JPH0210666Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a variable attenuator using a PIN diode used for gain control of a wideband variable gain amplifier.

[Conventional technology]

The gain of a variable gain amplifier whose gain control unit is a variable attenuator equipped with a PIN diode is controlled by changing the bias current of the PIN diode using an automatic gain control circuit equipped with an operational amplifier, a transistor, and the like. FIG. 3 is a connection diagram showing the configuration of this variable attenuator and automatic gain control circuit.

[Problem that the invention attempts to solve]

Now, although this variable attenuator 300 is configured so that the amount of attenuation decreases when the potential of the control voltage terminal 304 is high, the automatic gain control circuit 5
When this control voltage is lowered using 00, the bias current Ib flows into the drive source resistor 520, so that the control voltage does not fall below a certain value. This has the disadvantage that the variable range of the bias currents of the PIN diodes 310 and 311 is narrowed, and the dynamic range of the variable gain amplifier is narrowed.

The present invention eliminates these drawbacks,
It is an object of the present invention to provide a variable attenuator used as a gain control section of a variable gain amplifier that increases the dynamic range of the variable gain amplifier.

[Means for solving problems]

The present invention includes a gain control circuit that provides a variable DC bias current, and a first path that is inserted into a first path from a high-frequency signal input terminal to a high-frequency signal output terminal and is biased by the output current of the gain control circuit. a PIN diode, and a second PIN inserted in a second path connected in parallel to the first path and biased by the output current of the gain control circuit.
A variable attenuator including a diode and a bias resistor that is connected to a common potential from the output side of the first PIN diode and serves as a path for the bias current. It is characterized by having a third PIN diode connected in series with the PIN diode.

[Effect]

When the control voltage applied to the variable attenuator is reduced by the gain control circuit, the amount of attenuation of the variable attenuator increases, but the range in which the amount of attenuation can be varied is narrowed by the lowest limit value of this control voltage. By the operation of the PIN diode connected in series with the bias resistor, a state equivalent to a state in which the control voltage is lowered is realized, and the attenuation variable range is expanded.

〔Example〕

Hereinafter, an embodiment of the present invention will be explained based on the drawings.

FIG. 1 is a connection diagram showing the configuration of a circuit according to a first embodiment of the present invention, and FIG. 2 is a connection diagram showing the configuration of a circuit according to a second embodiment of the present invention.

First, the configuration of the circuit of the first embodiment will be explained based on FIG. This embodiment circuit has an input terminal 101
, an output terminal 102 , a control power supply terminal 103 ,
Control voltage terminal 104 and first PIN diode 1
10, a second PIN diode 111, a first bias resistor 120, and a second bias resistor 12
1, a third bias resistor 122, a first coupling capacitor 130, and a second coupling capacitor 13
1, a third coupling capacitor 132, and an automatic gain control circuit 500.

Input terminal 101 is connected to first coupling capacitor 130
is connected to one pole of the first capacitor 130
The other pole of is connected to the anode of the first PIN diode 110, the cathode of the first PIN diode 110 is connected to one pole of the second coupling capacitor 131, and the other pole of the second coupling capacitor 131 is connected to the anode of the first PIN diode 110. It is connected to the output terminal 102. The control voltage terminal 103 is connected to the anode of the second PIN diode 111, and the cathode of the second PIN diode 111 is connected to one end of the third bias resistor 122 and one pole of the third coupling capacitor 132. Ru. The other pole of the third coupling capacitor 132 is connected to the first coupling capacitor 130 and the first PIN.
It is connected to the connection point of the diode 110, and this connection point is connected to one end of the second bias resistor 121. The other end of the second bias resistor 121 and the other end of the third bias resistor 122 are connected to the control voltage terminal 104.

Control voltage terminal 104 is connected to automatic gain control circuit 500
The drive source resistor 520 has the other end connected to a common potential. The connection point between the first PIN diode 110 and one pole of the second coupling capacitor 131 is connected to one end of the first bias resistor 120, and the other end of the first bias resistor 120 is connected to the first bias resistor 120. It is connected to the anode of a characteristic level shift diode 150, and the cathode of the level shift diode 150 is connected to a common potential.

Next, the operation of this embodiment circuit will be explained based on FIG.

The circuit of the first embodiment is a variable attenuator with an L-shaped configuration, and in this circuit, the amount of signal attenuation between the input terminal 101 and the output terminal 102 increases as the potential of the control voltage terminal 104 decreases. On the other hand, bias current Ib
The potential corresponding to the voltage drop across the drive source resistance 520 caused by this is the lowest potential Va at the control voltage terminal 104.
It is. However, when the amount of attenuation increases, the level shift effect of the level shift diode 150 realizes a state equivalent to a state in which the control voltage becomes a potential lower than the lowest potential Va.

FIG. 4 shows this state, where the value on the horizontal axis corresponds to the control voltage value at the control voltage terminal 104, and the value on the vertical axis corresponds to the amount of attenuation. The characteristic curve shown by a solid line shows the characteristic of this example device, and the characteristic curve shown by a broken line shows the characteristic of the conventional example device. The attenuation variable range of the conventional example device is the range of attenuation amount a and attenuation amount b, and the attenuation amount variable range of this embodiment device is the range of attenuation amount a and attenuation amount c. It is shown that it is enlarged.

Next, the second embodiment circuit is a variable attenuator with a bridged T-type configuration, and the operating principle in this circuit is the same as that of the first embodiment circuit.

[Effect of idea]

As explained above, by adding simple parts to the variable attenuator, the present invention can improve the variable range of the variable attenuator without changing the automatic gain control circuit that outputs the control voltage of this attenuator. It has a remarkable effect on expanding the

[Brief explanation of the drawing]

FIG. 1 is a circuit connection diagram showing the configuration of a device according to a first embodiment of the present invention. FIG. 2 is a circuit connection diagram showing the configuration of a device according to a second embodiment of the present invention. FIG. 3 is a circuit connection diagram showing the configuration of a conventional device. Figure 4 is an operating characteristic diagram. 100, 200, 300...variable attenuator, 10
1,201,301...Input terminal, 102,20
2,302...Output terminal, 103,203,30
3... Control power supply terminal, 104, 204, 304...
...Control voltage terminal, 110, 111, 210, 21
1,310,311...PIN diode, 500
...Automatic gain control circuit.

Claims (1)

[Claims for Utility Model Registration] A gain control circuit that provides a variable DC bias current; and a gain control circuit that is inserted into a first path from a high-frequency signal input terminal to a high-frequency signal output terminal and that is biased by the output current of the gain control circuit. a second PIN diode inserted into a second path connected in parallel to the first path and biased by the output current of the gain control circuit; a bias resistor connected to a common potential from the output side of the diode and serving as a path for the bias current, a third variable attenuator connected in series with the bias resistor;
A variable attenuator characterized by being equipped with a PIN diode.