JPH0546113U - Variable attenuator circuit - Google Patents

Abstract

(57) [Summary] [Purpose] The signal line and control line are separated to eliminate interference from the control system. [Structure] The differential amplifiers 14 and 16 are used to separate a signal line and a control line. Since the attenuation rate is determined by I _B / I _A and the gain can be changed only by controlling the constant current source, the signal line and the control line are separated. The input impedance is kept constant, and when integrated into an IC, the temperature becomes stable.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an improvement of an attenuator circuit capable of varying a signal attenuation rate, that is, a variable attenuator circuit.

[0002]

[Prior Art]

When a signal is attenuated or amplified, a variable attenuator circuit is used as a means for adjusting the attenuation rate or gain. FIG. 3 shows the synthesis of a variable attenuator circuit according to a conventional example. In the circuit shown in this figure, the ratio of the input resistance and the feedback resistance of the operational amplifier 10 is changed by the tap switching control of the analog switch group 12 to change the gain. That is, the non-inverting input terminal of the operational amplifier 10 is grounded, and the six resistors R _{1 to} R ₆ are connected to the inverting input terminal through the analog switch group 12. In such a circuit, one of the analog switches belonging to the analog switch group 12, for example, only the analog switch that connects the connection point of R ₃ and R ₄ to the inverting input terminal of the operational amplifier 10 is turned on, and the other switch is turned on. When turned off, the input resistance of the operational amplifier 10 becomes R ₁ + R ₂ + R ₃ and the feedback resistance becomes R ₄ + R ₅ + R ₆ . Since the voltage gain of this circuit, that is, V _OUT / V _IN, is determined by the ratio of the feedback resistance and the input resistance, the voltage gain can be switched by the tap switching control for the input switch group 12.

[0003]

[Problems to be solved by the device]

 However, in such a conventional circuit, since the control line for controlling the analog switch directly enters the signal line, there is a problem in that the signal is likely to be interfered with from the control line.

The present invention has been made to solve the above problems, and by separating the signal line and the control line, a variable attenuator circuit that is less susceptible to interference from the control system is provided. The purpose is to provide.

[0005]

[Means for Solving the Problems]

 In order to achieve such an object, the first aspect of the present invention provides a first transistor which is diode-connected, a second transistor which is differentially connected to the first transistor and whose base is grounded, first and second transistors. The first and second active loads respectively connected to the collectors of the two transistors, and the first constant current source commonly connected to the emitters of the first and second transistors, and the base of the first transistor. A first differential amplifier to which a signal current is input, a third transistor whose base is grounded, a fourth transistor differentially connected to the third transistor, and collectors of the third and fourth transistors. A third constant current source commonly connected to the emitters of the third and fourth transistors, a third constant current source connected to the A second differential amplifier in which the collector potential of the first transistor is input to the base of the first transistor and a signal current is output from the collector of the fourth transistor, and the first and / or second constant current source is It is a variable constant current source. According to a second aspect of the present invention, the first transistor is diode-connected, the second transistor is differentially connected to the first transistor, and the first and second transistors are respectively connected to the collectors of the first and second transistors. A first differential circuit including first and second active loads, a first constant current source commonly connected to the emitters of the first and second transistors, and a signal current being input to the base of the first transistor. An amplifier, a third transistor, a fourth transistor differentially connected to the third transistor and having its base grounded, and third and fourth transistors connected to the collectors of the third and fourth transistors, respectively. A second constant current source, which is commonly connected to the emitters of the active load and the third and fourth transistors, and which outputs a signal current from the collector of the fourth transistor. A dynamic amplifier and an operational amplifier that controls the base potentials of the second and third transistors so that the collector potential of the first transistor and the ground potential are the same, and the first and / or second The constant current source is a variable constant current source.

A variable gain amplifier circuit according to a third aspect of the present invention is the variable attenuator circuit according to the first or second aspect, in which the signal voltage is converted into a current and is input to the base of the first transistor. It is characterized by including a resistor and an inverting amplifier that amplifies the signal current output from the second differential amplifier and converts it into a voltage.

[0007]

[Action]

In the first aspect of the present invention, the base-emitter voltage V _{BE1 of} the first transistor is determined from the current value I _A and the signal current I _IN of the first constant current source by the following equation (1).

[0008]

[Equation 1]

Here, k is Boltzmann's constant 1.38 × 10 ⁻²³ [J / K], T is absolute temperature [K], q is unit charge 1.6 × 10 ⁻¹⁹ [C], I _S1 Is the base-emitter dark current of the first transistor.

Similarly, the base-emitter voltage V _BE2 of the second transistor is determined by the following equation (2).

[0011]

[Equation 2]

Here, I _S2 is a base-emitter dark current of the second transistor.

Therefore, the differential input Δe ₀₁ in the first differential amplifier is

[0014]

[Equation 3]

However, here, for simplification, I _S1 = I _S2 .

The base-emitter voltage V _BE4 of the fourth transistor is

[0017]

[Equation 4]

Is represented as Where I _B is the current value of the second constant current source, I _OUT is the signal current output from the collector of the fourth transistor, I _S4 is the dark current between the base and emitter of the fourth transistor, and V _BE3 is The base-emitter voltage of the third transistor, Δe _02, is the differential input of the second differential amplifier. Similarly, the base-emitter voltage V _BE3 of the third transistor is expressed by the following equation (5).

[0019]

[Equation 5]

Therefore, from (4) and (5), the differential input Δe ₀₂ of the second differential amplifier is

[0021]

[Equation 6]

Is represented as Here again, I _S3 = I _S4 is set to simplify the formula.

Here, since the bases of the second transistor and the third transistor have the same potential, and the bases of the first and fourth transistors have the same potential, the differential input Δe ₀₁ = Δe ₀₂ , so

[0024]

[Equation 7]

The following equation holds. That is, in claim 1, the signal current I _OUT to be output, a value obtained by attenuating the signal current I _IN of the input at a ratio I _B / I _A of the current value of the constant current source. In the present invention, since the first and / or second constant current sources are variable constant current sources, I _A and / or I _B can be controlled. Therefore, in the first aspect, the attenuation factor can be set by controlling the constant current source separated from the signal path, and a variable attenuator circuit that is less susceptible to interference from the control system is realized.

Also, in claim 2 of the present invention, the equation (7) is established, and the signal line and the control line are separated. However, in this claim, the base of the fourth transistor is grounded, and the base potential of the third transistor changes in accordance with the signal current.

[0027] In claim 3, is input to the base of the first transistor data after the signal voltage is converted into a current I _IN, the signal current I _OUT that is output from the second differential amplifier the voltage by inverting amplifier Is converted to. That is, a variable attenuator amplifier circuit for voltage input voltage output is realized.

[0028]

【Example】

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

FIG. 1 shows the configuration of a variable attenuator circuit according to the first embodiment of the present invention. The embodiment shown in this figure comprises differential amplifiers 14, 16 and an operational amplifier 18. The differential amplifier 14 is composed of two transistors Q ₁ and Q ₂ , active loads Q ₅ and Q ₆ forming a current mirror circuit, and a constant current source I _A. The signal voltage V _IN is applied to the base of the transistor Q ₁ via the current conversion resistor R _IN . The current conversion resistor R _IN is a resistor that converts the signal voltage V _IN into the current I _IN .

The transistor Q ₁ is a so-called diode-connected transistor whose collector and base are short-circuited. The transistor Q ₁ is differentially connected to the transistor Q ₂ . The collectors of the transistors Q ₁ and Q ₂ are connected to the active loads Q ₅ and Q ₆ , respectively, and the emitters thereof are commonly connected to the constant current source I _A. Accession tee Broad Q ₅ and Q ₆ is the power source + V _cc, the constant current source I _A to the power supply -V _cc, are their respective connections.

The differential amplifier 16 is similar to the differential amplifier 14, the transistor Q _3, Q _4, Akti Iburodo Q _7, Q _8, and a constant current source I _B. Transistors Q ₃ and Q ₄ are differentially connected. Active loads Q ₇ and Q ₈ forming a current mirror circuit are connected to these collectors, respectively, and a constant current source I _B is connected to the emitters. Active load Q _7, and Q ₈ is the power supply + V _cc, a constant current source I _B to the power supply -V _cc, are connected.

The bases of the transistors Q ₂ and Q ₃ are both grounded and kept at a constant potential. Further, the base (and collector) of the transistor Q _{1 and} the base of the transistor Q ₄ are connected, so that the differential inputs of the differential amplifiers 14 and 16 have the same value. That is, the above equations (1) to (7) are established.

The inverting amplifier 18 takes out a signal current from the collector of the transistor Q _4, converts the Re this into a voltage by the feedback resistor R _OUT, and outputs it as the signal voltage V _OUT. Therefore, in this embodiment, the signal voltage V _IN is converted into the signal current I _IN , attenuated based on the equation (7), further converted into the signal voltage V _OUT , and then output. Further, in this embodiment, the current value of the constant current source I _B can be variably set. As a result, the attenuation factor becomes variably set, and the gain by controlling only the constant current source I _B which is separated from the signal path (attenuation factor) control becomes possible. Although the control of the current source I _B is described in the present embodiment, this may be controlled to the constant current source I _A , or both of them may be controlled.

In addition, according to the present embodiment, since the resistance tap method as shown in FIG. 3 is not used, the input impedance can be kept constant. This is because the signal path that determines the input impedance is determined by the transistors Q _{1 to} Q ₄ and the fixed resistors R _IN and R _OUT . Further, when the circuit of this embodiment is integrated, the temperature coefficients of the differential amplifiers 14 and 16 can be made almost 0, and the temperature coefficient of the resistors R _IN and R _OUT can be made to coincide with each other, and the whole circuit can be obtained. It is possible to almost eliminate the temperature fluctuation of the gain of. Therefore, a temperature-stable variable attenuator circuit is realized.

FIG. 2 shows the configuration of a variable attenuator circuit according to the second embodiment of the present invention. In the circuit shown in this figure, the base of transistor Q ₄ is grounded rather than connected to the connector and base of transistor Q ₁ . Further, the bases of the transistors Q ₂ and Q ₃ are not grounded but are connected to the output terminal of the operational amplifier 20. The inverting input terminal of the operational amplifier 20 is connected to the base collector of the transistor Q ₁ .

Also in such a circuit, the same operation and effect as those of the first embodiment can be obtained.

[0037]

[Effect of the device]

 As described above, according to the present invention, the signal attenuating rate is set by the two differential amplifiers, and the signal line and the control line can be separated. Will be realized. Further, the input impedance can be kept constant, and when integrated into an IC, the temperature coefficient can be eliminated to realize a stable variable attenuator circuit with no temperature fluctuation of the attenuation rate.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a variable attenuator circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a variable attenuator circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a variable attenuator circuit according to a conventional example.

[Explanation of symbols]

14, 16 differential amplifier 18 inverting amplifier 20 operational amplifier _{Q 1, Q 2, Q 3} , Q 4 transistors _{Q 5, Q 6, Q 7} , Q 8 active load I _A, I _B constant current source R _IN, R _OUT Resistance B _IN Input signal voltage I _IN Input signal current V _OUT Output signal voltage I _OUT Output signal current

Claims (3)

[Scope of utility model registration request] 1. A diode-connected first transistor, a second transistor differentially connected to the first transistor and having its base grounded, and first and second transistors connected to the collectors of the first and second transistors, respectively. A first differential amplifier including a second active load, a first constant current source commonly connected to the emitters of the first and second transistors, and a signal current input to the base of the first transistor; A third transistor whose base is grounded, a fourth transistor differentially connected to the third transistor, third and fourth active loads respectively connected to collectors of the third and fourth transistors, and a third transistor And a second constant current source commonly connected to the emitter of the fourth transistor, and the collector current of the first transistor at the base of the fourth transistor. Is input and a signal current is output from the collector of the fourth transistor, and the first and / or second constant current source is a variable constant current source. Adjustable attenuator circuit. 2. A diode-connected first transistor, a second transistor differentially connected to the first transistor, and first and second active transistors respectively connected to collectors of the first and second transistors. Road, first
And a first differential amplifier including a first constant current source commonly connected to the emitters of the second transistor and a signal current input to the base of the first transistor, a third transistor, and a third transistor. A fourth transistor differentially connected to the transistor and having a base grounded; and a third transistor connected to the collectors of the third and fourth transistors, respectively.
And a fourth active load, a second constant current source commonly connected to the emitters of the third and fourth transistors, and a second differential amplifier outputting a signal current from the collector of the fourth transistor, , An operational amplifier that controls the base potentials of the second and third transistors so that the collector potential of the first transistor and the ground potential are the same, and the first and / or second constant current source Variable attenuator circuit characterized by being a variable constant current source. 3. The variable attenuator circuit according to claim 1 or 2, wherein a current conversion resistor for converting a signal voltage into a current and inputting the current into the base of the first transistor, and a signal output from the second differential amplifier. A variable attenuator circuit comprising: an inverting amplifier that converts a current into a voltage.