements, it is necessary to switch, for example, a low-pass filter for signal demodulation in each mode. , mode discrimination is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide an information signal reproducing apparatus that can discriminate each mode and automatically switch to the mode recorded in each recording spectrum arrangement to reproduce the information.

Means for Solving the Problem For example, in FIG. 1, the limiter 2, delay circuit 3, exclusive OR gate 4, and low-pass filters 9+, . demodulation means for generating and smoothing a plurality of pulse signals with equal pulse widths within a period to demodulate and extract a plurality of modulated information signals, bandpass filters 5+, 52;
, the detection circuits 6+, 62, and the level comparator 7 extract a plurality of bands corresponding to the recording spectrum arrangement from the pulse signal, detect each band, compare the levels, and determine which recording spectrum arrangement corresponds to the modulated information signal. 3 is an example of a discriminating means.

Multiple bands are extracted from the action pulse output d, and by detecting each band and comparing the levels, it is determined in which mode the signal was recorded, and switch 1 is set according to the result of this determination.
By switching 0, the respective playback modes can be automatically switched and replayed.

Embodiment First, before providing the device of the present invention, a pulse count type F''M demodulator will be explained. When the signal shown in Fig. Take out the pulse of constant width τ shown in Figure (B).Here, if the pulse waveform A(t) shown in Figure (B) is expressed mathematically, A(t) = from the Fourier series theory.However, , ω=2πNf, where N is 1 of the input signal
The number of pulses generated within a period (N=2 in the case of FIG. 8 (A>, (B)), and f is the frequency of the input signal.

Since the first term in the above equation (1) is proportional to the frequency of the input signal, frequency demodulation is performed by removing the second term and the following with a low-pass filter.

The present invention makes use of the fact that the band appearing below the second term in equation (1) differs depending on the band of the input signal to discriminate between the A mode and the B mode.

Assume now that the frequencies of the A mode and B monido FM carriers are as shown in the table below. In this case, the term N = 1 on the front base, that is, the frequency component twice the input FM signal, is 7.4 MHz in the A mode and 11.8 MHz in the -B mode in the pedestal portion.

FIG. 1 shows a block system diagram of a first embodiment of the device of the present invention. In the same figure, for example, FMlri that has entered terminal 1
The limiter 2 detects the zero crossing point of the frequency signal a (FIG. 2 (A)) and converts it into a signal b (FIG. 2 (B)). C)). The signal C is converted into a signal d ((D) in the figure) by an exclusive OR gate 4.

Now, if the FM carriers in A mode and B mode are as shown in the table above, the bandpass filter 51 is 7.4 MHz.
The center of the passband is located nearby, and the bandpass filter 52 has 11
．． If the frequency characteristics are set so that the center of the passband is near 8MHz, the bandpass filter 51
In the case of B mode, the output level of the bandpass filter 52 becomes large. bandpass filter 5+,
The respective outputs of 52 are detected by detection circuits 61 and 62, respectively.
The levels are compared by a level comparator 7, and the signal is converted into, for example, an H level signal) and an L level signal, which are taken out from an output terminal 8 as a mode discrimination signal.

In this embodiment, since the bands of the signals reproduced and demodulated in A mode and B mode are different, the low pass filters 9+, 92
The 1° low-pass filter 9+ is switched by this mode discrimination signal.
, 92 are switched and taken out by a switch 10 which is changed over by a mode discrimination signal, and taken out as a demodulated luminance signal from an output terminal 12 via a de-emphasis circuit 11.

In addition, in the case of A mode, the FM frequency of the sync tip is 4.
multiplication (i.e., the component of k=2) is 13.6M)lZ, which is close to the passband of the bandpass filter 52, but since the component of k=2 is smaller than the component of 1, it can be determined using the above method. It is.

Also, in the above equation (1), if we set 2Nfτ=X, (
1) The amplitude of the component of each term in the equation is proportional to . Therefore, if this is plotted in a graph against X, it will look like the one shown in FIG. In Figure 3, when k = 1, the value of is always larger than when x = 2, but when comparing k = 2 and x = 3, the relationship in size is reversed around x = 0.5. do. In this way, k=
For 2 or more, higher-order components may have higher levels.

Therefore, considering the discrimination, first of all, if we assume that both modes are A and 8, the comparison between k = 1 is that the A mode's NI = 3 component (near 16 MHz) and the B mode's NI = 2 component. It is conceivable to treat the vicinity of the component (near 20 MHz) with a bandpass filter and compare. In this case, the A-mode component of 4 is close to the B-mode component of 2, and in the case of A mode, a bandpass filter that extracts around 16MH2 extracts the 3 component, and 20 .The component of =4 is extracted using a bandpass filter that extracts around 1MH2. Here, if you set a value so that the component of k = 3 is larger than the component of = 4 (for example, r = 30 n
If you choose 5ec, in A mode, N=2, x=
2Nfr=2X2X (4MH2)X (30nsec)
= 0.48, and (component of k=3)>(component of k=4) is not mistakenly determined as B mode. Under the condition that the component of k=4 is larger than the component of k=3, it is erroneously determined.

Note that the present invention is not limited to FM luminance signals,
A color signal may be FM'd, and the same applies to the case where a signal other than a video signal such as a PCM audio signal is FM'd.

Furthermore, the present invention can be similarly applied to a case where at least one of the signals recorded in a plurality of spectrum arrangements is something other than an FM signal, such as an AM signal, a PM signal, or a PCM signal.

FIG. 5 shows a block system diagram of a second embodiment of the device of the present invention, in which the same components as in FIG. 1 are given the same reference numerals. For example, “Television Society Technical Report jVR70-3
Page 16 of , shows a circuit that outputs four pulses during one period of the input signal. This embodiment is applied to a circuit that outputs four pulses during one period of such an input signal.

In the same figure, the FM signal e entering terminal 1 (Fig. 6 (
A)) is phase-shifted by a 90° phase shift circuit 13 to become a signal f ((B) in the same figure), and is sent to the limiter 1 as in the circuit shown in the first diagram.
42, W extension circuit 152, exclusive or gate 16
2 to become a signal h ((D) in the same figure). On the other hand, the signal e is converted into a signal Q ((C) in the same figure) via a limiter 141, a delay circuit 151, and a us-crusive OR gate 161, as in the circuit shown in the first figure. The signal q and the signal @h are converted into a signal i ((E) in the same figure) by an OR gate 17, which is supplied to a circuit similar to the circuit shown in the first diagram, and the low-pass filter is switched according to the A1 need and the B mode.

Other operations are similar to the circuit shown in the first diagram. in this way,
The present invention can also be applied to cases other than N=2.

FIG. 7 shows a block system diagram of a third embodiment of the IT system of the present invention. This device differs from the first and second embodiments in that the mode discrimination circuit 18 and the FM demodulation circuit 19 are provided as separate systems, and in particular, limiters 2+, 22, delay circuits 3+, 33, and exclusive OR gates are provided. 41. '
42 are provided separately for the mode discrimination circuit 18 and the FM demodulation circuit 19.

Other configurations, operations, and effects are described in Section 1. This is the same as the second embodiment.

Note that switching based on mode discrimination is not limited to switching the low-pass filters 9+ and 92 as in the present invention, but can also be applied to other parts of the signal system such as switching the frequency characteristics of an FM equalizer or various noise reduction circuits. It can also be done for FIG. 10 shows a block diagram of a luminance signal reproduction system in a VTR applied to such a case. In the figure, the signal reproduced by the magnetic head 20 is transmitted through a rotary transformer 21, a preamplifier 22, and a high-pass filter 2.
3 to the FM equalizer 24, where the frequency characteristics are determined by the output discrimination signal of the mode discrimination circuit 25.
It is switched and compensated according to the mode and B mode.

The signal whose frequency characteristics have been compensated by the FM equalizer 24 is supplied to a dropout compensation circuit (droop control circuit) 27 via an AGC circuit 26, where the dropout is compensated for. In this case, when a dropout is detected by the dropout detection circuit 29, dropout compensation is performed using the one horizontal scanning period delayed signal obtained from the glass delay lines 281 and 282, but in both A and 8 modes, the FM carrier Separate glass delay lines 28+, 2 that pass near the respective FM carrier frequencies since the frequencies are different.
82 is required. Therefore, the switch 36 is switched according to the A or B mode by the output discrimination signal of the mode discrimination circuit 25, and the outputs of the glass delay lines 28+ and 282 are switched.

The output of the drive converter circuit 27 is supplied to a double limiter 30, and the cutoff frequencies of the high-pass filter 31 and the low-pass filter 32 are switched according to the output discrimination signal of the mode discrimination circuit 25. The characteristics are considered to be optimal for each mode of FM carrier.

The output of the double limiter 30 is supplied to a level adjuster 34 via an FM demodulator 33, low-pass filters 9+, 92, and a switch 10, which consists of a circuit from terminal 1 to exclusive OR gate 4 in FIG. . If the frequency deviation is different in A and B modes, the demodulation output level will be different, so
They are aligned so that they are at the same level in the mode discrimination output.

The output of the level adjuster 34 is the de-emphasis circuit 11 (
(including non-linear de-emphasis circuit),
The characteristics are switched by the mode discrimination output so that a high quality image can be obtained in each mode.

Furthermore, the output of the de-emphasis circuit 11 is supplied to a noise reduction circuit 35. In this case, home VTR
Although various noise reduction circuits are used in such systems, many of these have side effects such as loss of image details. Therefore, even if this side effect can be practically tolerated as long as the image quality in A-mode is considered, this side effect may become a concern in a mode such as B mode, which aims to further improve the image quality. In such a case, according to the mode discrimination output, in the case of B mode, the operation of the noise reduction circuit 35 is reduced or switched to no operation at all.

In the case of this B mode, the time required for the SN ratio to be improved by the noise reduction circuit 35 is reduced, but the SN ratio can be improved by using a high-quality recording medium and by appropriately setting the emphasis, frequency shift, track width, etc. It is necessary to ensure that

Effects of the Invention According to the device of the present invention, for example, in a device for reproducing a recording medium recorded with a plurality of recording spectrum arrangements, the demodulation circuit can be automatically switched in each mode, and the demodulation circuit can be automatically switched to each mode. It has features such as being recyclable.

[Brief explanation of drawings]

Figures 1 and 2 are block diagrams and signal waveform diagrams of the first embodiment of the device of the present invention, Figure 3 is an amplitude characteristic diagram of the input signal with k as a parameter, and Figure P54 is a diagram with k as a parameter. 5 and 6 are block diagrams and signal waveform diagrams of the second embodiment of the device of the present invention, and FIG. 7 is a block diagram of the third embodiment of the device of the present invention, Fig. 8 is a signal waveform diagram for explaining the other operations of the pulse counter type frequency demodulator, Fig. 9 is a diagram for explaining the spectrum arrangement for each recording mode, and Fig. 10 is a diagram for explaining the spectrum arrangement for each recording mode. It is an applied block system diagram. 1...FM signal input terminal, 2.2+, 22,141°142...Limiter, 3.3+, 33,151°15
2...Delay circuit, 4.4+, 42.161°162・
...Exclusive or Gate, 5+, 52. 5+ ' + 52 ' ...Band filter, 6+
, 62...Detection circuit, 7...Level comparator, 8...
・Mode discrimination signal output terminal, 91.92.9+',
92'...Low pass filter, 10...Switch, 12
...Demodulated signal output terminal, 13...90° phase shift circuit,
17... OR gate, 18... Mode discrimination circuit, 1
9...FM demodulation circuit.

Claims (2)

[Claims] (1) A plurality of modulated information signals recorded with different recording spectrum arrangements are respectively supplied, a plurality of pulse signals having the same pulse width are generated within one cycle of the modulated information signal, and the pulse signals are smoothed to generate the plurality of pulse signals. a demodulation circuit that demodulates and extracts each of the modulated information signals; and a demodulation circuit that extracts a plurality of bands corresponding to the above-mentioned recording spectrum arrangement from the pulse signal, detects each of them, compares the levels, and determines which recording spectrum arrangement the modulated information signal is based on. An information signal reproducing device comprising: a discriminating circuit for discriminating. (2) The information signal reproducing apparatus according to claim 1, wherein the means for generating the pulse signal is used for both the demodulation circuit and the discrimination circuit.