JP5158862B2 - Broadband attenuation circuit - Google Patents

Description

  The present invention relates to an attenuation circuit, and more particularly to a broadband attenuation circuit that can obtain good characteristics over a wide band in a quasi-millimeter wave band.

  In recent years, as a new concept wireless communication technology, a UWB (Ultra Wide Band) wireless communication system, which is an ultra-wideband wireless system using a bandwidth of several hundred MHz to several GHz, has attracted attention. A UWB radar system is also being studied as an application of the UWB wireless communication system.

  In a broadband high-frequency circuit, a broadband attenuation circuit (attenuator) is required to adjust the gain of an amplifier or the like. For example, a UWB radar requires a broadband attenuation circuit that operates linearly in a quasi-millimeter wave band (18 GHz to 30 GHz), but a small and low-cost one is required for commercialization of UWB radar.

  Conventionally, π-type and T-type attenuation circuits are widely known. The basic configuration of the π-type and T-type attenuation circuits is shown in FIG. FIG. 4A shows the basic configuration of the π-type attenuation circuit 910, and FIG. 4B shows the basic configuration of the T-type attenuation circuit 920. In each attenuator, a desired attenuation can be obtained by appropriately setting the resistance values of the resistors R11, R12, R13 and R21, R22, R23.

As a variable attenuation circuit in which the attenuation characteristic of the attenuation circuit is variable, one using a PIN diode is widely known. In a variable attenuator circuit using a PIN diode, the resistance value of each PIN diode can be changed by adjusting the bias current of each PIN diode, and the attenuation can be adjusted accordingly. As a high-frequency variable attenuation circuit using a PIN diode, for example, one disclosed in Patent Document 1 is disclosed.
JP 2000-22466 A

  However, conventional π-type and T-type attenuation circuits can be used only in the frequency band up to several GHz when the actual circuit is configured as it is, and it operates properly in the quasi-millimeter wave band of higher frequencies. There is a problem of not doing. In particular, in the frequency band of 20 GHz or higher, the characteristics of the attenuation circuit are greatly different from those of the lower frequency band, and there is a problem that it cannot be put into practical use in such a quasi-millimeter wave band.

  Accordingly, the present invention has been made to solve the above problems, and an object of the present invention is to provide a broadband attenuation circuit that can obtain a suitable gain characteristic in a wide band even in a quasi-millimeter wave band.

A first aspect of the broadband attenuation circuit of the present invention is a broadband attenuation circuit capable of obtaining substantially flat attenuation characteristics over a quasi-millimeter wave band, and is formed on a substrate having a predetermined dielectric constant. comprising Te first input-output port and a transmission line which is routed between the second input-output port, and a grounding conductor portion which is grounded is formed as a ground pattern on the substrate, Further, a chip resistor for adjusting the amount of attenuation is connected in parallel in two or more stages only between the transmission line and the grounding conductor portion on the substrate, and a high frequency signal in a quasi-millimeter wave band is received. The amount of attenuation when input is determined approximately proportionally to the resistance value of the chip resistor and the number of stages.

Another aspect of the broadband attenuation circuit of the present invention is characterized in that the chip resistor is a variable resistor capable of adjusting a resistance value.

Another aspect of the broadband attenuation circuit of the present invention is characterized in that the chip resistor is a temperature-sensitive resistor whose resistance value changes depending on an ambient temperature.

Another aspect of the broadband attenuation circuit of the present invention is characterized in that the chip resistors are arranged in three or more stages in parallel .

  According to the present invention, it is possible to provide a broadband attenuation circuit that can obtain a suitable gain characteristic in a wide band even in the quasi-millimeter wave band.

  A broadband attenuation circuit according to a preferred embodiment of the present invention will be described in detail with reference to the drawings. Each component having the same function is denoted by the same reference numeral for simplification of illustration and description.

  A broadband attenuation circuit according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a substrate pattern of the broadband attenuation circuit 100, and FIG. 2 is a diagram showing a circuit configuration of the broadband attenuation circuit 100 of the present embodiment. As shown in FIG. 1, the broadband attenuation circuit 100 of this embodiment has a configuration in which a resistor unit 110 having a plurality of chip resistors 111 is disposed between a line pattern 101 and a ground pattern 102. For example, FIG. 1 and FIG. 2 show a case where five (five stages) chip resistors 111 are arranged in parallel with the resistor unit 110, but the resistor unit 110 of this embodiment includes the chip resistor 111. The number of stages (number) can be changed. Here, as the substrate parameters, the relative dielectric constant is 3.66, the substrate thickness is 0.254 mm, and the copper foil thickness is 18 μm. Further, the chip resistor 111 has a length of 1 mm and a width of 0.5 mm.

  The circuit configuration of the broadband attenuation circuit 100 of the present embodiment shown in FIG. 1 is shown in FIG. In FIG. 2, the resistance values of the chip resistor 111 are R1 to R5. In such a configuration, when an RF band high-frequency signal is input from the first port 103, the signal is attenuated by a predetermined attenuation amount and output from the second port 104.

  In the broadband attenuation circuit 100 of the present embodiment having the above-described configuration, the amount of attenuation can be adjusted by changing each resistance value of the chip resistor 111. In addition, the amount of attenuation of the broadband attenuation circuit 100 can also be changed by changing the number (number of stages) of chip resistors 111 arranged in the resistor unit 110.

  In the broadband attenuation circuit 100 of the present embodiment, a characteristic that the attenuation amount monotonously increases with respect to the resistance value and the number of stages of the resistor 111 arranged in the resistor unit 110 is obtained. The frequency characteristics of the broadband attenuation circuit 100 will be described below using an example of simulation results. In the following description, the line pattern 101 is a 50Ω line, and the resistance value of each resistor 111 is described as an attenuation circuit resistance value. Here, the case where the resistance values are all the same is taken as an example, but it is needless to say that the embodiments of the present invention are not limited to all the resistance values of the resistors 111 being the same.

  FIG. 3 shows the gain frequency characteristic of the broadband attenuation circuit 100 when the number of stages of the chip resistor 111 of the resistor unit 110 is five. 3A shows the gain frequency characteristic (S21 characteristic) of the broadband attenuation circuit 100 when the horizontal axis is the frequency, and FIG. 3B shows the gain when the horizontal axis is the attenuation circuit resistance value. Shows changes. In FIG. 3A, gain characteristics up to a frequency of 30 GHz when the attenuation circuit resistance values are 47Ω, 100Ω, and 150Ω are indicated by reference numerals 11 to 13, respectively. Also, in FIG. 3B, changes in gain characteristics with respect to the attenuation circuit resistance value when the frequency is 1 GHz and 26.5 GHz are indicated by reference numerals 14 and 15, respectively.

  From FIG. 3 (a), it can be seen that the change with respect to the frequency in the quasi-millimeter wave band is small regardless of the magnitude of the attenuation circuit resistance value, and good gain flatness is obtained in the range of 47 to 150Ω. Further, FIG. 3B shows that in the case of 26.5 GHz in the quasi-millimeter wave band (symbol 15), an attenuation characteristic having linearity with respect to the attenuation circuit resistance value is obtained.

  Similarly, FIG. 4 shows the reflection frequency characteristics of the broadband attenuation circuit 100 when the number of stages of the chip resistor 111 of the resistor unit 110 is five. 4A shows the reflection frequency characteristic (S11 characteristic) of the broadband attenuation circuit 100 when the horizontal axis is the frequency, and FIG. 4B shows the reflection characteristic using a Smith chart. is there. In FIG. 4A, the reflection characteristics up to a frequency of 30 GHz when the attenuation circuit resistance value R is 47Ω, 100Ω, and 150Ω are indicated by reference numerals 21 to 23, respectively, and also in FIG. The trajectories of the reflection characteristics at the resistance values are indicated by reference numerals 24-26, respectively.

  As shown in FIG. 4A, the broadband attenuation circuit 100 of the present embodiment has good reflection characteristics in the quasi-millimeter wave band, and S11 is −12 dB or less. Also, from the Smith chart shown in FIG. 4B, it can be seen that the reflection characteristics are good in the quasi-millimeter wave band at any attenuation circuit resistance value.

  In the broadband attenuation circuit 100 of the present embodiment shown in FIGS. 1 and 2, the number of stages of the chip resistor 111 arranged in the resistor unit 110 is five. However, the attenuation of the broadband attenuation circuit 100 can be changed by changing the number of stages. Characteristics can be adjusted. Hereinafter, characteristics of the broadband attenuation circuit 100 when the number of stages of the chip resistor 111 arranged in the resistor unit 110 is changed will be described.

  The gain frequency characteristic and reflection characteristic of the broadband attenuation circuit 100 when the resistance value of the chip resistor 111 arranged in the resistor unit 110 is fixed to 100Ω and the number of stages of the chip resistor 111 is changed are shown in FIGS. It is shown in FIG.

  FIG. 5 (a) shows gain frequency characteristics (S21 characteristics) up to a frequency of 30 GHz when the number of stages of the chip resistor 111 is one, three, and five. 33. From the figure, it can be seen that the gain frequency characteristic has good flatness in the quasi-millimeter wave band for any number of chip resistor stages.

  FIG. 5B shows the change in gain when the horizontal axis is the number of stages of the chip resistor 111 when the frequency is 1 GHz and 26.5 GHz, which are denoted by reference numerals 34 and 35, respectively. ing. From the figure, it can be seen that in the quasi-millimeter wave band, the gain characteristic shows a good linearity with respect to the number of stages of the chip resistor 111. Under this condition, not only the quasi-millimeter wave band but also 1 GHz shows a similar linearity.

  FIG. 6A shows reflection frequency characteristics (S11 characteristics) up to a frequency of 30 GHz when the number of stages of the chip resistor 111 is one, three, and five, and the respective gain characteristics are denoted by reference numerals 41 to 41. 43. From the figure, the reflection frequency characteristic is relatively reduced on the high frequency side, and the better the reflection characteristic, the greater the number of steps.

  In FIG. 6B, the reflection characteristic of the broadband attenuation circuit 100 is shown using a Smith chart. Also in this figure, the loci of the reflection characteristics when the number of stages of the chip resistor 110 is 1, 3, and 5 are indicated by reference numerals 44 to 46, respectively. From the figure, good reflection characteristics are obtained at any number of stages.

  As described above, according to the present invention, it is possible to provide a broadband attenuation circuit capable of obtaining a suitable frequency characteristic in a wide band in the quasi-millimeter wave band. In addition, since the broadband attenuation circuit of the present invention has a simple structure and can reduce the circuit board area, a low-cost broadband attenuation circuit can be provided.

  As a broadband attenuation circuit according to another embodiment of the present invention, a temperature-sensitive resistor can be used as a resistor disposed in the resistor unit 110. In a system to which the broadband attenuation circuit of the present embodiment is applied, the temperature characteristics thereof are grasped in advance, and the resistor used in the broadband attenuation circuit of the present embodiment has a temperature characteristic opposite to that of the system. Thus, the wideband attenuation circuit of the present embodiment can be a temperature compensation type attenuation circuit.

  As an example, as shown in FIG. 7, in a system in which the broadband attenuation circuit 200 of the present embodiment is configured to receive a high frequency signal output from the amplifier 210, the resistor 201 in the broadband attenuation circuit 200 is connected to the resistor 201. The temperature characteristic opposite to the temperature characteristic of the amplifier 210 is provided. As a result, even if the ambient temperature changes and the characteristics of the amplifier 210 change, the change can be compensated by the resistor 201.

  Next, the characteristics of the attenuation circuit of the π-type attenuation circuit 910 shown in FIG. 8 as a conventional example will be described using simulation results. As an example, FIG. 9 shows a substrate pattern example of a conventional attenuation circuit. The attenuation circuit 900 shown in the figure corresponds to the π-type attenuation circuit 910 shown in FIG. 8, and a chip resistor 903 is arranged on the line pattern 904, and between the line pattern 904 and the ground pattern 905. Chip resistors 901 and 902 are arranged. Corresponding to the π-type attenuation circuit 910 in FIG. 8, the resistance values of the chip resistors 901, 902, and 903 are R11, R12, and R13, respectively.

  Substrate parameters of the attenuation circuit 900 shown in FIG. 9 are the same as in FIG. 1 in that the relative dielectric constant is 3.66, the substrate thickness is 0.254 mm, and the copper foil thickness is 18 μm. The dimensions of the chip resistors 901 to 903 are 1 mm in length and 0.5 mm in width.

  FIG. 10 shows frequency characteristics of the π-type attenuation circuit 900 configured as described above. FIG. 4A shows the gain frequency characteristic (S21 characteristic) of the π-type attenuation circuit 900, and FIG. 4B shows the change of the gain characteristic with respect to the attenuation set value. FIG. 5C shows the reflection frequency characteristic (S11 characteristic) of the π-type attenuation circuit 900, and FIG. 6D shows the change of the reflection frequency characteristic with respect to the attenuation set value.

  In FIG. 10A, frequency characteristics up to 30 GHz when the respective resistance values are adjusted so that the attenuation set values in the low frequency band are 2 dB, 5 dB, 8 dB, and 12 dB are denoted by reference numerals 81 to 84, respectively. Show. According to the figure, the gain almost equal to the set value can be obtained up to about 5 GHz, and the attenuation amount is larger than the set value in the high frequency band, and it is an undesirable characteristic that fluctuates greatly depending on the frequency. Yes. In particular, when the frequency exceeds 17 GHz, the magnitude relationship between the attenuation setting value and the actual attenuation is reversed, and the adjustment range is considerably limited (around 10 dB).

  FIG. 10B shows the change of the gain characteristic with respect to the attenuation setting value when the frequency is 1 GHz (reference numeral 85) and when the frequency is 26.5 GHz (reference numeral 86). As indicated by the graph with reference numeral 85, when the frequency is 1 GHz, gain characteristics substantially equal to the attenuation set value are obtained. On the other hand, when the frequency shown by the reference numeral 86 is 26.5 GHz, not only does the attenuation setting value (calculated value) and the actual gain (S21) not match, but if the attenuation setting value is increased, it is actually On the contrary, the reverse characteristic is seen in which the absolute value of the gain decreases. Further, as the attenuation set value is increased, a change is observed in which the change in the absolute value of the gain gradually decreases and becomes saturated.

  In FIG. 10C, the reflection frequency characteristics up to 30 GHz when the respective resistance values are adjusted so that the attenuation set values in the low frequency band are 2 dB, 5 dB, 8 dB, and 12 dB are denoted by reference numerals 91 to 91, respectively. 94. As shown in the figure, the reflection characteristics are sufficiently reduced in the low frequency band, whereas the reflection characteristics are rapidly deteriorated (reflection increases) in the high frequency band.

  FIG. 10D shows the reflection frequency characteristics with respect to the attenuation amount setting value when the frequency is 1 GHz (reference numeral 95) and when the frequency is 26.5 GHz (reference numeral 96). As shown by the graph with reference numeral 95, when the frequency is 1 GHz, the reflection characteristic is reduced to 25 dB or less. However, when the frequency is 26.5 GHz indicated by reference numeral 96, the reflection characteristic is as high as -5 dB. ing. Note that the reflection characteristic does not change so much depending on the attenuation setting value, and in particular in the case of 26.5 GHz, the reflection characteristic is substantially constant in a state where the reflection amount is large.

  As is clear from the above simulation results, in the conventional π-type attenuation circuit (the same applies to the T-type attenuation circuit), the attenuation amount greatly deviates from the set value in the high frequency band, or the setting range is limited. Therefore, it cannot be put into practical use in such a frequency band, and this cannot be applied particularly to a system that uses a wide band in a quasi-millimeter wave band such as a UWB radar.

  Note that the description in the present embodiment shows an example of the broadband attenuation circuit according to the present invention, and the present invention is not limited to this. The detailed configuration and detailed operation of the broadband attenuation circuit in the present embodiment can be changed as appropriate without departing from the spirit of the present invention.

It is a figure which shows the board | substrate pattern of the broadband attenuation circuit which concerns on the 1st Embodiment of this invention. 1 is a diagram illustrating a circuit configuration of a wideband attenuation circuit according to a first embodiment of the present invention. It is a figure which shows the gain frequency characteristic of the wide band attenuation circuit which concerns on 1st Embodiment. It is a figure which shows the reflective frequency characteristic of the broadband attenuation circuit which concerns on 1st Embodiment. FIG. 5 is a diagram illustrating gain frequency characteristics when the number of stages of chip resistors is changed in the wideband attenuation circuit according to the first embodiment. In the wideband attenuation circuit according to the first embodiment, it is a diagram showing the reflection frequency characteristics when the number of stages of the chip resistor is changed. It is a block diagram of a system using a broadband attenuation circuit according to a second embodiment of the present invention. It is a block diagram which shows the conventional (pi) type attenuation circuit and T type attenuation circuit. It is a figure which shows the board | substrate pattern example of the conventional (pi) type attenuation circuit. It is a figure which shows the frequency characteristic of the conventional (pi) type attenuation circuit.

Explanation of symbols

100, 200 Broadband attenuation circuit 101 Line pattern 102 Ground pattern 103 First port 104 Second port 110 Resistor 111 Chip resistor 201 Resistor 210 Amplifier 910 π-type attenuation circuit 920 T-type attenuation circuit

Claims (4)

A broadband attenuation circuit capable of obtaining a substantially flat attenuation characteristic over a quasi-millimeter wave band,
A substrate having a predetermined dielectric constant;
A transmission line formed on the substrate and routed between the first input / output port and the second input / output port;
A grounding conductor portion formed as a ground pattern on the substrate and grounded,
Furthermore, the chip resistor for adjusting the amount of attenuation is connected in parallel in two or more stages only between the transmission line and the grounding conductor on the substrate,
A broadband attenuation circuit , wherein the attenuation when a quasi-millimeter-wave high-frequency signal is input is determined substantially in proportion to the resistance value and the number of stages of the chip resistor. 2. The broadband attenuation circuit according to claim 1, wherein the chip resistor is a variable resistor capable of adjusting a resistance value. 2. The broadband attenuation circuit according to claim 1, wherein the chip resistor is a temperature-sensitive resistor whose resistance value varies depending on an ambient temperature. 4. The broadband attenuation circuit according to claim 1, wherein the chip resistors are arranged in three or more stages in parallel. 5.

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