JPH0313111A - Voltage control attenuator - Google Patents

Abstract

PURPOSE:To reduce a circuit current and to simplify an RF part by forming whole diode connection between the bias voltage terminal of a pi type voltage control attenuator and grounding to be serially connected equivalent circuit. CONSTITUTION:Diodes D1-D3 are serially connected by the same polarity and a diode D4 is serially connected through a capacitor C4 to these diodes by the inverse polarity. The diode D3 is grounded through a capacitor C3 and the diode D4 is directly grounded. Then, a connecting point between the diode D3 and capacitor C3 is connected with a connecting point between the diode D4 and capacitor C4 by an induct L. Accordingly, all the diodes D1-D4 are serially connected for the direct current equivalent circuit and in this circuit, a bias voltage Vbias is impressed to the end part of the diode D1. Then, an attenuation quantity control voltage Vcont is impressed to a connecting point between the diodes D2 and D3. Thus, the circuit current can be decreased to be almost half. Since an attenuation quantity control voltage terminal can execute constant impedance operation in one spot, it can be realized to simplify the complicated RF part.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an attenuator for alternating current signals controlled by voltage or the like.
In particular, it relates to a π-type variable attenuator using a signal attenuation diode.

[Prior Art] Conventionally, this type of π-type voltage controlled attenuator has four signal attenuating diodes D, as shown in FIG.

~ D8 is used. That is, signal attenuation diodes D, each having the same polarity and connected in series.

D, and D are connected in series with opposite polarity.

Then, a DC bias voltage V bi, s is applied to the connection point of the diode D, and the attenuation control voltage ■6゜□ is applied to the connection point of each diode DS+D, , and D.
, and are connected to the high frequency input terminal RF,n and the output terminal RF,□ via capacitors C, , C, respectively.

In this configuration, the attenuation control voltage ■. . , from the input terminal RF, fi to the output terminal RF, .
It is possible to control the amount of attenuation of the AC signal.

At this time, as shown in Figure 4, the bias configuration is a parallel connection system of L wall voltage controlled attenuators driven by constant input impedance, so the DC bias applied to the signal attenuation diodes D and If the sum of the voltages Vs and V, and the sum of the DC bias voltages 6 and 8 applied to the signal attenuation diodes D6 and D6 are kept constant, that is, V
It is known that if hint is kept constant, the input/output impedance will be kept constant regardless of any change in attenuation.

[Problem to be solved by the invention]

The above-described conventional π-type voltage-controlled 1TfJ attenuator is, in principle, a parallel connection of L wall voltage-controlled attenuators, so the circuit current I2 needs to be approximately twice the current flowing through the diode D. Also, an attenuation control voltage V cost that controls the attenuation amount
Since two terminals are required to apply the voltage, there is a problem in that it becomes complicated to separate the bias circuit from an RF point of view.

SUMMARY OF THE INVENTION An object of the present invention is to provide a voltage-controlled attenuator that can reduce circuit current and simplify the RF section.

[Means for Solving the Problems] The voltage controlled attenuator of the present invention has first
The fourth attenuation diode is connected in series with the first diode through a capacitor with opposite polarity.

The third diode is grounded via a capacitor, and the fourth diode is directly grounded. Further, the connection point between the second and third diodes is configured as an attenuation control voltage terminal, the RF input terminal is connected via a capacitor, and the connection point between the first and fourth diodes is configured as a bias voltage terminal. and an RF output terminal via a capacitor.

Furthermore, the ground side of the third diode and the non-ground side of the fourth diode are connected via an inductor.

[Effect]

In this configuration, the DC equivalent circuit has first to fourth diodes connected in series, a bias voltage is applied to the end of the first diode, and an attenuation control voltage is applied to the connection point of the second and third diodes. This is the circuit to which the voltage is applied. Further, the RF equivalent circuit is a circuit in which three equivalent resistances are connected in a π type.

Thereby, the circuit current can be reduced, and constant impedance operation can be realized with one attenuation amount control voltage terminal.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention. In the figure, D and D are signal attenuation diodes, and diodes D1 to D are connected in series with the same polarity, and a diode D4 is connected in series with the opposite polarity via a capacitor C4.

And diode D.

is grounded via capacitor C8, and diode D4 is directly grounded. Also, take diode D2.

The connection point between the diodes DI and D4 is connected to the attenuation control voltage ■6°1 terminal, and the RF input terminal RFi is connected through the capacitor C1, and the bias voltage V b is connected to the connection point between the diodes DI and D4.
i @ I terminal, and the RF output terminal RF, □ is connected via the capacitor C1. And diode D
, and the connection point between the capacitor C1 and the connection point between the diode D4 and the capacitor C1 are connected through an inductor.

According to this configuration, the DC equivalent circuit becomes as shown in FIG. 2(a), in which all the diodes D, ~D4 are connected in series,
A bias voltage Vbi□ is applied to the end of the diode D1, and an attenuation control voltage V is applied to the connection point between the diodes D2 and D3.
This is the circuit to which C0FIL is applied. In addition, the RF equivalent circuit is as shown in Fig. 2(b), and the resistances R0 to R1 are set to π
It becomes a circuit connected to the mold.

Therefore, if we use diodes with the same characteristics for diodes D, ~D, then Vl - Vt V, = V.

Vb! a −−V + + V t + V 3
+Va. As a result, Vl - IV4 = ■z + V3 = VbL&s/2, so if ■bi□ is kept constant, v r + Va
, V, +V are kept constant, and the input/output impedance does not change even if the amount of attenuation changes.

In addition, in this circuit, by providing only one attenuation amount control voltage V Cant terminal for changing the amount of attenuation, the state of V, = ￥Z, V3 = V4 can be achieved, so the circuit can be simplified. It is possible. Furthermore, since the current flowing through diode D flows directly through diode D2, the circuit current r required to achieve the same amount of attenuation as the conventional circuit of FIG. 3 can be reduced to about 172 times the conventional circuit current r2.

[Effects of the Invention] As explained above, the present invention reduces the circuit current to about 172 cm by forming an equivalent circuit in which all the diode connections between the bias voltage terminal of the π-type voltage controlled attenuator and the ground are connected in series.
can be reduced to Furthermore, since constant impedance operation is possible with only one attenuation control voltage terminal for changing the attenuation, the complicated RF section can be simplified.

[Brief explanation of drawings]

1 is a circuit diagram of an embodiment of the present invention, FIG. 2(a) is a DC equivalent circuit diagram of the circuit in FIG. 1, and FIG. 2(b) is an RF equivalent circuit diagram of the circuit in FIG. 1. FIG. 3 is a circuit diagram of a conventional voltage controlled attenuator, and FIG. 4 is a DC equivalent circuit diagram of the circuit shown in FIG. D, ~D4. Di~D8...Diode, 01~
C6...Capacitor, L...Inductor, R3-R
3... Equivalent resistance, V b i Ill... Bias voltage, ■ゎ. □・・・Attenuation control voltage, RF,...
Input terminal, RFout...output terminal, 1. , I2...
・Circuit current. Figure 1: 8 (l) Minor image and bias voltage Figure 3 Vb: as Vcont (a) Figure 2 Figure 4

Claims (1)

[Claims] 1. It includes first to third attenuating diodes connected in series with the same polarity, and a fourth attenuating diode connected in series with opposite polarity to the first diode through a capacitor, and the third diode is connected to the capacitor. grounded through
The fourth diode is directly grounded and the second and third
The connection point between the first and fourth diodes is configured as an attenuation control voltage terminal, and an RF input terminal is connected through a capacitor, and the connection point between the first and fourth diodes is configured as a bias voltage terminal, and an RF input terminal is connected through a capacitor.
A voltage controlled attenuator, characterized in that the output terminals are connected, and the ground side of the third diode and the non-ground side of the fourth diode are connected via an inductor.