JPS6057728B2 - variable resistance attenuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable resistance attenuator with a wide variable range and good input matching characteristics.

Variable resistance attenuators are widely used in various electronic devices and communication devices as means for attenuating an input signal by an arbitrary amount. FIG. 1 shows an implementation example of a variable resistance attenuator using a PIN diode as a variable resistance.

The resistance value of PIN diode 1 is Rx) The resistance value of fixed resistors 2 and 3 is R, , R, respectively. , the resistance value of load resistor 4 is R
. Then, the voltage transfer function T between the input terminal pair 5, 6 and the output terminal pair 7, 8 is Ro1R.

It is expressed as T■Rx+Ro1R2゜゜゜゜゜゜゜(1).

The symbol 1 used in this description represents a resistance value when two resistance values are used in parallel. Also, the resistance value R is applied to the output terminal pair 7 and 8.
. The input impedance Zi seen from the input terminal pair 5 and 6 when a load resistor is connected is Zi■R,1(Rx+Ro
1R.

) ...(2). In addition, 9 and 10 are PI
This is a capacitor that prevents the DC bias current of the N diode from flowing into other circuit elements. Since the resistance value Rx of the PIN diode 1 changes depending on the current flowing therein, the amount of attenuation of the input signal can be arbitrarily changed according to equation (1). However, since the variable resistance attenuator is an L-shaped circuit, the input impedance changes as Rx changes according to equation (2). Therefore, it is impossible to achieve impedance matching with an external circuit at the input point. Therefore, if Rx is varied within a range with good input impedance matching and used as a variable resistance attenuator, the variable range of the amount of attenuation becomes a small value. Figure 2 shows a bridge T-type circuit, which is well known as a variable resistance attenuator that has a wide variable range of attenuation and can achieve impedance matching at the input point.The circuit is realized for the following reasons. There is no choice but to increase the discipline.

That is, the resistance value of the load resistor 11 is R. , variable resistor 12,1
If the resistance values of 3 are Rp and Rq, the input impedance is R. As is well known, in order to change the attenuation amount while keeping it constant, equation (3) must always be satisfied. However, the resistance value Rp of the two variable resistors 12 and 13
, Rq while satisfying the condition of equation (3) requires a special control circuit.

Therefore, in order to realize a bridged T-type variable resistance attenuator that can achieve impedance matching at the input point and continuously provide a wide range of attenuation, the configuration becomes complicated and the circuit requirements become large. The present invention has been made to improve the drawbacks of the conventional variable resistance attenuators as described above.

That is, an object of the present invention is to provide a variable resistance attenuator that can widen the variable range of attenuation and match the input impedance with a simple circuit using a PIN diode. Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 3 shows the configuration of the variable resistance attenuator of the present invention. Conventional variable resistance attenuator PIN diode 14
A fixed resistor 15 is added in parallel to the PIN diode 14.
The cathode side of the PIN diode 16 is connected to the cathode of another PIN diode 16. PIN diode 1
The current flowing through 4 is IXl, and the resistance value at that time is Rx. ．． P.I.
The current flowing through the N diode 16. Let the current be Iyl and the resistance value at that time be Ry. Here, the amount of forward voltage drop of the PIN diode takes a value of about 0.2 to 0.8 V depending on the magnitude of the current flowing through the PIN diode, and when the current is small, it is negligible, and the calculation is complicated. In order to avoid - Ignore the pressure drop as O. Let the resistance value of the fixed resistor 15 be r1 and the resistance value of the load resistor 17 be RO. The fixed resistors 18 and 19 determine the current flowing through the PfSJ diode, and their resistance values are set to Rl and R2, respectively.
shall be. 20, 21, and 22 are capacitors that prevent the DC bias current of the PIN diode from flowing into other circuit elements, and transmit the high frequency signal as it is.

23 and 24 are voltage supply terminals, and the voltages applied to them are Vx and y, respectively.

For X and Vy, one end of the fixed resistor R2 is grounded as shown in FIG. 3, and this is used as a reference potential.

First, an outline of the operation of the variable resistance attenuator according to the present invention will be explained.

The PIN diode 14 and the PIN diode 16 constitute an L-type circuit. By keeping the voltage Vy of the voltage supply terminal 24 constant, the sum of the current values flowing through the PIN diodes 14 and 16 becomes approximately constant. Therefore, by changing the voltage Vx applied to the voltage supply terminal 23, the current flowing through the PIN diodes 14 and 16 can be increased or decreased depending on the relationship between Vx and ■y, and the amount of attenuation of this variable resistance attenuator can be changed. can. Further, by adding a fixed resistor 15 having a resistance value similar to the load impedance in parallel to the PIN diode 14, good input impedance matching can be maintained. Further, the same thing can be said when the voltage supply terminal 23 is fixed and the voltage supply terminal 24 is changed. That is, the objective can be achieved by changing the relative value of Vx<5Vy. Hereinafter, the characteristics of the variable resistance attenuator according to the present invention shown in FIG. 3 will be explained in detail using specific numerical values.

Here, the input impedance Zi of the resistance values Rl and R2 of the fixed resistors 18 and 19 is the load resistance value R. The voltage Vx is set to a value that is large enough not to change significantly from the voltage Vx, and a value that does not cause the voltage Vx to become too large. Therefore, here, both Rl and R2 are set to 500Ω, and the load resistance value (2) is set to 50Ω. The voltage transfer function (2) between the input terminal pair 25, 26 and the output terminal pair 27, 28 is also expressed as the input impedance Zi.

The resistance value X of the PlN diode is the current 1 flowing through each
It is known that the operating resistance X is generally expressed by the following approximate formula. h is in the range of 0.7-1.

The PIN diode in this numerical example is a high frequency PIN diode ISU36 manufactured by NEC Corporation (k=58, h=0.
82) is used. In FIG. 3, the current 1 flowing through the PIN diode 14 and the PIN diode 16
x and Iy are controlled by voltages x and xy applied to voltage supply terminals 23 and 24, respectively. Usually, the mismatch attenuation amount r given by the following equation is often used as a measure of the goodness of matching between the human input impedance Zi and RO. If the value of r is 20 dB or more, signal waveform deterioration due to mismatching is so small that it can be ignored in practical terms. Now RO is 50
Ω, the impedance Zi at which r is 20 dB or more is within the range of 40.9 to 61.1 Ω. Here, the fixed resistor 15 is used to adjust input impedance matching, and if the resistance value γ is set to about the load impedance, good matching can be maintained. The reason is that the resistance value R of the PIN diode 14
When x becomes large and the amount of attenuation becomes large, the fixed resistance 1
5 resistance value γ and load impedance R. TogaγkuR. Then, the input impedance Zi is Zi R. This is because if γ>RO then Zi>RO, the input impedance matching deteriorates. Here, to simplify the calculations below, the value of the fixed resistance γ is set to R. When 45.5Ω is equal to lR2, equations (4) and (5) become as follows. Further, Rx and Ry are expressed by the formula (substitution) as described above.

In Figure 3, the connection point 29 of the two PIN diodes
The potential at is the electric potential applied to the voltage supply terminal 24
It is approximately equal to Iy, and if Vy is kept constant, the voltage at 29 will also be approximately constant. Therefore, the current flowing through the resistor R2 is constant and the following equation holds true. It is possible to divide it into
Here, the value of the maximum variable attenuation that can be taken while keeping the mismatch attenuation r at 20 dB or more is determined.

From equations (9), 0I, and (11), if O x K, then Zi
Is it IX? It is a downwardly convex function that is symmetric with respect to . Zi takes the maximum value in the following two cases. (a) Ry=1
That is, Ix = K (Iy = 0) At this time (b) Rx = 1, that is, I
x=0 (Iy=K) At this time, Vx ku■y Also, the reason why Zi takes the minimum value is (c) RX=Ry, that is, IX=Iy=? This is the case.

Therefore, in the first case, the maximum value of Zi is 61.1.
Consider the case where Ω (r=20 dB) is taken.

At this time, from the above, Z1 takes the maximum value of 61.1Ω. In case (a), Vx=1.16■, Vy=0. Since it is a relation, make sure to keep the current flowing through R2 constant.
If it is kept constant at 0.58V, the case (mouth) holds that Vx<. There is a time when it is 0.58V. The minimum possible value of Zi at this time is Zi = 54.1Ω, and r〉2
It has become 0dB.

Also, when 1.16V>Vx>0.58V holds, Ix
=0.58rnA as the border, Ix becomes Z at 0.58n1A
i is monotonically decreasing, 0.58rr1A<Ix 1.16n1
At A, Zi increases monotonically and reaches its minimum value at x=0.58n1A.

The above state of Zi is shown in 1 in FIG. 4, and r>20 dB in all cases. At this time, the attenuation amount is 3.7dB9.2dB according to the size of ■, and the variable width is 5
．． It becomes 5dB. The situation is shown in 1 of Fig. 5. Note that when Vx>1.16V, the larger Vx becomes, the larger the fall becomes, and accordingly Rx becomes smaller, and as a result, Zi decreases, and the amount of attenuation also becomes smaller, but this is omitted here because it is related to the limitation of current ■. . Next, consider a second case in which Zi takes a minimum value of 40.9Ω (r=20dB).

At this time, from the above (c) 1x = 1y - 1.41mA, Rx
When = Ry = 43.7j ■ y = 1.41V, VX
=2.82V. Therefore, when Vy is constant at 1.41V, the maximum value of Zi is taken when Zi=54
．． 7Ω, and r>20JB.

The state of Zi above is shown by 2 in FIG. 4, and in all cases r>20 dB. At this time, the amount of attenuation is 2.6 dB to 11.7 dB depending on the magnitude of Ix, and the variable width is 9.1 dB. The situation is shown in Figure 5, 2.
To summarize the above, in the variable resistance attenuator of the present invention, Vy
By setting r in the range of 0.58V x y x 1.41V, r>20dB can always be maintained, and the variable range of attenuation can be set to 5.5d.
It can be freely taken from B to 9.1 dB.

Here, we will compare the characteristics with the conventional variable resistance attenuator shown in FIG. The conditions are the same as in Figure 3: R1=
Assume that R2=500Ω, RO=50Ω, and the PIN diode is also the same. From equations (1) and (2), the amount of attenuation that the variable resistance attenuator in Fig. 1 can take while maintaining r>20 dB is 1.4 dB to 3.7 dB, and the variable width is 2. It becomes 2dB. On the other hand, the variable width of the variable resistance attenuator of the present invention is 5.5 to 9.1 as described above.
It is dB. Therefore, the variable resistance attenuator according to the present invention has the advantage of better input impedance matching and wider variable range than conventional ones. Furthermore, the control voltage V
The value of x can be very small compared to the conventional one. In the above explanation, the voltage y of the voltage supply terminal 24 is fixed, and P
Sum of current values flowing through IN diodes 14 and 16■+I
We have considered the case where y is kept almost constant and the attenuation amount is changed by changing the voltage Vx of the voltage supply terminal 23, but next we will consider the case where x is fixed and Vy is changed.

At this time, Vx=(R1+R2)Ix+R2■y=CON
stunt, which connects PIN diodes 14 and 1
The condition is that the weighted sum of the current value 1x<51y passed through the current value 1x<51y is constant. In that case, by changing the voltage Vy, it is possible to create a variable resistance attenuator, as seen by the change in ■. First, Ix takes the maximum value when Vy<. Vx-1
In the case of −, Ix=−■Enichi R,+R2Rl+R2ゝIy=0, and the amount of attenuation becomes the minimum.

Next, Ix becomes 0 when Vy〉■x, in which case 1
Is y the maximum value? Therefore, the amount of attenuation becomes the minimum. Also, Vx
〉■When y>Vx---, R1+R2 is obtained, and by changing the value of Vy, the currents 1x and Iy flowing through the PIN diodes 14 and 16 can be arbitrarily changed, and the amount of attenuation can be changed.

Further, by appropriately selecting the magnitude of the constant voltage Vx, a variable resistance attenuator can be realized in which the mismatch attenuation r can be set to 20 dB or more and the variable resistance range can be widened. Therefore, with the configuration shown in FIG. 3, the voltage Vx of the voltage supply terminal 23 is fixed,
Even if the voltage Vy of the voltage supply terminal 24 is changed, ■
A variable resistance attenuator having the same function as when y is fixed and Vx is variable can be realized. In addition, in the explanation of the embodiment shown in FIG. 3, γ is γ=4, which matches the load impedance.
Although 5.5Ω was taken, other suitable values can be taken depending on the setting of the necessary amount of mismatch attenuation and the variable width of the amount of attenuation.

Furthermore, in the above explanation, the voltage source connected to the voltage supply terminal 24 is assumed to be ideal, but if the impedance of the voltage source cannot be ignored, the impedance can be changed to the above-mentioned P.
It can be designed to be included in the resistance value Ry of the IN diode 16. Further, in the above explanation, even if the direction of the PIN diode is changed, that is, the cathode is changed to the anode side and the anode is changed to the cathode side, exactly the same thing is true.

Therefore, changing the orientation of the PIN diode does not change the essence of the invention. As explained above, according to the present invention, the attenuation amount can be varied over a wide range with a simple circuit.
In addition, a variable resistance attenuator capable of matching input impedance is obtained.

The amount of attenuation can be continuously and electrically controlled by changing the one-terminal voltage.

Since the variable resistance attenuator of the present invention has extremely small input mismatch, even if it is used in a high frequency region where the signal band ranges from several + MHz to several hundred MHz, signal deterioration due to multiple reflections at the input end will hardly occur. There is no.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing an example of a conventional variable resistance attenuator, FIG. 3 is a circuit diagram showing a variable resistance attenuator according to the present invention, and FIG. 4 is a circuit diagram showing a variable resistance attenuator according to the present invention. FIG. 5 is a diagram showing the input impedance characteristics of the device, and FIG. 5 is a diagram showing the attenuation characteristics. In the figure, 1, 14, 16...PIN diode, 2, 3, 15, 18, 19... fixed resistor,
4, 11, 17...Load resistance, 5 and 6, 25,
26... Input terminal pair, 7, 8, 27, 28...
... Output terminal pair, 9, 10, 20, 21, 22...
・Capacitor, 12, 13...Variable resistor, 23,
24: voltage supply terminal, 29: connection point, respectively.

Claims (1)

[Claims] 1 The anode (or cathode) is an input terminal, this anode (or cathode) is connected to the first bias voltage supply terminal via a resistor, the cathode (or anode) is an output terminal, and this cathode (or anode) is connected to the first bias voltage supply terminal via a resistor. ) is connected to a constant potential point via a resistor, the first PIN diode is AC-coupled to prevent DC bias current from flowing into the input side and output side, and the load impedance is connected to the output terminal. In the variable resistance attenuator configured, a fixed resistor is added in parallel to the first PIN diode so as to prevent a DC bias current from flowing, and a second resistor is added to the cathode (or anode) of the first PIN diode. The cathode (or anode) of the second PIN diode is connected to the second bias voltage supply terminal, and the anode (or cathode) of the second PIN diode is connected to the second bias voltage supply terminal. A variable resistance attenuator, characterized in that the amount of attenuation is adjusted by varying the relative value to the voltage of the second bias supply terminal.