JPH0760568B2 - FM modulation frequency discrimination device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention, in a magnetic recording / reproducing apparatus such as a VTR, automatically determines the types of luminance signal FM modulated waves having different modulation frequencies such as SVHS and VHS. The present invention relates to a discriminating device.

[Conventional technology]

FIG. 2 (a) shows frequency allocation in the VHS system, and FIG. 2 (b) shows frequency allocation in the SVHS system. In SVHS system VTR, it is necessary to play back the conventional VHS system tape with compatibility, so it is necessary to automatically determine whether the system recorded on the tape is VHS or SVHS and switch the system.

A conventional discriminating device of this type is shown in FIG. In FIG. 3, 1 is an input terminal, 10a and 10b are resonance circuits, 20a and 20b are AM detectors, 30 is a comparator, and 7 is an output terminal.

Next, the operation will be described. The first resonance circuit 10a is the fourth
As shown in Figure (a), it has a resonance peak near 3.4 MHz, and the second resonant circuit 10b has a peak of 5.4 as shown in Figure 3 (b).
It has a resonance peak near MHz. The outputs of these two resonators are converted into voltages proportional to the amplitude by separate AM detectors 20a and 20b, and are input to the comparator.

In the case of the FM signal in the VHS system shown in FIG. 2 (a), the resonator 10a resonates near 3.4 MHz, so that the AM detector 20a has a high voltage and the AM detector 20b has a low voltage. Therefore,
The comparator outputs a high voltage and determines that it is "VHS".
In the case of the SVHS method shown in FIG. 2 (b), the resonator 10b
Resonates, the AM detector 20b has a high voltage and the AM detector 20a has a low voltage. Therefore, the comparator 30 outputs a low voltage and determines "SVHS".

[Problems to be Solved by the Invention]

Since the conventional automatic discriminating device is configured as described above, it is possible to detect a video signal that strongly has a specific frequency component.
In the case of FM modulation, the side band overlaps with the band of the other resonance circuit, causing a malfunction.

The present invention has been made to solve the above-mentioned problems of the conventional ones, and an object of the present invention is to provide an FM modulation frequency discrimination device having stable discrimination performance for all video signals.

[Means for Solving the Problems]

A terminal for inputting FM luminance signals having different modulation frequencies for which the type should be discriminated, FM detection means for performing FM detection of the FM luminance signal, and the output of the FM detection means is a period sample of the synchronization signal of the luminance signal. A sample hold means for holding and a comparing / determining means for comparing the output of the sample / hold means with a reference voltage to determine the FM luminance signal are provided, and the VHS system or the SVHS system is discriminated by the frequency of the synchronizing signal. It is the one.

[Action]

In the present invention, generally, VHS type FM luminance signal is 3.4MHz, SVH
Since the S-system FM luminance signal is 5.4 MHz and is configured as described above, a stable determination operation can be performed without malfunction due to the contents of the video signal.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an FM modulation frequency discriminating apparatus according to an embodiment of the present invention, in which 1 is an input terminal, 2 is a multiplier, 3 is a phase shifter, 4 is a sync signal input terminal, 5 is a sample hold circuit, Reference numeral 6 is a comparator, 7 is an output terminal, and 8 is a reference voltage source.

Next, the operation will be described. Input from input terminal 1
The FM signal is input to one of the phase shifter 3 and the multiplier 2. The characteristics of the phase shifter 3 are as shown in FIG. 5, for example. The output DC voltage of the multiplier 2 is shown in FIG. The center voltage value is, for example, VHS / SVHS sync tip frequency 3.
It is chosen to be equal to the voltage corresponding to 4.4MHz in the middle of 4MHz / 5.4MHz.

The output of the multiplier 2 is sampled by the sample hold circuit 5 only during the period of the synchronizing signal and held during the other periods.
The synchronization signal is a signal obtained by synchronously separating the FM signal from the luminance signal demodulated by an FM detector different from this circuit. In this circuit, the voltage at the sync tip is taken out and sent to the comparator 6. This voltage is compared with the reference voltage 8 and a discrimination output is taken out as a comparator output.

As described above, according to the present embodiment, the FM modulation frequency signal whose type should be discriminated at the timing of the synchronization signal is sample-held to detect its frequency, so that it is stable regardless of the contents of the video signal. It is possible to determine.

Although the synchronizing signal is used as the sampling pulse in the above embodiment, it may be limited to the horizontal synchronizing signal or the vertical synchronizing signal, and the same object as that of the above embodiment can be achieved.

Further, as a sample hold circuit, the circuit current source of the multiplier may be turned on / off by a sampling pulse.

Also, the so-called quadrature type using a phase shifter as the FM detector was shown, but even if a peak differential type or a delayed multivibrator type FM detector is used,
Similar goals are met.

Further, it is also possible to apply such a method that a comparator is provided with hysteresis to reduce malfunction.

〔The invention's effect〕

As described above, according to the FM modulation frequency discrimination device of the present invention, the FMs of different modulation frequencies whose types should be discriminated
Luminance signal input terminal, FM detecting means for FM detecting the FM luminance signal, sample holding means for sampling and holding the output of the FM detecting means during the synchronizing signal of the luminance signal, and output of the sample holding means Is provided with a comparison / discrimination means for discriminating the FM luminance signal by comparing with the reference voltage. Therefore, an FM modulation frequency discrimination device having a stable discrimination performance can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an FM modulation frequency discrimination device according to an embodiment of the present invention, FIG. 2 is a diagram showing frequency allocation of VHS system and SVHS system, and FIG. 3 is a diagram showing a conventional FM modulation frequency discrimination device. , FIG. 4 is a diagram showing the resonance characteristics of the two resonance circuits of FIG. 3, FIG. 5 is a diagram showing the characteristics of the phase shifter of FIG. 1,
FIG. 6 is a diagram showing characteristics of the multiplier shown in FIG. In the figure, 1 is an input terminal, 2 is a multiplier, 3 is a phase shifter,
4 is a sync signal input terminal, 5 is a sample hold circuit, 6
Is a comparator, 7 is an output terminal, and 8 is a reference voltage source.

Claims (1)

[Claims] Claim: What is claimed is: 1. A terminal for inputting FM luminance signals having different modulation frequencies, the type of which should be discriminated, an FM detecting means for performing FM detection of the FM luminance signal, and an output of the FM detecting means for detecting the luminance signal. An FM modulation frequency discriminating apparatus comprising: sample and hold means for sampling and holding a period of a synchronizing signal; and comparison and discrimination means for discriminating the FM luminance signal by comparing the output of the sample and hold means with a reference voltage.