JPS62200809A - Voltage controlled variable attenuator - Google Patents

Abstract

PURPOSE:To realize a stable voltage controlled variable attenuator with less fault and simple constitution by constituting the variable attenuator with a PIN diode and adjusting at least one voltage impressed to said PIN diode so as to control the attenuation. CONSTITUTION:A T-shaped circuit network is constituted of series circuits T1, T2 and T3 each comprising a resistor (r) and a diode, especially a PIN diode D having an i-region between pn regions to decrease the junction capacitance, and series capacitors C1, C2 are provided respectively to a signal input terminal I and a signal output terminal O of said circuit network. In changing the control voltage Vc with respect to a voltage Vcc, the resistance of the PIN diodes D1, D2 is decreased or increased at the same time and the resistance of PIN diode D3 is increased or decreased conversely. Thus, the attenuation is changed while keeping the input/output impedance constant.

Description

[Detailed Description of the Invention] [Summary] By configuring a T-type three-terminal network using a diode as a variable resistance element, the amount of attenuation can be controlled simply by changing at least one control voltage supplied to the diode. This is a voltage controlled variable attenuator.

[Industrial application field]

The present invention relates to a voltage-controlled variable attenuator that is widely used as a circuit network for controlling the amount of attenuation of a signal.

[Conventional technology]

BACKGROUND ART Conventionally, a T-type variable attenuator has been known which has a mechanical configuration in which three variable resistors VR1, VH2, and VH2 are linked together as shown in FIG.

In the conventional type, variable resistors VR1, VH2, V
H2 is linked to change the resistance value to adjust the attenuation amount, but in order to change the attenuation amount without changing the input/output impedance Z, the above variable resistor VR1
It was necessary to adjust the resistance value of yVRg and the resistance value of VH2 so that they had a relationship as shown in FIG. In other words, in order to keep the input and output impedance Z constant, the respective resistance values are VRl - VH2 = 1 + 2m VH2 = m (VR+ +Z) (however, the voltage gain is expressed as AV% attenuation in X (dB)). [Problems to be solved by the invention] The conventional T-type variable attenuator as described above uses three interlocking variable resistors, and these variable resistors have mechanical contact parts. Therefore, it is easy to cause damage and is mechanically complicated, and in the case of a block configuration, it is necessary to use a screwdriver or the like to adjust the attenuation amount.

Furthermore, in order to automatically electrically control the amount of attenuation, a drive motor is required, resulting in the problem of an increase in the size of the device.

The present invention aims to provide a voltage-controlled variable attenuator that can electrically control the amount of attenuation, has no mechanical contact parts, and has stable operation.

[Means for solving problems]

In order to solve the above-mentioned conventional problems, the present invention has the following objectives:
As shown in the principle diagram in the figure, three diodes D1g D2 gD3 whose resistance value changes depending on the applied voltage are used to
These diodes constitute a variable attenuator of the form Dl −0
2. The amount of attenuation is controlled by changing at least one voltage of Vcc or Vc applied to D3.

[For production]

As shown in Figure 3, the diode operates as a resistor that has voltage dependence on the forward current and therefore on the applied voltage.
The amount of attenuation in the variable attenuator is controlled by controlling the resistance value of the diode by adjusting the voltage applied to the diode.

〔Example〕

FIG. 2 shows an embodiment of the present invention, in which a series circuit T+, T
2, T3 constitutes a T-shaped circuit network, and a series capacitor C1 is connected to the signal input terminal I and signal output terminal 0 of the circuit network.
, Ca are provided, and a voltage Vcc is applied between the capacitors C1 and C2 and the series circuits T1 and T2 of the above-mentioned resistors and PIN diodes through respective resistors R1. A control voltage Vc for controlling the amount of attenuation is applied to the midpoint of the network via a resistor R2.

In the above embodiment, the PIN diodes DI, D2
The resistance value of the PIN diode D3 decreases or increases at the same time, and the resistance value of the PIN diode D3 increases or decreases in the opposite direction, so that the resistance VRI in the known T-type attenuator shown in FIG.
, VR2 and VH2, the amount of attenuation can be changed while keeping the input/output impedance constant by increasing or decreasing the resistance value of the variable resistance element connected in series with the variable resistance element connected in parallel.

In the above embodiment, the attenuation amount is adjusted by applying the control voltage Vc, but Vcc or Vc
, Vcc may be varied as control voltages.

〔Effect of the invention〕

As explained above, the present invention configures a variable attenuator using a PIN diode, and controls the amount of attenuation by adjusting at least one voltage applied to the PIN diode, so no mechanical parts are used. Therefore, it is possible to obtain a voltage-controlled variable attenuator that is stable, has few failures, and has a simple configuration.

[Brief explanation of drawings]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is a circuit configuration diagram showing an embodiment of the invention, Fig. 3 is a current-resistance characteristic diagram of a diode, and Fig. 4 is a configuration showing a conventional variable attenuator. FIG. 5 is a diagram showing the relationship between the attenuation amount and the resistance value in the conventional example. Dl, D2, D3...diode, rl,
r2 yγ3, R1, R2-resistance, V cc...
Fixed potential, Vc... Control voltage for controlling the amount of attenuation. Saki 9: Bar 1 Fig. 4'-kIEf-@*4fL*'r'E (at) Fig. 5

Claims (1)

[Claims] Diodes (D_1, D_2) connected in series in opposite directions between the input terminal (I) and the output terminal (O), and a diode (D_3) connected between the connection point of the diodes (D_1, D_2) and ground. and means for supplying equal first voltages (Vcc) to the connection points between the input terminal (I), the output terminal (O), and the diodes (D_1, D_2), and the three diodes (D_1, D_2, D_3
) for supplying a second voltage (Vc) to the connection point of the first voltage (Vcc) or the second voltage (Vc).
A voltage controlled type characterized in that the diode (D_3) is connected so that when at least one of c) is changed, the resistance value decreases or increases inversely to the increase or decrease in the resistance value of the diodes (D_1, D_2). Variable attenuator.