JPS5937889B2 - Variable attenuator circuit using PIN diode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable attenuator circuit using a PIN diode.

A typical attenuator circuit using a PIN diode is the π-type circuit shown in FIG.

The attenuation amount is obtained by changing the impedance by changing the bias applied to the diode, and FIG. 1 shows its high frequency circuit.

1.2.3 are PIN diodes, and their respective impedances are Zl, Z2. Let's call it Z3.

Further, 5 is a signal source resistance Rs, and 6 is an output end resistance RL.

The attenuation α of the π-type circuit is +RL) becomes.

Therefore, in order to obtain the amount of attenuation, IZll must be thick 1
It is sufficient to reduce Z21.1Z31 and increase IZ12.

In order to obtain a large amount of attenuation, it is necessary that PIN diode 1 be reverse biased and PIN diode 2 and 3 forward biased.

Figure 2 shows the equinodal circuit of each diode at that time.

Resistors 7 and 9゜11 are Ro, R2, R3, and capacitance 8, respectively.
Letting cl be cl, and the coils 10 and 12 be R2 and R3, it will be 10jwL3.

Here, R2 and R3 include lead inductance.

To reduce 1Z21.1zsl in order to obtain sufficient attenuation, the resistance components R2 and R3 and the inductance component L2. L
3 can be made smaller, but usually L2. L3 is 3-4nH
Therefore, the influence of the inductance component is large especially in the UHF band, and there is a drawback that at a resistance value below a certain value, even if the resistance component is made small, it will not contribute to the amount of attenuation.

Therefore, in order to obtain a sufficient amount of attenuation, it is necessary to eliminate the influence of the L component.

An object of the present invention is to eliminate the above-mentioned drawbacks and provide an attenuator circuit that can obtain sufficient attenuation in all frequency regions of the VHF band and the UHF band.

The present invention is characterized in that the influence of strain inductance is eliminated by connecting a capacitor in series with the diode to cause series resonance.

An embodiment of the present invention is shown in FIG. 3, and the invention will be explained in detail using this embodiment.

In the figure, parts that are the same as those in FIG. 1 are designated by the same reference numerals.

13 is a capacitor inserted to cause series resonance with the strain inductance of the diode 3.

If this capacitance is C, it becomes a series impedance of the diode 3 and the capacitor 13, and at frequencies around f, the impedance of Z3 becomes smaller and the amount of attenuation becomes larger than before inserting C.

In this case f. At sufficiently lower frequencies, the impedance increases and the amount of attenuation decreases, but since a sufficient amount of attenuation can be obtained at frequencies that are already low, there is no problem even if the amount of attenuation decreases.

In other words, by inserting a capacitor that resonates with the strain inductance at high frequencies, you can obtain an average attenuation amount over a wide band from low frequencies to high frequencies (for example, when used in a TV tuner, from the VHF band (up to the JHF band)). Can be done.

FIG. 4 shows this effect in this embodiment, and it can be seen that the attenuation amount is averaged over a wide band and that a sufficient amount of attenuation is obtained even at high frequencies.

(The solid line indicates the case where the capacitor 13 of this embodiment is connected, and the broken line indicates the case where it is not inserted.

) Note that it goes without saying that the same effect can be obtained not only by connecting a capacitor in series with diode 3 as in this embodiment, but also by inserting a capacitor in diode 2 or both. be.

Further, the same effect can be obtained not only in the π-type circuit as in the embodiment but also in any attenuator circuit in which a diode is connected between the signal line and the ground.

Therefore, the amount of attenuation in the high frequency band of the PIN attenuator can be greatly improved with a simple circuit in which capacitors are connected, and furthermore, the amount of attenuation can be averaged over a wide band.

Furthermore, in conventional examples, it is common to use a bypass capacitor for DC cutting between the diode and the ground, and the capacitor is designed to minimize the influence of strain inductance. A leadless bypass capacitor such as a bare disk was used, but according to the present invention, it can be implemented by simply changing the bypass capacitor to a capacitor that resonates near the receiving frequency band, and even a capacitor with leads can be used. Therefore, it also leads to cost reduction.

[Brief explanation of drawings]

Figure 1 shows a high-frequency circuit of a π-type attenuator circuit using a PIN diode, Figure 2 shows an equivalent circuit of a PIN diode π-type attenuator high-frequency circuit with sufficient attenuation, and Figure 3 shows the circuit of Figure 1. FIG. 4 shows the frequency characteristics of the attenuation amount when a series resonant capacitor is added and when the series resonant capacitor is not added. 1.2,3...Pin diode, 13...
...Series resonance capacitance.

Claims (1)

[Claims] 1. A high-frequency variable attenuator that is equipped with one or more PIN diodes between a high-frequency signal line and the ground, and that controls attenuation by changing the impedance of the diodes through direct current control, in which at least one PIN diode is connected in series with at least one of the diodes. A variable attenuator circuit characterized in that the amount of attenuation of high frequencies within a receiving frequency band is improved by connecting a capacitor that resonates with the strain inductance of a diode.