JPH02156733A - High frequency attenuator with detector - Google Patents

Abstract

PURPOSE:To obtain an attenuation variable type high frequency attenuator by providing a lambda/4 line having the characteristic to the input and output side, connecting a parallel circuit comprising a PIN diode and an impedance element whose impedance is nearly equal to the characteristic impedance to the lambda/4 line and connecting a 3rd PIN diode between the start terminals of both the lambda/4 lines. CONSTITUTION:When the resistance R of PIN diodes D1-D3 is very low, since the impedance when viewing the lambda/4 lines l1, l2 from terminals a, b is infinite, the attenuation is minimized and when the resistance R of the PIN diodes D1-D3 is very high, the attenuation is a maximum. Then a signal entering from the input side is consumed in a termination resistor R1 equal to the characteristic impedance Z0 through the lambda/4 transmission line whose characteristic impedance is Z0. Since a detector 10 has a high input impedance, no circuit loss is caused therein.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a high frequency attenuator with a detector used in a radio circuit.

(Prior art) In a multi-stage high-frequency circuit, it is extremely difficult to achieve sufficient matching between each circuit.In a normal high-frequency circuit for radio equipment, one frequency is transmitted, so the frequency characteristics of each stage are flat. There is no problem even if the overall human output characteristics are flat, but in circuits where intermodulation occurs due to multi-frequency input, such as relay amplifiers, it is necessary to fully utilize the ability of the transistor as an amplification element. , the frequency characteristics of each stage must be made flat.

The above-mentioned ability of the transistor means that intermodulation does not occur as much as possible, and sufficient matching minimizes intermodulation products. This flattens the frequency response and
and to maximize the gain.

However, using transistors with inherently small intermodulation products will reduce circuit distortion even with poor matching, but transistors with small intermodulation products are expensive and have low DC input current. This has the drawback of increasing power consumption.

On the other hand, in direct repeating amplifiers that detect loop current, such as frequency offset repeaters, when the amount of loop loop increases, the gain of the amplifier is changed to keep the amount of loop loop constant, so it is essential to provide an attenuator. Also, an attenuator is required even when setting the relay gain according to the size of the service area.

In that case, it is impossible to insert all the attenuators in one place into the amplifier circuit due to the NF and distortion regulations of the repeater.

In other words, by inserting all attenuators in one place, it is necessary to reduce the distortion of the amplifier in front of the attenuator by the amount of attenuation, and in order to obtain a large amount of attenuation in one place, the distortion required of the transistor must be reduced. This is because the amount becomes too small to be realized. Therefore, as shown in FIG.
An attenuator will be inserted between each stage of the amplifier circuit. In addition, in FIG. 5, A, ~A, , are high frequency amplifiers, ATT
, , -ATT are high frequency attenuators (where m≦n),
However, in such a high-frequency amplification circuit, it is not preferable to use transistors with small intermodulation products in each amplification stage because this further increases the cost. Therefore, a high frequency attenuator that can easily bring out the potential of the transistor is needed.

By the way, variable attenuation type high frequency attenuators using PIN diodes whose high frequency resistance changes by changing the DC bias current have been known.

This type of high frequency attenuator has a circuit configuration as shown in FIG. 6, for example. In the figure, DI and D2 indicate PIN diodes having a resistance value R that changes depending on the bias current, and l is a J/4 line with a characteristic impedance Z0.

Further, C is a high frequency bypass capacitor and a DC blocking capacitor.

The circuit shown in Figure 6 requires a P[N diode D.

are connected in series in a direct current manner with polarity that allows the same bias current to flow from the common variable bias power supply circuit B, which has the advantage of simplifying the variable bias power supply circuit B, but there are also drawbacks as described below. .

Now, in the circuit shown in Fig. 6, its input impedance and output impedance are Zin and Zou, respectively.
If so, the impedance Z in.

Zout is expressed by (Equation 11 and Equation (2)), respectively.

Zin= ■ R+ Z e Z, R Zo + Z o + R) ”Z a ”'-----・ll Zout=R+ Za R Also, the attenuation amount L ass of this high frequency attenuator is as follows (3)
6 Loss -201! og (1+')
-------f31 As is clear from the above equation (1), the human power impedance Zin is equal to the characteristic impedance Z11 of the line, so no reflection of the input wave occurs, but the output impedance Zout is determined by the above equation (2). As is clear from the above, as the resistance R of the PIN diode becomes larger, the difference from the characteristic impedance Z0 becomes larger, and the reflection characteristics deteriorate.

When using such an attenuator with poor reflection characteristics,
For example, in Figure 7 (■
In a circuit like the one shown in Figure 8 (where 1 is a filter, 2 is an attenuator, and 2 is an amplifier), when both input and output are terminated with an impedance equal to the characteristic impedance, the characteristic curve of the filter 2 is as shown by the solid line in Figure 8. It becomes flat within the transmission band, but
When the human force reflection characteristics of the attenuator (■) are poor, it becomes wavy as shown by the broken line. Furthermore, when the output reflection characteristic is poor, if reflection is repeated between the attenuator (2) and the amplifier (2), the characteristic curve of the filter (2) similarly becomes wavy, and the deviation characteristic within the transmission band deteriorates.

(Object of the Invention) The present invention eliminates the drawbacks of the conventional high-frequency attenuator as described above, fully brings out the ability of the transistors in each amplification stage of a multi-stage amplifier, and provides a low-cost, low-current consumption high-frequency amplifier circuit. It is an object of the present invention to provide a high-frequency attenuator with a detector that can be configured.

(Structure of the Invention) The high-frequency attenuator with a detector of the present invention is provided with a λ/4 line with a characteristic impedance Z0 on the input side and an output side, and a characteristic impedance Z at the end of each of these λ/4 lines. Parallel circuits of impedance elements and PIN diodes having substantially equal impedance are connected, and a third PIN diode is connected between the starting ends of the input side and output side λ/4 lines,
A variable attenuation type high frequency device in which the above three PIN diodes are connected in series with direct current so that a common bias current can flow from a single variable bias power supply circuit, and the resistance value can be varied all at once. It is characterized by comprising an attenuator and a detector having a high input impedance connected to the terminal impedance element of the input side λ/4 line of the high frequency attenuator.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

In FIG. 1, the high-frequency attenuator has a λ/4 line with a characteristic impedance Z on its input and output sides, respectively! 1
．． It has 12. A resistor R+ equal to the characteristic impedance Z0 is connected between the terminal end of the input side λ/4 line 11 and the ground via a DC blocking capacitor C1. Further, the cathode of a first PIN diode D is connected to the terminal end of the input side λ/4 line fi, and the anode of this PIN diode D is connected to a variable bias power supply circuit via a high frequency blocking coil L. It is connected to the positive terminal of B and is also grounded via a high frequency bypass capacitor C1.

On the other hand, a resistor R1 equal to the characteristic impedance Z is connected between the terminal end of the output side λ/4 line 12 and the ground via a DC blocking capacitor Ct.
An N diode Dt is connected with its cathode connected to the ground side. Looking at this configuration from a high frequency perspective, there are resistors R1 and PI between the terminal end of the input side λ/4 line 11 and ground.
A parallel circuit with the N diode D1 is connected, and a parallel circuit with the resistor R8 and the PIN diode D2 is also connected between the end of the output side λ/4 line 1O and the ground. It turns out.

Moreover, a third PIN diode D is connected between the starting ends of the input side and output side λ/4 lines 11 and 12, and its anode is connected to the input side λ/4 line! is connected to the starting end side of , in such a manner that the cathode is on the starting end side of the output side λ/4 line 12,
As a result, the three diodes D, -D are connected in series in a DC manner with polarities that allow the same bias current from the common variable bias power supply circuit B to flow therethrough.

The bias current obtained from the variable bias power supply circuit B changes the resistance values of the PIN diodes D, -Ds all at once, thereby making it possible to change the amount of attenuation. FIG. 2 is a diagram showing the relationship between the resistance value R of the PIN diodes D1 to D5, the input/output impedance λ (denoted by VSWR), and the amount of attenuation. Further, the input impedances Z and R and the attenuation amount Loss of this circuit are 0 as shown by equations (4) and (5).Since the circuit is symmetrical, the input impedance and output impedance are equal.

Z i, l= (R+Z@) ,・・・・・−−−−−−・−(4)1n (R+Z*) 1・・・・・・・・・・・・−・−+51However ,R,=R
,=Z.

Furthermore, a detector 10 having a high input impedance is connected to a resistor R8 connected to the terminal end of the input side λ/4 line 1, so that a DC output can be obtained from this detector 10. FIG. 3 shows an example of the configuration of this detector 10, where D4 is a detection diode, C5 is a high impedance capacitor, C4 is a charging capacitor, R1 is a DC return resistor, and R4 is a discharge resistor.

The configuration of the high frequency attenuator with detector according to the present invention has been described above, and its operation will now be described.

When the t resistance R of the PIN diodes D, ~D, is extremely low, λ/
Since the impedance looking at the 4-line 11.12 is (to), the attenuation is the minimum, and the PIN diode D
When the resistance 4fiR of I""D y is extremely large, the amount of attenuation becomes maximum. In that case, even if there is reflection from the output side, it will be attenuated by the attenuator, so it will not return to the input side. The signal input from the input side passes through a λ/4 transmission line with a characteristic impedance Z0 and is consumed by a terminating resistor R1 equal to the characteristic impedance Z0. A detector lO is connected to this terminal resistor R6.
0 has high human power impedance, so there is no circuit loss.

When the high frequency attenuator with detector according to the present invention is inserted into the high frequency attenuator position of the circuit shown in FIG. 5, the result is shown in FIG. and the first
When adjusting the stage amplifier A1, the high frequency attenuator AT
The attenuation amount of T is maximized, and while monitoring the output of the detector 10, adjustments are made so that the frequency characteristics of the amplifier A1 are flat and the gain is maximized. Next, when adjusting the second stage amplifier At, minimize the attenuation amount of the high frequency attenuator ATT, and maximize the attenuation amount of the high frequency attenuator ATT. Adjust. Hereinafter, in a similar manner, amplifier A x ,
By adopting such an adjustment method in which it is only necessary to adjust -A n, the performance of the transistors of the amplifiers A1 to An can be fully utilized.

(Effects of the Invention) In the high-frequency attenuator with a detector according to the present invention, the high-frequency attenuator is provided with a λ/4 line with a characteristic impedance Z0 on the input side and an output side, and a characteristic impedance Z0 is provided at the end of each λ/4 line. A parallel circuit of an impedance element and a PIN diode having an impedance approximately equal to is connected, and a third PIN diode is connected between the starting ends of both λ/4 lines, and the three PIN diodes D
1 to D are connected in series in a DC manner with polarity such that a common bias current can flow from a single variable bias power supply circuit, and the resistance value can be varied all at once. Not only can you obtain a variable-attenuation high-frequency attenuator with extremely good reflection characteristics by simply adjusting the bias current, but you can also adjust the amplifier circuit in the preceding stage while monitoring it with the detector attached to this high-frequency attenuator. Therefore, the ability of the transistor in the amplifier circuit can be fully utilized. Therefore, it is possible to use transistors with low cost and low current consumption, which results in low cost and low current consumption.
A high frequency attenuator with low current consumption can be constructed.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of one embodiment of the present invention, Figure 2 is a PI'N
A graph showing the relationship between diode resistance and attenuation, Figure 3 is a circuit diagram of a detector, Figure 4 is a block diagram of a high frequency attenuator to which the present invention is applied, and Figure 5 is a general attenuator equipped with an attenuator. 6 is a circuit diagram of a conventional high frequency attenuator, FIG. 7 is a block diagram of a high frequency circuit equipped with a filter and an attenuator, and FIG. 8 is a diagram showing its filtering characteristics. It is. Dl, D2, D,...-PIN diode 11, ff
i, -・λ/4 line line - variable bias power supply circuit

Claims (1)

[Claims] Characteristic impedance Z_ on the input side and output side, respectively.
A parallel circuit of an impedance element having an impedance approximately equal to the characteristic impedance Z_0 and a PIN diode is connected to each end of each of these λ/4 lines, and the input side and the output side A third PIN diode is connected between the starting ends of the side λ/4 line, and the three PIN diodes are connected in series in direct current with polarity such that a common bias current can flow from a single variable bias power supply circuit. a variable-attenuation high-frequency attenuator configured so that the resistance value can be varied all at once; A high frequency attenuator with a detector, which is characterized by consisting of a detector.