JPS63179693A - Color signal reproducing circuit - Google Patents

Abstract

PURPOSE:To contrive to simplify circuit by using a common tuning/detection circuit in time division. CONSTITUTION:When 1st changeover switch 5 connects a color signal system corresponding to a format of a recording signal in plural color signal systems 1, 11 to the tuning/detection circuit 4, the circuit 4 generates a discrimination signal representing the detection of a color signal and sends it to a mode changeover circuit 2 and a holding circuit 6. In this case, a 2nd changeover switch 51 is switched interlocking with the 1st switch 5 to give the discrimination signal to a prescribed input terminal of the mode switching circuit 2. When the switch 5 gives a the color signal system not corresponding thereto to the circuit 4, the holding circuit 6 keeps the discrimination signal hold and the discrimination signal is supplied from the holding circuit 6. Thus, the color signal is discriminated and switched by the single tuning and detection circuit 4 regardless of the number of the color systems.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a color signal reproducing circuit installed in a signal reproducing device such as a VTR.

(Prior art) In VTRs that use the SECAM system, in addition to the regular SECAM format, MESECAM format is used so that a single color signal circuit can also process PAL color signals. Color signals are recorded in a format called (pseudo-secum). S
In the ECAM format, the color signal is counted down to 174 and frequency-divided into a band centered around 1 MHz, and the luminance signal is FM modulated and recorded into a band centered around 4 MHz.9 On the other hand, MESE
The CAM format converts the SECAM color signal to a low frequency (approximately 800 kHz) without counting down (passing it through a PAL recording circuit) and records it. These formats are not compatible, and recording in one format When playing a magnetic tape in the other format, no color appears.

Therefore, in order to reproduce color signals of both formats using the same circuit, it is necessary to perform format discrimination during four reproductions and reproduce the signal in a format corresponding to the recorded signal.

Figure 3 shows a magnetic tape (9) on which video signals are recorded in either SECAM or MESECAM format.
2 shows a conventional reproducing circuit that reproduces a video signal from and supplies it to an output terminal (14).

The video signal recorded on the magnetic tape (9) is reproduced by a pair of magnetic heads (8) (81), and the reproduced signal is switched by an RF switching pulse j obtained from a rotation detection element installed in the VTR cylinder. Via the head changeover switch (52), the brightness signal system (12)
, the first color signal system (1) which is the S E CAM color signal circuit, and the second color signal system (1) which is the MESECAM color signal circuit.
It is supplied to the color signal system (11).

The color signals output from each color signal system (1) and 11) are present on the back porch during the horizontal blanking period in the first tuning/detection circuit (4a) and the second tuning/detection circuit (4b), respectively. The presence or absence of color subcarriers at 4 and 25 MHz is detected, and the detection signal is sent to level comparators (7) (71).
). As a result, the output of one level comparator becomes high level, and the mode switching circuit (2) operates based on this, and the main switching circuit (2) operates according to the format of the color signal recorded on the magnetic tape (9). This is done by switching the switch (53).

The color signal reproduced from the magnetic tape (9) is SECA
In the case of M format, the output signal of the first color signal system (1) passes through the main changeover switch (53) to the mixing circuit (
13). Furthermore, when the color signal reproduced from the magnetic tape (9) is in the MESECAM format, the output signal C of the second color signal system (11) is sent to the mixing circuit (13) via the main changeover switch (53). , and the luminance signal d output from the luminance signal system (12).

(Problem to be solved) However, in the conventional reproducing circuit, the color signal switching circuit (3) is equipped with a tuning/detection circuit (4a) (
It is necessary to equip two series of 4b), and the whole circuit is complicatedζ
There was a problem.

(Means for Solving the Problems) The present invention provides a single tuning/detection circuit (4 ) to solve the above problem by providing a reproducing circuit that can discriminate and switch color signals.

In the color signal reproducing circuit according to the present invention, the color signal switching circuit (3) is a tuning circuit that determines the presence or absence of color signals to be output from the plurality of color signal systems (1) and (11), respectively.
The detection circuit (4) and the tuning/detection circuit (
4), and the output signal of the tuning/detection circuit (4) which is switched in synchronization with the first changeover switch (5) is connected to the plurality of input terminals of the mode switching circuit (2). A second selector switch (51) connected to the selector switch (51), which is interposed between each output terminal of the selector switch <51) and the mode switching circuit (2), and which should be connected to each input terminal of the mode switching circuit (2). Holding circuit (6) that holds each discrimination signal for a certain period of time
It is equipped with.

(Function) Among the plurality of color signal systems (1) and (11), the color signal system corresponding to the recording signal format (hereinafter referred to as the corresponding color signal system) outputs a color signal having a regular frequency. However, outputs having normal frequencies cannot be obtained from other color signal systems (hereinafter referred to as non-compatible color signal systems).

Therefore, when the first selector switch (5) connects the corresponding color signal system to the tuning/detection circuit (4), the tuning/detection circuit (
4) creates a discrimination signal representing the detection of a color signal, and sends it to the mode switching circuit (2) and the holding circuit <6> via the second changeover switch (51). At this time, the second selector switch (
51) is switched to a contact position according to the corresponding color signal system by interlocking with the first changeover switch (5), and connects the discrimination signal to a predetermined input terminal of the mode changeover circuit (2).

When the first selector switch (5) connects the incompatible color signal system to the tuning/detection circuit (4), the discrimination signal is not output from the tuning/detection circuit (4).

Also, at this time, the holding circuit (6) is connected to the first selector switch (5).
) maintains the hold of the discrimination signal when the corresponding color signal system is connected to the tuning/detection circuit (4)l\, and the mode switching circuit (2) is supplied with the discrimination signal from the holding circuit (6). be done.

As a result, the discrimination signal is continuously input to the mode switching circuit (2) only to the input terminal corresponding to the corresponding color signal system, and thereby the main changeover switch (53) outputs the signal from the corresponding color signal system. It is switched so that only the color signal is connected to the subsequent circuit l\.

(Effects of the Invention) According to the color signal reproducing circuit according to the present invention, color signals can be discriminated and switched by using the common tuning/detection circuit (4) in a time-division manner as described above. In this case, the tuning/detection circuit (4), which required multiple series, can be replaced with a single series, and the circuit can be greatly simplified.

(Example) FIG. 1 shows a color signal reproducing circuit according to the present invention in a SECAM
The figure shows an example of the system implemented in a VTR, and includes a first color signal system (1), a second color signal system (11), and a mode switching circuit (2).
), etc., which are the same as the conventional circuit shown in FIG.

The tuning/detection circuit (4) installed in the color signal switching circuit (3) has the same configuration as the conventional circuits (4a) and (4b), and includes a gate circuit (41), a 4.25 MHz single-peak tuning circuit ( 42), first detection circuit (43), tuning amplifier (4
4) and a second detection circuit (45) are connected in series. The opening/closing of the gate circuit (41) is controlled by a gate pulse k synchronized with the horizontal synchronization signal, and the gate circuit (41) receives 4.25 MHz and 4.41 MHz signals (H
~ID signals) are allowed to pass through. The first detection circuit (43) receives 4, which is output from the tuning circuit (42).
The 25 MHz signal is shaped into a pulse signal for each horizontal retrace. Further, the tuned amplifier (44) generates a sine wave having approximately the same period as the pulse signal output from the detection circuit (43), that is, approximately half the frequency of the horizontal synchronization frequency r, and generates a second The detection circuit (45) detects the sine wave.

The output ends of the first color signal system (1) and the second color signal system (11) are connected to the tuning/detection circuit (
4). The output signal of the tuning/detection circuit (4) is connected to a second level comparator (7) and a second level comparator (71) via a second selector switch (51) which is switched by the same RF switching pulse.

The signals e and `` connected to both level comparators (7) (71) are connected to first and second capacitors (51) (62) respectively equipped in the holding circuit (6). Each capacitor (61) (62) has a charging time constant smaller than the repetition period of the RF switching pulse and a discharging time constant larger than the period.

The level comparators (7) and (71) respectively generate high-level pulse signals g and h when the output signal C1 from the tuning/detection circuit (4) exceeds a predetermined reference level, and the mode switching circuit (2).

Based on the pulse signal, the mode switching circuit (2)
Create a switching signal i for the main changeover switch (53),
Switch the main changeover switch (53).

The operation of the color signal reproducing circuit will be explained below.

When the signal recorded on the magnetic tape (9) is in SECAM format, the first color signal system (1) outputs a color signal having a regular frequency, but the output of the second color signal system <11) Signal C does not have a regular frequency.

Therefore, the first changeover switch (5) is set to the first color signal system (1).
When switched to the side, the tuning/detection circuit (4) detects the H-ID signal included in the color signal, and the detected signal is transferred to the side of the first level comparator (7) which is switched at this time. The signal is sent to the first Lebel comparator (7) via the second selector switch (51), and is charged to the first capacitor (61) of the holding circuit (6).

The No. 1 Lebel comparator (7) is the tuning/detection circuit (4)
It is detected that the discrimination signal e obtained from the input signal e has a level equal to or higher than a predetermined value, and a high-level pulse signal g is generated and sent to the mode switching port fl@(2).

As a result, the mode switching circuit (2) switches the main changeover switch (53) and supplies the output signal of the first color signal system (1) to the mixing circuit (13).

Furthermore, when the first changeover switch (5>) is switched to the second color signal system <11) and the second changeover switch (51) is switched to the second level comparator (71) side, the second level comparator (71) is switched to the second level comparator (71) side. ) is not receiving a signal of sufficient level,
Therefore, the comparator (71) is connected to the mode switching circuit (2).
It does not output pulses to. On the other hand, the first capacitor (6) of the holding circuit (6) is connected to the first Lebel comparator (7).
61) discharge signal is input.

As a result, the Lebel comparator (7) continues to generate the pulse signal g for the mode switching circuit (2).

Therefore, the main changeover switch (53) is the first color signal system (1).
The output signal of the color signal system (1) is switched to the mixing circuit (1) via the main changeover switch (53).
3), mixed with the luminance signal d, and output to the output terminal (1
4).

The signal recorded on the magnetic tape (9) is MESECA
In the case of M format, when the first and second changeover switches (5) and (51) are switched to the second electric signal system (11) and second level comparator (71) sides, (62) is charged.

Furthermore, when the first and second selector switches (5) and (51) are respectively switched to the first electric signal system (1) and the second level comparator (7), the second level comparator (71) is switched to the second level comparator (71). A discharge signal for the capacitor (62) is supplied.

As a result, the second level comparator (71) sends a high-level pulse signal to the mode switching circuit (2), and the main changeover switch (53) is switched to the second color signal system (11).

According to the above-mentioned color signal reproducing circuit, only one tuning/detection circuit system is required compared to conventionally two systems, so the circuit is greatly simplified.

It should be noted that the configuration of each part of the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made within the technical scope of the claims.

For example, as shown in FIG. 2, the first selector switch (5) is composed of switches (55) (56) for each color signal system,
The operation of each switch (55) (56) is controlled by a switch changeover circuit (54) which receives the gate pulse k and RF switching pulse j as input signals, and the operation of the gate circuit (41) in FIG. It is also possible to use a changeover switch (5). Moreover, the switching period of the first and second changeover switches (5) <51> is the same as that of the tuned amplifier (44).
It can be set to any value as long as it does not synchronize with the switch switching signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a color signal reproducing circuit according to the present invention, FIG. 2 is a block diagram showing another configuration of the first changeover switch, and FIG. 3 is a block diagram of a conventional circuit.

Claims (1)

[Scope of Claims] [1] A plurality of color signal systems (one
) (11), a main changeover switch (53) that selectively connects the output signals of each signal system (1) and (11) to the subsequent circuit, and a mode changeover circuit (53) that controls the main changeover switch (53).
In a color signal reproducing circuit comprising a color signal switching circuit (3) equipped with a color signal switching circuit (2), the color signal switching circuit (3) selects the color to be output from each color signal system (1) and (11). Tuning/detection circuit (4) that determines the presence or absence of a signal
and a first changeover switch (5) that sequentially connects the output signals of each color signal system (1) and (11) to the tuning/detection circuit (4) while switching them at a constant cycle, and in synchronization with the first changeover switch. A second changeover switch (51) connects the output signal of the switched tuning/detection circuit (4) to a plurality of input ends of the mode changeover circuit (2), and each output end of the second changeover switch (51) and the mode. Equipped with a holding circuit (6) that is interposed between each input terminal of the mode switching circuit (2) and holds each discrimination signal to be connected to each input terminal of the mode switching circuit (2) for a certain period of time. A color signal regeneration circuit featuring: [2] The first color signal system (1) is a SECAM color system, the second color signal system (11) is a MESECAM color system, and the tuning/detection circuit (4) detects the output from each color signal system. 4.25MH2 included in the SECAM color signal
Or a tuning circuit that detects the 4.41MH2 color subcarrier (
42) and a detection circuit (43). [3] The holding circuit (6) is a second selector switch (51)
first and second capacitors (
61) (62), each capacitor is
and a color signal reproduction according to claim 2, which has a charging time constant smaller than the switching period of the second changeover switch (5) (51) and a discharging time constant larger than the switching period. circuit.