JPH0576029A - Variable chroma filter - Google Patents

Abstract

PURPOSE:To independently vary the central frequency omega0 and Q of a filter, and to attain the band constraint of an optimal chroma signal corresponding to the source of an input video signal by varying the currents of a constant power source supplied to a specific filter by a prescribed ratio. CONSTITUTION:A first integration circuit A is constituted of the first differential amplifier constituted of a capacitor C2, and transistors Q2 and Q3, current mirror circuit constituted of transistors Q4 and Q5, the second differential amplifier constituted of transistors P1 and P2, and steady-current power sources CI1 and CI2. And also, the second integration circuit B is constituted in the same way, and a signal integrated by a capacitor C1 is feed backed to the circuit A. Thus, a chroma filter is constituted of a biquad type filter, and when control currents at the prescribed current ratio are supplied to the circuit, the central frequency omega0 and Q can easily be varied independently of each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chroma filter (hereinafter, also referred to as a band limiting filter) provided in a color signal processing circuit of a color television receiver or the like.

[0002]

2. Description of the Related Art In a color signal processing circuit of a color television receiver, in order to extract a chroma signal from a luminance signal,
A band limiting filter (BPF) is provided. The characteristics of the band limiting filter (chroma filter) have been conventionally fixed for each television receiver.

[0003]

[SUMMARY OF THE INVENTION Incidentally, the color signal is supplied together with the luminance signal is amplitude-modulated on a subcarrier (3.58MH _Z), when performing signal processing to separate the color signal component is input Unless it is extracted by a band limiting filter having a characteristic suitable for the frequency spectrum of the video signal thus generated, the double sidebands are unbalanced, which causes orthogonal distortion. Further, if distortion occurs during demodulation, the color transient will eventually deteriorate and the image quality will be impaired. For example, when the source of the input video signal is a VTR and when it is a laser disk, the video signal band and the band of the color signal are slightly different, and if these signals are extracted by the same chroma filter. The image deterioration as described above occurs.

[0004]

In order to solve the above problems, the present invention provides a first digital data for controlling Q of a bike quad type filter and a first digital data for controlling ω ₀ of the bike quad type filter. First and second converters for converting the two digital data into analog voltages respectively, and the analog outputs of the first and second converters independently control Q and ω _{0 of the} biquad filter. And a current source circuit for generating first and second control currents,
The second control current value is switched according to the input video signal source, and the passing frequency characteristic of the biquad filter is controlled according to the source of the input video signal. is there.

[0005]

When a chroma filter is constructed by a biquad filter and a control current having a predetermined current ratio is supplied to this circuit, the center frequencies ω ₀ and Q can be easily varied independently. Therefore, by supplying the data corresponding to the source of the input signal to the current source circuit which forms this control current, it is possible to always monitor with a good image quality.

[0006]

FIG. 1 shows an embodiment of a variable chroma filter using the bike quad type filter of the present invention. In this figure, a first integrating circuit A includes a first differential amplifier composed of a capacitor C ₂ and transistors Q ₂ Q _3, a current mirror circuit composed of transistors Q ₄ and Q ₅ , and the first differential amplifier. The load of the diode D ₁ . D ₂ supplies a current to the second differential amplifier composed of the transistors P ₁ and P ₂ for receiving the output of the _first differential amplifier, and the first differential amplifier and the second differential amplifier. It is composed of constant current sources CI ₁ and CI ₂ .

The second integrator B has a circuit configuration similar to that of the first integrator A, and a capacitor C ₁
The signal integrated by is fed back to the first integrating circuit A. Next, the transfer function G (S) of the above circuit will be obtained. Transistors Q ₆ , Q _{7 of} the second integrator B
Assuming that the current i ₁ flows in the direction shown in the figure, the current flowing in the diode D ₃ is the current flowing in the diode D ₄
, The base voltage of the transistor P ₄ becomes lower than the base voltage of the transistor P ₃ , and the current i _S1 flows in the transistors P ₃ and P ₄ in the direction shown in the figure.

When the forward voltages of the _diodes D ₃ and D ₄ are V _D3 and V _D4 , and the base-emitter voltages of the transistors P ₃ and P ₄ are V _BEP3 and V _BEP4 , the following equations are established. ..

[Equation 1] As is well known, the base-emitter voltage V _BE of a transistor is expressed by the following equation.

[Equation 2] Where q is the Coulomb constant (1.6 * 10 ^-19 ), T is the Boltzmann constant (1.38 * 10 ^-23 ), I _SS is the reverse saturation current of the transistor, and I _C is the collector current of the transistor. Using the expression

Equation 3 is obtained. The condition for the expression 3 to be satisfied is

[Equation 4] Becomes

If (R ₄ + R ₅ ) i ₁ = V _out , and (R ₄ + R ₅ ) = R,

[Equation 5] Therefore

[Equation 6] Here, since the transistors Q ₈ and Q ₉ form a current mirror circuit, the current 2i _S1 flows from the capacitor C ₁ toward the current mirror circuit to balance the current. This current is integrated by the capacitor C _1, to form a terminal voltage V ₁ of the capacitor. That is,

[Equation 7] The voltage V ₁ and the output voltage V _OUT are equal to those of the transistors Q ₂ and Q _3.
, The current i ₂ flows through the first differential amplifier as shown in the figure. This first differential amplifier is also the above 1
Similar to the formula, the current relation is established by the following formula

[Equation 8] However, V _D1 and V _D2 are quasi-directional voltage drops of the _diodes D ₁ and D ₂ , and V _BEP1 and V _BEP2 are base-emitter voltages of the transistors P ₁ P ₂ .

From the above equation, the following equation 9 is obtained.

[Equation 9] From this formula

[Equation 10] If R ₂ + R ₃ = R, then V ₁ −V _OUT = R · i ₂ as in the case of the second integrator B, and equation 10 is

[Equation 11] Here, the transistors Q ₄ and Q ₅ are current mirrors, and the current i _S2 as shown in the figure flows into the capacitor C ₂ because the currents are balanced. Therefore, the output V _OUT is

[Equation 12] Substituting Equation 7 into this equation and rearranging

[Formula 13]

This equation shows the transfer function G (S) of the circuit of FIG. Here, the general transfer function H (S) in the biquad filter is

[Equation 14] Comparing Equation 14 and Equation 13 above, the center frequency ω ₀ ,
Quality Factor Q

[Formula 15]

[Formula 16]

From the above equations 15 and 16, the following can be said. A, only Q is changed by changing the ratio of the current I ₁ and the current I _{2 while} keeping the values of the current products I ₁ and I ₂ constant. B, if the product of the current I ₁ and the current I ₂ is changed and the ratio of each current is made constant, only ω ₀ can be changed. Therefore, if the currents I ₁ and I ₂ of the current source CI ₂ and the current source CI ₄ of FIG. 1 can be changed so as to satisfy the above conditions A and B, Q and ω ₀ of the chroma filter can be changed independently. Will be able to.

An embodiment of such a current source is shown in FIG.
In this figure, the current of the variable current source CI ₀ is I ₀ ,
The output current of the current mirror circuit composed of the transistors P ₅ and P ₆ is I ₁ ′, and the output current of the current mirror circuit composed of the transistors P ₇ and P ₈ is I ₂ . Furthermore diode - de D _5, the transistors _{Q 12, Q 14, Q 15} , Q 18 made of the current mirror - I ₁ as the current shown in the circuit, I
_{Let 3} , I ₄ , and I ₅ . Transistors Q ₁₀ , Q ₁₁ ,
The base-emitter voltages of Q ₁₃ , and Q ₁₅ , Q ₁₇ , and Q ₁₉ are V _BE10 , V _BE11 , V _BE13 , V _BE15 , V _BE17 , and V _BE19.
Then, the following equation is established.

[Equation 17] Rearranging this 17 equation using 2 equations,

[Equation 18] From this formula

[Formula 19] Is required.

Therefore, the output currents I ₁ 'and I ₂ of FIG.
By using as the currents I ₁ and I _{2 in} , the Q and ω ₀ can be independently changed as follows. That is, when changing only Q, if the current I ₀ of the variable current source CI ₀ is made constant, the currents I ₄ and I ₅ become constant currents, so the right side of the equation 19 has a constant value. here,
When the current I _C of the variable current source _C I _C is controlled by the control voltage V _C , the direction and magnitude of the current I _C can be changed. When this current I _C is changed, the current I ₁ ′
Will change. Since the product of the current I ₁ ′ and the current I ₂ is constant as shown in Equation 19, the current I 1
Will _{be 1} 'the current I ₂ is reduced with increasing, although the ratio of the current I ₁ and the current I ₂ varies, the product becomes constant, it can be varied independently Q.

[0015] Then when changing the omega ₀ changes the current I ₀ of the variable current source CI _0. Then, the current I ₁ , the current I _4, and the current I ₅ are output currents of the current mirror, and therefore change at the same rate. From Equation 19, the magnitude of the product of the current I ₁ ′ and the current I ₂ changes, but if the variable current source CI _C is constant, the ratio of the current I ₁ ′ and the current I ₂ does not change, and Only the product changes, so that ω ₀ can be independently varied. In FIG. 3, the outputs of the current source circuit shown in FIG. 2 are connected in place of the current sources CI ₁ and CI ₂ of the variable chroma filter shown in FIG. 1, and the same symbols represent the same elements.

FIG. 4 is an explanatory view for controlling the chroma filter constituted by the biquad type filter of the present invention in conjunction with the digital data from the bus 5. Among the data sent from the bus 5, a signal for controlling Q is taken in by the D / A converter 3, converted into an analog signal and supplied to the current source circuit 2. Then, the control current I ₁ and the control current I ₂ are controlled by this analog voltage, and the Q characteristic of the variable chroma filter 1 changes. Also, the data taken in the D / A converter 4 is converted into an analog voltage and similarly supplied to the current source circuit 2 to generate a control current that changes the center frequency ω ₀ of the variable chroma filter 1. Data supplied by the bus 5
For example, in the case of a monitor-television, the input video signal is VT.
The control data is output from the microcomputer as different control data depending on whether the reproduction output of R, the laser disk, or the output of the video camera.

[0017]

As described above, since the chroma filter of the present invention is configured so that the band limiting characteristic for the color signal can be easily controlled from the outside in the color signal processing circuit, it is inputted. Depending on the video signal used, optimum color reproducibility can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a variable chroma filter according to the present invention.

FIG. 2 is a circuit diagram showing a specific example of a current source circuit according to the present invention.

FIG. 3 is a connection diagram of a variable chroma filter and a current source circuit.

FIG. 4 is an explanatory diagram showing an embodiment of the present invention.

[Explanation of symbols]

 1 is a variable chroma filter 2 is a current source circuit 3 is a D / A converter 5 is a data bus

[Equation 3]

[Equation 13]

[Equation 15]

[Equation 16]

[Procedure amendment]

[Submission date] December 6, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

[Title of Invention] Variable chroma filter

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chroma filter (hereinafter, also referred to as a band limiting filter) provided in a color signal processing circuit of a color television receiver or the like.

[0002]

2. Description of the Related Art A color signal processing circuit of a color television receiver is provided with a band limiting filter (BPF) in order to cut unnecessary bands. The characteristics of the band limiting filter (chroma filter) have been conventionally fixed for each television receiver.

[0003]

[SUMMARY OF THE INVENTION Incidentally, the color signal on a subcarrier (3.58MH _Z) is supplied with an amplitude-modulated (hereinafter, this signal referred chroma signal), when performing the processing of the chroma signal , If not extracted by a band-limiting filter having a characteristic suitable for the frequency spectrum of the input chroma signal, the double sidebands are unbalanced, which causes orthogonal distortion. When this distortion occurs, the color transient is deteriorated as a result, and the image quality is deteriorated. For example, the band of the chroma signal is different when the source of the input video signal is the IF output, the VTR, and the laser disk, and when these signals are extracted by the same chroma filter, Image deterioration as described above occurs.

[0004]

In order to solve such a problem, the present invention provides a first control voltage for controlling Q of a bike quad type filter and a second control voltage for controlling ω ₀ of the bike quad type filter. By the control voltage of
A current source circuit for generating first and second control currents for independently controlling Q and ω _{0 of the} biquad filter,
The first and second control current values are switched according to the input video signal source so that the pass-frequency characteristics of the biquad filter are controlled according to the source of the input video signal. It is composed.

[0005]

When a chroma filter is constructed by a biquad filter and a control current having a predetermined current ratio is supplied to this circuit, the center frequencies ω ₀ and Q can be easily varied independently. Therefore, by supplying the data corresponding to the source of the input signal to the current source circuit which forms this control current, it is possible to always monitor with a good image quality.

[0006]

FIG. 1 shows an embodiment of a variable chroma filter using the bike quad type filter of the present invention. In this figure, a first integrating circuit A includes a first differential amplifier composed of a capacitor C ₂ and transistors Q ₂ Q _3, a current mirror circuit composed of transistors Q ₄ and Q ₅ , and the first differential amplifier. _Second differential amplifier composed of diodes D ₁ and D _{2 serving} as a load of the first differential amplifier, transistors P ₁ and P ₂ receiving the output of the _first differential amplifier, and the first differential amplifier, It is composed of constant current sources CI ₁ and CI ₂ which respectively supply currents to the two differential amplifiers.

The second integrator B has a circuit configuration similar to that of the first integrator A, and a capacitor C ₁
The signal integrated by is fed back to the first integrating circuit A. Next, the transfer function G (S) of the above circuit will be obtained. Transistors Q ₆ , Q _{7 of} the second integrator B
Assuming that the current i ₁ flows in the direction shown in the figure, the current flowing in the diode D ₃ is the current flowing in the diode D ₄
, The base voltage of the transistor P ₄ becomes lower than the base voltage of the transistor P ₃ , and the current i _S1 flows in the transistors P ₃ and P ₄ in the direction shown in the figure.

When the forward voltages of the _diodes D ₃ and D ₄ are V _D3 and V _D4 , and the base-emitter voltages of the transistors P ₃ and P ₄ are V _BEP3 and V _BEP4 , the following equations are established. ..

[Equation 1] As is well known, the base-emitter voltage V _BE of a transistor is expressed by the following equation.

[Equation 2] Where q is Coulomb's constant (1.6 * 10 ^-19 ), k is Boltzmann constant (1.38 * 10 ^-23 ), I _SS is the reverse saturation current of the transistor, I _C is the collector current of the transistor, and T is the absolute temperature. Using Equation 1 and Equation 2,

[Equation 3] Is obtained. The condition for the expression 3 to hold is

[Equation 4] Becomes

If (R ₄ + R ₅ ) i ₁ = V _out , and (R ₄ + R ₅ ) = R,

[Equation 5] Therefore

[Equation 6] Here, since the transistors Q ₈ and Q ₉ form a current mirror circuit, the current 2i _S1 flows from the capacitor C ₁ toward the current mirror circuit to balance the current. This current is integrated by the capacitor C _1, to form a terminal voltage V ₁ of the capacitor. That is,

[Equation 7] The voltage V ₁ and the output voltage V _OUT are the same as those of the transistors Q ₂ and Q _3.
, The current i ₂ flows through the first differential amplifier as shown in the figure. This first differential amplifier is also the above 1
Similar to the formula, the current relation is established by the following formula

[Equation 8] However, V _D1 and V _D2 are forward voltages of the _diodes D ₁ and D ₂ , and V _BEP1 and V _BEP2 are base _voltages of the transistors P _{1 and} P ₂ .
This is the voltage between the emitter and emitter.

From the above equation, the following equation 9 is obtained.

[Equation 9] From this formula

[Equation 10] If R ₂ + R ₃ = R, then V ₁ −V _OUT = R · i ₂ as in the case of the second integrator B, and equation 10 is

[Equation 11] Here, the transistors Q ₄ and Q ₅ are current mirrors, and the current i _S2 as shown in the figure flows into the capacitor C ₂ because the currents are balanced. And input V _IN
The output V _OUT so intertwined the V _OUT by adding the

[Equation 12] Substituting Equation 7 into this equation and rearranging

[Equation 13]

This equation shows the transfer function G (S) of the circuit of FIG. 1, which is in the form of a high pass filter in a biquad filter. Here, a general transfer function H of the high-pass filter in the bike quad type filter
(S) is

[Equation 14] Comparing Equation 14 and Equation 13 above, the center frequency ω ₀ ,
Quality Factor Q

[Equation 15]

[Equation 16]

From the above equations 15 and 16, the following can be said. A, only Q is changed by changing the ratio of the current I ₁ and the current I _{2 while} keeping the values of the current products I ₁ and I ₂ constant. B, if the product of the current I ₁ and the current I ₂ is changed and the ratio of each current is made constant, only ω ₀ can be changed. Therefore, if the currents I ₁ and I ₂ of the current source CI ₂ and the current source CI ₄ of FIG. 1 can be changed so as to satisfy the above conditions A and B, Q and ω ₀ of the chroma filter can be changed independently. Will be able to.

An embodiment of such a current source is shown in FIG.
In this figure, the current of the variable current source CI ₀ is I ₀ ,
The output current of the current mirror circuit composed of the transistors P ₅ and P ₆ is I ₁ ′, and the output current of the current mirror circuit composed of the transistors P ₇ and P ₈ is I ₂ . Further, the current of the current mirror circuit composed of the diode D ₅ , transistors Q ₁₂ , Q ₁₄ , Q ₁₅ , and Q _{16 is changed} to I ₁ and I as shown in the figure.
_{Let 3} , I ₄ , and I ₅ . Transistors Q ₁₀ , Q ₁₁ ,
The base-emitter voltages of Q ₁₃ , and Q ₁₅ , Q ₁₇ , and Q ₁₉ are V _BE10 , V _BE11 , V _BE13 , V _BE15 , V _BE17 , and V _BE19.
Then, the following equation is established.

[Equation 17] Rearranging this 17 equation using 2 equations,

[Equation 18] From this formula

[Formula 19] Is required.

Therefore, the output currents I ₁ 'and I ₂ of FIG.
By using as the currents I ₁ and I _{2 in} , the Q and ω ₀ can be independently changed as follows. That is, when changing only Q, if the current I ₀ of the variable current source CI ₀ is made constant, the currents I ₄ and I ₅ become constant currents, so the right side of the equation 19 becomes a constant value. Here, if the current I _C of the variable current source _C I _C is controlled by the control voltage V _C , the direction and magnitude of the current I _C can be changed. When this current I _C is changed, the current I ₁ ′ changes. Then, the current I ₁ ′ and the current I ₂
Since the product of and is constant as in equation 19, the current I ₂ decreases as the current I ₁ ′ increases, and the ratio of the current I ₁ and the current I ₂ changes, but the product is constant. Next to
Q can be changed independently.

[0015] Then when changing the omega ₀ changes the current I ₀ of the variable current source CI _0. Then, the current I ₁ , the current I _4, and the current I ₅ are output currents of the current mirror, and therefore change at the same rate. From Equation 19, the magnitude of the product of the current I ₁ ′ and the current I ₂ changes, but if the variable current source CI _C is constant, the ratio of the current I ₁ ′ and the current I ₂ does not change, and Only the product changes, so that ω ₀ can be independently varied. In FIG. 3, the outputs of the current source circuit shown in FIG. 2 are connected in place of the current sources CI ₁ and CI ₂ of the variable chroma filter shown in FIG. 1, and the same symbols represent the same elements.

FIG. 4 is an explanatory view for controlling the chroma filter constituted by the biquad type filter of the present invention in conjunction with the digital data from the bus 5. Among the data sent from the bus 5, a signal for controlling Q is taken in by the D / A converter 3, converted into an analog signal and supplied to the current source circuit 2. Then, the control current I ₁ and the control current I ₂ are controlled by this analog voltage, and the Q characteristic of the variable chroma filter 1 changes. Also, the data taken in the D / A converter 4 is converted into an analog voltage and similarly supplied to the current source circuit 2 to generate a control current that changes the center frequency ω ₀ of the variable chroma filter 1. Data supplied by the bus 5
The data is related to, for example, the type of the source of the video signal, and is output from the microcomputer as control data that differs depending on whether the input video signal is a VTR reproduction output, a laser disk, an IF output or the like. It is a thing.

[0017]

As described above, since the chroma filter of the present invention is configured so that the band limiting characteristic for the chroma signal can be easily controlled from the outside in the color signal processing circuit, it is inputted. Depending on the video signal used, optimum color reproducibility can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a variable chroma filter according to the present invention.

FIG. 2 is a circuit diagram showing a specific example of a current source circuit according to the present invention.

FIG. 3 is a connection diagram of a variable chroma filter and a current source circuit.

FIG. 4 is an explanatory diagram showing an embodiment of the present invention.

[Explanation of reference numerals] 1 variable chroma filter 2 current source circuit 3, 4 D / A converter 5 data bus

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Claims (1)

[Claims] 1. A first digital de controlling the Q of the biquad filter - second digital de controlling the omega ₀ of data and the biquad filter - first converting data to each analog voltage, A second converter and first and second independent controls of Q and ω _{0 of the} biquad filter by analog outputs of the first and second converters.
A current source circuit for generating a control current, and the first and second control current values are switched by the input video signal source so that Q and ω ₀ of the biquad filter are controlled. A variable chroma filter characterized by being constructed.