JPH07322292A - Discriminating circuit for reproduction mode of vtr - Google Patents

Abstract

PURPOSE:To select the mode in response to a reproduction signal of a VTR by smoothing an output signal of a frequency identification circuit identifying an oscillated frequency of a frequency conversion VCO of a chroma signal so as to discriminate the reproduction mode depending on the smoothed output. CONSTITUTION:When a PAL signal is reproduced, a chroma signal is shifted by 90 deg. at an interval of one field. The phase of an NTSC signal is shifted at all times and the phase shift direction is inverted by each field. Thus, m an error component is generated from an APC detection circuit 4. A detection output is fed to a VCO 8 via an LPF 13 and an adder circuit 14 and its oscillated frequency is changed. When the frequency change changes up to a prescribed range 1284+ or -3 or over, a signal from an error output circuit 11 is rectified by a rectifier smoothing circuit 16 and a stable DC voltage is obtained. A microcomputer 15 is set to the mode reproducing the NTSC signal. The operation control of the frequency of the VXO 3, the count K of the discrimination circuit 10 and the phase rotation of a frequency divider 5 is switched to that for the NTSC signal. Thus, the reproduction mode is discriminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a VTR reproduction mode discriminating circuit for reproducing video signals of various broadcasting systems.

[0002]

2. Description of the Related Art In South America, PA is used in addition to the NTSC system.
A VTR called an L / M system that records and reproduces a video signal by one unit is used. Both sync signals have the same frequency. The frequencies of both chroma signals are slightly different. The frequency of the NTSC chroma signal is
It is 3.579545 MHz, and that of the PAL / M system is 3.57561149 MHz. Since the frequencies of both are very close to each other, it is difficult to discriminate them, for example, in order to determine the reproduction mode. To distinguish between the two, for example, the burst signal of the NTSC system always arrives at a constant phase, whereas the burst signal of the PAL / M system is 1
It is conceivable that the phase detector is used by utilizing the phase alternation every H (H is one horizontal synchronizing signal period).

When the reproduction mode is identified by the phase detector, the VTR reproduction mode may be switched to the mode corresponding to the type of the reproduction signal according to the identification content.

[0004]

However, there is a problem that the phase detector requires a large number of elements (including capacitors).

[0005]

The present invention has been made in view of the above points, and a VCO that oscillates at a frequency corresponding to a horizontal synchronizing signal frequency, and an oscillation output signal frequency of the VCO fluctuates from a desired value. And a smoothing circuit for smoothing the output signal of the frequency identifying circuit, and the reproduction mode is determined according to the output signal of the smoothing circuit. .

[0006]

According to the present invention, the output signal of the frequency discriminating circuit for discriminating the oscillation output signal frequency of the VCO used for frequency conversion of the chroma signal of the VTR is smoothed, and the reproduction mode is discriminated by the smoothed output. .

[0007]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
This is a case of reproducing a PAL system chroma signal. (1)
Is applied with a low-frequency converted signal (frequency 40 1 / 8f _H, where f _H is a horizontal synchronizing signal frequency) from a VTR reproducing head (not shown), and a frequency (f _SC +40 1 is applied from BPF (19). / 8f _H, however, f _SC is a signal of the chroma signal frequency) is applied, the main converter for generating a signal of a frequency f _SC, (3) is VX which oscillates at a frequency f _SC
O and (4) are APC detection circuits that generate a control signal for locking the signal from the BPF (2) to the phase of the signal from the VXO (3), and (21) is the reproduction horizontal synchronization from the terminal (6). The signal (Fig. 2 (a)) is divided by 1/8,
The frequency dividing circuit (7) for generating the pulse of (7) is closed during the “H” level period of the pulse of FIG. 2B, and the oscillation output signal of the VCO (8) oscillating at 321 f _H is passed. The switch (9) is a counter for counting 321f _H pulses during the pulse “H” level period (4H) of FIG. 2B, and (10) is the count value K of the counter (9) within a predetermined range ( 1284 ± 3) or more than a predetermined range (12
84 + 3 <K) or less than a predetermined range (1284-3>)
The determination circuit (11) for determining whether or not K) is within the predetermined range is shown in FIG. 3B when the predetermined range or more, and FIG. 3A when the predetermined range or less. In case of 3
An error output circuit for generating the signal of (c), (14) is
A signal obtained by converting the output signal of the error output circuit (11) into a direct current by the LPF (12) and a signal obtained by converting the output signal of the APC detection circuit (4) into a direct current by the LPF (13) are added to obtain VCO ( 8) Adder circuit for controlling frequency, (1
5) is a microcomputer (microcomputer) that discriminates the reproduction mode signal according to the voltage obtained by rectifying and smoothing the output signal of the error output circuit (11) by the rectifying and smoothing circuit (16).

First, the case where the reproduction mode of the signal processing circuit of FIG. 1 and the mode of the reproduction signal match will be described. Now, it is assumed that a signal of frequency 40 1 / 8f _H of the PAL / M system is applied to the input terminal (17). Then, the frequency is the chroma signal frequency of the NTSC system and P
The frequency of the VXO (3) switched to that of the AL / M system is that of the PAL / M system. The frequency is N
A frequency 320f _H when TSC, the frequency of the VCO switched to 321f _H when PAL (8) is to have become 321f _H. The 321f _H output signal of the VCO (8) is divided into a signal having a frequency of 40 (1/8) f _{H by} the frequency dividing circuit (5) and applied to the sub converter (18). A signal of frequency f _SC is applied from the VXO (3) to the sub converter (18), frequency multiplication is performed, and a signal of frequency (f _SC +40 (1/8) f _H ) is generated from the BPF (19). To do. Then, the chroma signal returned to the frequency f _SC from the BPF (2) is obtained according to the frequency multiplication in the main converter (1).

On the other hand, the chroma signal is detected by the APS detection circuit (4), and its error signal is applied to the VCO (8) via the LPF (13) and the addition circuit (14). As a result, the phase of the chroma signal obtained at the output terminal (20) is synchronized with that of VXO (3). The horizontal synchronizing signal of FIG. 2 (a) synchronized with the chroma signal of the input terminal (17) is divided by the frequency dividing circuit (21) based on the signal of FIG. 2 (b), and the switch (7) is operated for 4H period. When is closed, the signal of frequency 321f _H is counted by the counter (9). As shown in FIG. 2B, the determination circuit (10) determines the count value immediately after the 4H period. Now, if the discrimination circuit (10) is in the mode for receiving the PAL / M type signal, the output signal of the error output circuit (11) is as shown in FIG.
It becomes like. Then, the output signal of the LPF (12) does not change from the original value, and the VCO (8) maintains the frequency of 321f _H.

On the other hand, the value of the output signal of the rectifying / smoothing circuit (16) does not change, and the microcomputer (15) outputs VTR of PAL /
It continues to be discriminated that the mode is reproducing the signal of the M system. It is assumed that the reproduction signal is switched to the NTSC system signal from this state. At this time, since the apparatus of FIG. 1 is in the mode for processing the PAL signal, the following problems occur.

When the PAL signal is reproduced as shown in FIG. 4, a 90-degree phase shift (omitted in FIG. 1) of the chroma signal is performed every other field. However, the NTSC signal is always phase-shifted by 90 degrees, and its phase direction is inverted for each field. Therefore, if the above-mentioned reproduction is simply performed, the error component is APC even if it is caused by this phase relationship.
It is generated from the detection circuit (4) as shown in FIG. Figure 4
The detection output of (C) is the LPF (13) and the addition circuit (1
4) is applied to the VCO (8), and the oscillation frequency of the VCO (8) changes as shown in FIG. Where V
When the frequency change of CO (8) changes to a predetermined range (1284 ± 3) or more, the error output circuit (11) outputs the signal shown in FIG.
An output as shown in (e) is generated. The signal of FIG. 4 (e) is rectified by the rectifying / smoothing circuit (16) as shown in FIG.
A stable DC voltage can be obtained by smoothing the signal of (f).

According to the DC voltage, the microcomputer (15)
The apparatus of FIG. 1 switches to a mode for reproducing NTSC signals. The operation control of the frequency of the VXO (3), the count value K of the discriminating circuit (10), and the phase rotation of the frequency dividing circuit (5) is switched to that for NTSC. Therefore, according to the apparatus of FIG. 1, it is possible to determine the reproduction mode.

[0013]

As described above, according to the present invention, the VTR
The playback mode of can be easily identified. Particularly, according to the present invention, there is an effect that a large number of elements are not required for the discrimination.

[Brief description of drawings]

FIG. 1 is a block diagram showing a reproduction mode discrimination circuit of a VTR of the present invention.

FIG. 2 is a waveform diagram for use in explaining FIG.

FIG. 3 is a waveform diagram for use in explaining FIG.

FIG. 4 is a waveform diagram for use in explaining FIG.

[Explanation of symbols]

 (8) VCO (9) Counter (10) Discrimination circuit (11) Error output circuit

Claims (2)

[Claims] 1. A VCO that oscillates at a frequency according to a horizontal synchronizing signal frequency, a frequency identification circuit that identifies that the oscillation output signal frequency of the VCO fluctuates from a desired value, and an output signal of the frequency identification circuit is smoothed. And a smoothing circuit for performing the determination of the reproduction mode according to the output signal of the smoothing circuit. 2. The frequency discriminating circuit includes a counter for counting the frequency of the oscillation output signal of the VCO for a certain period according to a horizontal synchronizing signal period, and a count value of the counter is within a desired range or otherwise. 2. The VTR reproduction mode discriminating circuit according to claim 1, further comprising a discriminating circuit for discriminating whether or not the discriminating circuit and an error output circuit for generating a pulse in accordance with a discriminative output of the discriminating circuit.