JPS581852B2 - Den Atsuseigi Yoga Takahentei Kogensuki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable resistance attenuator in which each variable arm of the variable resistance attenuator can be controlled by a common control voltage by means of a bridged T-network.

Bridged T-networks are widely used as variable resistance attenuators.

Its basic configuration is as shown in Figure 1, with input terminal 1
and output terminal 3 are coupled by two series resistors R0, a resistor R1 is coupled between the coupling point and ground, and a resistor R2 is coupled between terminal 1 and terminal 3.

If such a circuit is connected between a power source and a load each having an image impedance R0, and each impedance is selected to satisfy the condition R1・R2=r02(1),
This becomes a constant resistance circuit network, and the operational attenuation amount A due to this circuit network is A=loge(R2+R0)/R0(Naper)(2).

This bridge T-type circuit connects variable resistors to R1 and R2 that always satisfy the condition of equation (1), and is widely used as a variable resistance attenuator, but requires a special interlocking variable resistor. Therefore, it is unsuitable for use as a voltage-controlled type in automatic control systems, etc.

In order to compensate for this, some circuits have been constructed in which resistors R1 and R2 are each voltage-controlled variable resistors so that formula (1) is always satisfied, but this not only makes the circuit extremely complicated, but also The disadvantage is that the variation of is quite imperfect.

The present invention eliminates such drawbacks, and the above-mentioned resistor R
It is an object of the present invention to provide a variable resistance attenuator with a simple configuration and excellent characteristics by coupling a variable resistance circuit equivalent to the variable resistance circuit given as 1 as a resistor R2 via a gyrator.

This will be explained in detail with reference to the example drawings.

FIG. 2 is a circuit configuration diagram of an embodiment of the present invention.

In the figure, 1 and 2 are input terminals, 3 and 4 are output terminals, 5 and 6 are resistors with a resistance value R0, 7 and 8 are variable resistance circuits, 9 is a gyrator, and 10 is a control voltage generation circuit.

Two resistors 5 and 6 having a resistance value R0 are connected in series between terminal 1 and terminal 2, and terminal 1 and terminal 3 are led to a variable resistance circuit 7.

A connection point between resistors 5 and 6 and terminals 2 and 4 (ground potential) are connected to a variable resistance circuit 8 via a gyrator 9.

Both variable resistance circuits 7 and 8 are controlled by a signal voltage generated by a control voltage generation circuit 10.

Here, the gyrator 9 used has a four-terminal constant as shown in FIG.

That is, for the gyrator 8, the input and output voltage is u1
, u2, and the input/output current is i1+i2, then the impedance seen from the input side is: Here, if the same variable resistance circuits 7 and 8 are used and the resistance value is R1, equation (4) becomes, 1) formula is satisfied.

In this way, if the resistor R2 is connected via the gyrator 9 to the variable resistor circuit 8 equal to the resistor R1, the two equivalent variable resistor circuits 7 and 8 create a bridge T-type variable resistor attenuator. can be obtained.

FIG. 4 shows a more detailed circuit diagram of an embodiment of the present invention.

In the figure, each part is given the same reference numeral as in the configuration diagram shown in FIG. 2, but the configuration of each part is shown in detail.

The variable resistance circuits 7 and 8 are constructed by connecting an operational amplifier 71 and a field effect transistor 72 in series and providing resistance feedback.

If the value of the feedback resistor is chosen high, the field effect transistor 72
The current flowing through is almost constant, and stable operation is maintained.

The AC impedance between the drain and source of the field effect transistor 72 changes depending on the gate current.

An example is shown in which the gyrator 9 is composed of two resistors and one negative resistor.

The variable resistance circuits 7 and 8 are equal circuits, and a common control voltage provides the same equivalent resistance value.

As described above, according to the present invention, a voltage controlled variable resistance attenuator with a simple circuit configuration can be obtained.

Since the circuit of the present invention uses a single control signal voltage, it is suitable for automatic control systems.

Further, since the control signal voltage controls two equal circuits, there is no deviation in control characteristics with respect to the signal, and a wide range of control is possible.

Note that the variable resistance circuit, gyrator, and control voltage generation circuit described in the above description are not limited to these, and the present invention can be similarly implemented by using other circuits.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a bridging T-type variable resistance attenuator. FIG. 2 is a configuration diagram of an embodiment of the present invention. FIG. 3 is an explanatory diagram of the four-terminal constant of the gyrator. FIG. 4 is a circuit diagram of an embodiment of the present invention. 1, 2... Input terminal, 3, 4... Output terminal, 5, 6... Resistor (resistance value R.), 7, 8...・Variable resistance circuit, 9...
ginator, 10... control voltage generation circuit,
71... operational amplifier, 72... field effect transistor.

Claims (1)

[Claims] 1. A first terminal 1, a second terminal 2 that is paired with this terminal and serves as an input terminal and connected to a common potential point, and a third terminal 3, which is paired with this terminal. A fourth terminal 4, which serves as an output terminal and is connected to a common potential point, and two terminals connected in series between the first terminal 1 and the third terminal 3, each having a resistance value of R0. Resistance (5 and 6)
A first variable resistance circuit 7 connected between the first terminal 1 and the third terminal 3 and having a variable resistance value R1, and a connection point of the two resistors and a common potential point. and a second variable resistance circuit whose resistance value R2 is variable, and between the resistance values R0, R1 and R2, R1・R2=
In a variable resistance attenuator using a bridged T-type circuit network configured to satisfy R02, the first variable resistance circuit 7 has a resistance value R1 due to a DC voltage.
The second variable resistance circuit includes a gyrator 9 having a four-terminal constant, and a gyrator 9 connected in cascade to the gyrator 9 as the first variable resistance circuit 7. A voltage controlled variable resistance attenuator comprising a voltage controlled variable resistance circuit 8 which is a circuit equivalent to the voltage controlled variable resistance circuit used and which is commonly controlled by the above DC voltage.