JPH0424918B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a VTR capable of recording and reproducing SECAM color television signals, for example.
The present invention relates to a filter circuit suitable for use in a video tape recorder.

Background technology and its problems In the SECAM system, the carrier frequency is
The R-Y signal (red difference signal) FM-modulated at 4.40625 MHz and the B-Y signal (blue difference signal) FM-modulated at a carrier frequency of 4.25 MHz are transmitted alternately every horizontal period. . In this case, the amplitudes of these FM-modulated R-Y signals and B-Y signals (hereinafter referred to as color signals) are suppressed near the carrier frequency by a bandpass filter having frequency characteristics as shown in Figure 1. transmitted from. this is,
This is to suppress the carrier wave amplitude near achromatic colors to reduce dot interference.

In a television receiver, the signal is processed after passing through a filter circuit having a frequency characteristic as shown in FIG. 2, which is opposite to the frequency characteristic shown in FIG.

Now, when recording color television signals using the SECAM method on a VTR, the color signals are passed through a filter circuit (also called a bell filter) having frequency characteristics as shown in Figure 2, and are converted into signals with flat frequency characteristics. recorded.

This is because in a VTR, normally the luminance signal is FM modulated and the color signal is low frequency converted and recorded, but in the case of SECAM system, the color signal is
This is done to avoid this problem since if the FM modulated signal is distributed over a wide band and the frequency characteristics remain as shown in Figure 1, there will be interference with the luminance signal at the tail of the chrominance signal, which is inconvenient. . Also, the first
If the frequency characteristics remain as shown in the figure,
This is because when noise is mixed in during tape recording, the SN ratio in the vicinity of the carrier frequency is particularly degraded, so the SN ratio is made equal across the entire band.

As a filter circuit with frequency characteristics as shown in Figure 2, used during recording on this VTR,
For example, the one shown in FIG. 3 has been proposed.

In the figure, reference numeral 1 denotes an input terminal to which a color signal having frequency characteristics as shown in FIG. 1 is supplied, and this terminal 1 is connected to the base of an npn transistor 2. The emitter of this transistor 2 is grounded via an impedance circuit 3. Further, the collector of the transistor 2 is connected via a resistor 4 to a power supply terminal 5 to which DC voltage +B is supplied. An output terminal 6 from which an output signal is obtained is led out from the connection point between the collector of the transistor 2 and the resistor 4.

The frequency characteristics of the example in Fig. 3 are as follows: G ₁ = R/Z (1) R: resistance value _of resistor 4 Z: impedance of impedance circuit 3, as shown in Fig. 2. It has a frequency characteristic.

Conversely, the color signal reproduced by this VTR is
The signal is returned to the state before recording through a filter circuit (also called an inverse bell filter, which has a frequency characteristic complementary to that of a bell filter) having frequency characteristics as shown in FIG. The signal is then subjected to subsequent signal processing and supplied to, for example, a television receiver.

As a filter circuit with frequency characteristics as shown in Figure 1, used during VTR playback,
For example, the one shown in FIG. 4 has been proposed.

In the figure, numeral 7 is an input terminal to which a reproduced color signal is supplied, and this terminal 7 is connected to the base of an npn transistor 8. The emitter of this transistor 8 is grounded via a resistor 9, and its collector is connected via an impedance circuit 10 to a power supply terminal 11 to which a positive DC voltage +B is supplied. An output terminal 12 from which an output signal is obtained is led out from a connection point between the collector of the transistor 8 and the impedance circuit 10.

In this example of FIG. 4, the resistor 9 and impedance circuit 10 are the same as the resistor 4 and impedance circuit 3 in the example of FIG. 3, and the frequency characteristic G ₂ of this example of FIG. 4 is G ₂ = It is expressed as Z/R (2) and has frequency characteristics as shown in FIG.

In VTRs that can record and play back conventional SECAM color television signals,
The filter circuits shown in the example of FIG. 3 and the example of FIG. 4 are provided separately and independently in the recording system and the reproducing system, respectively. Therefore, the center frequency must be adjusted in each filter circuit, and when integrated into an integrated circuit, separate external components are required, and the integrated circuit requires two pins for these. There were some drawbacks.

Purpose of the invention The present invention has been made in view of the above points, and is
It is an object of the present invention to provide a filter circuit which realizes a filter having the frequency characteristics as shown in FIG. 2 and FIG. 2 without the above-mentioned drawbacks.

SUMMARY OF THE INVENTION In order to achieve the above object, the filter circuit according to the present invention includes, for example, the SECAM
In a filter circuit applied to a video signal recording and reproducing device of the above-mentioned method, first and second transistors 15 and 22 connected in series are connected to a connection midpoint 28 between the first and second transistors 15 and 22. Impedance circuit 2 for bell filter
00 and the first and second transistors 15, 2
switch circuits 16 and 27 that selectively put one of the transistors 2 into operation according to the recording or reproduction state of the recording/reproduction device, and when recording, a color signal of the SECAM method is applied to the base 13 of the first transistor 15. is supplied, the switch circuit 1
6 and 27, only the first transistor 15 is put into operation so that the frequency characteristic of the circuit formed by the first transistor 15 and the impedance circuit 200 becomes a bell filter characteristic, and during reproduction, the second transistor 22 on the base 21 of
When the reproduced color signal of the SECAM method is supplied, only the second transistor 22 is activated by the switch circuits 16 and 27, and the frequency characteristics of the circuit formed by the second transistor 22 and the impedance circuit 200 are reversed. It is designed to have bell filter characteristics.

The present invention is configured as described above, and during recording and playback of the SECAM type recording/playback device, respectively,
A filter having frequency characteristics as shown in FIGS. 1 and 2 is formed around the first and second transistors. Since it is composed of one impedance circuit, the center frequency can be adjusted by 1
When it is integrated into an integrated circuit, fewer external parts are needed, and only one pin is required for this purpose.

Embodiment Hereinafter, an embodiment of the filter circuit according to the present invention will be described with reference to FIG. In this example, it is used in a VTR that can record and play back SECAM color television signals. Further, this example is an integrated circuit example, and a portion surrounded by a broken line 100 indicates the inside of the integrated circuit.

In the same figure, 13 is an input terminal to which a color signal (FM modulated R-Y signal and B-Y signal) having frequency characteristics as shown in FIG. 1 is supplied during recording, and this terminal 13 is connected to a resistor. via vessel 14
Connected to the base of npn transistor 15.
The base of this transistor 15 is the switch circuit 1
6, and its emitter is connected to the fixed terminal REC side of the switch circuit 16 via a constant current circuit 17. The movable terminal of this switch circuit 16 is grounded. Further, the collector of the transistor 15 is connected via a resistor 18 to a power supply terminal 19 to which a positive DC voltage +B is supplied. An output terminal 20 from which an output signal is obtained is led out from a connection point between the collector of the transistor 15 and the resistor 18.

Further, 21 is an input terminal to which a reproduced color signal is supplied during reproduction, and this terminal 21 is connected to the base of an npn transistor 22. This transistor 22 is configured differentially with an npn type transistor 23. A predetermined voltage V ₀ is supplied to the base of the transistor 23, and its collector is connected to the power supply terminal 19.
connected to. In addition, transistors 22 and 23
The emitters of are connected through resistors 24 and 25, respectively, and the connection point thereof is connected through a constant current circuit 26 to the fixed terminal PB side of a switch circuit 27.
The fixed terminal REC side of this switch circuit 27 is electrically floating, and its movable terminal is grounded. Further, the collector of the transistor 22 is connected to the emitter of the transistor 15, and a pin 28 is led out from the connection point. Further, an output terminal 29 from which an output signal is obtained is led out from the collector of this transistor 22. Also, resistors 24 and 25
is assumed to have the same resistance value as resistor 18.

Also, pin 30 is set to low level “0” during recording.
A control signal that becomes high level "1" during reproduction is supplied. The control signal supplied to this pin 30 is supplied to the above-mentioned switch circuits 16 and 27 as a switching control signal. The movable terminals of these switch circuits 16 and 27 are switched to the fixed terminal REC side during recording and to the fixed terminal PB side during playback.

The pin 28 is also connected to the collector of a pnp transistor 34 through a series circuit of resistors 32 and 33. Further, the pin 28 is connected to the connection point of the resistors 32 and 33 via a series circuit of a resistor 35, a capacitor 36, and a variable coil 37.
Further, this connection point is grounded via a capacitor 38. Further, the emitter of the transistor 34 is connected to a power supply terminal 39 to which a DC voltage + _Vcc is supplied. Further, the pin 23 is connected to a power supply terminal 39 through a series circuit of a resistor 40, a diode 41, and resistors 42 and 43, and a connection point between the resistors 42 and 43 is connected to the base of the transistor 34.

Here, resistors 32, 35, 40, 42, 4
3. An impedance circuit 200 is configured by the capacitor 36 and the variable coil 37. Further, the resistor 33 and the capacitor 38 constitute a circuit for removing unnecessary signal components on the power supply line.

Reference numeral 44 denotes an npn type transistor for controlling on/off of the transistor 34, and the base of this transistor 44 is connected to a terminal 45 via a resistor to maintain a low level "0" during recording and a high level "1" during playback. ” is supplied. Also,
The emitter of this transistor 44 is grounded, and its collector is connected to the connection point between the resistor 42 and the diode 41.

In this case, the transistor 44 is turned off during recording and turned on during reproduction. Accordingly, the transistor 34 is turned off and on. Note that the diode 41 is also made conductive and non-conductive accordingly.

Further, the pin 30 is supplied with a signal from a terminal 45 that has a low level "0" during recording and a high level "1" during playback.

This example is configured as described above, and for the record, the changeover switches 16 and 27 are connected to the fixed terminal REC.
Since it is switched to the side, transistors 22 and 25 in the integrated circuit do not operate, and only transistor 15 operates. In addition, an external transistor 4
4 is turned off and transistor 34 is turned off, so the emitter of transistor 15 is connected to pin 28.
and is grounded via an impedance circuit 200. In this case, the diode 41 is made conductive, so the impedance circuit 200 includes the resistors 32, 35, 40, 42, 43, and the capacitor 3.
6. Consists of a variable coil 37.

After all, during this recording, a filter is formed by the transistor 15 and the impedance circuit 200, and its frequency characteristic g ₁ is: g ₁ = r/z (3) r: resistance value of the resistor 18 z: resistance value of the impedance circuit 200 Expressed as impedance, it has a frequency characteristic as shown in FIG. Therefore, a color signal with flat frequency characteristics is obtained at the output terminal 20.

Also, during playback, the changeover switches 16 and 27
is switched to the fixed terminal PB side, so transistor 15 in the integrated circuit does not operate, and transistors 22 and 23 operate. Further, the externally connected transistor 44 is turned on, and the transistor 34
is turned on, so the collector of transistor 22 is connected to impedance circuit 200 through pin 28.
It is connected to the power supply terminal 39 via. in this case,
Since diode 41 is rendered non-conductive, impedance circuit 200 is comprised of resistors 32 and 35, capacitor 36, and variable coil 37.

After all, during this reproduction, a filter is formed by the transistor 22 and the impedance circuit 200, and its frequency characteristic g ₂ can be expressed as g ₂ =z/r (4), resulting in a frequency characteristic as shown in Fig. 1. . That is, the frequency characteristics are complementary to those shown in FIG. 2. However, in this case, resistor 4
0, 42, and 43 do not constitute the impedance circuit 200, and the Q is higher in this case. This is to compensate for changes in frequency characteristics caused by passing the reproduced color signal supplied to the input terminal 21 through the bandpass filter.

In this case, a color signal having the frequency characteristics of the state before recording is obtained at the output terminal 29.

According to the filter circuit of this example, a filter having frequency characteristics as shown in FIG. 2 is formed during recording, and a filter having frequency characteristics as shown in FIG. 1 is formed during playback. is demonstrated. And each filter is 1
Since the two impedance circuits 200 are shared, the center frequency can be adjusted in one place (variable coil 3
7), which reduces the number of external parts when integrated into an integrated circuit, and requires only one pin 28 for this purpose. Furthermore, the impedance of the impedance circuit 200 is changed between recording and reproduction to compensate for changes in frequency characteristics caused by the bandpass filter through which the reproduction signal is passed.
During playback, color signals in the same state as before recording can be obtained. Further, since only the transistors forming the filters are operated during recording and reproduction, wasteful power consumption can be avoided.

Effects of the Invention As is clear from the embodiments described above, according to the filter circuit according to the present invention, the filter circuit shown in FIGS.
A filter with frequency characteristics as shown in the figure is formed, and since it is composed of a single impedance circuit, the center frequency only needs to be adjusted in one place, reducing the number of external components when integrated into a circuit. , only one pin is required for this purpose. Therefore, the present invention is suitable for application to a VTR capable of recording and reproducing SECAM color television signals.

[Brief explanation of drawings]

1 and 2 are diagrams showing frequency characteristics, FIGS. 3 and 4 are block diagrams showing an example of a conventional filter circuit, and FIG. 5 is a diagram showing an example of a filter circuit according to the present invention. FIG. 13 and 21 are input terminals, 15 and 22 are transistors, 20 and 29 are output terminals, and 200 is an impedance circuit.

Claims (1)

[Claims] 1. In a filter circuit applied to a SECAM video signal recording/reproducing device, first and second transistors connected in series, and a connection midpoint between the first and second transistors. an impedance circuit for a bell filter connected to the recording/reproducing apparatus; and a switch circuit that selectively puts either one of the first and second transistors into an operating state according to the recording or reproducing state of the recording/reproducing apparatus. Sometimes, the base of the first transistor
When a SECAM color signal is supplied, only the first transistor is activated by the switch circuit, so that the frequency characteristic of the circuit formed by the first transistor and the impedance circuit becomes a bell filter characteristic. and at the time of playback, the base of the second transistor mentioned above.
When a reproduced color signal of the SECAM method is supplied, only the second transistor is activated by the switch circuit, and the frequency characteristic of the circuit formed by the second transistor and the impedance circuit becomes an inverse bell filter characteristic. A filter circuit characterized in that: