JP2003309444A - Variable attenuator for high frequency signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable attenuator for high frequency signal capable of suppressing production of distortion even when the number of high frequency signal waves is abounding and even when a high level signal is processed. <P>SOLUTION: PIN diodes 24, 25 are provided in series between an input terminal 21 and an output terminal 22, and the anodes are connected in common, to which a bias voltage VC is given. A resistor 27 is placed between the cathode of the PIN diode 24 and ground, and a series circuit comprising PIN diodes 28 to 31 and a capacitor 32 is provided on the variable attenuator. The anodes of the PIN diodes 29, 30 are connected in common, to which a bias voltage VR is given via a resistor 41. Further, a resistor 34 is provided between the cathode of the PIN diode 25 and ground, and a series circuit comprising PIN diodes 35 to 38 and a capacitor 39 is provided on the variable attenuator. The anodes of the PIN diodes 36, 37 are connected in common, to which the bias voltage VR is given via a resistor 42. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable attenuator for high frequency signals used in, for example, a CATV main amplifier.

[0002]

2. Description of the Related Art Conventionally, for example, in a CATV main line amplifier or the like.
Uses a variable attenuator for high frequency signals. High frequency
The variable attenuator for wave signals is as shown in FIGS. 8 (a) and 8 (b).
Generally, a circuit in which a resistor is formed in a π type or a T type is used. Figure
8 (a), (b), R _VIs installed in series on the line
Series resistance, R_WIs a parallel resistance provided in series with the line
Is.

The input / output impedance of the attenuator is Z
(Ω) and the attenuation amount is n (dB), the series resistance R _V and the parallel resistance R _W in the π-type variable attenuator are

[Equation 1] Can be sought by.

The series resistance R _V and the parallel resistance R _W in the T-type variable attenuator are given by

[Equation 2] Can be sought by.

Some high frequency signal variable attenuators use PIN diodes instead of the resistors. Figure 9
FIG. 4 shows an example of the configuration of a conventional π-type variable attenuator using a PIN diode. As shown in FIG. 9, a capacitor 3, PIN diodes 4, 5 and a capacitor 6 are provided in series between the input terminal 1 and the output terminal 2. In this case, the PIN diodes 4 and 5 have their anodes commonly connected to each other to supply the bias voltage V _C.

The connection point between the capacitor 3 and the PIN diode 4 is grounded via the resistor 7, and is also grounded via the series circuit of the PIN diode 8 and the capacitor 9 connected in the reverse direction. The connection point between the diode 5 and the capacitor 6 is grounded via the resistor 10 and is also grounded via the series circuit of the PIN diode 11 and the capacitor 12 connected in the reverse direction. And the above P
The bias voltage V _R is applied to the anodes of the IN diodes 8 and 11 via the resistors 13 and 14.

In the above structure, the resistance values of the PIN diodes 4, 5, 8 and 9 are variably set by setting the bias voltage V _C to the PIN diodes 4 and 5 and the bias voltage V _R to the PIN diodes 8 and 9 variably. Can be changed to set an arbitrary amount of attenuation.

[0008]

As described above, the variable attenuator using the PIN diode is more applicable than the resistance type variable attenuator because the attenuation amount can be controlled by the bias voltage of the PIN diode. However, conventional PIN
The variable attenuator using a diode has a problem that a high-frequency signal has a large number of waves or a second-level distortion occurs as shown in FIG. 10 when a high-level signal is passed. FIG. 10 shows that the variable attenuator is 25.25 MHz, 37.25 MHz.
When inputting 2 waves of 90 dBμV / m, 2 dB, 6
Second-order distortion at attenuation levels of 10 dB, 16 dB, 3
It is a characteristic view which shows the generation | occurrence | production state of secondary distortion. In addition, FIG.
It is a frequency characteristic diagram of the said variable attenuator.

A conventional variable attenuator using a PIN diode has a characteristic of 90 dBμV /, as shown in the characteristic diagram of FIG.
If the attenuation amount is 2 dB with respect to the input of m, the second-order distortion is −
Although it can be set to 80 dB or less, the second-order distortion becomes −70 dB at an attenuation amount of 6 dB, which can be practically used at −75 dB.
It cannot be less than B.

In the future, terrestrial digital (television) broadcasting (ISDB-T: Terrestrial Integrated Services Di
Gital Broadcasting) is scheduled to start in 2003 in the Kanto, Kinki and Chukyo Wide Areas, and by 2006 in other regions. For this reason, the variable attenuator used for the CATV main line amplifier or the like needs to be compatible with multiple channels and is required to have less distortion.

The present invention has been made to solve the above problems, and provides a variable attenuator for a high frequency signal which can suppress the occurrence of distortion even when the number of high frequency signals is large or a high level signal. The purpose is to do.

[0012]

A first aspect of the present invention is a variable attenuator for high frequency signals, which is formed in a π type or a T type by using a PIN diode, and is provided in series on a signal line between input and output terminals. 1 PIN diode and the first
A first bias circuit that supplies a bias current to the PIN diode, a second PIN diode that is provided in parallel with the signal line between the input and output terminals, and a bias current that supplies to the second PIN diode. A second bias circuit, a third PIN diode connected in series with the second PIN diode with an opposite polarity, and a third bias diode that supplies a bias current to the third PIN diode.
The bias circuit of No. 1 is provided, and the distortion generated in the second PIN diode and the third PIN diode is canceled as an opposite phase.

By connecting the third PIN diode to the second PIN diode in reverse polarity to the second PIN diode as described above, the second-order distortion generated in the first PIN diode and the third PIN diode are generated.
Second-order distortion generated by the PIN diode of becomes the opposite phase,
It is possible to cancel the secondary distortion generated in each PIN diode mutually.

A variable attenuator for a high frequency signal according to a second aspect of the present invention includes a first phase inversion transformer for outputting a high frequency input signal by inverting the same phase and a phase and outputting the same from the first phase inversion transformer. P that variably attenuates high frequency signals in phase
A first variable attenuator circuit using an IN diode, a second variable attenuator circuit using a PIN diode for variably attenuating the phase-inverted high frequency signal output from the first phase inversion transformer, and the first variable attenuator circuit A second output which mixes the output signal of the variable attenuation circuit and the output signal of the second variable attenuation circuit
And a phase inversion transformer of.

In the above configuration, the high frequency input signal is
The same phase and phase are inverted by the first phase inversion transformer and input to the first and second variable attenuation circuits. The in-phase and phase-inverted high-frequency signals have a second-order distortion caused by the PIN diode when passing through the first and second variable attenuation circuits, and have a waveform including the second-order distortion. However, when the high-frequency signal containing the second-order distortion that has passed through the first and second variable attenuation circuits is mixed by the second phase-inversion transformer, the second-order distortion component of the opposite phase is canceled out and there is no distortion. It is output as a signal. As a result, it becomes possible to construct a variable attenuator for high-frequency signals that is highly variable and has low distortion.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows an example of the configuration of a π-type high frequency signal variable attenuator using a PIN diode according to the first embodiment of the present invention. In FIG. 1, 21 is an input terminal, 22 is an output terminal, and a capacitor 23 is provided on a signal line between the input terminal 21 and the output terminal 22.
PIN diodes 24 and 25 and a capacitor 26 are provided in series. The PIN diodes 24 and 25 have their anodes commonly connected to each other to supply a bias voltage V _C.

The connection point between the capacitor 23 and the PIN diode 24 is grounded via the resistor 27, and is also grounded via the series circuit of the PIN diodes 28, 29, 30, 31 and the capacitor 32. That is, for the signal line between the input terminal 21 and the output terminal 22, P
IN diodes 28, 29, 30, 31 and capacitor 3
Two series circuits are provided in parallel. In this case, the anodes of the PIN diodes 29 and 30 are commonly connected so that the PIN diodes 28 and 29 and the PIN diodes 30 and 31 have opposite polarities, and the cathode side of the PIN diode 28 is connected to the cathode of the PIN diode 24. Then, the cathode of the PIN diode 31 is connected to the capacitor 32. In addition, the PIN diodes 28, 2
High frequency choke 33 for 9, 30, 31 series circuit
Are connected in parallel.

The connection point between the PIN diode 25 and the capacitor 23 is grounded via a resistor 34, and is also grounded via a series circuit of PIN diodes 35, 36, 37, 38 and a capacitor 39. In this case, PI
N diodes 35 and 36 and PIN diodes 37 and 38
PIN diode 36 and PI so that and are opposite polarities.
The anodes of the N diodes 37 are commonly connected to each other, and the PIN
The cathode side of the diode 35 is connected to the cathode of the PIN diode 25, and the cathode of the PIN diode 38 is connected to the capacitor 39. In addition, the PIN diode 3
A high frequency choke 40 is connected in parallel to the series circuit of 5, 36, 37 and 38.

Then, the PIN diodes 29, 30
Giving a bias voltage _{V R} through the anode to the resistor 41, the resistor to the anode of the PIN diode 36, 37 42
A bias voltage V _R is applied via.

In the above structure, the bias voltage V _C causes a bias current to flow through the PIN diode 24 through the resistor 27 and a bias current through the PIN diode 25 through the resistor 34.

Further, the bias voltage V _R causes a bias current to flow through the PIN diodes 28 and 29 through the resistors 41 and 27, and the PIN diodes 30 and 31 receive the resistor 4 at the resistor 4.
1, the bias current flows through the high frequency choke 33 and the resistor 27. By further bias voltage _{V R,} the bias current flows through the resistor 42, 34 to the PIN diodes 35 and 36, resistance to PIN diodes 37 and 38 4
2. A bias current flows through the high frequency choke 40 and the resistor 34.

Bias voltage V _C applied to the PIN diodes 24 and 25, and PIN diodes 28 to 31,
Bias voltage _{V R} applied to the PIN diodes 36 to 39
Is set according to the amount of attenuation of the variable attenuator. in this case,
For example, a constant bias voltage _{V R} of the PIN diode 28～31,36～39, PIN diodes 24 and 25
The amount of attenuation can be adjusted arbitrarily by variably setting the bias voltage V _C to be applied to the variable resistor by the variable resistor.

In the variable attenuator using the PIN diode, the second-order distortion occurs when the forward current (bias current) for operating the PIN diode is low, but it has been described in the first embodiment. Multiple PINs
By connecting the diodes in series and increasing the bias current of each diode, it is possible to operate in a location having good linearity in characteristics, and it is possible to reduce the occurrence of secondary distortion.

Further, the PIN diodes 30 and 31 are connected to the PIN diodes 28 and 29 in opposite polarities, and the PIN diodes 37 and 38 are connected to the PIN diodes 35 and 36 in opposite polarities, respectively.
Second-order distortion generated by the diodes 28, 29, 35, 36 and 2 generated by the PIN diodes 30, 31, 37, 38
Next distortion becomes opposite phase, and it occurred in each PIN diode. 2
The secondary distortions can cancel each other out.

FIG. 2 is a diagram of the variable attenuator 25.2.
Two waves of 5MHz and 37.25MHz, 95dBμV / m
When input with, 2dB, 6dB, 10dB, 16dB
It is a characteristic view which shows the generation | occurrence | production state of the secondary distortion and the tertiary distortion in the attenuation amount of. FIG. 3 is a frequency characteristic diagram of the variable attenuator.

In the variable attenuator for high frequency signals according to the first embodiment, as shown in the characteristic diagram of FIG. 2, the secondary distortion is -77 dB or less when the attenuation amount is 10 dB or less, and the secondary distortion is sufficiently generated. Could be made smaller.

In the above embodiment, a plurality of PINs are used.
A method of reducing the occurrence of secondary distortion by operating with a large bias current by connecting diodes in series;
The case where the PIN diodes are connected to opposite polarities so that the secondary distortion is generated in the opposite phase and the method of canceling the secondary distortion generated in each PIN diode is combined is shown. However, each method is separately used to perform variable attenuation. It is possible to reduce the occurrence of second-order distortion even if the device is configured.

(Second Embodiment) FIG. 4 is a circuit configuration diagram of a high frequency signal variable attenuator according to a second embodiment of the present invention. In the variable attenuator for high frequency signals according to the second embodiment, phase inversion transformers 51 and 52 are inserted in the input / output section,
First and second variable attenuation circuits 53 and 54 are provided in parallel between the phase inversion transformers 51 and 52.

The phase inversion transformer 51 has one end of the primary winding connected to the input terminal 21 and the other end grounded. The secondary winding of the phase inversion transformer 51 has first and second variable attenuation circuits 53 and 54 connected at both ends, and a resistor 55 and a capacitor 56 are provided in parallel between the midpoint and the ground.

The phase inverting transformer 52 has first and second variable attenuation circuits 53 and 54 connected to both ends of the primary winding, and a resistor 57 and a capacitor 58 are provided in parallel between the midpoint and the ground. There is. The secondary winding of the phase inversion transformer 52 has one end connected to the output terminal 22 and the other end grounded.

The first variable attenuation circuit 53 has PIN diodes 61 and 62 connected in series between the phase inversion transformers 51 and 52. The PIN diodes 61 and 62 are
The anodes are connected in common and a bias voltage V _C is applied.

A series circuit of a reverse-connected PIN diode 63 and a capacitor 64 is provided between the cathode of the PIN diode 61 and ground, and the PIN diode 6 is provided.
A series circuit of a reverse-connected PIN diode 65 and a capacitor 66 is provided between the second cathode and the ground. And
Biasing voltage _{V R} through respective resistors 67 and 68 to the anode of the PIN diode 63 and 65.

The second variable attenuator circuit 54 is provided with PIN diodes 71 and 72 in series between the phase inversion transformers 51 and 52. The PIN diodes 71 and 72 are
The anodes are connected in common and a bias voltage V _C is applied.

A series circuit of a reverse connection PIN diode 73 and a capacitor 74 is provided between the cathode of the PIN diode 71 and the ground, and the PIN diode 7 is connected.
A series circuit of a reverse-connected PIN diode 75 and a capacitor 76 is provided between the second cathode and the ground. And
Biasing voltage _{V R} through respective resistors 77 and 78 to the anode of the PIN diode 73 and 75. In this case, for example, PIN diodes 63, 65, 73, 7
By setting the bias voltage V _R applied to 5 to a constant value and variably setting the bias voltage V _C applied to the PIN diodes 61 and 62 with a variable resistor, the amount of attenuation can be arbitrarily adjusted.

In the above-mentioned structure, the input terminal 21 has the configuration shown in FIG.
When the high-frequency signal shown in (a) is input, this high-frequency signal is output by the phase inversion transformer 51 as a signal of the same phase shown in (b) of the figure and a signal of the opposite phase shown in (c) of the figure. , For example, an in-phase signal is input to the first variable attenuation circuit 53, and an in-phase signal is input to the second variable attenuation circuit 54.

The high frequency signals are variable attenuator circuits 53, 5
Second-order distortion is generated by the PIN diode when passing through No. 4, and the waveform has a second-order distortion as shown in FIGS. The high frequency signal including the secondary distortion that has passed through the variable attenuation circuits 53 and 54 is mixed by the phase inversion transformer 52. At this time, the opposite-phase second-order distortion component included in the high-frequency signal is canceled out, and a signal without second-order distortion is output from the phase inversion transformer 52 via the output terminal 22 as shown in FIG. It

FIG. 6 shows a case where the variable attenuator is 25.2.
Two waves of 5MHz and 37.25MHz, 95dBμV / m
When input with, 3dB, 6dB, 10dB, 16d
2 at B, 20 dB, 24 dB, 28 dB attenuation
It is a characteristic view which shows the generation | occurrence | production state of secondary distortion and tertiary distortion. FIG. 7 is a frequency characteristic diagram of the variable attenuator.

As shown in the characteristic diagram of FIG. 6, the variable attenuator for a high frequency signal according to the second embodiment can sufficiently reduce the second-order distortion to −75 dB or less even with an attenuation amount of 28 dB. The result was obtained. That is, according to the second embodiment, a variable attenuator for high frequency signals with high variable and low distortion could be constructed.

Although the above embodiment has been described with respect to the case where it is applied to the π type high frequency signal variable attenuator, it can be similarly applied to the T type high frequency signal variable attenuator. .

[0041]

As described above in detail, according to the present invention, it is possible to reduce the occurrence of secondary distortion by connecting a plurality of PIN diodes in series and operating with a large bias current. Further, by connecting the PIN diodes in opposite polarities so that the second-order distortion is generated in the opposite phase, it is possible to cancel the second-order distortion generated in each PIN diode. In addition, by inserting a phase inversion transformer in the input / output unit and providing the first and second variable attenuating circuits in parallel between the phase inversion transformers, the secondary distortion generated in the first and second variable attenuating circuits can be obtained. Can be canceled out as opposite phases, and a variable attenuator for high frequency signals with high variable and low distortion can be constructed.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a high-frequency signal variable attenuator according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an attenuation amount of the high-frequency signal variable attenuator in the same embodiment, and a state of occurrence of second-order distortion and third-order distortion.

FIG. 3 is a frequency characteristic diagram of the high-frequency signal variable attenuator according to the same embodiment.

FIG. 4 is a circuit configuration diagram of a high-frequency signal variable attenuator according to a second embodiment of the present invention.

FIG. 5 is a signal waveform diagram for explaining the operation in the same embodiment.

FIG. 6 is a diagram showing an attenuation amount of the high-frequency signal variable attenuator and a state in which second-order distortion and third-order distortion are generated in the same embodiment;

FIG. 7 is a frequency characteristic diagram of the high-frequency signal variable attenuator according to the same embodiment.

FIG. 8 is a diagram showing a basic configuration of a variable attenuator for high frequency signals.

FIG. 9 is a circuit configuration diagram of a π-type variable attenuator using a conventional PIN diode.

FIG. 10 shows the attenuation amount and 2 of the conventional variable attenuator shown in FIG.
The figure which shows the generation | occurrence | production state of secondary distortion and tertiary distortion.

11 is a frequency characteristic diagram of the conventional variable attenuator shown in FIG.

[Explanation of symbols]

21 ... Input terminal 22 ... Output terminals 23, 26, 32, 39 ... Capacitors 24, 25, 28, 29, 30, 31, 35, 36, 3
8 ... PIN diodes 27, 34, 41, 42 ... Resistors 33, 40 ... High frequency chokes 51, 52 ... Phase inversion transformer 53 ... First variable attenuation circuit 54 ... Second variable attenuation circuits 55, 57, 67, 68, 77, 78 ... Resistors 56, 58, 64, 66, 74, 76 ... Capacitors 61, 62, 63, 65, 71, 72, 73, 75 ... P
IN diode

Claims (4)

[Claims] 1. In a variable attenuator for a high frequency signal, which is formed in a π type or a T type by using a PIN diode, a first PIN provided in series in a signal line between input and output terminals.
A diode, a first bias circuit for supplying a bias current to the first PIN diode, a second PIN diode provided in parallel to a signal line between the input / output terminals, and the second PIN diode A second bias circuit for supplying a bias current to the second bias circuit,
A plurality of PIN diodes connected in series,
A variable attenuator for high frequency signals, characterized in that the IN diode is operated with a bias current larger than that when used alone. 2. In a high frequency signal variable attenuator configured to be a π type or a T type using a PIN diode, a first PIN provided in series to a signal line between input and output terminals.
A diode, a first bias circuit for supplying a bias current to the first PIN diode, a second PIN diode provided in parallel to a signal line between the input / output terminals, and the second PIN diode A second bias circuit for supplying a bias current to the second PIN and the second PIN circuit.
Third P connected in series with opposite polarity to diode
An IN diode and a third bias circuit that supplies a bias current to the third PIN diode are provided, and the distortion generated in the second PIN diode and the third PIN diode is canceled as an opposite phase. Characteristic variable attenuator for high frequency signals. 3. The variable attenuator for high frequency signals according to claim 2, wherein each of the second PIN diode and the third PIN diode is configured by connecting a plurality of PIN diodes in series. 4. A first phase inversion transformer for outputting the same phase and phase inversion of a high frequency input signal, and a PIN diode for variably attenuating the same phase high frequency signal output from the first phase inversion transformer. Of the first variable attenuator circuit, a second variable attenuator circuit using a PIN diode that variably attenuates the phase-inverted high frequency signal output from the first phase inversion transformer, and the first variable attenuator circuit. A variable attenuator for a high frequency signal, comprising: a second phase inverting transformer that mixes and outputs an output signal and an output signal of a second variable attenuator circuit.