JPS6228888B2 - - Google Patents

Description

Detailed Description of the Invention The present invention provides two different output characteristics to the control output characteristics of a gain control circuit by changing the magnitude of the DC control voltage applied to one control terminal. The present invention relates to a DC gain control device that generates a gain control voltage that can add coarse adjustment and fine adjustment functions.

As is well known, a gain control circuit has the function of arbitrarily changing the ratio of the output signal to the input signal, and is essential for controlling the color saturation or hue of color television receivers, for example. It is a circuit. By the way, when performing gain control using such a gain control circuit, it is important that coarse adjustment and fine adjustment functions are added. By the way, the coarse adjustment range for color saturation is from the point where the colors disappear and the screen becomes black and white to the point where the colors become saturated and blurring occurs and the image is crushed.On the other hand, the fine adjustment range is the range where the colors become saturated The desired level range is approximately 6 decibels lower than the level at which smearing occurs.

In addition, the coarse hue adjustment range is usually a range that results in a hue change of more than ±30 degrees based on the skin tone, while the fine adjustment range is usually about ±7 degrees based on the skin tone. This is the range in which a hue change occurs.

The normal relationship between coarse adjustment and fine adjustment is that first, coarse adjustment is used to get closer to the adjustment range, and then fine adjustment is performed to make the necessary fine adjustments.
When a coarse adjustment range and a fine adjustment range are defined, such as the above-mentioned color saturation or hue adjustment, each adjustment is independent.
To perform such adjustments, conventional gain control devices have a circuit configuration that includes both a coarse adjustment circuit and a fine adjustment circuit, and supplies the gain control voltage obtained from these circuits to the gain control circuit. was taken.

FIG. 1 is a diagram showing the configuration of a gain control voltage generating section in a conventional gain control device, which is composed of fixed resistors 2, 3 and a variable resistor 4 between a power supply voltage application terminal 1 and a ground point. A coarse adjustment circuit consisting of a semi-fixed resistor 5, fixed resistors 6, 7 and 8, and a variable resistor 9 are arranged, and a gain control voltage from both circuits is selected. The circuit configuration is such that a switch means 10 is provided for taking out the gain control voltage, and by selecting the contact X or Y of the switch means 10, a gain control voltage is supplied to a gain control circuit 11 to perform gain control.

In addition, in recent years, various circuits have been integrated into semiconductor integrated circuits (ICs), and the gain control circuits mentioned above have also been integrated into ICs. By setting one of the differential inputs to the above-mentioned gain control voltage, the dividing ratio of the signal current to the transistors forming the differential amplifier is changed, and gain control is performed. However, the differential voltage that is applied to the gain control terminal of the differential amplifier to ensure the switch operation of the differential amplifier is about ±150 mV, and the control voltage that can apply such a small voltage is shown in Figure 1. It is extremely difficult to generate with high precision using the gain control voltage generator shown in
In practice, a control voltage generator is further provided, where the voltage is converted into a minute voltage and supplied as a differential voltage.

Furthermore, the change in the output signal V _put with respect to the control voltage V _cpot of a conventional gain control device that performs gain control in this manner is approximately proportional as shown in FIG. 2, and the fine adjustment range A is , the output is within coarse adjustment range B from zero to saturation, and because this range is extremely narrow, some viewers may not be able to operate the fine adjustment circuits in television receivers, etc. It establishes possible relationships and is pre-built in an adjusted state as an automatic circuit.

The present invention is completely different from such conventional DC gain control devices, and is capable of controlling the magnitude of the voltage obtained from a variable DC voltage generation circuit section consisting of only one variable resistor placed between a power supply voltage application terminal and a ground point. depending on,
The present invention provides a DC gain control device that can generate gain control voltages for fine adjustment and coarse adjustment, and can also make the output characteristics of a gain control circuit different during fine adjustment and coarse adjustment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of a DC gain control device according to the present invention will be described below based on embodiments with reference to the drawings.

FIG. 3 is a block diagram showing the configuration of the gain control voltage generating section of the DC gain control device of the present invention.
A variable resistor 12 connected between the power supply voltage application terminal 1 and the ground point, a level detector 14 that detects the level of the voltage obtained at the voltage generation point 13 connected to the sliding terminal of the variable resistor 12, and the same level. A switch circuit section 15 that operates as a switch based on the output from the detector 14, one of the differential inputs is supplied from the voltage generation point, the other is supplied from the DC bias supply circuit section 16,
The first and second differential amplifiers 171 and 172 are operated by selectively connecting emitter current sources by the switch operation of the switch circuit section 15, and the outputs of these differential amplifiers are combined to generate a gain control voltage. The gain control voltage generating circuit section 18 generates a gain control voltage. Note that 19 and 20 are terminals to which a gain control voltage is output.

Regarding the operation of the gain control voltage generation section having the above configuration, the level detector 14 executes a level detection operation according to the magnitude (level) of the voltage generated at the voltage generation point 13, and the detection result is Based on this, the switch circuit section 15 operates. Switch circuit section 1
5 has two current paths, and when one of them is in the closed state, the other one is in the open state. dynamic amplifier 171 or second
An emitter current source is connected to either one of the differential amplifiers 172. The input voltages of one of the first and second differential amplifiers 171 and 172 are equal voltages generated based on the voltage obtained at the voltage generation point 13, and the input voltage of the other is supplied from the DC bias supply circuit section 16 to each input voltage. This is a separately supplied voltage. The differential amplifier connected to the emitter current source operates according to the above differential input, voltage conversion is performed in the gain control voltage generating circuit section 18 connected to the collector circuit of this differential amplifier, and the terminal 19 and 20
A gain control voltage is output. In addition, terminal 19
and 20 are coupled to a gain control voltage application terminal of a gain control circuit (not shown), and the gain control circuit executes a gain control operation according to this voltage.

The configuration and basic operation of the DC gain control device of the present invention have been explained above using the block diagram, and its specific circuit configuration is as shown in FIG.

That is, the level detector 14 detects the transistor 2 depending on whether the voltage at the point 13 is below a predetermined value.
It operates to apply a base bias to either one of 1 and 22. The collectors of the transistors 21 and 22 are connected to the emitter of the transistor 29 of the first DC bias supply circuit composed of resistors 23 to 27, a diode 28, and a transistor 29 via resistors 30, 31 and 32, 33, respectively. There is. The switch circuit section 15 is composed of transistors 34 and 35 whose emitters are commonly connected and whose bases are connected to a connection point between resistors 30 and 31 and a connection point between resistors 32 and 33, respectively. Note that the resistor 26 and diode 28 in the first bias circuit are connected to the emitter common connection point.
An emitter current source consisting of a transistor 36 and its emitter resistor 37 is connected to which the voltage generated across the series connection of is applied as a base bias. A second DC bias supply circuit that generates a reference bias is comprised of resistors 38-40. Furthermore, the collector of the transistor 34 is connected to the common emitter connection point of the first differential amplifier composed of transistors 41, 42 and resistors 43, 44, and the collector of the transistor 35 is connected to the common emitter connection point of the first differential amplifier composed of transistors 41, 42 and resistors 43, 44. The emitters of the second differential amplifier are connected to the common connection point.

The base of one transistor 41 of the first differential amplifier is connected to the resistors 50 and 51 connected to the emitter of an emitter follower transistor 49 to which the voltage V _a appearing at the connection point between the resistors 38 and 39 is applied. Also, the base of one transistor 45 of the second differential amplifier is connected to the base of the voltage V _b appearing at the connection point of the resistors 39 and 40, and has a polarity opposite to that of the transistor 49. The emitter of the follower transistor 52 is connected to a connection point between resistors 53 and 54 connected to the emitter of the follower transistor 52 . Further, the bases of the other transistors 42 and 46 of the first and second differential amplifiers are connected to the emitters of emitter follower transistors 55 and 56 of complementary polarity, which have their bases connected in common and are connected to the voltage generation point 13. resistor 5 connected to
7 and 58 and to the connection point of resistors 59 and 60, respectively.

The control voltage generation circuit section is composed of two emitter follower transistors 61 and 62 whose bases are commonly connected and connected to the connection point between the resistors 23 and 24 of the first DC bias supply circuit. .
Transistor 41 is connected to the emitter of transistor 61.
and 45 are connected, a terminal 19 is attached to this point, and a transistor 62
The collectors of transistors 42 and 46 are connected to the emitter of , and a terminal 20 is attached to this point.

In the DC gain control device of the present invention having the above configuration, for example, when the transistor 22 whose operating state is controlled by the level detector 14 becomes conductive and the transistor 21 becomes conductive, the base potential of the transistor 34 changes to the transistor 29. On the other hand, the emitter potential of transistor 35
The base potential of the transistor 29 is the potential obtained by dividing the emitter potential of the transistor 29 by the resistors 32 and 33. Due to this change in the base potential, one of the two transistors 34 and 35 constituting the switch circuit section, ie, transistor 34, becomes conductive, and the other transistor 35 becomes conductive. Therefore, the current source transistor 36 is connected to the first differential amplifier via the conductive transistor 34, and only the first differential amplifier becomes operational. That is, the current of the current source is shunted to the transistors 41 and 42, which are the main components of the first differential amplifier, according to the voltage applied to their respective bases, and the emitter follower transistor connected to the collector thereof is divided. The voltage is converted by 61 and 62 and outputted to terminals 19 and 20 as a gain control voltage.

Contrary to the above, when the transistor 21 is conductive and the transistor 22 is briefly disconnected, the transistor 35 of the switch circuit section is conductive, while the transistor 34 is briefly disconnected, so that the current source transistor 36 is turned off. connected to the differential amplifier side of 2,
Therefore, the second differential amplifier becomes operational, and the current of the current source is shunted in accordance with the voltage applied to the bases of transistors 45 and 46, and this is converted into voltage by emitter follower transistors 61 and 62. , is output to terminals 19 and 20 as a gain control voltage.

By the way, the reference voltage of the first differential amplifier is V
_a and the reference voltage of the second differential amplifier is _Vb . Therefore, the voltage at which the states of the transistors 21 and 22 switch is V _c , and the voltage generation point 1
When the variable voltage generated at 3 is in the range of 0 to _Vc , the transistor 21 is turned on and the transistor 22 is turned off.On the other hand, when the variable voltage generated at Vc is in the range of more than _Vc to the power supply voltage _Vcc , the transistor 22 is turned on. The control operation by the level detector 14 is executed so that the transistor 21 is turned off, and V _cc is set between the above-mentioned voltages V _cc , V _a , V _b and V _c .
>V _a >V _c >V _b >0, when the variable voltage obtained at the voltage generation point 13 is at a low level (0 to V _c ), the transistors 45 and 46
On the other hand, at a high level (above V _c and up to V _cc ), an output characteristic with a control characteristic determined by the second differential amplifier mainly composed of transistors 41 and 42 is obtained. An output characteristic having a control characteristic determined by one differential amplifier is obtained.

FIG. 5 shows the output V put and the control voltage V _cp when gain control is performed using the gain control voltage obtained by the DC gain control device of the present invention described above _.
ot. This is a diagram showing the relationship between fine adjustment range A.
The control voltage V _cpot obtained at the voltage generation point 13 exceeds V _c to V _cc , while the rough adjustment range B is a range in which V _cpot is from 0 to V _c .

By the way, as shown in the figure, the output characteristics in the fine adjustment range A and the coarse adjustment range B are different; and 4
This can be obtained by changing the gain of the differential amplifier by selecting the resistance values of 7 and 48. That is, in order to obtain the output characteristics shown in the figure, the resistor 4
The values of resistors 47 and 48 may be selected to be smaller than the values of resistors 3 and 44.

Note that in order to stabilize the circuit operation against the temperature of the power supply voltage _Vcc and temperature changes, resistors 30 and 32, 31 and 33, 43 and 44, 47 and 4 are required.
Preferably, the values of 8, 50 and 57, 51 and 58, 53 and 59 and 54 and 60 are chosen to be equal.

As is clear from what has been explained above,
In the DC gain control device of the present invention, both fine adjustment and coarse adjustment circuits with different output characteristics are formed by the control voltage varying from the power supply voltage _Vcc to zero volts. Since it can be determined by selecting the value of the resistor as a component, it is not necessary to provide a special peripheral circuit.
Further, the DC gain control device of the present invention has a variable resistor 1
All except 2 are composed of circuit elements that can be integrated into ICs, and it is easy to integrate them into ICs. Further, unlike conventional DC gain control devices, there is no need to make fine adjustments after incorporating the device into a device, and therefore, an adjustment step can be eliminated from the device manufacturing process.

Although the above explanation has been made using the control of color saturation or hue of a color television receiver as an example, the present invention can be widely applied to other devices equipped with a gain control function to achieve similar effects. It is played.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a conventional DC gain control device, FIG. 2 is a diagram showing an output characteristic curve when the same device is used, and FIG. 3 is a block diagram showing the configuration of the DC gain control device of the present invention. 4 is a circuit diagram showing a specific configuration of the DC gain control device of the present invention, and FIG. 5 is a diagram showing the output characteristics when the DC gain control device of the present invention is used. 1... Power supply voltage application terminal, 2, 4, 6-8...
Fixed resistor, 3, 9, 12... Variable resistor, 5... Semi-fixed resistor, 10... Switch means, 11... Gain control circuit, 13... Control voltage generation point, 14... Level detector, 15... ...Switch circuit section, 16...
DC bias supply circuit section, 171, 172... Differential amplifier, 18... Gain control voltage generation circuit section, 1
9, 20... Voltage output terminal for gain control, 21, 2
2...Switch transistor, 23-27...Resistor for first DC bias supply circuit configuration, 28...
...Diode, 29...Transistor for configuring the first DC bias supply circuit, 30-33...Resistor for voltage division, 34, 35...Transistor for configuring the switch circuit section, 36...Transistor for current source, 37, 43, 44, 47, 48, 50, 5
1, 53, 54, 57-60...emitter resistance,
38-40...Resistors forming a second DC bias supply circuit for generating reference bias, 49, 52,
55, 56, 61, 62... Emitter follower transistor.

Claims (1)

[Claims] 1. A level detector that detects the level of a variable DC voltage, having two current paths, and a switch operation that closes one of the current paths and opens the other by the output from the level detector. The switch circuit section that executes
first and second differential amplifiers which are alternatively connected to the current source via each current path of the switch circuit section and whose gains are selected to have different values;
and a first reference voltage having a higher value than the variable DC level at the time of execution of the switching operation of the level detector and a second reference voltage having a lower value at each one terminal of the second differential amplifier. a bias supply circuit that supplies a reference voltage of the same magnitude; a gain control voltage generation circuit that combines the outputs of the first and second differential amplifiers to generate a gain control voltage; A DC gain control device characterized in that a predetermined control voltage obtained from the variable DC voltage is applied to the other input terminal of the differential amplifier. 2. A patent claim characterized in that an emitter follower circuit having the same configuration is arranged between the reference voltage input terminal and control voltage input terminal of the differential amplifier and the voltage generation point and variable DC voltage generation point of the bias supply circuit. The DC gain control device according to item 1.