JP3526195B2 - SECAM chroma filter circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention mainly relates to SECAM.
The present invention relates to a SECAM chroma filter circuit suitable for use in a VTR and a TV receiver compatible with a standard TV (television) signal.

[0002]

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

In such a receiver, the tuner 81
The high-frequency characteristics of the chroma signal band are often attenuated by a voice trap filter, Nyquist slope, etc. in the path, and the signal that should originally be output as shown in A of FIG. 9 becomes B. In the SECAM method, the chroma signal is F
Since it is M-modulated and transmitted, and the frequency to be transmitted differs depending on the hue, in the characteristics like B, in terms of a color bar, the BY color difference signal has cyan, magenta, and blue hues and the RY color difference. In the signal, the amplitude becomes smaller in the hues of cyan, green and blue. In the hues of cyan and blue, which have small amplitudes in both color difference signals, there is a problem that tailing (medaka) noise peculiar to FM demodulation is likely to occur in a weak electric field.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The AM chroma filter circuit has a problem that medaka noise peculiar to FM demodulation is likely to occur in 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 problems, in the SECAM chroma filter circuit of the present invention, the bell filter circuit is composed of a filter capable of outputting HPF (high pass filter) characteristics, A means for adding the HPF characteristic to the filter characteristic output is provided so that the bell filter output or the addition output is selected. H to add
The level of the PF characteristic is made variable to enhance versatility and a means for selecting the bell filter characteristic output or the HPF characteristic output is added to reduce the weak electric field noise.

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. Therefore, the band characteristic can be selectively used according to the application, and the high frequency component can be used. The amplitude balance in the band can be compensated by emphasizing the optimum amount. Also, HP
By using only the F characteristic, noise on the low frequency side can be suppressed more intensively than in the case of addition.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below 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 in which the signal from the tuner path and the signal from the external device are switched or the chroma signal S1 extracted therefrom is input to the input terminal 11 of the bell filter circuit 12. Bell filter circuit 12 is gm
It is composed of a filter circuit using a (transconductance) amplifier, and outputs a signal S2 having a bell filter characteristic from an output terminal 13 and a signal S3 having an HPF characteristic 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 having the bell filter characteristic and the composite signal S4 is supplied to the external control terminal 1
It is selected by the control signal input to the output terminal 7 and output to the chroma processing circuit 18 in the subsequent stage.

A specific example of the bell filter circuit 12 configured by using the 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 input to the positive input of the gm amplifier gm2 via the buffer amplifier B1. The output of the gm amplifier gm2 is passed through the capacitor C2 to SECA.
The M chroma signal S1 is supplied. Also, gm amplifier gm
2 output is gm amplifier g through buffer amplifier B2.
Input to the negative input of m1 and g via the attenuator m.
Input to the negative input of the m-amp gm2. Buffer amplifier B
The output of 2 is supplied to the output terminal 14. Buffer amplifier B
A resistor R connected in series between the output of 1 and the other end of the capacitor C2 whose one end is connected to the output of the gm amplifier gm2.
1, R2 are connected, and the connection point of the resistors R1, R2 is connected to the output terminal 13. Further, a buffer amplifier B1 and a resistor R1
An inverting amplifier-A is inserted between and.

Bell filter circuit 12 constructed in FIG.
, The transfer function HP (S) of the output of the buffer amplifier B2 is HP (S) = S ² / [S ² + (m ・ gm2 / C2) S + gm1 ・ gm2 / C1 ・ C2], and HPF (High-pass filter) characteristic. 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], which is the BPF (band pass filter) characteristic. Becomes BP
Since the F characteristic output is an output with an inverted polarity, it 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 pair (1.6) ^1/2 / 1
By adding with the ratio of 6, the bell filter characteristic is obtained. Here, as the simplest example, resistance addition is configured by R1 and R2.

The bell filter characteristic defined by the SECAM system is as shown in FIG. 2A, and although it is attenuated on the low frequency side and the high frequency side with respect to the center frequency fo, it is not infinitely small. When the bell filter characteristic and the HPF characteristic are combined by the adder 16, the B characteristic shown in FIG. 2 is obtained, and the high frequency band can be reinforced and the low frequency band can be relatively attenuated.

When the frequency characteristic of the tuner circuit is known in advance, it is sufficient to set a predetermined amount of synthesis, which is possible with FIG. However, the circuit after the bell filter circuit and the tuner are usually different circuits (IC), and it is not known what kind of tuner the bell filter circuit is combined with.

Therefore, a second embodiment of the present invention in which the versatility is improved will be described with reference to FIG. In this embodiment, the 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 adds the adder 1
Output to 6. The amount of reinforcement in the high frequency band is adjusted and controlled according to the frequency characteristics of the tuner circuit combined from the control terminal 32. As a result, the selection range of tuner circuits 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 the pre-filter connected to the preceding stage of the bell filter circuit and various capacitive coupling circuits.

Therefore, the switch circuit 15 does not select the bell filter characteristic but always selects the output of the adder 16,
When 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 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 the third embodiment of the present invention. In this embodiment, the HPF filter characteristic output S3 is input to the switch circuit 41 without passing through the adder, and the bell filter characteristic output S2 is input.
And switch. The high frequency compensation is simply realized only by 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, the filter that extracts the chroma signal from the composite video signal is independent because it determines the transfer function separately from the bell filter circuit, but this can be absorbed and integrated in the bell filter circuit to omit the extraction filter. . In the bell filter circuit 12, the bell filter characteristic and the HPF characteristic are obtained from the same circuit at the same time. Therefore, 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 having Q of 16, the attenuation amount in the high frequency band is larger than that in the Bell filter characteristic, and the low frequency band is attenuated to infinity.

Another effect will be produced when the HPF characteristic is selected when the electric field is weak, which will be described below. SEC
In the AM method, the frequency arrangement of FM modulation is determined by the hue, and noise on the low frequency side of the center frequency fo appears red on the screen and blue on the high frequency side. The human eye is sensitive to reddish colors and perceives red noise as unpleasant. Therefore, T
It is desirable to suppress red weak electric field noise as a viewing sensation of the V receiver and VTR. In the HPF characteristic, the amount of suppression on the low frequency side is particularly large compared to that on the high frequency side, which is suitable for this.

It is also conceivable that the switch circuit 41 of FIG. 4 is used for the purpose of coping with a weak electric field in addition to the switch circuit 15 of FIGS. FIG. 6 is a circuit configuration diagram for explaining the fourth embodiment of the present invention in which the switch circuit 41 corresponds to a weak electric field.

In FIG. 6, a switch circuit 41 is inserted after the switch circuit 15, and the gain control circuit 31 shown in FIG.
It is also possible to use the high-frequency band reinforcement function and the HPF characteristic switching function together. In this case, the weak electric field is separately determined, and the control terminal 42 is controlled according to 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 connected in cascade for simplification of description, 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 of FIG. 1 has been described, but the present invention is not limited to this, and is general. A bell filter circuit may be used. Hereinafter, a case in which a general bell filter circuit is used and which is applied to each of the above-described embodiments will be described with reference to FIG. 7.

Changing the band balance of the filter is equivalent to operating the zero frequency in terms of the pole / zero frequency of the transfer function of the bell filter. Therefore, it can be realized not only by adding the BPF function and the original signal as shown in FIG. 1 but also by using one filter circuit.

The filter circuit of FIG. 7 has two gm amplifiers g.
m1, gm2 and capacitors C1, C2 and j, k,
It was constructed by using four attenuators of m and n. The transfer function H in this configuration (S) 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. HP in the circuit of FIG.
It means that n is controlled by adding F.
However, in the configuration of FIG. 7, the HPF characteristic is the buffer amplifier B
In some cases, it may not be possible to extract from the output of No. 1, and FIG. In that case, n in FIG.
If a switching means for setting (and k if necessary) to zero is added, the bell filter characteristic and the HPF are output from the output terminal 13.
The characteristics can be obtained, and the switch circuit 15 can be omitted. By adding a means capable of varying the amount of attenuation to the attenuators j and n in FIG. 7 and controlling from the external control terminal 64, it is possible to perform optimum high frequency reinforcement for the tuner characteristic as in FIG.

[0026]

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

[Brief description of 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.

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.

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

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 a configuration of a conventional SECAM-compatible TV receiver.

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

[Explanation of symbols]

11 ... Input terminal, 12 ... Bell filter circuit, 13, 14
... output terminal, 15, 41 ... switch circuit, 16 ... adder, 17, 42 ... control terminal, 18 ... chroma processing circuit, 3
1 ... Gain control circuit, 32, 42, 61 ... Control terminals.

Claims (6)

(57) [Claims] 1. A enter the chroma signal of the SECAM television system, a bell filter circuit and an output of the output and the high-pass filter characteristic of the bell filter characteristics defined by the SECAM system, the high pass filter characteristic consists outputs of an adder for adding at a predetermined ratio with an output of the bell filter characteristics, and selection means for selecting either the output of the bell filter characteristics and the output of said adder, said selected A SECAM chroma filter circuit, wherein the output selected by the means is taken out as a filter output. Wherein an output for outputting a high-pass filter characteristic of the bell filter circuit, the signal between the input of said adder
The SECAM chroma filter circuit according to claim 1, further comprising a gain control means for varying a gain. 3. Enter the chroma signal of the SECAM television system, a bell filter circuit and an output of the output and the high-pass filter characteristic of the bell filter characteristics defined by said formula, the high pass filter characteristic an adder for adding at a predetermined ratio output or the output of the high pass filter characteristic and output via a gain control circuit is an output of the bell filter characteristics, the output of the bell filter characteristics, of the adder An SECAM chroma filter circuit, comprising: an output and a selection means for selecting one of the outputs of the high-pass filter characteristics. By wherein a result of determining the amount of noise included in the input chroma signal, characterized by comprising controlling the selection means to select the output <br/> of the high pass filter characteristic according The SECAM chroma filter circuit according to Item 3 . 5. The 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 at least one of a high pass gain and a low pass gain. 2. The selection means for switching the gain of the above-mentioned is constituted.
The SECAM chroma filter circuit according to any one of (1) and (3 ) . By 6. A signal information whether said input chroma signal via a tuner, SECAM chroma according to any one of claims 1 to 5, wherein the performing the control of said selection means Filter circuit.