JP2784803B2 - Line signal generator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line signal generating circuit suitable for use in, for example, a gamma correction circuit of a liquid crystal television receiver.

[Summary of the Invention]

According to the present invention, first and second transistors whose emitters are connected to each other via a resistor and whose bases are connected to a first reference potential source are connected to respective collectors,
A first differential amplifier including third and fourth transistors having one base connected to a second reference potential source and an input signal supplied to the other base; a differential output of the first differential amplifier; Is supplied to each base, and a second differential amplifier composed of fifth and sixth transistors whose emitters are commonly connected is provided between the emitters of the third and fourth transistors and the third reference potential source. The first current source, the fifth and sixth
A plurality of Gilbert amplifiers having a second current source provided between the emitter of the transistor and a reference potential source;
A switch having first and second differential circuit configurations for dividing the first and second current sources into predetermined ratios by a control signal, wherein the first and second switches correspond to input signals. By obtaining a predetermined output characteristic added from the output side of the second differential amplifier, various broken line signals can be obtained.

[Conventional technology]

As shown in FIG. 10, an applied voltage versus a luminance signal of a liquid crystal panel used in a conventional liquid crystal television receiver has a so-called non-linearity that becomes saturated as the applied voltage increases. Conventionally, a gamma correction circuit as shown in FIG. 11 has been used to correct this nonlinearity. That is,
In FIG. 11, an input voltage V is supplied from an input terminal (1) to a log conversion circuit (2) to obtain an output voltage of log (v), which is passed through an amplifier (3) having an amplification factor of A · log (v). After obtaining the output voltage V ^{A, the} output voltage V ^A is inversely converted by the exponential function conversion circuit 4 to derive the output voltage V ^A to the output terminal 5. FIG. 12 shows the input / output characteristics at this time.

A non-linear circuit for extracting a non-linear output by using one transistor and N pairs of transistors whose collector and emitter are connected in parallel with each other is disclosed in JP-A-59-125170.
No., published in Japanese Unexamined Patent Publication No.

[Problems to be solved by the invention]

By the way, the conventional circuit as shown in FIG. 11 has input / output characteristics as shown in FIG. 12, so that as the input voltage increases, the output voltage increases and eventually the output voltage is saturated. When such a characteristic is used as a gamma correction circuit of a liquid crystal panel, the liquid crystal panel has a drawback that a bright portion of an image such as white is substantially crushed, the contrast is reduced, and the image quality is deteriorated.

The present invention has been made in view of the above, and an object of the present invention is to provide a broken line signal generation circuit capable of generating a broken line signal having arbitrary characteristics.

[Means for solving the problem]

In the polygonal line signal generation circuit according to the present invention, the first and second emitters whose emitters are connected to each other via the resistors (21j to 23j) and whose bases are connected to the first reference potential sources (31, 32) are connected to the respective collectors. Third and second transistors (21g to 23g, 21h to 23h) are connected, one base is connected to a second reference potential source (21i to 23i), and an input signal is supplied to the other base. 4 transistors (21a-23a, 21b-23
b) a first differential amplifier (21c-23c),
The differential output of the differential amplifier is supplied to each base, and the fifth and sixth transistors (21
d to 23d and 21e to 23e).
f) a first current source (21k to 23k, 21l to 23l) provided between the emitters of the third and fourth transistors and a third reference potential source (earth); a fifth and sixth transistor A plurality of Gilbert amplifiers (21 to 23) having second current sources (21o to 23o) provided between the emitters of the first and second potential sources (ground) and control signals for the first and second current sources. And a switch (25, 26) having a first and second differential circuit configuration for dividing the input signal into a predetermined ratio by the first and second switches. A predetermined output characteristic added from the output side of the amplifier is obtained.

[Action]

One Gilbert amplifier is composed of the first and second differential amplifiers and the first and second current sources, and a plurality of these are provided. Then, a control signal is supplied to the first and second switches, whereby the current flowing through the first and second current sources is divided into a predetermined ratio, and a predetermined ratio is output from the output side of the second differential amplifier of the final stage Gilbert amplifier. , That is, a broken line signal is performed.

〔Example〕

Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. 1 to 9, taking a case where gamma correction is performed as an example.

First, before entering the embodiment of the present invention, the basic principle of the present invention will be described with reference to FIGS.

FIG. 4 shows the configuration of the basic principle. In FIG. 4, (10) is an input terminal to which one of the three primary color signals of R, G, and B is supplied. The primary color signals are clamped by the pedestal clamp circuit (11) to the clamp potential V _CLP (equivalent to the pedestal level) of the clamp power supply (12), and the amplifiers (13) to (13) with different input / output characteristics respectively
Supplied to (15).

For example, so-called Gilbert amplifiers are used as the amplifiers (13) to (15), and their input / output characteristics are respectively shown in FIG.
To C.

The signals amplified by the amplifiers (13) to (15) are added to the adder (1
The signal is added in 6) and is taken out to the output terminal (17) as a signal having input / output characteristics as shown in FIG. 5D. Among the input / output characteristics of FIG. 5D, an amplifier (13) is provided between the straight lines A and B.
Operates and the amplifiers (14) and (15) are in a non-operation state,
The amplifier (14) operates between the straight lines BC and the amplifier (1).
3) and (15) are in a non-operating state, and the amplifier (15) operates and the amplifiers (13) and (14) are in a non-operating state between the straight lines CD.

FIG. 6 shows a general circuit configuration of a Gilbert amplifier. Here, the Gilbert amplifier (13) is representatively shown.

The Gilbert amplifier (13) is a pair of transistors (13
a) a differential amplifier (13c) composed of (13b) and another differential amplifier (13f) composed of a pair of transistors (13d) and (13e). Each collector is connected to the positive power supply terminal + Vcc via the emitter-collector of the transistor (13g) and (13h) and to the base of each of the transistors (13d) and (13e). The base of the transistor (13a) is connected to the input terminal (13g), and the base of the transistor (13b) is connected to the reference power supply (13i).

The emitters of the transistors (13a) and (13b) are interconnected via a resistor (13j) and the current sources (13
h) and (13l) are grounded. Transistor (13
The collector of d) is connected to the positive power supply terminal + Vcc via the load resistor (13r) and to the output terminal (13s). The collector of the transistor (13e) is connected to the positive power supply terminal + V
Connected to cc. Transistors (13d), (13e)
Are connected together and then grounded via a current source (13o).

The bases of the transistors (13g) and (13h) are commonly connected, and are connected to a connection point of bias resistors (13t) and (13u) provided between a positive power supply terminal + Vcc and the ground.

Now, the reference potential of the reference power supply (13i) is set to Vx,
j) is the value of Rin, the value of the resistor (13r) is Rout, and the current source (13
k), the current flowing through (13l) is Iin and the current flowing through the current source (13o) is Iout, the input voltage Vin applied to the input terminal (13q) and the output voltage extracted to the output terminal (13s).
The input / output characteristics of Vout are as shown in FIG.

Therefore, three quilt amplifiers (13) to (15) are used, the value Rin of each resistor (13j) is set to the same value, the load resistor (13r) is made common, and Vx, Iin, and Iout When the values are set to appropriate values, each of the three Gilbert amplifiers (13)
The input / output characteristics of (15) can be as shown in FIGS. 8A to 8C, respectively. However, V ₁ , V ₂ and V ₃ are the respective reference potentials of the Gilbert amplifiers (13), (14) and (15) corresponding to Vx, and have a relationship of V ₁ <V ₂ <V ₃ .

Since the final output characteristic is obtained by adding the outputs of three amplifiers, it can be expressed as shown in FIG. If the clamp voltage V _CLP is set to the reference potential V ₁ by the _petestal clamp circuit (11) in FIG. 4, the input / output characteristics of the two-point broken line as shown in FIG. 5D can be obtained.

Here, since the luminance characteristics differ depending on the inch size and the maker of the liquid crystal panel, and due to the amount of correction by the set maker, the points A and D in the input / output characteristics of FIG. 5D are fixed, and the points B and C are fixed. Need to be variable. FIG. 1 shows an example of a circuit implemented to realize this.

FIG. 1 shows a circuit configuration of the present embodiment. In FIG. 1, (20) is an input terminal to which an input signal Vin is supplied, (2)
1), (22) and (23) are first, second and third Gilbert amplifiers respectively, (24) is an output terminal from which an output signal Vout is taken out, and (25) and (26) are differential circuits, respectively. First of configuration
And the second switch, (27), (28), (29) and (3
_{Reference numeral} 0) denotes control terminals to which control signals V _CTL1 , V _CTL2 , V _CTL3 and V _CTL4 are supplied, respectively.

The first Gilbert amplifier (21) is a first differential amplifier (21c) including a pair of transistors (21a) and (21b) and a second differential amplifier (21d) including a pair of transistors (21d) and (21e). 21f) and transistors (21a), (21
Each collector in b) is a transistor (21g), (21h)
Is connected to a positive power supply terminal + Vcc through the emitter-collector of each of the transistors (21d) and (21e). The base of the transistor (21a) is connected to the input terminal (20), the base of the transistor (21b) is connected to a reference power source (21i) having a reference potential V _1.

The emitters of the transistors (21a) and (21b) are interconnected via a resistor (21j) and respectively pass through the collector-emitter of the transistors (21k) and (21l) constituting a first current source. Grounded via resistors (21m) and (21n), respectively.

The collector of the transistor (21a) is connected to the output terminal (24), and the collector of the transistor (21e) is connected to the positive power supply terminal + Vcc. Also, transistors (21d),
After each emitter of (21e) is connected in common, it passes through the collector-emitter of the transistor (21o) constituting the second current source and is grounded via the resistor (21p).

The bases of the transistors (21g) and (21h) are commonly connected, and are connected to a connection point of bias resistors (31) and (32) provided between a positive power supply terminal + Vcc and the ground.

The second and third Gilbert amplifiers (22) and (23) have exactly the same circuit configuration as the first Gilbert amplifier (21), and therefore, the same reference numerals denote the same subwoofers here. And the description of the connection configuration is omitted. However, the reference power supplies (22i) and (23i) of the second and third Gilbert amplifiers (22) and (23) have different reference potentials from the reference power supply (21i) of the first Gilbert amplifier (21). Each of them takes a value of V ₂ and V ₃ , which are in a potential relationship of V ₁ <V ₂ <V ₃ . Also, the third Gilbert amplifier (23)
Output side, that is, the output terminal (24) and the positive power supply terminal + Vcc
A load resistor (33) is connected between them.

The first switch (25) includes a constant current source (25a), a pair of transistors (25b), (25
c), a pair of transistors (2
5d), (25e), and transistors (25b), (25c)
Are connected in common to a positive power supply terminal + Vcc via a constant current source (25a), and the transistors (25
The base of b) is connected to the control terminal (27), and the base of the transistor (25c) is connected to the reference power supply (25f).

The emitters of the transistors (25d) and (25e) are connected together and then connected to the collector of the transistor (25b), the base of the transistor (25d) is connected to the control terminal (29), and the base of the transistor (25e) is Reference power supply (2
5g) is connected.

The collector of the transistor (25d) passes through the collector-emitter of the transistor (25h) in a diode connection configuration, is grounded via the resistor (25i), and is connected to the transistor (2d).
The collector (and base) of 5h) is a transistor (21k) which is a first current source of the first Gilbert amplifier (21),
(21l) Connected to each base. Transistor (25e)
Is a diode-connected transistor (25
The collector (and base) of the transistor (25j) is connected to the transistor (22k) which is the first current source of the second Gilbert amplifier (22) through the collector-emitter of the transistor (j) and the ground through the resistor (25k). ) And (22l). The collector of the transistor (25c) passes through the collector-emitter of the transistor (25l) in a diode connection configuration and is grounded via a resistor (25m). The collector (and base) of the transistor (25l) is connected to a third Gilbert amplifier ( The transistor (23), which is the first current source of (23)
k) and (23l) are connected to each base.

The second switch (26) has exactly the same circuit configuration as the first switch (25). Therefore, here, the same reference numerals are assigned to the corresponding parts, and the description of the connection configuration is omitted. I do. However, the base of the transistor (26b) of the second switch is connected to the control terminal (28), and the base of the transistor (26d) is connected to the control terminal (30). The collector (and base) of the transistor (26h) is connected to the base of the transistor (21o), which is the second current source of the first Gilbert amplifier (21), and the collector (and base) of the transistor (26j) is The transistor (26l) is connected to the base of a transistor (22o) as a second current source of the second Gilbert amplifier (22).
Is connected to the base of a transistor (23o), which is the second current source of the third Gilbert amplifier (23).

Here, assuming that the current flowing through the constant current source (25a) is Iin and the currents flowing through the transistors (25h), (25j) and (25l) are Iin ₁ , Iin ₂ and Iin ₃ , respectively, Iin = Iin ₁ + Iin ₂ + Iin _Three
= There is a certain relationship. The current flowing through the constant current source (26a) is represented by Iout, transistors (26h), (26j) and (26l).
The When the respective current flowing to Iout _1, Iout ₂ and Iout _3, Io
_{ut = Iout 1 + Iout 2 +} Iout 3 = in fixed relationship. In other words, the respective Gilbert amplifiers (21), (22) and (23)
Current sources Iin _{1 to} Iin ₃ and Iout _{1 to} Iout ₃
It is made by dividing out. In this embodiment, although not shown, it is assumed that a pedestal clamp circuit as shown in FIG. 4 is provided at a stage preceding the Gilbert amplifier (21).

FIG. 2 shows the input / output characteristics obtained by the circuit of this embodiment. The method of deriving the input / output characteristics is the same as that described with reference to FIGS.

In this embodiment, the broken line characteristic can be obtained by arbitrarily changing the positions of points B and C in FIG. 2. The manner of the change will be described with reference to FIG. .

Assume that the input / output characteristics of the circuit shown in FIG. 1 are as shown in FIG. 3A. In this state, the control terminal (2) applied to the base of the transistor (25b) of the first switch (25)
When the control voltage _VCTL1 from 7) is lowered, the transistor (25
The current flowing through b) increases and the current flowing through transistor (25c) decreases. As a result, the transistors (25h), (2
The currents Iin ₁ and Iin ₂ flowing through 5j) increase (however, the mixing ratio of the two is constant), and the current Iin ₃ flowing through the transistor (25l) decreases. As a result, the input / output characteristics change as shown in FIG. 3B, and both points B and C are shifted rightward on the X axis.

Next, the control voltage V from the control terminal (28) applied to the base of the transistor (26b) of the second switch (26)
_{When CTL2} is lowered, the current flowing through the transistor (26b) increases and the current flowing through the transistor (26c) decreases. Consequently transistor (26h), a current flows through the (26j) Iout _1, Iout ₂ increases (provided that both mixing ratio constant), the current Iout ₃ through transistor (26l) is reduced. As a result, the input / output characteristics change as shown in FIG. 3C, and both the points B and C are shifted upward on the Y axis.

Next, the control voltage V from the control terminal (29) applied to the base of the transistor (25d) of the first switch (25)
_{When CTL3} is lowered, the current flowing through the transistor (25d) increases, and the current flowing through the transistor (25e) decreases.
As a result increased current Iin ₁ flowing transistor (25h) is current Iin ₂ through transistor (25j) is reduced. As a result, the input / output characteristics change as shown in FIG.
The point is shifted rightward on the X axis, and the X coordinate of point B is determined. Position in the X-axis direction at this time current Iin ₃ point C because it is irrelevant remains positions moved at the time of lowering the control voltage V _CTL1. That is, at this point, the X coordinate of the point c has been determined.

Next, the control voltage V from the control terminal (30) applied to the base of the transistor (26d) of the second switch (26)
_{When CTL4} is lowered, the current flowing through the transistor (26d) increases and the current flowing through the transistor (26e) decreases.
As a result, Iout ₁ flowing through the transistor (26h) increases,
Current Iout ₂ flowing transistor (26j) is reduced. As a result, the input / output characteristics change as shown in FIG.
The Y coordinate of point B is determined by shifting the axis upward. That is, B
The position of the point (XY coordinates) is determined. At this time, the current Iout ₃
Is not relevant, the position of point C in the Y-axis direction is
_It remains at the position it moved when _CTL2 was lowered. That is, the Y coordinate, that is, the position (XY coordinate) of the point C is determined.

Thus, by moving only the points B and C, the input / output characteristic as shown in FIG. 3A can be changed to the input / output characteristic as shown in FIG. 3E, and a desired polygonal line characteristic can be obtained. And, since it has a characteristic of improving the contrast even in a bright picture (part), a good image quality (contrast) can be obtained, for example, in a liquid crystal television receiver.

This is an example, and the control terminals (28) to (30)
It is _needless to _say that an arbitrary polygonal line characteristic can be obtained by arbitrarily changing the control voltages V _{CTL1 to} V _CTL4 applied to.

〔The invention's effect〕

As described above, according to the present invention, there are provided a plurality of Gilbert amplifiers, and first and second switches for dividing current sources of these guild amplifiers into a predetermined ratio by a control signal,
Since the first and second switches obtain predetermined output characteristics from the output side of the final stage Bokibert amplifier corresponding to the input signal, various broken line signals can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. FIGS. 2 and 3 are diagrams for explaining the operation of FIG.
FIG. 9 is a diagram for explaining the basic principle of the present invention.
10 to 12 are views for explaining the conventional example. (21), (22), (23) are Gilbert amplifiers, (25),
(26) is the switch, (21c), (22c) and (23c) are the first
The differential amplifiers (21f), (22f), and (23f) are the second differential amplifiers, (21k), (21l), (22k), (22l), and (23f).
k) and (23l) are the first current sources, (21o), (22o) and (23
o) is a second current source.

Continuation of the front page (56) References JP-A-2-260976 (JP, A) JP-A-63-296473 (JP, A) JP-A-59-127479 (JP, A) JP-A-63-269610 (JP) , A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H04N 5/14-5/217 H03G 5/00-11/08

Claims (1)

(57) [Claims] An emitter is connected to each other via a resistor, and first and second transistors each having a base connected to a first reference potential source are connected to respective collectors.
A first differential amplifier including third and fourth transistors having one base connected to a second reference potential source and an input signal supplied to the other base; a differential output of the first differential amplifier; Is supplied to each base, and a second differential amplifier composed of fifth and sixth transistors whose emitters are commonly connected, the emitters of the third and fourth transistors and the third
A first current source provided between the reference potential sources
A plurality of Gilbert amplifiers having a second current source provided between the emitter of the sixth transistor and the reference potential source; and dividing the first and second current sources into a predetermined ratio by a control signal. A switch having a first and second differential circuit configuration, wherein a predetermined value added from the output side of the second differential amplifier by the first and second switches in response to an input signal. A polygonal line signal generation circuit characterized by obtaining the output characteristic of (1).