JPH07298095A - Dc transmission ratio correction circuit - Google Patents

Abstract

PURPOSE:To correct a DC transmission ratio depending on a setup by varying a DC transmission ratio correction quantity with a simple configuration without provision of an externally mounted resistor. CONSTITUTION:The circuit is provided with black level extension circuit means 2, 3 extending a luminance signal level from an input terminal 1 set to a black level than a preset 1st level, an average video level detection means (R2., MOSFET8, Cext) detecting an average video level of the luminance signal outputted from the black level extension circuit means 2, 3, a means 6 changing the 1st level of the black level extension circuit means 2, 3 depending on an average video level detected by the average video level detection means, a voltage division means (MOSFET8) dividing a voltage between the average video level and the luminance signal outputted from the black level extension circuit means 2, 3 and a means (5, SW) comparing the divided voltage with a reference voltage and changing the level of the luminance signal outputted from the black level extension circuit means 2, 3 depending on the comparison result for a blanking period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a luminance signal DC transmission rate correction circuit in a television receiver.

[0002]

2. Description of the Related Art Generally, in a color television receiver, in order to reproduce colors faithfully, a pedestal clamp is performed so that the pedestal level does not change, and the DC component is reduced to 1
00% transmission. Therefore, in order to correct the fluctuation of the black level due to the video source to obtain an image with a sense of depth, a circuit for DC component reproduction and black level correction is adopted.

These circuits detect the darkest level of the video signal excluding the horizontal and vertical blanking periods and control the pedestal level according to the level to stabilize the black level. The brightness is adjusted by changing the reference level of the pedestal.

Further, there is also one that controls the gain of a black signal of about 50 IRE or less according to the black level to extend the signal on the black side to improve the openness of the black side and stabilize the black level. .

By the way, in addition to the direct current reproduction by the direct current reproducing circuit, the pedestal level in the blanking period is corrected according to the average video level (hereinafter referred to as APL), which is suitable for a color television receiver. A good image may be obtained.

An example of such a DC transmission rate correction circuit is shown in FIG.

FIG. 2 is a circuit diagram showing a conventional DC transmission rate correction circuit.

As shown in FIG. 2, reference numeral 10 is an input terminal, and a luminance signal is input to the input terminal 10. The luminance signal input from the input terminal 10 is supplied to the black expansion circuit 20 connected to the input terminal 10. The black decompression circuit 20 performs a black decompression process of the input luminance signal, that is, a signal on the black side of the black decompression point is further expanded to the black side, and a process is performed to produce a sharp image and output. To do.

The output signal from the black expansion circuit 20 is supplied to a buffer amplifier 30 connected to the black expansion circuit 20, is amplified to a predetermined level by the buffer amplifier 30, and then is output as a luminance signal via a resistor R1. The luminance signal is supplied to the terminal 40 and is output using the luminance signal output terminal 40.

The other end of the resistor R1 is connected to the output end of the current output amplifier 50 via a switch circuit SW which is turned on only during the blanking period by a control signal supplied from a control means (not shown). Further, the non-inverting input terminal of the current output amplifier 50 is biased to the potential Vref.

On the other hand, the output terminal of the buffer amplifier 30 is a pin 7 provided as a connecting element via a resistor R2.
0, and the output end of the resistor R2 is C
It is connected to the inverting input terminal of the current output amplifier 50 via a point.

A resistor Rext configured as an external component is connected to the pin 70, and the resistor Rext is connected to a capacitor Cext whose other end is grounded through a point d. Further, the output end side of the resistor Rext is d
It is connected to the input end of the amplifier 60 via the point and the second connection pin 80. That is, the resistance Rext and the capacitance Cext are configured as external parts, and by using the resistance Rext and the capacitance Cext, the APL is detected, and the black color is detected according to the change amount of the APL. The black expansion point of the expansion circuit 20 is changed. Therefore, two connection pins 70, 80 are required to connect the resistor Rext and the capacitor Cext.

Next, the operation of the DC transmission rate correction circuit having such a configuration will be described. First, the luminance signal input to the input terminal 10 is supplied to the black decompression circuit 20, and the black decompression circuit 20 further expands the signal on the black side from the black expansion point to the black side to display the image. It is processed so as to have a stickiness, and then output to the buffer circuit 30.

Further, the resistors R2, Rext and Cext connected to the buffer circuit 30 cause Cext and Rext.
At the connection point d of ext, the APL of the luminance signal Y is detected.

The level difference between the APL and the luminance signal Y output from the buffer circuit 30 is the resistance R2 and the resistance Re.
It is divided by xt and supplied to the inverting input terminal of the current output amplifier 50.

On the other hand, the bias Vref is supplied to the non-inverting input terminal of the current output amplifier 50, and when the level of the inverting input terminal is higher than this level, the buffer 30 causes only the blanking period via the resistor R1. The current is drawn. Therefore, the luminance signal is output with the DC of the blanking period lowered by an amount corresponding to the voltage drop of the resistor R1 generated at this time. That is, the drawn current changes according to the potential difference at the input end of the current output amplifier 50.

Therefore, the DC transmission rate can be corrected by changing the DC level of the output luminance signal Y during the blanking period.

The APL detected at the Cext end is
It is input to the amplifier 60 and the black expansion point of the black expansion circuit 20 is set. That is, the black expansion point is also changed according to APL.

By the way, with the recent multi-functionalization, miniaturization of various circuit devices is required, and as is well known, IC (semiconductor integrated circuit) is progressing.

Therefore, in response to the demand for the semiconductor integrated circuit as described above, for example, a DC transmission rate correction circuit as shown in FIG. 2 is realized by the semiconductor integrated circuit, and the DC transmission rate correction amount is received by the color television. Since it is necessary to change the amount of the resistor Rext in order to change it depending on the machine, the resistor Rext must be provided as an external component of the semiconductor integrated circuit and according to each set. There is a problem.

Further, since the resistor Rext is provided as an external component, if the black expansion point is to be determined by the APL detected by Cext, the connecting pin for supplying the APL to the semiconductor integrated circuit is naturally required. That is, there is an inconvenience regarding the recent trend toward miniaturization of semiconductor integrated circuits.

[0022]

As described above, in the conventional DC transmission rate correction circuit, the resistor Rext and the capacitor Ce are used.
xt is used to detect APL, a black expansion circuit is used to determine a black expansion point based on this APL, and the resistance Rext is used to vary the APL to change the correction amount of the DC transmission rate. However, such a DC transmission rate correction circuit is made into a semiconductor integrated circuit, for example,
In the case where the DC transmission rate correction amount is to be changed according to the color television receiver, the resistance Re
Since it is necessary to change the resistance value by xt, there is a disadvantage that this resistance Rext must be provided as an external component.

Further, by configuring the resistor Rext as an external component, when operating so as to set the black expansion point based on the APL detected by using the capacitor Cext, for example, this APL is used as the black expansion circuit. However, there is a problem that a pin for connecting the external component and the black expansion circuit is indispensable in order to supply the above.

Therefore, the present invention has been made in view of the above-mentioned problems, and it is possible to realize a semiconductor integrated circuit with a simple structure, and to change the DC transmission rate correction amount without providing an external resistor. It is an object of the present invention to provide a DC transmission rate correction circuit that can perform the correction of the DC transmission rate according to the set.

[0025]

According to a first aspect of the present invention, there is provided a DC transmission rate correction circuit which receives a luminance signal from an input terminal and which is on a black side of a preset first level for the input luminance signal. Of the luminance signal output from the black extension circuit means and the average image level of the luminance signal output from the black extension circuit means are detected, and the average image level and the black extension circuit means outputs the average image level. A MOS field effect transistor composed of a gate electrode, a drain electrode and a source electrode for dividing the potential difference from the luminance signal is provided, and the voltage applied to the gate electrode can be changed, and the drain can be changed based on the change in the voltage applied to the gate electrode. The average image level is output by changing the voltage division ratio for dividing the potential difference by using the impedance characteristic between the electrode and the source electrode. Detection means, means for changing the first level in the black expansion circuit means in accordance with the average image level detected by the average image level detecting means, and a voltage divided by the average image level detecting means. And a reference potential, and means for changing the level of the blanking period of the luminance signal output by the black expansion circuit means according to the comparison result.

A DC transmission rate correction circuit according to a second aspect of the present invention is the DC transmission rate correction circuit according to the first aspect, wherein the average image level detecting means has a resistor and a drain electrode or a source at an output end of the resistor. The M0S field effect transistor having electrodes connected thereto and the other connected to the black expansion circuit means and one connection pin, and an external capacitance capacitor connected through the one connection pin. .

[0027]

In the present invention, the luminance signal input from the input terminal is further extended to the black side to output the luminance signal on the black side from the first level set by using the black extension circuit means, and output.
The average image level is detected from this output luminance signal by using the average image level detecting means. Next, the black expansion point is set by the black expansion circuit means according to this average image level. The potential difference between the average video level and the output luminance signal of the black expansion circuit means is divided into voltage dividing means (MOSFET).
And the divided voltage is compared with the reference voltage using the current output amplifier. After that, the current output amplifier outputs a current according to the comparison result, and a switch circuit that is turned on only during the blanking period is used to cause a voltage drop by the resistor 1 during the blanking period. As a result, the DC transmission rate correction is performed. The amount can be changed. That is, by changing the gate electrode voltage of the MOSFET, not only the average video level but also the DC transmission rate correction amount can be changed. As a result, by using the MOSFET without changing the characteristics of the DC transmission rate correction circuit in the conventional technique, the resistor Rext as an external component is unnecessary, and at least one pin can be removed.

[0028]

EXAMPLES Examples will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a DC transmission rate correction circuit according to the present invention.

As shown in FIG. 1, reference numeral 1 is an input terminal to which a luminance signal is input. The luminance signal input from the input terminal 1 is supplied to the black expansion circuit 2 as black expansion circuit means connected to the input terminal 1. The black expansion circuit 2 performs black expansion processing of the input luminance signal, that is, the signal on the black side of the black extension point is further extended to the black side, so that the brightness signal of the luminance signal is added so that the image becomes sharp. It processes and outputs.

The output signal from the black expansion circuit 2 is supplied to a buffer amplifier 3 connected to the black expansion circuit 2, amplified by the buffer amplifier 3 at a predetermined level, and then output as a luminance signal via a resistor R1. The luminance signal is supplied to the terminal 4 and is output using the luminance signal output terminal 4.

The other end of the resistor R1 is connected to the output end of the current output amplifier 5 via a switch circuit SW which is turned on only during the blanking period by a control signal supplied from a control means (not shown). . The non-inverting input terminal of the current output amplifier 5 is biased to the potential Vref.

On the other hand, the output terminal of the buffer amplifier 3 is
It is connected to the drain electrode (or source electrode) of a MOS transistor 8 (hereinafter, referred to as MOSFET) as a voltage dividing means which is a feature of this embodiment via a resistor R2. The MOSFET 8 is, for example, a field effect transistor configured by using a MOS having a structure in which an oxide film is formed on the surface of a silicon semiconductor and a metal electrode is stacked on the oxide film, and the metal electrode (hereinafter referred to as a gate electrode). It is an element capable of controlling the current between both electrodes (between the drain electrode and the source electrode) by the voltage applied to ().

The gate electrode of the MOSFET 8 has a potential Vval by, for example, BUS control.
Variably controllable. That is, the equivalent impedance between the source electrode and the drain electrode can be changed according to the voltage of the gate electrode.

The source electrode (or drain electrode) of the MOSFET 8 is connected to one end of a capacitor Cext having the other end connected thereto and the input end of the amplifier 6 via a connection pin 7. The output of the amplifier 6 is connected to the black expansion circuit 2 to determine the black expansion point. The above-mentioned MOSFE
The drain electrode and the source electrode at T8 may be connected to either side of the connected portions.

Next, the operation of the DC transmission rate correction circuit having such a configuration will be described in detail. First, as shown in FIG.
The luminance signal Y input to the input terminal 1 is further expanded by the black expansion circuit 2 to the black side from the black expansion point by the black expansion circuit 2, and then the resistor R1 is supplied via the buffer amplifier 3.
To the connection point a between the resistor R2 and the resistor R2.

The signal output to the connection point between the resistors R1 and R2, that is, the point a, is the resistors R2 and M0SFE.
APL is detected at the point d by the impedance between the source and drain of T8 and the capacitor Cext.

Next, A detected at this point d
PL is supplied to the black expansion circuit 2 through the amplifier 6, and the black expansion circuit 1 sets the black expansion point of the luminance signal.

That is, this APL is used to determine the black expansion point of the black expansion circuit 2, and the potential difference between this APL and the luminance signal Y output from the buffer amplifier 3 is set as the resistance R2. A voltage divided by the impedance between the source electrode and the drain electrode of the MOSFET 8 is supplied to the inverting input terminal of the current output amplifier 5, and the current output amplifier 5 is used to compare the divided voltage with a reference voltage. A current corresponding to this comparison result is obtained. That is, a current proportional to the voltage difference between the two input terminals of the blanking period current amplifier 5 is extracted from the buffer amplifier 3 via the resistor R1, and as a result, the output terminal 4 of this circuit receives DC during the blanking period. The level, that is, the direct transmission rate correction amount can be changed and output.

The amount of change in the DC level needs to be changed according to the set. By changing the gate electrode voltage of the MOS FET 8, the impedance between the source electrode and drain electrode of the MOS FET 8 is changed,
The voltage division ratio of the potential difference between the luminance signal Y and APL is changed so as to cope with the change.

As described above, according to this embodiment, M
By changing the gate electrode voltage of OSFET8,
It is possible to change the DC level, that is, the DC transmission rate correction amount, and thus to eliminate the need for the resistor Rext which has been conventionally required, so that it is possible to realize a semiconductor integrated circuit.

Further, in order to determine the black expansion point by using the detected APL, in the prior art, this APL was connected to the semiconductor integrated circuit by using the connection pin and supplied. According to the method, this connection pin can be eliminated.

As a result, it is possible to effectively correct the DC transmission rate according to the set and to provide a DC transmission rate correction circuit suitable for semiconductor integrated circuit implementation.

In the present embodiment, the drain electrode and the source electrode of the MOSFET may be connected to either the point c side or the point d side (see FIG. 1). It suffices if the gate electrodes of the MOSFETs are connected so that they can be variably biased.

Further, although the switch circuit which is turned on only in the blanking period has been described in the present embodiment, for example, a blanking circuit for detecting the blanking period is provided, and a switching control signal from the blanking circuit is used. The switch circuit may be controlled to be turned on during the blanking period.

[0045]

As described above, according to the present invention, the resistance as an external component necessary for changing the DC transmission rate correction amount in the prior art is changed by changing the gate electrode voltage, for example, the drain electrode. By substituting the MOSFET 8 capable of controlling the current between the source electrodes, the DC transmission rate correction amount can be changed without changing the characteristics of the DC transmission rate correction circuit. The resistor Rext can be made unnecessary. Further, in order to determine the black expansion point by using the detected APL, in the prior art, this APL was connected and supplied to the semiconductor integrated circuit using the connection pin, but according to the present embodiment. This connection pin can be eliminated. As a result, it is clear that a DC transmission rate correction circuit suitable for semiconductor integrated circuits can be realized and that the DC transmission rate can be effectively corrected according to the set.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a DC transmission rate correction circuit according to the present invention.

FIG. 2 is a circuit diagram of a conventional DC transmission rate correction circuit.

[Explanation of symbols]

 1 ... Luminance signal input terminal 2 ... Black expansion circuit 3 ... Buffer amplifier 4 ... Luminance signal output terminal 5 ... Current output amplifier 6 ... Amplifier 7 ... Pin 8 ... MOSFET R1, R2 ... Resistor SW ... Blanking period switch Vref ... Bias voltage Vval ... Variable bias Cext ... Capacitor

Claims (2)

[Claims] 1. A black expansion circuit means for inputting a brightness signal from an input terminal and further expanding the brightness signal on the black side from a preset first level to the input brightness signal to the black side, said black expansion circuit. It comprises a gate electrode, a drain electrode and a source electrode for detecting the average image level of the luminance signal output by the circuit means and for dividing the potential difference between the average image level and the luminance signal output by the black expansion circuit means. And a voltage dividing ratio for dividing the potential difference by using the impedance characteristic between the drain electrode and the source electrode on the basis of the change in the voltage applied to the gate electrode. And an average image level detecting means for outputting the average image level detected by the average image level detecting means. The means for changing the first level in the black expansion circuit means according to the level and the potential obtained by the voltage division by the average image level detecting means and the reference potential are compared, and the comparison result is shown. And a means for changing the level of the blanking period of the luminance signal output by the black expansion circuit means in response thereto. 2. The average image level detecting means includes a resistor,
A drain electrode or a source electrode is connected to the output terminal of the resistor, the other is connected to the black expansion circuit means and one connection pin, and an M0S field effect transistor, and an external capacitor connected via the one connection pin. 2. The DC transfer rate correction circuit according to claim 1, wherein the DC transfer rate correction circuit comprises a capacitor.