JPH0239715A - Reflection type variable resistance attenuator - Google Patents

Abstract

PURPOSE:To eliminate the need for a special current limit adding circuit by serially connecting a resistance having a resistance value equal to the characteristic impedance of a 90 deg. hybrid serially with a PIN diode. CONSTITUTION:Resistances 8 and 9 having a resistance value equal to the characteristic impedance of a 90 deg. hybrid circuit 1 are serially inserted between respective coupling port 3, passing port 4 and PIN diodes 6 and 7. Thus, a bias current value necessary to one attenuating quantity has only one value and consequently, at the time of using for an automatic gain control circuit, etc., a special added circuit for the bias current limit is not made necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a variable resistor, and more particularly to a highly stable reflective variable resistance attenuator composed of a 90 degree hybrid and a PIN diode.

(Prior Art) Variable resistance attenuators are widely used in various electronic devices as means for attenuating an input signal by an arbitrary amount. among them,
A variable resistance attenuator using a PIN diode as a variable resistor for signal attenuation is one of the typical types as it has little change in capacitance. Attenuation by a PIN diode utilizes the fact that the resistance value of the PIN diode changes depending on the magnitude of the bias current flowing therethrough, and a desired amount of attenuation can be obtained by adjusting the bias current.

FIG. 5 shows an example of a reflective variable resistance attenuator using this type of PIN diode, and its basic components are a 90-degree reflective hybrid circuit 1, a PIN diode 6.7, and choke coils Ll and L2. . The resistance value of the PIN diode 6.7 is supplied from the terminal 10 and the choke coil Ll.

regulated by the bias current flowing through L2,
The 90 degree hybrid circuit 1 has an input port 2 and an output port 5. It has a coupling port 3 and a passage port 4 that serve as connection terminals with the PIN diode 6.7. The relationship between the bias current and the signal attenuation amount in such a reflective variable resistance attenuator is as shown in FIG.
．． 7 resistance impedance is 90 degrees hybrid circuit 1
The amount of attenuation becomes maximum when the bias current BO becomes equal to the characteristic impedance of .

(Problem to be Solved by the Invention) The attenuation characteristic showing the relationship between the bias current and the amount of attenuation of the conventional reflective variable resistance attenuator described above is a symmetrical curve as shown in FIG. , tA has two values, B1 and 82, for the bias current. Moreover, the amount of attenuation at each bias current value B1 and 82 has both an increasing direction and a decreasing direction, so if this attenuator is used as an automatic gain control circuit or an automatic level control circuit, the operation will become unstable. . Therefore, conventionally, in order to use only one current value range, it was necessary to provide an additional circuit for limiting the bias current value M range to be used, which resulted in a complicated circuit and an increase in cost.

(Means for Solving the Problems) A reflective variable resistance attenuator according to the present invention includes a 90-degree hybrid circuit having an input port, an output port, a coupling port, and a passing port, and a 90-degree hybrid circuit whose resistance value changes depending on a bias current. and a characteristic impedance of the 90 degree hybrid circuit, which is inserted in series between the first and second PIN diodes, the coupling port and the first PIN diode, and between the pass port and the second PIN diode, respectively. and a bias current supply circuit that supplies the bias current to the PIN diode.

(Example) Hereinafter, an actual 7m example of the present invention will be described in more detail with reference to the drawings.

Fig. 1 shows a circuit showing an embodiment of the present invention, and the same elements and circuits as the conventional circuit shown in Fig. 5 are indicated using the same symbols. The device is 90 degree hybrid circuit 1, PIN die board 6
．． 7. It includes choke coils L1 and B2, and a bias current is supplied from a terminal 10 to the PIN diode 6.7 in order to adjust the resistance value (conductance) thereof.

The 90-degree hybrid circuit 1 has input ports 2. The coupling port 39 includes a passage port 4 and an output port 5. The reflective variable resistor according to the present invention further includes a resistor 8.9 having a resistance value equal to the characteristic impedance of the 90 degree hybrid circuit 1 connected in series between each of the coupling port 31 passing port 4 and the PIN diode 6.7. It is inserted.

In a reflective variable resistance attenuator with such a configuration, the PIN
It is clear that the resistance values of the series circuit of diode 6 and resistor 8 and the series circuit of PIN diode 7 and resistor 9 change from zero to 50 ohms for a change in bias current from zero to infinity.

As a result, the attenuation characteristic that shows the relationship between the amount of signal attenuation and the amount of attenuation, as shown in FIG. It has only one value, and therefore does not require a special additional circuit for limiting bias current even when used in an automatic gain control circuit or the like.

3 and 4 are circuit diagrams showing other embodiments of the present invention, the basic configurations of which are the same as the embodiment shown in FIG. 1, except that the bias current to the PIN diode 6.7 is The supply methods are different. In other words, in the embodiment shown in FIG.
2 and is supplied via the 90 degree hybrid circuit 1.

On the other hand, in the embodiment shown in FIG. 4, the choke coil Ll,
L2 is connected to the connection points of the resistors 8 and 9 and the PIN diode 6.7, and bias Th K is supplied from the terminal 10 via these choke coils.

(Effects of the Invention) As explained above, in the present invention, the PIN diode and 9
In a reflective variable resistance attenuator using a 0 degree hybrid circuit, the bias current required for one amount of attenuation can be reduced by simply connecting a resistor with a resistance value equal to the characteristic impedance of the 90 degree hybrid in series with the PIN diode. Since only one value is determined, there is no need for a special current limiting circuit for limiting the range of bias current values as in the prior art, which simplifies the circuit and reduces costs.

-6,7...PIN diode, 8.9...Resistor -10...Bias terminal.

Claims (1)

[Claims] a 90-degree hybrid circuit having an input port, an output port, a coupling port, and a passing port; first and second PIN diodes whose resistance values change depending on a bias current; and the coupling port and the first PIN diode. first and second resistors each having a resistance value equal to the characteristic impedance of the 90-degree hybrid circuit, which are inserted in series between each other and between the pass port and the second PIN diode, and the bias applied to the PIN diode. A reflective variable resistance attenuator comprising a bias current supply circuit that supplies current.