JPH0317512Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to an addition circuit that adds a luminance signal and a color signal.

(b) Prior art Conventionally, there is a circuit as shown in Figures 3 and 7 in Section 101 of "Design of Transistor Circuits" (published by Radio Technology Co., Ltd.) as a circuit with a wide dynamic range. It is a uniform circuit diagram.

To explain the drawing numbers in Fig. 1, 1 is a DC power supply terminal, 2 is a power supply line, 3 is an input terminal for inputting a predetermined signal, and 4, 5, 6, 7 are the first, second, third and third terminals, respectively. A fourth resistor, 8 a first transistor, 9 a second transistor, 10 a diode, and 11 an output terminal that outputs an input signal input to the input terminal as a predetermined signal.

To explain the circuit configuration and circuit operation with regard to FIG. The base of the is connected to the input terminal 3, and the emitter is connected to the first resistor 4.
Connect the other end and connect the collector to diode 1
0 and the base of the second transistor 9, the other end of the diode 10 is connected to one end of the second resistor 5, and the collector of the second transistor 9 is connected to the other end of the third resistor 6 and the output. Connecting to the terminal 11 and connecting the emitter to one end of the fourth resistor 7,
The other ends of the second and fourth resistors 5 and 7 are grounded.

Here, it is assumed that the resistance values of the second and fourth resistors 5 and 7 and the sizes of the diode 10 and the second transistor 9 are equal, and the second transistor 9
Assuming that the current amplification factor of is large, the diode 10,
second transistor 9, second and fourth resistors 5,
7 constitutes a current mirror circuit. In addition, the DC power supply voltage input to DC power supply terminal 1 is Vcc,
The resistance values of the first and third resistors 4 and 6 are R ₁ and
R ₃ , the voltage between the base and emitter of the first transistor 8 is V _BE , the DC voltage at the input terminal 3 is V ₁ , and the DC voltage at the output terminal 11 is V ₂ , the voltage drop due to the first resistor 4 The current flowing due to the applied voltage is (Vcc- _V1 - _VBE )/ _R1 ... As mentioned above, a current mirror circuit is constructed from the diode 10, the second transistor 9, and the second and fourth resistors 5 and 7. Therefore, the emitter current of the second transistor 9 is also the same current. Furthermore, if the load impedance on the output side is made large, the current flowing through the third resistor 6 becomes the same current. Therefore, the voltage drop caused by the third resistor 6 is (Vcc - V ₁ - V _BE ) R ₃ /R ₁ ..., and the DC voltage V ₂ at the output terminal 11 is V ₂ = Vcc + (V ₁ + V _BE - Vcc). R ₃ /R ₁ ... becomes.

From the formula, when the circuit shown in Figure 1 is used as an amplifier, the resistance value R ₃ of the third resistor 6 is equal to that of the first resistor 4.
A value larger than the low resistance value R ₁ must be selected. Therefore, if R ₃ > R ₁ when there is no signal, in which the input terminal 3 is held at the DC voltage V ₁ , the voltage drop due to the third resistor 6 is larger than the voltage drop due to the first resistor 4. Therefore, the DC voltage V ₂ at the output terminal 11 becomes lower than the DC voltage V ₁ at the input terminal 3, which is lower in potential by V _BE than the point A. Therefore, when the DC voltage V ₁ at the input terminal 3 is a voltage intermediate between the DC power supply voltage Vcc and the ground, the DC voltage V ₂ at the output terminal 11 approaches the ground, so that the input signal input to the input terminal 3 If the amplitude of is increased, the lower side of the output signal output from the output terminal 11 is likely to be clipped due to the saturation of the second transistor 9, and the dynamic range of the amplifier becomes narrower. Then the second transistor 9
In order to set the DC voltage V ₂ at the output terminal 11 to around the intermediate voltage mentioned above, when widening the dynamic range of It has sometimes become necessary to make V ₁ higher than the above-mentioned intermediate voltage.

(c) Purpose of the invention The present invention is intended to eliminate the above-mentioned drawbacks, and aims to provide an adder circuit with a wider dynamic range of the output stage.

(d) Structure of the invention The present invention is an adder circuit that adds a luminance signal and a color signal. a third resistor, a second transistor, and a fourth resistor connected in series between the line and the ground; and a third resistor connected in parallel to the first transistor, the diode, and the second resistor.
and a fifth resistor, the collector of the first transistor is connected to the base of the second transistor, the emitter of the first transistor is connected to the collector of the third transistor, and the collector of the first transistor is connected to the collector of the third transistor. A first input terminal for inputting a luminance signal is connected to the base of the first transistor, a second input terminal for inputting a color signal is connected to the base of the third transistor, and a collector of the second transistor is connected to the base of the third transistor. This is an adder circuit that connects the and output terminals.

(E) Embodiments The details of the present invention will be specifically explained by referring to illustrated embodiments.

FIG. 2 is a circuit diagram showing the adding circuit of the present invention. To explain the figure numbers, 3 is the first input terminal to which the luminance signal is input, 12 is the second input terminal to which the color signal is input, and 13 is the second input terminal to which the color signal is input. The third transistor, 14, is the fifth resistor. Note that the same parts as in FIG. 1 are given the same figure numbers.

To explain the circuit configuration of FIG. 2, FIG. 2 is the circuit of FIG. 13 is connected to the second input terminal 12, and its collector is connected to the emitter of the first transistor 8 and the other end of the first resistor 4, and the emitter is grounded via the fifth resistor 14. The other configurations are the same as in FIG. 1.

In FIG. 2, the current flowing due to the voltage dropped by the first resistor 4 is the same as , and this current is branched from point B. If the current flowing through the collector of the third transistor 13 is I, then the first
The emitter current of the transistor 8 is (Vcc-V ₁ -V _BE )/R ₁ -I..., and a current mirror circuit is constituted by the diode 10, the second transistor 9, and the second and fourth resistors 5 and 7. Therefore, the emitter current of the second transistor 9 becomes the same current as . In addition, in order to increase the load impedance on the output side, the current flowing through the third resistor 6 becomes the same current, and the voltage drop caused by the third resistor 6 is (Vcc−V ₁ −V _BE )R ₃ /R ₁ − R ₃ I)... Therefore, the DC voltage V ₂ ′ at the output terminal 11 is V ₂ ′=Vcc+(V ₁ +V _BE −Vcc)R ₃ /R ₁ +R ₃ I
... becomes.

When the circuit of the present invention shown in Fig. 2 is used as an amplifier, R ₃ > R ₁ must be satisfied in the formula, but when comparing the formula and formula under the same condition, the formula is better than the formula. It can be seen that the DC voltage at the output terminal 11 has increased by R ₃ I. If I is selected so that V ₂ ' in the equation becomes Vcc/2, the amplitude of the input signal input to the first and second input terminals 3 and 12 is increased, and the output terminal 1
When the amplitude of the output signal output from 1 is increased, the output signal is less likely to be clipped compared to the conventional circuit shown in FIG. 1, and the dynamic range of the output stage can be expanded.

In addition, second, fourth and fifth resistors 5, 7, 14
Let the resistance values of R ₂ , R ₄ and R ₅ be respectively (R ₂ =
R ₄ ), the voltage gain Gv ₁ of the conventional circuit shown in Fig. 1 is Gv ₁ ≒ R ₂ R ₃ /R ₁ R ₄ = R ₃ R ₁ ..., and the voltage gain of the circuit of the present invention shown in Fig. 2 is Gv ₂ becomes Gv ₂ ≒ R ₁ R ₂ R ₃ / R ₁ R ₄ R ₅ = R ₃ R ₅ ....

Since the fifth resistor 14 is a feedback resistor of the third transistor 13, it is clear that R ₁ >R ₅ , and when comparing the formulas with the formulas, Gv ₂ >Gv ₁ . . . .

FIG. 2 shows an adder circuit that adds a luminance signal and a chrominance signal. To explain its operation, the luminance signal is input to the first input terminal 3, and the luminance signal is input to the second input terminal 12.
First, when the color signal input to the second input terminal 12 is kept constant and the luminance signal input to the first input terminal 3 is changed, the luminance signal is input in the positive direction. When the voltage swings to , the voltage drop due to the first resistor 4 which is the feedback resistance of the first transistor 8 becomes small, and the voltage drop of the first transistor 8 becomes small.
The emitter current of decreases. Since the diode 10, the second transistor 9, and the second and fourth resistors 5 and 7 constitute a current mirror circuit as described above, the emitter current of the second transistor 9 decreases and the emitter current of the second transistor 9 decreases. It becomes equal to the emitter current of transistor 8, and the output signal swings in the positive direction. Conversely, when the luminance signal swings in the negative direction, the voltage drop across the first resistor 4 increases, the emitter current of the first transistor 8 increases, and the emitter current of the second transistor 9 also increases. Similarly, it becomes equal to the emitter current of the first transistor 8, and the output signal swings in the negative direction.

Next, when changing the color signal input to the second input terminal 12 while keeping the luminance signal input to the first input terminal 3 constant, when the color signal swings in the positive direction, the third
Since the collector current of the first transistor 13 increases, the emitter current of the first transistor 8 decreases, and the output signal swings in the positive direction as described above. Conversely, when the color signal swings in the negative direction, the collector current of the third transistor 13 decreases, so the emitter current of the first transistor 8 increases, and the output signal swings in the negative direction as described above. Therefore, FIG. 2 is a non-inverting amplifier.

(F) Effects of the invention According to the adder circuit of the present invention, the dynamic range of the output stage of the adder circuit can be expanded with a simple configuration, and there are advantages such as cost reduction in production.

[Brief explanation of the drawing]

FIG. 1 is a general circuit diagram in which the output stage has a wide dynamic range, and FIG. 2 is a circuit diagram showing an adder circuit according to the present invention. Explanation of main figure numbers, 2... Power line, 3... First input terminal, 4... First resistor, 5... Second resistor, 6... Third resistor, 7... Third resistor. resistance of 4, 8
...First transistor, 9...Second transistor, 10...Diode, 11...Output terminal,
12... Second input terminal, 13... Third transistor, 14... Fifth resistor.

Claims (1)

[Scope of utility model registration request] In an addition circuit that adds a luminance signal and a color signal, a first resistor, a first transistor, a diode, and a second resistor are connected in series between the power supply line and the ground.
a third resistor, a second transistor, and a fourth resistor connected in series between the power supply line and the ground; and a third resistor connected in parallel to the first transistor, the diode, and the second resistor. transistor and a fifth resistor, the first
A first transistor that connects the collector of the transistor and the base of the second transistor, and connects the emitter of the first transistor and the collector of the third transistor, respectively, and inputs a luminance signal to the base of the first transistor. a second input terminal for inputting a color signal to the base of the third transistor;
An adder circuit characterized in that the collector and output terminal of a transistor are connected.