JP2937765B2 - Voltage control amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage control amplifier circuit capable of accurately setting a variable output range.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing an example of a conventional voltage controlled amplifier circuit. Transistor Q1 forming a differential pair
0 and the emitter of the transistor Q11 are connected to each other,
Connect to current source 12. In the current source 12, a bias current and a signal current superimposed on the bias current flow. The base of the transistor Q10 is a control voltage source E10,
The collectors are respectively connected to power supply terminals 10 to which a power supply voltage V _CC is applied via a load resistor R10. Transistor Q1
1 has a reference voltage source E11 and a collector has an output terminal 1
1 and the load terminal R11 and connected to the power supply terminal 10.
In such a circuit, the gain can be changed by changing the control voltage of the control voltage source E10, and an output obtained by differentially amplifying the signal is obtained at the output terminal 11. However, if the control voltage of the control voltage source E10 is much higher than the voltage of the reference voltage source E11, all the current flows through the transistor Q10, and an output may not be obtained at the output terminal 10.

FIG. 3 is a characteristic diagram showing the relationship between the output current of a signal and the control voltage, and shows how the output current becomes 0 when the control voltage is large. When the variable range is set such that the end of the variable range of the output becomes zero, for example, when this circuit is used as an electronic volume, there is no particular inconvenience. However, when the variable range is set such that the end of the variable range does not become 0, it is difficult to set an accurate variable range of the output. This is because the variable range is set by partially using the sloped portion of the characteristic C1 in the characteristic diagram of FIG. 3, so that the output current is changed even by a small change in the control voltage or the sloped portion. FIG. 3 shows a case where the variable range of the output current is 12 dB. W1 is
The variable width of the control voltage.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a voltage controlled amplifier circuit in which the variable range of the output is expressed in dB and the variable range of which the end does not become 0 can be set accurately. Is to do.

[0005]

SUMMARY OF THE INVENTION A voltage controlled amplifier circuit according to the present invention has first and second differential amplifier circuits and first and second differential shunt circuits. The second shunt circuit is connected in a double-balanced manner, with each being a lower differential pair and the two differential amplifier circuits being a common upper differential pair. The first and second shunt circuits are differential pairs. Are connected so that their bases are connected in common, and the collector current ratio is set to be the maximum and minimum ratio of the variable range of the output obtained from the upper differential pair. An input signal superimposed on a bias voltage as an input of a lower differential pair forming a first shunt circuit, and a bias voltage being applied as an input of a lower differential pair forming a second shunt circuit. And

[0006]

The ratio of the collector current of the transistor forming the differential pair of the shunt circuit is set to the ratio between the maximum and the minimum of the variable range of the output obtained from the upper differential pair. At the minimum, the output does not change due to a change in the control voltage. This facilitates setting of the maximum and minimum of the variable range, and allows the variable range to be set accurately.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an embodiment of a voltage controlled amplifier circuit according to the present invention. In FIG. 1, the transistors Q1 and Q2 have their emitters connected to each other to form a differential pair, and form a first differential amplifier circuit A1 together with a load resistor R1. The transistors Q3 and Q4 also have their emitters connected to each other and form a second differential amplifier circuit A2 together with the load resistor R2. Transistors Q1, Q2, Q3, Q
4 have the same characteristics.

The emitters of the transistor Q5 and the transistor Q6 are connected to each other, and form a differential first shunt circuit A3 together with a resistor R3 commonly connected to the emitters. The resistor R3 sets a current flowing through the entire shunt circuit A3. The emitter of the transistor Q5 is a multi-emitter.
The collector current is doubled (12 dB). In other words, this differential pair changes the current flowing through the resistor R3 to 4:
It is a circuit that shunts to 1. The transistor Q7, the transistor Q8, and the resistor R4 form a differential second shunt circuit A4 in the same manner as the first shunt circuit. The emitter of the transistor Q7 is a multi-emitter, and a collector current four times (12 dB) as compared to the transistor Q8 flows. The characteristics of the transistors Q5 and Q7 and the characteristics of the transistors Q6 and Q7 are the same.

In the first and second differential amplifier circuits A1 and A2, the collectors of the transistors Q1 and Q3 are connected and connected to the output terminal 2, and the power supply to which the power supply voltage V _CC is applied via the load resistor R1. Connected to terminal 1. The collectors of the transistors Q2 and Q4 are also connected, and are connected to the power supply terminal 1 via the load resistor R2. The anodes of the control voltage source E3 are connected to the bases of the transistors Q1 and Q4, and the cathodes of the variable voltage source E3 are connected to the bases of the transistors Q2 and Q3. In the first and second shunt circuits A3 and A4, the collectors of the transistors Q5 and Q8 are connected and connected to the emitters of the transistors Q1 and Q2 of the first differential amplifier circuit A1. Also, the collectors of the transistors Q6 and Q7 are connected, and the second differential amplifier circuit A
2 are connected to the emitters of the transistors Q3 and Q4.

An input signal S superimposed on the bias voltage of the voltage source E1 is applied to the bases of the transistors Q5 and Q6. The bias voltage of the voltage source E2 is applied to the bases of the transistors Q7 and Q8. The bias voltages of the voltage sources E1 and E2 are equal. The values of the load resistors R1 and R2 are equal, and the values of the resistors R3 and R4 are equal. Such a voltage controlled amplifier circuit includes first and second shunt circuits A
3 and A4 are lower differential pairs, and the first and second differential amplifier circuits A1 and A2 are common upper differential pairs of the first and second shunt circuits A3 and A4. The output current variable range is set to 12 dB, that is, the ratio between the maximum and the minimum of the output current is set to 4: 1.

Next, the operation will be described with reference to the characteristic diagram showing the relationship between the control voltage and the output current of the signal in FIG. When the control voltage of the control voltage source E3 is maximized in the variable width W2, the transistors Q1 and Q4 are turned on and the transistors Q2 and Q3 are turned off. Then, a current corresponding to the input signal S flowing through the transistor Q5 flows through the transistor Q1 and the output terminal 2. Of course, the current corresponding to the input signal S is superimposed on the bias current corresponding to the voltage sources E1 and E2 flowing through the transistors Q5 and Q8. Conversely, when the control voltage is minimized, the transistors Q2,
Q3 turns on, and transistors Q1 and Q4 turn off. Then, a current corresponding to the input signal S flowing through the transistor Q6 flows through the transistor Q3 and the output terminal 2. This current is superimposed on the bias current as in the case of the maximum control voltage.

Since the ratio of the collector currents of the transistors Q5 and Q6 is set to 4: 1, the output current corresponding to the input signal S obtained at the output terminal 2 is 4 at the maximum and minimum control voltages. : 1 and there is a 12 dB difference. Then, the output current does not become zero. Second
The shunt circuit A4 serves to make the bias current flowing through the output terminal 2 always the same. Between the maximum and the minimum of the control voltage, the output current having a gain according to the control voltage is output terminal 2
Is obtained.

In the characteristic C2 shown in FIG. 2, the variable range of the output current is set so that the output current does not change in response to a change in the control voltage when the variable range is maximum and minimum. Therefore, the variable range can be set more accurately than in the conventional case where the slope portion of the characteristic C1 in FIG. 3 is partially used. In the embodiment, the variable range of the output current has been described as the output. However, it is needless to say that the output voltage can be similarly described. Although the setting of the current shunted by the shunt circuit is performed by using a multi-emitter transistor, it can be performed by connecting a resistor for setting the current to a normal transistor.

[0014]

As described above, in the voltage controlled amplifier circuit of the present invention, the output does not change regardless of the control voltage when the output variable range is maximum and minimum. Therefore, it is easy to set the maximum and minimum of the variable range, and the variable range can be set accurately. In the case of setting a variable range of the output that does not include 0, conventionally, the variable range is set by partially using the slope portion of the characteristic indicating the relationship between the control voltage and the output. Although it is difficult to accurately set the output variable range due to a small change in the output, the present invention solves such a technical problem at once.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a voltage controlled amplifier circuit according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between an output current and a control voltage in FIG.

FIG. 3 is a characteristic diagram showing a relationship between an output current and a control voltage of a conventional voltage controlled amplifier circuit.

FIG. 4 is a circuit diagram showing an example of a conventional voltage controlled amplifier circuit.

[Explanation of symbols]

 2 Output terminal E3 Control voltage source S Input signal A1 First differential amplifier circuit A2 Second differential amplifier circuit A3 First shunt circuit A4 Second shunt circuit

Claims (3)

(57) [Claims] A first differential amplification circuit and first and second differential shunt circuits, each of the first and second shunt circuits being a lower differential pair; , The two differential amplifier circuits are connected in a double balanced type as a common upper differential pair.
And the second shunt circuit are configured such that transistors forming a differential pair have their bases connected in common and the ratio of their collector currents is the maximum and minimum ratio of the variable range of the output obtained from the upper differential pair. A control voltage as an input of the upper differential pair, an input signal superimposed on the bias voltage as an input of the lower differential pair forming the first shunt circuit, and a control voltage of the lower differential pair forming the second shunt circuit. A voltage controlled amplifier circuit to which a bias voltage is applied as an input. 2. The first and second shunt circuits, wherein a collector having a large collector current and a collector having a small collector current are connected to each other, and the connected collectors are connected to the first and second differential amplifiers. The voltage controlled amplifier circuit according to claim 1, wherein the voltage controlled amplifier circuit is connected to a circuit. 3. The voltage controlled amplifier circuit according to claim 1, wherein the first and second shunt circuits have a multi-emitter emitter on one side of the transistor forming the differential pair.