JPH06177694A - Variable attenuator - Google Patents

Abstract

PURPOSE:To easily control an attenuation amount and to save electric power. CONSTITUTION:RF signals outputted from a signal generator 6 are divided into equal halves by the two lines 10 and 11 of an electric distributor 1 and are distributed to two routes (1) and (2). A variable phase shifter 2 is inserted to at least one of the routes (1) and (2) and is provided with variable capacitance diodes 28 and 30 operated in reverse bias. Since a current does not flow into the variable capacitance diodes 28 and 30, the electric power can be saved. Then, the capacitance of the variable capacitance diodes 28 and 30 is changed corresponding to a single control signal Vs and the phase of the inputted RF signals is shifted. Since control can be performed by the single control signal Vs, the control can be facilitated. An electric power synthesizer 3 respectively synthesizes the RF signals through the respective routes (1) and (2). The variable phase shifter 2 makes the respective RF signals compensated corresponding to the phase difference of the RF signals of the respective routes (1) and (2) at the electric power synthesizer 4 and attenuates the level of the synthesized RF signals.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a variable attenuator.

[0002]

2. Description of the Related Art Conventionally, R in VHF, UHF, SHF bands, etc.
As a variable attenuator that attenuates an F signal by an arbitrary amount, a PIN diode type variable attenuator as shown in FIG. 8 is known. The variable attenuator shown in FIG. 8 has a PIN diode D1,
D2 and D3 are arranged in a π type, and the whole is shielded.

Input and output coaxial connectors J1 and J2 are provided at both ends of the PIN diode D1 via capacitors C1 and C2.
Are connected. Further, between the diodes D2 and D3 and the diode D1, capacitors C3 and
C4 is connected. The current supply terminal A is connected to the anode side of the diode D1 via the choke coil L1. Meanwhile, the diodes D2 and D
On the anode side of 3, choke coils L3 and L
The current supply terminal B is connected via 4. In addition,
The cathode side of the diode D1 is connected to the ground terminals E1 and E2 via the choke coil L2. Similarly, the cathode side of the diodes D2 and D3 is connected to the ground terminal E.
1 and E2.

When a positive DC voltage is applied as the control signal Vs1 to the current supply terminal A of the variable attenuator configured as described above, the PIN diode D1 is forward biased and the choke coil L1, PIN diode D1, and choke coil are connected. A current flows through the path of L2 and ground. Similarly, when a positive DC voltage is applied to the current supply terminal B as the control signal Vs2, the PIN diodes D2 and D3 are forward biased, and the choke coil L3 and PIN diode D
2, the current flows through the ground path, the choke coil L4, the PIN diode D3, and the ground path.

By the way, the PIN diode has a property that the RF resistance value greatly changes according to the flowing current. Therefore, as shown in FIG. 9, the above-described circuit of FIG. 8 is replaced with an unbalanced π-type attenuator circuit as a high frequency equivalent circuit. The circuit of FIG. 9 controls the currents flowing through the PIN diodes D1 to D3,
It becomes a continuously variable attenuator. In addition, in FIG. 9, R1, R
2 and R3 are PIN diodes D1 and D, respectively.
The resistances corresponding to 2 and D3 are shown.

In the equivalent circuit of FIG. 9, the relationship between the input-to-output power ratio (N) and the resistance values (R1, R2, R3) is as follows, where the input impedance is Z1 and the output impedance is Z2. It is shown by the formulas (1) to (3). R1 = {(N-1) / 2} √ (Z1 · Z2 / N) (1) 1 / R2 = (1 / Z1) {(N + 1) / (N-1)}-(1 / R1) ... (2) 1 / R3 = (1 / Z2) {(N + 1) / (N-1)}-(1 / R1) (3) Therefore, the input / output impedance is 50Ω and the power ratio of the input to the output (hereinafter , And the resistance value (R1, R2, R3) is R1 = 71.15Ω ... D1 resistance value R2 = R3 = 96.25Ω ... D2 and D3 resistance value Become.

Due to the current-resistance characteristics of the PIN diode, 0.3 mA for 71.15Ω and 0.2 mA for 96.25Ω, 0.3 mA and PI for the PIN diode D1.
An attenuator can be realized by applying 0.2 mA to each of the N diodes D2 and D3. Here, the attenuation amount G (dB)
And resistance values (R1, R2, R3), and PI
The relationship with the N diodes D1, D2 and D3 is as shown in FIG. However, the input / output impedance is 50Ω
And

The PIN diode type attenuator described above has various advantages such as high speed switching and long life.

[0009]

However, when the attenuation amount is made variable, the two control signals Vs1 and Vs2 are used to generate the non-linear currents as shown in FIG.
It is necessary to supply the diodes D1, D2 and D3. Further, in order to match the input and output impedances and simultaneously obtain a desired attenuation amount, two control signals Vs1 and Vs
Although 2 must be set to the optimum value, it is difficult to determine this optimum value. Moreover, since the PIN diodes D1, D2 and D3 are used by being biased in the forward direction, it is necessary to constantly supply a current of several mA to several tens of mA to the PIN diodes D1, D2 and D3, and it is not possible to save power. It was

The present invention solves the above technical problems,
An object of the present invention is to provide a variable attenuator capable of easily controlling the amount of attenuation and saving power.

[0011]

In order to solve the above technical problems, the present invention has the following configurations. A variable attenuator according to the present invention divides a supplied RF signal into equal parts, divides the equally divided RF signal into a plurality of paths, and a power combiner that combines the RF signals passing through the paths, respectively. ,
At least one of the paths has a variable-capacitance diode that operates in a reverse bias and has a variable-capacitance diode that changes the capacity of the variable-capacitance diode according to a single control signal, and shifts the phase of an input RF signal. In the power combiner, each RF signal is canceled according to the phase difference of the RF signal of each path,
And a variable phase shifter that attenuates the level of the combined RF signal.

[0012]

The power distributor divides the supplied RF signal into equal parts,
The equally divided RF signal is distributed to a plurality of paths. The variable phase shifter has a variable capacitance diode that is inserted in at least one of the paths and operates with a reverse bias, changes the capacitance of the variable capacitance diode according to a single control signal, and changes the capacitance of the input RF signal. Shift the phase. The power combiner combines the RF signals passing through the respective paths. The variable phase shifter cancels each RF signal according to the phase difference of the RF signal of each path in the power combiner, and attenuates the level of the combined RF signal.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a variable attenuator according to an embodiment of the present invention, and FIG. 2 is a perspective view showing a mounted state of the variable attenuator. The variable attenuator includes a power distributor 1, a variable phase shifter 2, a fixed phase shifter 3, and a power combiner 4. The power distributor 1, the variable phase shifter 2, the fixed phase shifter 6 and the power combiner 4 are integrally formed on the high dielectric constant substrate 5 (see FIG. 2).

The RF signal output from the signal generator 6 is
It is provided to the power distributor 1. The power distributor 1 is composed of a Wilkinson type power splitter or the like, and has a 1/4 wavelength line 10 formed as a thick film on a high dielectric constant substrate 5,
11 and a resistor 12. The RF signal input from one end of the lines 10 and 11 is divided into two paths by the lines 10 and 11. The resistor 12 is the line 10,
It is connected between the other ends of 11 and enhances the isolation of the RF signal of the path from the path.

In this embodiment, a variable phase shifter 2 and a fixed phase shifter 3 which will be described later are inserted only in the path. For the sake of convenience, it is assumed that the phase of the RF signal shifts only in the variable phase shifter 2 and the fixed phase shifter 3 in the path, and the phase shift of the RF signal does not occur in the path. The RF signal from the path passing through the variable phase shifter 2 and the fixed phase shifter 3 and the RF signal from the path are given to the power combiner 4.

The power combiner 4 is similar to the power distributor 1 in that
The high dielectric substrate 5 is provided with a quarter wavelength line 16 and a line 18 and a resistor 20. The resistor 20 is a line 16,
It is connected between one ends of 18 and receives RF signals of the path with increased isolation. The RF signals from the paths and the paths are combined at the other ends of the lines 16 and 18. The power combiner 4 outputs the combined RF signal to the load 22.

If the input impedance of the power distributor 1 and the output impedance of the power combiner 4 are Z0 (for example, 50Ω), the lines 10 and 11 of the power distributor 1 will be described.
Characteristic impedance of the power combiner lines 16 and 18
The characteristic impedance of each is √2 · Z0.
The resistance values of the resistors 12 and 20 are 2 · Z0. Then, the dielectric constant εr of the high dielectric constant substrate 5 is set to 21, and 1 GH
If εeff ≈εr in z, then c / √εeff = λ0 · f0
Therefore, the quarter wavelength, that is, the lines 10, 11, 1
The length of 6, 18 is about 16 mm. Therefore, the lines 10, 11, 16 and 18 are set within a few mm when they are meandered. Here, √εeff is the effective dielectric constant of the high dielectric constant substrate 5, λ0 is the length of one wavelength on the high dielectric constant substrate 5, f0 is the frequency, and c is the speed of light.

The variable phase shifter 2 has a control signal Vs (Vs ≧
0) is given. The control signal Vs is applied to the cathodes of the variable capacitance diodes 28 and 30 from the terminal 13 through the choke coils 24 and 26 that cut the AC components that may be included in the control signal Vs, respectively. A DC cut capacitor 32 is connected between the cathode of the variable capacitance diode 28 and the line 10. A DC cut capacitor 34 is connected between the cathode of the variable capacitance diode 30 and the fixed phase shifter 3. The anodes of the variable capacitance diodes 28 and 30 are commonly connected. A coil 36 is connected between the anodes of the variable capacitance diodes 28 and 30 and the terminal 31 which is grounded. Therefore, the variable capacitance diodes 28 and 30 are reverse biased. Therefore, no current flows through the variable capacitance diodes 28 and 30. Therefore, it is possible to save power.
The variable capacitance diodes 28 and 30 and the coil 36 form a high pass filter. The cutoff frequency of the high pass filter is set near the frequency of the RF signal.

The phase of the input RF signal is deviated by the capacitances of the variable capacitance diodes 28 and 30 and the inductance of the coil 36. Here, as the voltage of the control signal Vs increases, the variable capacitance diodes 28, 30
The reverse bias voltage of 1 increases and the capacitances of the variable capacitance diodes 28 and 30 decrease. vice versa,
When the voltage of the control signal Vs becomes smaller, the reverse bias voltages of the variable capacitance diodes 28 and 30 become smaller,
The capacitances of the variable capacitance diodes 28 and 30 increase, respectively. Therefore, the phase of the input RF signal can be shifted by changing the voltage of the control signal Vs.

As the voltage of the control signal Vs increases and the capacitances of the variable capacitance diodes 28 and 30 decrease,
The variable phase shifter 2 reduces the degree of advance of the phase of the RF signal on the path output from the line 10. The phase shift characteristic of the variable phase shifter 2 is shown by line L1 in FIG. This phase shift characteristic was measured by setting the frequency of the RF signal to 1 GHz. Also, the choke coil 24,
Instead of 26, a resistor having a resistance value of 4.7 kΩ was used. Also,
ISS210K was used for the variable capacitance diodes 28 and 30. Furthermore, the coil 36 is 3 mmφ · 1T (about 10 n
H). When the control signal Vs is changed from 0V to 20V, -1 at Vs = 0V as shown by the line L1.
The phase advances by 00 degrees. When Vs = 20V, the phase is delayed by +2 degrees. Therefore, by changing the control signal Vs,
The phase of the RF signal can be freely deviated from −100 degrees to +2 degrees, and a phase difference can be freely set between the path RF signal and the path RF signal. Note that there may be 2nπ (n: 0 or a positive integer) turns depending on the wiring or the like. The insertion loss due to the variable phase shifter 2 at this time is the line L
Shown in 2.

The fixed phase shifter 3 advances the phase of the RF signal output from the variable phase shifter 2 by a fixed amount, for example, 90 degrees. The fixed phase shifter 3, the power distributor 1, the variable phase shifter 2 and the fixed phase shifter 3 form a hybrid integrated circuit. Here, when the RF signal needs to be greatly attenuated, it is necessary to make the phase difference between the paths up to 180 degrees. However, the phase difference between the path that can be displaced by the variable phase shifter 2 and the path is from -100 degrees to +2 degrees. Therefore, as shown by the line L3 in FIG. 3, the fixed phase shifter 3
Allows the path RF signal to be offset from -190 degrees to -88 degrees. The fixed phase shifter 3 is
It can be created by the line length of a route such as wiring in the variable phase shifter 2 or the difference between the line lengths of routes.

RF of the path output from the fixed phase shifter 3
The signal and the RF signal on the path are combined by the power combiner 4. If there is a phase difference between the RF signal of the route and the RF signal of the route, the level of the synthesized RF signal becomes R of the route.
It attenuates according to the phase difference between the F signal and the RF signal on the path. When the phase difference is 0, the amount of attenuation is almost 0 as shown by the line L1 in FIG. It should be noted that the reason why it does not become 0 is that the level of the RF signal of the path differs from that of the path due to the insertion loss of the variable phase shifter 2. Phase difference is 180
In the case of degrees, the amount of attenuation is ∞. In addition, the phase difference is 0
When it is between 180 degrees, the amount of attenuation increases as the phase difference increases. Therefore, by changing one control signal Vs, the attenuation amount of the RF signal can be changed arbitrarily, and the control becomes easy.

If the fixed phase shifter 3 is not provided, the phase difference between the path that can be displaced by the variable phase shifter 2 and the path is -10.
It is from 0 to +2 degrees. Therefore, the variable phase shifter 2
When the output of the above is directly applied to the line 16 of the power combiner 14, the variable range of the attenuation amount is 0 to 5 dB as shown in FIG.
Is. When the fixed phase shifter 3 is provided, the phase difference between the path and the line that can be displaced by the variable phase shifter 2 and the fixed phase shifter 3 is -190 degrees to -88 degrees. Therefore, when the output of the fixed phase shifter 3 is applied to the line 16 of the power combiner 14, the variable range of the attenuation amount is 3 to almost ∞ dB as shown in FIG. Therefore, whether or not to insert the fixed phase shifter 3 may be determined according to the request for the attenuation amount.

FIG. 5 is a diagram showing a variable attenuator according to another embodiment of the present invention, in which parts corresponding to those of the embodiment of FIG. 1 are designated by the same reference numerals. This variable attenuator comprises a variable phase shifter 2 inserted in the path. Therefore, the fixed phase shifter 3 is removed. The possible range of the phase shift of each variable phase shifter 2 is −
It is 100 degrees to +2 degrees. Therefore, in the two variable phase shifters 2, it becomes −200 degrees to +4 degrees. by this,
A phase difference of 0 degrees to 180 degrees can be provided between the paths, and the variable range of the attenuation amount is approximately 0 to approximately ∞ dB.
Can be arbitrary.

FIG. 6 is a diagram showing a variable attenuator according to another embodiment of the present invention, in which parts corresponding to those of the embodiment of FIG. 1 or 5 are designated by the same reference numerals. This variable attenuator includes a variable phase shifter 2 inserted in a path, a variable phase shifter 40 inserted in a line, and a fixed amount of phase of the RF signal, for example, 9
A fixed phase shifter 41 for advancing 0 degrees is provided.

A constant positive DC voltage Vcc is applied to the terminal 13 of the variable phase shifter 2. Terminal 31 of variable phase shifter 2
Is applied with a control signal Vs (Vcc ≧ Vs ≧ 0). In addition, the AC component that can be included in the control signal Vs is
Bypassed to ground by capacitor 42.

A control signal Vs is applied to the variable phase shifter 40. The control signal Vs is applied from the terminal 44 to the anodes of the variable capacitance diodes 48 and 50 via the coil 46. A DC cut capacitor 52 is connected between the anode of the variable capacitance diode 48 and the line 11 of the power distributor 1. A DC cut capacitor 53 is connected between the anode of the variable capacitance diode 50 and the fixed phase shifter 41. The cathode of the variable capacitance diode 48 is a choke coil 52 that cuts off an AC component.
Is connected to a terminal 54 which is grounded via. The cathode of the variable capacitance diode 50 is connected to the terminal 54 via a choke coil 56 that cuts an AC component. Therefore, the variable capacitance diodes 48 and 50 are reverse biased. Therefore, no current flows through the variable capacitance diodes 48 and 50. Therefore, it is possible to save power. The variable capacitance diodes 48 and 50 and the coil 46
And form a high pass filter. The cutoff frequency of the high pass filter is set near the frequency of the RF signal.

The phase of the RF signal input to the variable phase shifter 40 is deviated by the capacitances of the variable capacitance diodes 48 and 50 and the inductance of the coil 46. Here, as the voltage of the control signal Vs increases, the reverse bias voltages of the variable capacitance diodes 48 and 50 increase, and the capacitances of the variable capacitance diodes 48 and 50 decrease. On the contrary, when the voltage of the control signal Vs becomes small,
The reverse bias voltages of the variable capacitance diodes 48 and 50 are low, and the capacitances of the variable capacitance diodes 48 and 50 are high. Therefore, the phase of the input RF signal can be shifted by changing the voltage of the control signal Vs.

Here, when Vs is increased, the reverse bias voltage of the variable capacitance diodes 28 and 30 is decreased, and the reverse bias voltage of the variable capacitance diodes 48 and 50 is increased. Conversely, if Vs is reduced, the variable capacitance diode 2
The reverse bias voltages of 8 and 30 increase, and the reverse bias voltages of the variable capacitance diodes 48 and 50 decrease. Therefore, the phase shift characteristic of the variable phase shifter 2 is as shown by the line L1 shown in FIG. On the other hand, the variable phase shifter 40
The phase shift characteristic of is as shown by the line L2 in FIG. Accordingly, the variable phase shifter 2 and the variable phase shifter 40 allow +102 degrees to 0 between the paths.
A phase difference of -102 degrees can be provided.

Here, in the path, the fixed phase shifter 41 further advances +90 degrees as shown by the line L3 in FIG. Therefore, the variable phase shifter 2 and the variable phase shifter 40 and the fixed phase shifter 41 can provide a phase difference of +192 degrees to 0 to -12 degrees between the paths. The insertion loss of the variable phase shifter 40 is shown in FIG.
It is almost equal to the insertion loss of the variable phase shifter 2 indicated by the line L2. Therefore, the levels of the RF signals on the paths become equal to each other, so that the amount of attenuation can be varied in the range of 0 to ∞.

In the above embodiment, two routes,
However, it may be divided into three or more routes. Further, the variable phase shifters 2 and 40 and the fixed phase shifters 3 and 41 may be formed integrally with the power distributor 1 or the power combiner 4, or may be formed separately. You may

[0032]

As described above, in the present invention, the capacitance of the variable capacitance diode is changed according to a single control signal. Therefore, control becomes easy. Further, the variable capacitance diode is operated with a reverse bias.
Therefore, current does not flow in the variable capacitance diode, so that power can be saved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a variable attenuator according to an embodiment of the present invention.

FIG. 2 is a diagram showing a mounted state of the variable attenuator of FIG.

FIG. 3 is a diagram showing phase shift characteristics by the variable phase shifter 2 and the fixed phase shifter 3.

FIG. 4 shows R when there is a phase difference in the power combiner 4.
It is a figure which shows the relationship between an F signal and an attenuation rate.

FIG. 5 is a circuit diagram of a variable attenuator according to another embodiment of the present invention.

FIG. 6 is a circuit diagram of a variable attenuator according to another embodiment of the present invention.

FIG. 7 is a diagram showing phase shift characteristics of the variable phase shifter 2, the variable phase shifter 40, and the fixed phase shifter 41.

FIG. 8 is a circuit diagram showing a configuration of a conventional PIN type variable attenuator.

9 is a high frequency equivalent circuit diagram of the variable attenuator shown in FIG. 8. FIG.

10 is a diagram showing a current value of a PIN diode corresponding to each attenuation amount of the variable attenuator shown in FIG.

[Explanation of symbols]

 1 ... Power distributor 2 ... Variable phase shifter 4 ... Power combiner 28, 30, 48, 50 ... Variable capacitance diode ... Path Vs ... Control signal

Claims (1)

[Claims] 1. A power divider for equally dividing a supplied RF signal and dividing the equally-divided RF signal into a plurality of paths, and a power combiner for combining the RF signals through the respective paths with each other. It has a variable-capacitance diode that is inserted in one path and operates in reverse bias, changes the capacitance of the variable-capacitance diode according to a single control signal, shifts the phase of the input RF signal, and combines the power. In the above, each RF signal is canceled according to the phase difference of the RF signal of each path,
A variable attenuator for attenuating the level of a synthesized RF signal.