JPS6238347Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a control circuit that controls the amount of attenuation of a variable attenuator using semiconductor elements such as diodes and transistors.

Generally, a variable attenuator using semiconductor elements such as diodes and transistors is used to adjust the gain of television public listening amplifiers and the like.

Conventionally, there are various types of variable attenuators such as bridge T-type attenuators, π-type attenuators, and T-type attenuators. For example, Figure 1 shows the circuit configuration of a bridge T-type attenuator using diodes. It is something. In the figure, 1 is a signal input terminal, 2 is a signal output terminal, and 3 is a control voltage terminal. In addition, 4 to 6 are coupling capacitors, 7 is a bypass capacitor, and 8 and 9 are diodes whose resistance value changes greatly depending on the passing current, such as a PIN diode.
10 to 12 are bias resistors for determining the bias voltage of the PIN diodes 8 and 9, respectively; 13;
14 is a resistor for impedance matching, and 15 is a bias power supply terminal.

This bridge T-type attenuator is well known,
Each circuit constant is determined appropriately, a DC voltage E ₁ is applied to the bias power supply terminal 15, and a DC voltage E ₂ is applied to the control voltage terminal 3 as a control voltage. In this case, E ₁ is a fixed voltage and its polarity is negative, and E ₂ is also negative in polarity and smaller in magnitude than E ₁ . When this control voltage _E2 is changed, the current flowing through the PIN diodes 8 and 9 changes,
Since the resistance value changes, the amount of attenuation between input terminal 1 and output terminal 2 changes. That is, |
At E ₂ ｜=｜E ₁ ｜, the amount of attenuation is minimum,
|E ₂ |＜|E ₁ |That is, as |E ₂ | becomes smaller than |E ₁ |, the attenuation begins to increase, and |E ₂ |=
At 0, the amount of attenuation is maximum.

By the way, a variable resistor has conventionally been used as a control circuit that supplies the control voltage _E2 , but
As this variable resistor, a B-type variable resistor VR in which the relationship between rotation angle and resistance value changes linearly as shown in FIG. 2 is generally used. In the figure, 21 is a bias power supply terminal connected to the bias power supply terminal 15 of FIG. 1, 22 is a slider of a variable resistor VR connected to the control voltage terminal 3 of FIG. 1, and 23 and 24 are This is a ground terminal. Also, R ₁
is the resistance for setting the minimum attenuation amount.

The control voltage E ₂ supplied from this control circuit changes linearly as shown by A in FIG.

On the other hand, in a variable attenuator using a semiconductor (for example, a diode), the relationship between the control voltage and the attenuation amount changes in a curve (for example, logarithmically) depending on the voltage-current characteristics of the semiconductor. For this reason, variable resistance
The relationship between the rotation angle of VR and the amount of attenuation is curved as shown by A in Figure 4. That is, variable resistance VR
When a control voltage that changes directly with respect to the rotation angle is applied, the amount of attenuation expressed in decibels shows a curved change.

Therefore, when adjusting the gain of an amplifier that has an attenuator with such characteristics, near the maximum gain point the gain change is small relative to the rotational change of the control variable resistor VR, and conversely, when the gain is at the minimum point, the gain change is small relative to the rotational change of the control variable resistor VR. Near this point, the amount of gain change relative to the amount of rotational change increases, resulting in poor gain adjustment operability.

One way to solve this problem is to use a variable resistor with curve-changing characteristics, but at present, such variable resistors have many restrictions on shape, material, etc., and have low marketability.

This idea was made in view of the above circumstances,
The purpose of this is to provide a control circuit for a variable attenuator that can correct the decibel attenuation change characteristic with respect to rotation angle when using a variable resistor with a linear change characteristic in an inexpensive and simple manner, and improve the operability of gain adjustment. Our goal is to provide the following.

An embodiment of this invention will be described below with reference to the drawings.

In FIG. 5, one end a of a fixed terminal of a variable resistor VR is connected to the bias power supply terminal 31 at the negative output end of the DC power source _E1 . This variable resistance
A fixed resistor R ₁ for setting the minimum attenuation amount is connected between the other end b of the fixed terminal of VR and the ground terminal 32 of the positive output end of the DC power source E ₁ . Further, a resistor R ₂ is connected between the other end b of the variable resistor VR and the slider 33 thereof.

In other words, this control circuit can be configured as a variable resistor by adding a fixed resistor _R2 to the control circuit shown in Figure 2.
The control voltage E ₂ obtained between the VR slider 33 and the ground terminal 34 is made to have a characteristic close to a curved (logarithmic) change as shown in FIG.
As a result, the change in the amount of attenuation of the variable attenuator with respect to the rotation angle of the variable resistor VR is corrected to an operation that approaches a linear change as shown by B in FIG.

Therefore, by controlling the attenuation amount of the variable attenuator using this control circuit, controlling this variable attenuation amount, and adjusting the gain of the amplifier etc. using this variable attenuator, the maximum and minimum points of gain can be adjusted. However, the amount of change is made uniform, and the operability of gain adjustment is improved.

In the above embodiment, the fixed resistor _R2 is used as the resistor connected between the slider 33 of the variable resistor VR and the fixed terminal, but it goes without saying that a variable resistor may be used instead.

As described above, according to this invention, in the control circuit of a variable attenuator using a conventional semiconductor element, a fixed resistor or a variable resistor is connected between the fixed terminal of the variable resistor and the slider, and the variable resistor is Since the control voltage is changed in a curved manner with respect to the rotation angle, it is possible to correct the change in attenuation amount in the variable attenuator with respect to the rotation angle to a linear change, which greatly improves the operability of gain adjustment of amplifiers, etc. improve.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram of a variable attenuator using a diode, Fig. 2 is a conventional control circuit configuration diagram of the variable attenuator, Fig. 3 is a control voltage characteristic diagram with respect to the rotation angle of the variable resistor, and Fig. 4 5 is a characteristic diagram of the attenuation amount of the variable attenuator with respect to the rotation angle of the variable resistor, and FIG. 5 is a configuration diagram of a control circuit according to an embodiment of this invention. 31...Bias power supply terminal, 32, 34...
...Ground terminal, 33...Slider, E ₁ ...DC power supply, VR...Variable resistance, R ₁ ...Fixed resistance, R ₂ ...
Fixed resistance.

Claims (1)

[Scope of utility model registration request] A control circuit that supplies a voltage for controlling the amount of attenuation in a variable attenuator using a semiconductor element includes a DC power source, a variable resistor with one end of a fixed terminal connected to one output end of the DC power source, and a variable resistor that has one end of a fixed terminal connected to one output end of the DC power source. A fixed resistor connected between the other end of the fixed terminal and the other output end of the DC power supply, and a resistor connected between the other end of the fixed terminal of the variable resistor and its slider. . A control circuit for a variable attenuator, characterized in that the control voltage is obtained between the other end of the DC power supply and the slider of the variable resistor.