JPH06105335A - Filter circuit - Google Patents

Abstract

PURPOSE:To reduce the number of filters themselves by revising a frequency characteristic through the changeover of minimum number of elements at recording and reproduction and using a single filter circuit so as to eliminate an undesired component from a low freqency chrominance signal at the recording or reproduction. CONSTITUTION:A low frequency chroma signal is selected at recording and a reproduced video signal in which a low frequency chroma signal is superimposed on an frequency-modulated luminance signal at reproduction is selected by a switch SW 1. Parts of elements such as resistors R8, R9 are adjusted to revise a frequency characteristic of a trap block 20 at recording and reproduction and a desired component is taken out by the trap block 20 which takes out desired component in the output signal of switch SW1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low frequency chroma filter circuit used for processing a video signal of a video tape recorder (VTR), and particularly for recording and reproducing a low frequency chroma signal.

[0002]

2. Description of the Related Art Conventionally, a recording / reproducing system in a VTR has a luminance signal FM-modulated, and a chroma signal is frequency-converted to a low frequency, that is, low-frequency converted, and then an FM luminance signal FM is used.
A video signal on which a low-frequency chroma signal is superimposed with a wave as a bias is recorded on a magnetic tape through a recording amplifier, and at the time of reproduction, the video luminance signal is separated into an FM luminance signal and a low-frequency chroma signal. It is general to demodulate and frequency-convert the low frequency chroma signal to the original high frequency band.

In the case of a so-called 8 mm VTR, the luminance signal is 5
FM modulation is performed with the MHZ vicinity as the FM carrier, and 3.5
The 8 MHZ chroma signal is low-pass converted to 743 kHZ using 4.32 MHZ as a conversion carrier, and this signal is superimposed on the FM luminance signal, and recorded on a magnetic tape via a recording amplifier and a head. Further, at the time of reproduction, the FM luminance signal and the low frequency chroma signal are separated from the reproduced FM signal obtained from the head amplifier by a low-pass filter or a trap, and the FM luminance signal is converted into a baseband signal by the FM demodulator. The demodulated low-frequency chroma signal is frequency-inverted to 3.58 MHZ and then subjected to known signal processing.

By the way, the low-pass converted chroma signal is
During recording, it is applied to a filter circuit as shown in FIG. 2 for the purpose of removing out-of-band components. This filter circuit has a resistor R connected to an input terminal 10 to which a low frequency chroma signal is input.
1 and a capacitor C1 high-pass filter (HP
F) 1, 1.5 MH consisting of a coil L1 and a capacitor C2 connected in series between the output stage of this HPF1 and ground
A low-pass filter (LPF) 3 including an audio trap 2 of Z, a coil L2 connected in series to the base of the transistor T1 at the output stage and a rear stage, resistors R2 and R3, and a capacitor C3 inserted between the base and the ground.
The characteristics of each element are set so as to have the frequency characteristics shown in FIG. Where 1.5MHZ
Corresponds to the center frequency of the audio signal, and operates to remove this component as an unnecessary component in the audio trap 2. The output of the filter circuit, that is, the low-frequency chroma signal from which the unnecessary frequency component is removed is the transistor T
A recording amplifier, which is output from the emitter of 1 to the output terminal 11 and is superimposed on the luminance signal FM-modulated by another circuit,
It is recorded on the magnetic tape through the head.

By the way, in general, when reproducing a magnetic tape in which a chroma signal is recorded with a constant recording current, the output characteristics of the head are doubled in a relatively low frequency band such as a low frequency chroma signal. The output doubles, so-called 6 dB
It is on the octave curve. Therefore, in consideration of this, the frequency characteristic of the filter circuit at the time of recording as shown in FIG.
It is stipulated by the standard to have a slope and absorb 6 dB octave.

Next, at the time of reproduction, the output of the head amplifier is applied to a filter circuit as shown in FIG. 3 for the same purpose as recording. This filter circuit is composed of pilot and audio signal traps 4 and 5 for tracking servo, and a low pass filter (LPF) 7 for removing a luminance signal component. After that, the resistor R4 connected to the emitter of the transistor T2 input to the base, and the pilot trap 4 for removing the pilot signal, which includes the coil L3 and the capacitor C4 inserted in series between this resistor and the ground, are at the frontmost stage. An audio trap 5 for removing an audio signal, which includes a resistor R5 connected to the resistor R4 and a coil L4 and a capacitor C5 connected between the resistor R5 and the ground, is disposed.
Furthermore, the resistor R5 is the base, and the collector is the power supply voltage VCC.
Is provided with a buffer 6 including a transistor T3 whose emitter is connected to the ground via a resistor R6 and a resistor R6, and the emitter of the transistor T3 and an output terminal 8 are provided at the last stage.
A resistor R7 connected in series to the coil, coils L5 and L6, a capacitor C6 connected in parallel with the coil L6, and a resistor R
7, a capacitor C7 connected between the connection point of the coil 7 and the coil L5 and the ground, a capacitor C8 connected between the connection point of the coil L5 and the coil L6 and the ground, a capacitor C9 connected between the output terminal 8 and the ground, L consisting of resistor R12
PF7 is arranged.

Further, the emitter of the transistor T3 is
A chromatographic lap 9 for removing a chroma signal and extracting an FM luminance signal, and an FM demodulator 14 for FM demodulating the output of the chromatographic lap 9 are sequentially connected, and the FM demodulated luminance signal is led to an output terminal 13. And is output to the subsequent luminance signal processing circuit. Further, the low frequency chroma signal output to the output terminal 8 is frequency-converted to the original high frequency by the reproduction chroma processing circuit in the subsequent stage.

As shown in FIG. 5, the frequency characteristic of the filter circuit at the time of reproduction is such that the pilot signal around 150 KHZ and the audio signal around 1.5 MHZ are alleviated, and moreover the slope is smaller than that in FIG. It is generally standardized so as to be small.

[0009]

The structure of the conventional low-pass chroma filter circuit generally has two types of circuits for recording and reproducing as shown in FIGS. 4 and 5, respectively. The individual characteristics were fixed almost invariably. Therefore, it is necessary to provide two types of filter circuits having slightly different frequency characteristics for the purpose of removing substantially similar unnecessary components.

[0010]

According to the present invention, a low-frequency chroma signal obtained by low-frequency converting a chroma signal during recording is input.
A terminal, a second terminal for inputting a reproduced video signal in which a low-frequency chroma signal is superimposed on an FM-modulated luminance signal at the time of reproduction, a first terminal side at the time of recording, and a second terminal side at the time of reproduction Switch means for switching to, and a filter means for extracting a desired component in an output signal of the switch means,
It is characterized by comprising frequency changing means for changing the frequency characteristic of the filter means in accordance with recording and reproducing.

[0011]

Since the present invention is configured as described above, the same common traps and filters necessary for both recording and reproduction such as audio traps and LPFs are used as much as possible, and the single traps are used for recording and reproduction. One filter circuit can remove unnecessary components from the low-frequency chroma signal.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block of this embodiment. still,
In FIG. 1, the same parts as those of FIGS. 2 and 3 of the conventional example are designated by the same reference numerals and the description thereof will be omitted.

SW1 is an analog switch for selecting a low band chroma signal for recording input from the input terminal 10 and a reproduced video signal input to the input terminal 12, and specifically, a pair of transistors T4 and T5. And the base of the transistor T4 is a capacitor C1 for cutting direct current.
0 is connected to the input terminal 12, and the collector is connected to the control signal input terminal 15. The base of the transistor T5 is connected to the input terminal 10, and the power supply voltage VCC is applied to the collector. Both transistors T4, T5
The emitters of are both connected to one end of a resistor R4. A coil L3 and a capacitor C are connected between the other end of the resistor R4 and the ground.
4 and the transistor T6 are connected in series, and the base of the transistor T6 is connected to the input terminal 15. A control signal PBH which becomes H (high) level only during reproduction is input to the input terminal 15.

Further, the resistor R4 and the transistor T3 in the subsequent stage
The resistors R5 and R8 are connected in series between the bases of the two, and the coil L4, the capacitor C5 and the resistor R9 are connected in series between the base and the ground. Further, the collector and the emitter of the switching transistor T7 are connected to both ends of the resistor R8, the transistor T8 is inserted between one end of the resistor R9 and the ground, and the bases of both the transistors T7 and T8 are connected to the input terminal 15. There is. The trap block 20 is connected from the resistor R4 to the stage before the transistor T3.
Called.

The structure subsequent to the transistor T3 is schematically shown in FIG.
The buffer 6 and the LPF 7 have the same structure as the above, but the output of the LPF 7 is connected to the output terminal 8 connected to the reproduction chroma signal processing circuit, and is connected to the recording amplifier as shown in FIG. Connected to the output terminal 11.

Next, a filter having the above-mentioned circuit configuration
The operation of the circuit will be described. A low-frequency chroma signal whose frequency has been converted to a low-frequency during recording is input to the base of the transistor T5 via the input terminal 10. During this recording, the control signal PBH is always at the L (low) level, so the transistor T4 is turned off and the switch SW
As the output of 1, the low frequency chroma signal from the transistor T5 is output.

Further, since the control signal PBH is at L level, all the transistors T6, T7 and T8 are turned off.
It becomes a state. Here, since the transistor T6 is turned off, the resistor R4, the coil L3, the capacitor C
The pilot trap 4 composed of 4 is deactivated, and the transistors T7 and T8 are turned off, whereby the resistors R5 and R8, the coil L4, the capacitor C5, and the resistor R9.
By this, an audio trap is configured, and by adjusting the resistance values of the resistors R8 and R9 in advance,
The filter inclination and the depth of the audio trap can be made to match the optimum characteristics, that is, the characteristics shown in FIG. 4, and the recording low frequency chroma signal of 1.5 MHz which is the SW1 output.
Audio components near Z can be removed. The recording low-pass chroma signal that has passed through the trap block 20 passes through the buffer 6 including the transistor T3 and the resistor R6, passes through the LPF 7 for removing the luminance signal, and then passes through the recording amplifier 11.
And is superimposed on the luminance signal FM-modulated by another circuit and recorded on the magnetic tape.

Incidentally, at the time of this recording, the above-mentioned recording low frequency chroma signal is also generated at the output terminal 8 via the LPF 7, but this output terminal 8 is connected to a reproducing system circuit for processing the reproduced chroma signal, and Since these reproduction system circuits are inoperative during recording, there is no particular problem. Similarly, the circuit after the FM demodulator 14 and the output terminal 13 is also a reproducing system, and therefore becomes inoperative during recording, and the signal supplied to the chromatolap 9 does not pose a problem.

On the other hand, at the time of reproduction, a reproduced FM video signal which is an output of the head amplifier is supplied to the input terminal 12 which is one terminal of SW1. Also, during this reproduction, the control signal PB
Since H rises to H level, a bias is applied to the base of the transistor T4 by the voltage dividing resistors R10 and R11. If this bias voltage is set to a voltage value sufficiently higher than the base of the other transistor T5, the transistor T4 is turned on and the transistor T5 is turned off.
In the F state, the SW1 output becomes a reproduced FM video signal.

Further, the control signal PBH maintains the H level, so that the transistors T6, T7 and T8 are all turned on. When the transistor T6 is turned on, the pilot trap 4 including the resistor R4, the coil L3, and the capacitor C4 is turned on. Further, since the capacitors T7 and T8 are turned on, both ends of the resistors R8 and R9 are short-circuited, and the audio trap is composed of the resistor R5, the coil L4, and the capacitor C5. Both the pilot trap and the audio trap thus configured have the same configuration as the pilot and audio trap of FIG.
A filter having the characteristics shown in FIG. 5 is formed.

The reproduced FM video signal that has passed through the trap block 20 passes through the buffer 6 and then the chroma component 9 removes the chroma component and the FM demodulator 14 performs F
It is M-demodulated and output to the output terminal 13 as a reproduction luminance signal for signal processing. Further, the output of the buffer 6 is the LPF 7
Also, only the reproduced low frequency chroma component is taken out and output to the output terminal 8, and the reproduced chroma processing circuit in the subsequent stage frequency-inverts it to 3.58 MHZ for chroma processing.

During reproduction, the LPF 7 is connected to the output terminal 11.
Although an output is output, this is not a problem because a recording system circuit that is inoperative during reproduction is connected to the output terminal 11 after the output terminal 11.

[0023]

As described above, according to the present invention, the common traps and filters necessary for both recording and reproduction are maximally used, and the frequency characteristics are minimized by switching the elements. And a single filter circuit makes it possible to remove unnecessary components from the low-frequency chroma signal at the time of recording or reproduction, and it is possible to reduce the number of filters themselves.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of a low-pass chroma filter circuit during recording in a conventional example.

FIG. 3 is a circuit diagram of a low-pass chroma filter circuit during reproduction in a conventional example.

FIG. 4 is a characteristic diagram of a low-pass chroma filter circuit during recording.

FIG. 5 is a characteristic diagram of a low-pass chroma filter circuit during reproduction.

[Explanation of symbols]

 10 input terminal 12 input terminal SW1 switch 20 filter block R8 resistor R9 resistor

Claims (1)

[Claims] 1. A first terminal to which a low-frequency chroma signal obtained by low-frequency converting the chroma signal is input at the time of recording, and a reproduction video signal in which the low-frequency chroma signal is superimposed on an FM-modulated luminance signal at the time of reproduction are input. A second terminal, a switch means for switching the low-frequency chroma signal on the side of the first terminal at the time of recording, and a reproduced video signal on the side of the second terminal at the time of reproduction, and an output signal of the switch means. A filter circuit comprising a filter means for extracting a desired frequency component, and a frequency changing means for changing the frequency characteristic of the filter means according to recording and reproducing.