JP3235745B2 - Gain control amplifier circuit and primary color signal amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Table of Contents] The present invention will be described in the following order. Industrial application Conventional technology (FIGS. 5 to 7) Problems to be solved by the invention (FIG. 8) Means for solving the problems (FIGS. 1 and 2) Operation (FIGS. 3 and 4) (FIGS. 1 to 4) Effects of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gain control type amplifying circuit, and more particularly to a gain controlling type amplifying circuit suitable for a pre-drive circuit for amplifying three primary color signals (hereinafter referred to as R, G and B signals) and outputting the amplified signals to a cathode ray tube. is there.

[0003]

2. Description of the Related Art Conventionally, in order to extend the frequency characteristics of a gain control amplifier for amplifying and outputting each primary color video signal (R, G, B) by an arbitrary gain G to a wide band, each primary color video signal (R, G, B) is required. It has been considered that a gain control amplifier for amplifying each signal so as to reduce the crosstalk between G and B) is constituted by an individual integrated circuit for each primary color signal.

At this time, since the integrated circuits corresponding to the respective primary color video signals (R, G, B) can be designed on the same substrate pattern, the frequency characteristics of the three channels can be easily adjusted.
This is also advantageous in improving the frequency characteristics.

However, it is extremely difficult to make all the gain control curves of the integrated circuits corresponding to the primary color video signals (R, G, B) coincide with each other due to variations in the resistance value and the current amplification factor _hFE generated during the semiconductor manufacturing process. And FIG.
In general, the gain control characteristics are all different as shown in FIG.

Particularly, the gain characteristics near the minimum gain vary among the three primary color video signals (R, G, B), so that it is difficult to match them. For example, a primary color video signal (R,
As a gain-adjusting amplifier circuit for G and B), it is conceivable to use a Gilbert-type gain control amplifier 1 composed of two differential amplifier stages as shown in FIG. Has a problem that the linearity at the maximum and minimum gains is deteriorated.

Here, the preceding stage of the gain control amplifier 1 is constituted by a differential pair of transistors Q1 and Q2 in which emitters are connected via an input resistor R _IN and diodes D1 and D2 are connected to respective collectors. It is, to control the differential voltage of the differential output V1 and V2 applied to the subsequent stage of the differential pair by by connexion adjusting the differential voltage between the base voltage applied to the base of the transistor Q1 and Q2 to control voltage V _X Has been made.

A constant current source 2 for drawing a constant current _I0 is connected to each emitter of the transistors Q1 and Q2.

[0009] The subsequent stage of the gain control circuit 1
It is constituted by a differential pair of transistors Q3 and Q4 which input the differential outputs V1 and V2 to the base, respectively. The collector current flowing by the differential voltage between the differential outputs V1 and V2 is connected to a common emitter. The load current R _L is multiplied by the signal current I _S flowing through the
Is increased or decreased and output as an output signal V _OUT .

In the gain control circuit 1, the collector current (2I _{0) corresponding to the} current flowing into the two current sources 2 flows into one of the transistors Q1 and Q2 constituting the preceding differential pair at the time of maximum gain or minimum gain. ) Flows, but hardly flows to the other side, so that the effect of the base-emitter resistance re starts to be noticeable, degrading the linearity of the gain control characteristic (FIG. 7).

Therefore, in the vicinity of the minimum gain, a potential difference occurs in the output signals corresponding to the respective primary color video signals (R, G, B) and the characteristic curves do not have the same slope, so that the gains of the respective primary color video signals are equalized. Was difficult. For this reason, in order to match the output voltage at the time of the minimum gain, it is necessary to keep the value of the input dynamic range R _IN · I _{0 at} a constant voltage at all times. For this purpose, the accuracy of the power supply voltage value and the band gap voltage value must be further improved. Need to be managed.

[0012]

In order to control the accuracy of the power supply voltage value and the bandgap voltage value, FIG.
The current flowing through the constant current source 2 may be controlled by the correction circuit 11 having a current mirror configuration as shown in FIG. At this time, the current flowing through the bias resistors R11 and R12 is defined as i,
Assuming that the base potential of the transistor Q11 is Va, the current I0 flowing through the bias resistors R13 and R14 is expressed by the following equation.

(Equation 1)

(Equation 2)

(Equation 3) Holds.

Accordingly, the constant current I ₀ is given by the following equation:

(Equation 4) Given as At this time, assuming that the resistance ratio between the resistors R11 and R12 is 3: 1, the current I ₀ represented by the equation (4) becomes

(Equation 5) Becomes

Thus, the input dynamic range R _IN.
I ₀ is given by

(Equation 6) , The temperature characteristic of the input resistor R _IN is canceled by the denominator internal resistors R13 and R14 having the same temperature characteristic. If the power supply voltage V _CC has no temperature characteristic and the accuracy of the voltage value is high, the The value of the dynamic range R _IN · I ₀ can be set to a constant voltage.

[0015] However, since the control of the control microcomputer of the control voltage V _X, the power supply voltage must be the same power supply voltage V _CC and power supply for the microcomputer, the power supply V _CC1 of the integrated circuit for pre-driver Another power supply terminal must be provided, and the configuration is complicated.

It is also conceivable that the emitter potential of the transistors Q1 and Q2 is feedback-controlled using a differential amplifier so that the resistance re between the base and the emitter becomes invisible. In this case, the maximum gain or the minimum gain is obtained. In some cases, the transistors Q1 and Q2 are cut off, and oscillation is likely to occur.

The present invention has been made in consideration of the above points, and the variation in each gain characteristic and the variation in luminous efficiency of the pre-driver integrated circuit corresponding to each of the primary color video signals R, G, and B are compared with those of the prior art. Accordingly, the present invention aims to propose a gain control type amplifier circuit which can be more easily adjusted.

[0018]

In order to solve this problem, according to the present invention, a first and a second current source 2 are connected to an emitter, respectively, and a first and a second transistor Q1 and a second transistor Q1 forming a differential pair are provided. The first and second differential inputs (V _REF1 + V _X ) and V _X input to the base of Q2 are logarithmically amplified by first and second diodes D1 and D2 connected to the collector, respectively. A first differential amplification stage that outputs the first and second differential outputs, and a third and fourth differential pair that uses the first and second differential outputs as third and fourth differential inputs. To the transistors Q3 and Q4 of
The third and fourth collector currents flowing on the basis of the differential input by multiplying the signal current I _S that flows as a common emitter current in the third current source 3 connected to the common emitters, which are connected to the multiplication result to the collector A second differential amplifier stage output from a load _RL, and a first or second diode D1 or D2
Connected in parallel to either one of the first or second
As a and a fourth current source 23 to the transistor Q1 or Q2 flowing a constant current I _0.

[0019]

A fourth current source connected to the collectors of transistors Q1 and Q2 forming a differential pair and in parallel with one of first and second diodes D1 and D2 for outputting a differential output signal. By connecting the resistor 23, control is performed such that no current flows through the first or second diode D1 or D2 at the time of the minimum gain. As a result, when the first and second differential inputs (VREF1 + VX) and VX match, the output voltage value becomes constant and the linearity near the minimum gain is improved. And can be adjusted more easily.

[0020]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

In FIG. 1, reference numeral 20 denotes a gain control system for three primary color video signals as a whole, which is incorporated in three sets of integrated circuits 21 (21R, 21G, 21B) to which primary color input signals RI, GI, BI are respectively inputted. The gain characteristics of the primary color output signals RO, GO, BO output from the gain control amplifiers 22 (22R, 22G, 22B) can be easily adjusted.

In this embodiment, the gain control amplifier 22 (FIG. 2) has the same configuration as the gain control amplifier 1 shown in FIG. 5 except that a Wilson current mirror type current source 23 is provided in parallel with the diode D1. The current source 23 draws a current I ₀ having the same current value as the constant current I ₀ flowing through the constant current source 2 connected to the emitters of the transistors Q 1 and Q 2 forming a differential pair. ing.

Here, the gain control amplifier 21R,
Control voltage V _X for controlling the gain of 21G and 21B
Can be controlled by varying the resistance value of the variable resistor R _CONT for user gain control. Each gain control amplifier 22R, 22
The slopes of the gain control characteristic curves of G and 22B can be adjusted by gain adjustment resistors R _R , R _G and R _B connected to the variable resistor R _CONT via the buffer amplifier 24 (FIG. 4). .

The resistance values of the gain adjustment resistors R _R , R _G , and R _B are the same as those of the variable resistor R _CONT , and the linearity of each gain characteristic curve of the gain control amplifiers 22R, 22G, and 22B is maintained. _It is set in advance at the maximum voltage V _SET .

[0025] In the above configuration, the value of the control voltage V _X when the minimum gain is set to 0, illustrating the gain characteristics of the gain control amplifier 22 to the value at the maximum gain as V _MAX. The value of the control voltage V _X is 0
For (that is, when the minimum gain), the collector currents of the transistors Q1 and Q2 for the base voltage are equal to each other of the transistors Q1 and Q2 constituting the differential pair are both the I _0.

At this time, since the collector current flowing through the transistor Q1 is supplied from the current source 23 connected in parallel to the diode D1, the current flowing through the diode D1 is always 0 irrespective of variations in input resistance and the like (FIG. 3). . Thus, the values of the gain characteristic curves of the primary color output signals RO, GO, BO corresponding to the primary color input signals RI, GI, BI all coincide with the origin.

[0027] Referring now gradually increases the value of the control voltage V _X, while the current begins to increase gradually flowing through the diode D1, the current flowing through the diode D2 starts to decrease. At this time, since a sufficiently large collector current flows through the transistors Q1 and Q2 forming the differential pair, the gain characteristic curve does not deteriorate due to the influence of the resistance re between the base and the emitter, and the primary color output signals RO, GO, BO Is a straight line passing through the origin.

Eventually, the value of the control voltage V _X becomes V _MAX
(That is, when the maximum gain is reached), the collector current of 2 · I ₀ flows through the transistor Q1, while the collector current flowing through the transistor Q2 becomes _0, and the collector currents of I ₀ and 0 flow through the diodes D1 and D2, respectively. become.

At this time, a nonlinear characteristic appears on the gain characteristic curve as in the conventional circuit (FIG. 3). However, in order to match the characteristics of each primary color output signal, an output level value at the minimum gain and a straight line near the minimum gain are used. It is not necessary to keep the value of the input dynamic range (R _IN · I ₀ ) constant because the matching of gender is important, and with this gain control system, the primary color output can be obtained with a wider frequency characteristic and less crosstalk. Signals RO, GO, and BO can be output.

According to the above configuration, the gain control amplifier 22R, as a pre-driver circuit for each primary color signal,
22G, the gain control amplifier 22R with 22B and respectively provided, 22G, by connecting a current source 23 in parallel within the diode D1 of the diode connected in each differential pair constituting the 22B, a control voltage V _X is 0 In this case, that is, at the time of the minimum gain, the current flowing through the diode D1 can always be controlled to zero.

As a result, the output levels of the primary color output signals RO, GO and BO at the time of the minimum gain can always be fixed to 0, and the characteristic curves near the minimum gain are all straight lines. Since the gain characteristics can be easily matched in this manner, variations in the gains of the gain control amplifiers 22R, 22G, and 22B and variations in the luminous efficiency of the cathode ray tube can be easily absorbed.

In the above-described embodiment, the case where a current having the same value as the current I ₀ flowing through the current source 2 connected to each emitter is caused to flow out of the current source 23 has been described.
The present invention is not limited to this, and other values may be used as long as the current value is constant.

In the above-described embodiment, the constant current sources 2 are connected to the emitters of the transistors Q1 and Q2, respectively.
Although the description has been made of the case where the individual connection is made, the present invention is not limited to this, and one constant current source for flowing a double current (2 · I ₀ ) may be connected to the common emitter.

Further, in the above-described embodiment, the current source 2
3 in parallel with the diode D1 and the transistor Q4
The primary color output signal is output from the load resistor _RL connected to the collector of the present invention, the present invention is not limited to this, and the current source 23 may be connected in parallel to one of the diodes D1 and D2. , And the output may be taken out from the transistor Q3 side.

Further, in the above embodiment, the case where the present invention is applied to the gain control amplifier for increasing the three primary color signals has been described. However, the present invention is not limited to this, and a plurality of analog signals are amplified and output in parallel. The present invention can be widely applied to the case where the gain characteristics of the amplifying circuits are uniform.

[0036]

As described above, according to the present invention, one of the first and second diodes connected to the collectors of the transistors forming the differential pair and outputting the first and second differential outputs. By connecting a fourth current source in parallel to one of them, at the time of minimum gain, control is performed so that current does not flow through the first or second diode connected in parallel with the fourth current source. The voltage value when the first and second differential inputs match is set to an arbitrary value. Further, since a sufficiently large current flows through the first and second transistors near the minimum gain, the characteristic curve in the range can be made straight.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a primary color signal amplifying device according to the present invention.

FIG. 2 is a connection diagram showing an embodiment of a gain control type amplifier circuit according to the present invention.

FIG. 3 is a characteristic curve diagram for explaining a gain characteristic.

FIG. 4 is a characteristic curve diagram for explaining adjustment between a plurality of gain characteristics.

FIG. 5 is a characteristic curve diagram for explaining a conventional gain characteristic.

FIG. 6 is a connection diagram showing a conventional gain control type amplifier circuit.

FIG. 7 is a characteristic curve diagram for explaining a conventional gain characteristic.

FIG. 8 is a connection diagram showing a conventional gain control type amplifier circuit.

[Explanation of symbols]

1, 10 ... gain control circuit, 2, 3, 23 ...
... current source, 20 ... gain control system, 21
…… Integrated circuit, 22 …… Gain control amplifier, 2
4 ...... buffer amplifier, V _X ...... control voltage V _X, V _REF1 ...... reference voltage.

Claims (3)

(57) [Claims] A first current source and a second current source are respectively connected to an emitter, and first and second differential inputs input to bases of a first and second transistors forming a differential pair are connected to a collector. A first differential amplifier stage that logarithmically amplifies the first and second differential outputs, respectively, and outputs the first and second differential outputs as first and second differential outputs; The third and fourth differential inputs are inputted to the third and fourth transistors forming a differential pair, and the signal current flowing as a common emitter current to a third current source connected to the common emitter is applied to the third current. And a second differential amplifier stage that multiplies a collector current flowing based on the fourth differential input and outputs the multiplication result from a load connected to the collector; and one of the first and second diodes. Connected in parallel to Or gain controlled amplifier circuit, characterized in that it comprises a fourth current source for pouring a constant current to the second transistor. 2. The method according to claim 1, wherein the fourth current source supplies a constant current having a value equal to a current value drawn from the second or third current source to the first or second transistor. 2. The gain control type amplifier circuit according to 1. 3. A first, second and third gain control type amplifying means respectively corresponding to the three primary color signals and amplifying each primary color signal and outputting the amplified primary color signal to the display means. The first and second current sources are respectively connected to an emitter,
First and second differential inputs, which are input to the bases of the first and second transistors forming a differential pair, are logarithmically amplified by first and second diodes connected to the collector, respectively. And a first differential amplifier stage for outputting as a second differential output, and a third and fourth differential pair forming the differential pair using the first and second differential outputs as third and fourth differential inputs. And a collector current flowing based on the third and fourth differential inputs is multiplied by a signal current flowing as a common emitter current into a third current source connected to the common emitter, and the multiplication result is obtained. A second differential amplifier stage that outputs from a load connected to a collector, and is connected in parallel to one of the first and second diodes, and supplies a constant current to the first or second transistor. With a fourth current source , Primary color signal amplifier apparatus characterized by amplifying the primary color signals.