JPH0233387Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a gain control amplifier in which the gain changes with exponential characteristics according to the control voltage, and in particular, distortion is reduced by matching the operating points of each transistor used. The present invention relates to a balance adjustment circuit for a gain control amplifier.

Conventionally, this type of gain control amplifier has a first
The one shown in the figure is known. The gain control amplifier shown in this figure has a control voltage Vc between both bases.
is applied, and has a transistor pair 3 consisting of transistors 1 and 2 (both NPN transistors) whose emitters are commonly connected, and a transistor pair 6 consisting of transistors 4 and 5 (both NPN transistors) configured in the same way. Input signals v _{i and} −v _i having opposite phases to each other are supplied to the common emitters of transistor pairs 3 and 6, respectively, and the resulting difference between the collector voltages of transistors 1 and 4 is calculated by a subtraction circuit. Detected by 7 and output signal
It is extracted as v ₀ .

In this gain control amplifier, the collector currents of transistors 1, 2, 4, and 5 are i ₁ , i ₂ , i ₃ , i ₄
In this case, due to the nature of the PN junction of the transistor, there is the following relationship: {i ₁ =i ₂ e ^KV ₀ i ₃ =i ₄ e ^KV ₀ }(1) (where K=q/KT). Note that q is the electron charge, k is Boltzmann's constant, and T is the junction temperature. In addition, the current values of constant current sources 9 and 10 inserted between the common emitters of transistor pairs 3 and 6 and the negative power supply terminal 8 are both connected to I, and the current values of constant current sources 9 and 10 are connected in series to input signal sources 11 and 12, respectively. The resistance values of resistors 13 and 14 are both Ri
given that, holds true. Also, a resistor 1 is inserted between the collectors of the transistors 1 and 4 and the positive power supply terminal 15.
If the resistance values of 6 and 17 are both R ₀ , the voltage v ₀ of the output signal is v ₀ = R ₀ (i ₃ − i ₁ )...(3), so this formula (3) can be written as (1) ) and (2), the voltage v ₀ becomes: v ₀ = R ₀ /Ri・2vi/(1+e ^-KV ₀ )...(4) From this equation (4), this gain control amplifier The voltage gain Av of is Av=v ₀ /vi=2R ₀ /Ri ( _1+e −KV ₀ ) (5), and it can be seen that it changes with an exponential characteristic according to the control voltage V ₀ .

By the way, as is clear from equations (2) and (3), such a gain control amplifier operates the transistor pairs 3 and 6 in a complementary manner depending on the polarity of the input signal, and By extracting the difference between the collector voltages of transistors 1 and 4 in transistor pair 6, the entire transistor performs a push-pull operation, thereby reducing even-order distortion. 2, 4, and 5 each have different unique characteristics (base-emitter voltage characteristics, base resistance, etc.), so in order to reduce this even-order distortion, it is necessary to take into account the variations in each of the above characteristics. Transistors 1 and 2, which became misaligned,
It is necessary to provide a balance adjustment circuit to correct the operating points 4 and 5 so that they match.

This idea was made in view of the above circumstances,
In a gain-controlled amplification having two transistor pairs, the operating points (i.e., base-emitter voltage, base current, etc.) of each transistor, which are uneven due to variations in the characteristics of each transistor in these transistor pairs, are matched. It is an object of the present invention to provide a balance adjustment circuit for a gain control amplifier that can be corrected so as to.

In this invention, a control voltage is applied between the bases and two pairs of transistors are connected in common, and input signals having opposite phases are supplied to the common emitters of the two transistor pairs. In addition, in the gain control amplifier configured to obtain an output signal from a predetermined collector of the two transistor pairs, a resistor is interposed between each base of each transistor of the two transistor pairs and a ground point. a current adjustment circuit that is connected to the control input terminal of each of the other transistors of the two transistor pairs; A resistor is inserted between each, and currents of equal amount and in opposite directions are supplied from the base sides of these resistors, and the base emitter between each base and the emitter corresponding to each base is The present invention is characterized by comprising a base voltage adjustment circuit that adjusts the ratio of voltages between the two.

Hereinafter, embodiments of this invention will be described with reference to the drawings.

FIG. 2 is a circuit diagram showing the configuration of a gain control amplifier equipped with the first embodiment of this invention, and in this figure, parts corresponding to those in FIG. 1 are given the same reference numerals. . In FIG. 2, reference numeral 18
4 is a base voltage adjustment circuit for balancing the base-emitter voltages of one transistor 1 in transistor pair 3 and one transistor 4 in transistor pair 6;
Reference numeral 9 denotes a base current adjustment circuit for balancing the base currents (that is, the base resistances) of the other transistor 2 in the transistor pair 3 and the other transistor 5 in the transistor pair 6.

The base voltage adjustment circuit 18 and base current adjustment circuit 49 will be explained in more detail below. First, in the base voltage adjustment circuit 18, the control voltage input terminal 19 is connected to the non-inverting input terminal of an operational amplifier 20 constituting a voltage follower, and the output terminal of the operational amplifier 20 is connected via a resistor 21 (value R ₁ ). and the base of transistor 1 and transistor 22
(NPN transistor) collector and constant current source 23
(the current value is I ₁ /2) and the base of the transistor 4 and the transistor 25 (NPN transistor paired with the transistor 22) via the resistor 24 (value R ₁ ). The collector is connected to the current output terminal of a constant current source 26 (current value is I ₁ /2). transistor 22,
Both bases of 25 are grounded, and a variable resistor 27 (value R ₂ ) is inserted between both emitters, and the sliding terminal of this variable resistor 27 is connected to a constant current source 28 (current value is
I ₁ ) is connected to the current input terminal. The current input terminals of the constant current sources 23 and 26 are both connected to the positive power supply terminal 15.
The current output terminal of the constant current source 28 is connected to the negative power supply terminal 8.

According to the base voltage adjustment circuit 18 having the above configuration, by operating the variable resistor 27, the resistance 2
1 and 24, it is possible to supply currents in equivalent and opposite directions from point A to point B and from point A to point C, as shown in the diagrams 1 and 24, and as a result, a current can be supplied between both ends of resistors 21 and 24. It is possible to generate voltage drops of equal amount and opposite polarity with respect to point A. According to this base voltage adjustment circuit 18, each base voltage of the transistors 1 and 4 is adjusted to
It is possible to change their average value in the opposite polarity direction while keeping it the same as the control voltage V ₀ , thereby matching the base-emitter voltages of transistors 1 and 4 without changing the gain (i.e., balancing be able to)

Next, in the base current adjustment circuit 49, the base of transistor 2 is grounded via a resistor 29 (value R ₃ ), and the base of transistor 5 is grounded via a resistor 30.
(value R ₃ ), and a variable resistor 31 (value R ₄ ) between the bases of transistors 2 and 5.
is inserted, and the sliding terminal of this variable resistor 31 is grounded. In this case, each of the above resistance values
There is a relationship (R ₃ R ₄ /2)=R ₁ between R _{3 and} R ₄ and the resistance value R 1 of the resistors 21 and 24.

According to the base current adjustment circuit 49 having the above configuration, the base currents of the transistors 2 and 5 can be made to match (that is, balanced) without changing their average value, that is, without changing the gain. can.

3 and 4 are characteristic diagrams for explaining the operation of the gain control amplifier equipped with this embodiment. As shown in FIG. 3, according to this embodiment, the variable resistor 27 is operated. By doing so, the V _BE −I ₀ characteristic curve of transistor 1 can be expressed as, for example, a solid line a ₁ , a broken line a ₂ ,
As shown by the broken line a ₃ and correspondingly, the V _BE -I characteristic curve of the transistor 4 is plotted by the solid line b ₁ , the broken line b ₂ , the broken line
b ₃ , thereby increasing the base-emitter voltage V _BE of both transistors 1 and 4.
can be balanced (that is, the respective V _BE −I ₀ characteristic curves of both transistors 1 and 4 are shown as solid lines a ₁ ,
(can be adjusted to position b ₁ ).
As a result, the currents i ₁ and i ₃ vary depending on the voltage v _i
The current (i ₃ −i ₁ ) changes symmetrically between positive and negative, as shown by _the curve z in FIG _. The voltage v ₀ of the output signal corresponding to ) almost no longer includes even-order distortion.

Next, FIG. 5 is a circuit diagram showing the configuration of a gain control amplifier equipped with a second embodiment of this invention. This second embodiment differs from the first embodiment in that the base voltage adjustment circuit 18 is provided with a DC servo circuit that automatically corrects the DC offset of the voltage _v0 of the output signal of this gain control amplifier. The point is that That is, in the base voltage adjustment circuit 18, the output of the subtraction circuit 7 is passed through the integration circuit 35 consisting of a resistor 32, a capacitor 33, and an operational amplifier 34.
The direct current component is extracted from the output of the subtraction circuit 7. Also, the DC component extracted in this way is connected to the resistor 36,
Transistor 22 via a voltage divider circuit consisting of 37
Based on the negative feedback.

According to this second embodiment, if the DC potential at voltage v ₀ increases, the transistor 22
Since the base potential of decreases, current 1 ₁ increases and current 1 ₃ decreases, the current potential at voltage v ₀ decreases, and if the DC potential at voltage v ₀ decreases, the above operation occurs. By the exact opposite operation, the same DC potential is increased, and the DC offset of voltage _v0 is automatically corrected.

Next, FIG. 6 is a circuit diagram showing a configuration example when the first embodiment is applied to another gain control amplifier. The gain control amplifier shown in this figure includes a first current mirror circuit 38 connected as a load to each collector of transistors 1 and 4, and a second current mirror circuit 38 connected as a load to each collector of transistors 2 and 5.
The input signal (voltage) supplied to the input terminal 40 is
v _i ) through resistor 41 (value R _i ) to transistor 1
On the other hand, the inverting amplifier 42 with a large gain and the inverting amplifier 43 with a gain of "-1" connect the common emitters of the transistor pairs 3 and 6 to the collectors of the transistors 3 and 6 in opposite phases according to the input signal (voltage vi ₎ . As a result, the current taken out from the collector of the transistor 5 is converted into a voltage v ₀ by a current-voltage conversion circuit 46 consisting of an operational amplifier 44 and a feedback resistor 45, and outputted from an output terminal 47. It is something. In this case, the base voltage adjustment circuit 18 is inserted between the control voltage input terminal 19 and the bases of the transistors 1 and 4, and the base current adjustment circuit 49 is inserted between the bases of the transistors 2 and 5 and the ground point. inserted in between. In the base voltage adjustment circuit 18 and base current adjustment circuit 49 shown in FIG. 6, the same reference numerals are given to the parts corresponding to those in FIG. 2.

As explained above, the balance adjustment circuit according to this invention has a resistor inserted between the base of each transistor and the ground point of each of the two transistor pairs constituting the gain control circuit, and the resistance ratio A current adjustment circuit that adjusts the ratio of base current flowing to each base by adjusting the current, and a resistor is interposed between each base of the other transistor of the two transistor pairs and the control input terminal. It supplies equal and opposite currents to each other from the base sides of these resistors, and adjusts the base-emitter voltage ratio between each of these bases and the emitter corresponding to each of these bases. Since it is configured with a base voltage adjustment circuit designed to do so, the operating point of each transistor used can be matched with an extremely simple circuit configuration, thereby reducing distortion such as even-order distortion. . Further, by using the balance adjustment circuit for the gain control amplifier according to this invention, it is possible to extremely easily construct a DC servo circuit that automatically corrects the DC offset of the output signal.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of the configuration of a conventional gain control amplifier, and FIG. 2 is a circuit diagram showing an example of the configuration of a gain control amplifier equipped with the first embodiment of the present invention.
3 and 4 are characteristic diagrams for explaining the operation of the same example, FIG. 5 is a circuit diagram showing the configuration of a gain control amplifier equipped with a second embodiment of this invention, and FIG.
The figure is a circuit diagram showing another example of the configuration of a gain control amplifier equipped with the first embodiment of this invention. 1, 2, 4, 5...transistor, 3, 6...
Transistor pair, 18...Base voltage adjustment circuit, 49...Base current adjustment circuit.

Claims (1)

[Claims for Utility Model Registration] A control voltage is applied between the bases, and two transistor pairs are provided whose emitters are commonly connected, and input signals having opposite phases to each common emitter of the two transistor pairs are provided. In the gain control amplifier, the gain control amplifier obtains an output signal from a predetermined collector of the two transistor pairs, and a resistor is provided between each base of each transistor of the two transistor pairs and a ground point. A current adjustment circuit is inserted between each of the bases of the other transistor of the two transistor pairs, and a control input terminal. A resistor is inserted between each of these resistors, and currents of equal and opposite directions are supplied from the base sides of these resistors, and the base between each of these bases and the emitter corresponding to each of these bases is - A balance adjustment circuit for a gain control amplifier, characterized by comprising a base voltage adjustment circuit that adjusts the ratio of the voltage between emitters.