JPH11178003A - Secam chroma filter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of a killifish noise at a specific spectrum by compensating an attenuated high frequency chroma component and improving in-band amplitude balance. SOLUTION: A bell filter circuit 12 receives a chroma signal S1 of a SECAM television system and provides an output S2 with a bell filter characteristic which is specified by the SECAM system and an output S3 with a high-pass filter characteristic. An adder 16 adds the outputs S2, S3 at a prescribed ratio. A switching circuit 15 selects an output S4 from the adder or the output S2 with the bell filter characteristic from the bell filter circuit 12, and the selected output is used for the filter output. Since the output S2 is used for the filter output when the filter characteristic is required and the output of the adder is selected when a compensated output is required, a proper band characteristic use is selected depending on applications.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention mainly relates to SECAM.
TECHNICAL FIELD The present invention relates to a SECAM chroma filter circuit suitable for use in a TV receiver and a VTR corresponding to a TV (television) signal of a system.

[0002]

2. Description of the Related Art FIG. 8 shows a configuration example of a conventional TV receiver compatible with the SECAM system. Broadcasted SECA transmitted
The tuner 81 selects and detects the TV signal of the M system,
Output as a composite video signal. A composite video signal from an external video device and a signal from the tuner 81 are switched by a switch 82.
And outputs it to the bell filter circuit 83. The bell filter circuit 83 cancels the inverse bell filter characteristic applied on the transmission side, and makes the chroma amplitude constant regardless of the hue, and outputs the chroma amplitude to the SECAM chroma processing circuit 84.

In such a receiving apparatus, a tuner 81
In many cases, the high frequency characteristics of the chroma signal band are attenuated by an audio trap filter, a Nyquist slope, or the like, and the signal that should be output as shown in FIG. In the SECAM method, the chroma signal is
Since the frequency is transmitted by M modulation, and the transmission frequency is different depending on the hue, in the case of the characteristic such as B, in the case of the color bar, the BY color difference signal is the cyan, magenta, and blue hues and the RY color difference In the signal, the amplitude decreases in the hues of cyan, green, and blue. In the cyan and blue hues in which the amplitude is small in both color difference signals, there is a problem that tailing (medaka) noise peculiar to FM demodulation tends to occur when a weak electric field is applied.

[0004]

The above-mentioned conventional SEC
The AM chroma filter circuit has a problem that medaka noise peculiar to FM demodulation is easily generated at a weak electric field.

An object of the present invention is to compensate for attenuated high-frequency chroma components, improve the in-band amplitude balance, and reduce the occurrence of medaka noise in a specific hue.

[0006]

In order to solve the above-mentioned problems, in a SECAM chroma filter circuit of the present invention, a bell filter circuit is constituted by a filter capable of outputting HPF (high-pass filter) characteristics, and a bell filter circuit is provided. A means for adding the HPF characteristic to the filter characteristic output is provided to select between the bell filter output and the addition output. H to be added
The versatility is enhanced by changing the level of the PF characteristic, and a weak electric field noise is reduced by adding means for selecting between the bell filter characteristic output and the HPF characteristic output.

When the bell filter characteristic is required, the bell filter characteristic output is used, and when the compensated output is required, the addition output can be selected. Is emphasized by an optimal amount, thereby compensating the amplitude balance in the band. Also, HP
By using only the F characteristic, noise in the low frequency side can be suppressed more heavily than in the case of addition.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit configuration diagram for explaining a first embodiment of the present invention. The SECAM composite video signal obtained by switching the signal from the tuner path and the signal from the external device or the chroma signal S1 extracted therefrom is input to the input terminal 11 of the bell filter circuit 12. The bell filter circuit 12 has a gm
(Transconductance) It is composed of a filter circuit using an amplifier, and outputs a signal S2 having bell filter characteristics from an output terminal 13 and a signal S3 having HPF characteristics from an output terminal 14, respectively.

The signal S2 is input to one fixed terminal of the switch circuit 15, and the signal S4 obtained by combining the signals S2 and S3 in the adder 16 is input to the other fixed terminal of the switch circuit 16. In the switch circuit 15, one of the output S2 of the bell filter characteristic and the synthesized signal S4 is connected to the external control terminal 1.
7 and is output to the chroma processing circuit 18 at the subsequent stage.

A specific example of the bell filter circuit 12 constituted by using a gm filter will be described. That is, the output of the gm amplifier gm1 whose positive input is grounded is grounded via the capacitor C1, and is input to the positive input of the gm amplifier gm2 via the buffer amplifier B1. The output of the gm amplifier gm2 is connected to the SECA through the capacitor C2.
An M chroma signal S1 is supplied. Also, gm amplifier gm
2 is output from a gm amplifier g via a buffer amplifier B2.
input to the negative input of m1 and g via the attenuator m.
Input to the negative input of m amplifier gm2. Buffer amplifier B
2 is supplied to an output terminal 14. Buffer amplifier B
1 and the other end of the capacitor C2, one end of which is connected to the output of the gm amplifier gm2.
1 and R2, and the connection point of the resistors R1 and R2 is connected to the output terminal 13. Further, a buffer amplifier B1 and a resistor R1
, An inverting amplifier-A is inserted.

The bell filter circuit 12 shown in FIG.
When the transfer function HP (S) of the output of the buffer amplifier B2 is obtained, HP (S) = S ² / [S ² + (m · gm2 / C2) S + gm1 / gm2 / C1 / C2], and HPF (High-pass filter) characteristics. Similarly, the transfer function BP at the output of the buffer amplifier B1
(S) is BP (S) =-[(gm1 / C1) S] [S ² + (m · gm2 / C2) S + gm1 / gm2 / C1 / C2], and is a BPF (bandpass filter) characteristic. Becomes BP
Since the F-characteristic output is an output with an inverted polarity, the output is returned to the positive phase by the inverting amplifier-A, and the BPF characteristic positive-phase output and the original signal are
(16- (1.6) ^1/2 ) / 16 to (1.6) ^1/2 / 1
By adding at a ratio of 6, a bell filter characteristic is obtained. Here, as the simplest example, the resistance is formed by R1 and R2.

The bell filter characteristic defined by the SECAM system is as shown in FIG. 2A. Although the low frequency side and the high frequency side are attenuated with respect to the center frequency fo, they do not become infinitesimal. When the bell filter characteristic and the HPF characteristic are combined by the adder 16, the characteristic becomes the B characteristic shown in FIG. 2, and the high band can be reinforced and the low band can be relatively attenuated.

If the frequency characteristics of the tuner circuit are known in advance, a predetermined amount of synthesis may be set, and this is possible with FIG. However, the circuit after the bell filter circuit and the tuner are usually separate circuits (IC), and it is not known what tuner is combined with the tuner circuit.

Therefore, a second embodiment of the present invention in which versatility is enhanced will be described with reference to FIG. In this embodiment, a gain control circuit 31 is added to the path from the output terminal 14 to the adder 16 in FIG. The gain control circuit 31 receives the HPF characteristic signal S3, controls the amplitude, and
Output to 6. The amount of reinforcement in the high frequency range is adjusted and controlled in accordance with the frequency characteristics of the tuner circuit combined from the control terminal 32. Thereby, the selection range of the tuner circuit to be combined can be expanded.

As described above, if the frequency characteristic is switched in response to the switching between the tuner and the external input, the control signal of the switch circuit 15 can be handled by interlocking with the input switching signal. However, the in-band characteristics of the input chroma signal are also affected by a pre-filter and various capacitive coupling circuits connected before the bell filter circuit.

Therefore, the switch circuit 15 always selects the output of the adder 16 without selecting the bell filter characteristic,
If the reinforcement level of the gain control circuit 31 is switched, it can be used not only for the frequency characteristic of the tuner but also for the purpose of compensating the band characteristic of the own circuit. In this case, since it is not necessary to select the bell filter characteristic, the selection switch circuit 15 can be omitted.

FIG. 4 is a circuit configuration diagram for explaining a third embodiment of the present invention. In this embodiment, the output S3 of the HPF filter characteristic is input to the switch circuit 41 without passing through the adder, and the output S2 of the bell filter characteristic is input.
And switch. The high-frequency compensation is simply realized by using only the HPF characteristic.

FIG. 5 shows the bell filter characteristic by A and the HPF characteristic by C, and the effect of FIG. 4 will be described. Normally, a filter for extracting a chroma signal from a composite video signal is independent because the transfer function is determined separately from the bell filter circuit, but this is absorbed and integrated with the bell filter circuit, and the extraction filter can be omitted. . In the bell filter circuit 12, since the bell filter characteristic and the HPF characteristic are simultaneously obtained from the same circuit, if the HPF characteristic is regarded as a signal that has passed through both the extraction filter and the bell filter,
There is no need to provide an independent extraction filter. Since the transfer function of the HPF characteristic based on the bell filter characteristic is a filter with a Q of 16, the attenuation in the high frequency band is larger than that in the bell filter characteristic, and the low frequency band is attenuated to infinity.

Further, if the HPF characteristic is selected when the electric field is weak, another effect is produced. SEC
In the AM system, the frequency arrangement of the FM modulation is determined by the hue, and noise on the lower side than the center frequency fo appears red on the screen and blue on the higher side. The human eye is sensitive to reddish colors, and the red noise is unpleasant. Therefore, T
It is desirable to suppress red noise in a weak electric field as a viewing feeling of a V receiver or a VTR. In the HPF characteristic, the amount of suppression particularly on the low frequency side is larger than that on the high frequency side, which is preferable.

The switch circuit 41 of FIG. 4 may be used for the purpose of dealing with a weak electric field separately from the switch circuit 15 of FIGS. FIG. 6 is a circuit configuration diagram for explaining a fourth embodiment of the present invention in which the switch circuit 41 is adapted for a weak electric field.

In FIG. 6, a switch circuit 41 is inserted after the switch circuit 15 so that the gain control circuit 31 shown in FIG.
, And the function of switching HPF characteristics can be used together. In this case, the weak electric field determination is separately performed, and the control terminal 42 is controlled based on the result.

In this embodiment, in addition to the effects of the third embodiment, the effects of the second embodiment are combined. In FIG. 6, the switch circuits 15 and 41 are cascaded for the sake of simplicity, but a switch circuit of three alternatives may be used.

In each of the embodiments described above, the case where the circuit configuration of the bell filter is the bell filter circuit 12 shown in FIG. 1 has been described. However, the present invention is not limited to this, and the present invention is not limited to this. A bell filter circuit may be used. Hereinafter, a case in which a general bell filter circuit is applied to each of the above-described embodiments will be described with reference to FIG.

Varying the band balance of the filter is equivalent to manipulating the zero frequency in terms of the pole / zero frequency of the transfer function of the bell filter. Therefore, the present invention can be realized not only by adding the function of the BPF and the original signal as shown in FIG. 1 but also by using a single filter circuit.

The filter circuit of FIG. 7 has two gm amplifiers g
m1, gm2 and capacitors C1, C2 and j, k,
It was configured using four attenuators m and n. The transfer function H (S) in this configuration is H (S) = [n · S ² + (k · gm2 / C2) S + j · gm1 / gm2 / C1 / C2] / [S ² + (m ·
gm2 / C2) S + gm1 / gm2 / C1 / C2], and the gain can be set arbitrarily. In the circuit of FIG.
By adding F, n is controlled.
However, in the configuration of FIG.
3 may not be taken out, and FIG. 3 may not be implemented as it is. In that case, n in FIG.
By adding a switching means for setting (and k as necessary) zero, the bell filter characteristic and the HPF
Characteristics can be obtained, and the switch circuit 15 can be omitted. If a means for varying the amount of attenuation is added to the attenuators j and n in FIG. 7 and controlled from the external control terminal 64, optimum high-frequency reinforcement for the tuner characteristics can be performed as in FIG.

[0026]

As described above, the SEC of the present invention is
According to the AM chroma filter circuit, the occurrence of medaka noise in a specific hue is reduced by compensating the in-band imbalance of the chroma signal, and the band is further narrowed in the weak electric field to reduce the red system color noise. A good viewing feeling can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram for explaining a first embodiment of the present invention.

FIG. 2 is a characteristic diagram for explaining the operation of FIG. 1;

FIG. 3 is a circuit configuration diagram for explaining a second embodiment of the present invention.

FIG. 4 is a circuit configuration diagram for explaining a third embodiment of the present invention.

FIG. 5 is a characteristic diagram for explaining the operation of FIG. 4;

FIG. 6 is a circuit configuration diagram for explaining a fourth embodiment of the present invention.

FIG. 7 is a circuit configuration diagram for explaining a fifth embodiment of the present invention.

FIG. 8 is a circuit configuration diagram for describing the configuration of a conventional SECAM-compliant TV receiver.

FIG. 9 is a characteristic diagram for explaining the operation of FIG. 8;

[Explanation of symbols]

11 input terminal, 12 bell filter circuit, 13, 14
... output terminals, 15, 41 switch circuits, 16 ... adders, 17, 42 ... control terminals, 18 ... chroma processing circuits, 3
1: gain control circuit, 32, 42, 61: control terminals.

Claims (8)

[Claims] 1. A bell filter circuit which receives a chroma signal of a SECAM television system and has an output of a bell filter characteristic and an output of a high-pass filter characteristic defined by the SECAM system, and An adder that adds the output and the output of the bell filter characteristic at a predetermined ratio; and a selection unit that selects one of the output of the adder and the output of the bell filter characteristic. A SECAM chroma filter circuit, wherein an output selected by the above is extracted as a filter output. 2. The SE according to claim 1, wherein gain control means is inserted between an output terminal for outputting a high-pass filter characteristic of the bell filter circuit and an input of the adder.
CAM chroma filter circuit. 3. A bell filter circuit which receives a chroma signal of a SECAM television system and has an output of a bell filter characteristic and an output of a high-pass filter characteristic defined by the SECAM system; A gain control circuit for inputting an output to vary the signal gain thereof; an adder for adding an output of the gain control circuit and an output of the bell filter characteristic at a predetermined ratio; and an output of the adder or the gain. Selecting means for selecting whether the output is a control circuit or not, wherein the output of the selecting means is extracted as a filter output. 4. A bell filter circuit which receives a chroma signal of a SECAM television system and has an output of a bell filter characteristic and an output of a high-pass filter characteristic defined by the SECAM system, and an output of the bell filter characteristic. A SECAM chroma filter circuit comprising: selecting means for selecting and outputting one of the outputs of the high-pass filter characteristics. 5. A bell filter circuit which receives a chroma signal of a SECAM television system and has an output of a bell filter characteristic and an output of a high-pass filter characteristic defined by the system, An adder for adding an output or an output of the high-pass filter characteristic to a signal via a gain control circuit and an output of the bell filter characteristic at a predetermined ratio; an output of the bell filter characteristic; an output of the adder; Selecting means for selecting one of the outputs of the high-pass filter characteristics. 6. The SECAM chroma filter circuit according to claim 5, wherein a selection means is controlled to select a high-pass filter characteristic based on a result of determining a noise amount included in the input chroma signal. . 7. A bell filter circuit receives a chroma signal of a SECAM television system, has an output of a bell filter characteristic defined by the system, and has at least one of a high-pass gain and a low-pass gain. 2. The method according to claim 1, wherein said selecting means switches a gain.
6. The SECAM chroma filter circuit according to any one of 3 to 5. 8. The SECAM according to claim 1, wherein the selection means is controlled based on information as to whether or not the input chroma signal is a signal via a tuner.
Chroma filter circuit.