JP4361539B2 - Line length switching type phase shift circuit - Google Patents

Description

  The present invention relates to a line length switching type phase shift circuit used in high frequency circuits of various wireless communication devices.

As a line length switching type phase shifter used in a conventional high frequency circuit, there is a 4-bit phase shifter using an RF-MEMS (Micro Electro Mechanical System) switch (for example, see Non-Patent Document 1). This phase shifter uses four switches per bit. In this example, as a line length switching type phase shifter having two branch portions, two switches are provided on each path, and at least four switches are required as a whole. The reason why two switches are required on one path is that the following two conditions must be satisfied. One is that the impedance when the off switch is viewed from the branch is infinite. The other is that the difference between the electrical lengths of the respective paths constituted by the switch and the line in the ON state is 360 / n degrees (n is a natural number). As long as the same switch is used, at least three switches are required.
An RF-MEMS switch is a micro mechanical switch realized by creating a movable part on a substrate such as silicon by microfabrication technology, and is being used as a low-loss, low-distortion switching device (for example, non-patent) Reference 2).

M. Kim, Member, JB Hacker, RE Mihailovich, and JF DeNatale "A DC-to-40 GHz Four-Bit RF MEMS True-Time Delay Network", IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 11, NO. 2 , FEBRUARY 2001 pp56-58 S. Soda, Y. Yoshida, M. Hangai, T. Nishino, S. Izuo, M. Taguchi, “HIGH POWER HAND ING CAPABI ITY OF MOVAB E-WAVEGUIDE DIRECT CONTACT MEMS SWITCHES”, Transducers 2005

  In a conventional line length switching type phase shift circuit using an RF-MEMS switch, four switches are required, and when used at a frequency with a short wavelength such as a millimeter wave band, the length is not negligible compared to the line length to be switched. It will be. In addition, there is a problem that the loss increases when the number of switches is large at such an ultra-high frequency.

  The present invention has been made to solve the above problems, and has an object to obtain a line length switching type phase shift circuit which simplifies the circuit and is miniaturized so that the wavelength can be adapted to a short frequency. To do.

  The line length switching type phase shift circuit according to the present invention includes a branch part provided on each of the input side and the output side, two paths formed between the branch parts, and a line length provided in each path 2 for switching the line length. Each switch with contacts, the electrical length difference between the two contacts of both switches is 360 / n degrees (where n is a natural number), and the input side when any switch is open The electrical length from the branch portion to the contact point of the open switch is made to be a half wavelength of the operating frequency.

  According to the present invention, two two-contact mechanical switches having different contact intervals with a difference in electrical length between contacts of 360 / n degrees (n is a natural number) are used. By setting the electrical length to the contact to be half the wavelength of the operating frequency, the previous two conditions can be satisfied, so it is suitable for use with a short wavelength with only two switches. A phase shift circuit that is reduced in size and size can be configured. Further, since the number of switches used is small, there is an effect that the loss at the super high frequency can be reduced.

Embodiment 1 FIG.
FIG. 1 is an explanatory diagram showing a basic configuration of a line length switching type phase shift circuit according to Embodiment 1 of the present invention.
In the figure, this phase shift circuit has a branching section 11 that branches a high-frequency signal input to an input terminal 10 into two. In addition, switches 12 and 15 are provided on the two paths separated by the branching unit 11. The switch 12 is a two-contact switch that is provided in one path and has two contacts 13 and 14 for switching the line length. Similarly, the switch 15 is also a two-contact switch that is provided in the other path and has two contacts 16 and 17 for switching the line length. Here, the difference between the electrical length between the two contacts 13 and 14 of the switch 12 and the electrical length between the two contacts 16 and 17 of the switch 15 is set to be 360 / n degrees (n is a natural number). That is, switches 12 and 15 are switches having different distances between the contacts. Signals taken out from the contacts 14 and 17 on the output side of the switches 12 and 15 are configured to be guided to the output terminal 19 via another branching portion 18.

Next, the operation will be described.
When the switch 12 is turned off and the switch 15 is turned on, the impedance is infinite because the contacts 13 and 14 are separated in an open state. When the distance of the transmission line from the branching portion 11 to the contact 13 is set to a half wavelength of the operating frequency, the impedance viewed from the branching portion 11 to the switch 12 becomes infinite, so that nothing is connected. . Accordingly, all signals input to the input terminal 10 are transmitted through the switch 15. Further, if the distance between the branch part 18 and the contact point 14 is the same as the distance from the branch part 11 to the contact point 13, all signals appearing at the branch part 18 passing through the switch 15 are transmitted to the output terminal 19. .

  On the other hand, when the switch 15 is turned off and the switch 12 is turned on, the impedance is infinite because the contacts 16 and 17 are separated in an open state. When the distance of the transmission line from the branch part 11 to the contact 16 is set to a half wavelength of the operating frequency, the impedance viewed from the branch part 11 to the switch 15 becomes infinite, so that nothing is connected. . Therefore, all signals input to the input terminal 10 are transmitted via the switch 12. If the distance between the branching portion 18 and the contact point 17 is the same as the distance from the branching portion 11 to the contact point 16, all signals appearing at the branching portion 18 passing through the switch 12 are transmitted to the output terminal 19.

  Here, for example, the contact point of each switch is such that the passing phase from the contact point 16 to the contact point 17 when the switch 15 is on is 45 degrees larger than the passing phase from the contact point 13 to the contact point 14 when the switch 12 is on. Set the interval. Then, the passing phase of the signal passing through the phase shift circuit can be made to differ by 45 degrees when the switch 12 is on and the switch 15 is off and the switch 12 is off and the switch 15 is on.

  As described above, according to the first embodiment, the switches 12 and 15 having the two contacts for switching the line length are provided in the two paths formed between the branch portions 11 and 18, respectively. The difference in electrical length between the two contacts of 15 is 360 / n degrees (n is a natural number), and the switch contacts that are open from the branch on the input side when either of the switches 12 and 15 is open Since the electrical length is set to be half the operating frequency, the phase shift circuit condition can be satisfied, and simplification and miniaturization suitable for use at a short wavelength with only two switches. A phase shift circuit can be configured. In addition, since the number of switches used is small, loss at ultra high frequency can be reduced.

Embodiment 2. FIG.
FIG. 2 is a sectional view showing the structure of the operating state of the RF-MEMS switch according to Embodiment 2 of the present invention. FIG. 2A shows an off state, and FIG. 2B shows an on state.
In FIG. 2, the RF-MEMS switch uses a silicon substrate (insulating substrate) 28 having a cavity 281 excavated by etching. On the upper surface of the silicon substrate 28, the input terminal 20 and the output terminal 23 of the coplanar line are formed so as to face each other with the cavity 281 interposed therebetween. A silicon nitride thin film (insulator thin film) 27 serving as a movable portion is stretched over the hollow layer of the cavity 281, and coplanar lines 21 and 22 are formed thereon. These coplanar lines 21 and 22 are formed continuously with the input terminal 20 and the output terminal 23, respectively. Further, contacts 24 and 25 projecting from the thin film 27 toward the cavity 281 are provided at the end portions of the coplanar lines 21 and 22 (however, the ground conductor of the coplanar lines is continuous and does not form an end portion). Is provided. A conductor layer 26 is provided on the bottom surface 282 of the cavity 281. When the RF-MEMS switch is turned on, a line is sandwiched between the silicon substrate 28 and the silicon nitride thin film 27, and a ground conductor (not shown) on the thin film 27 is formed. ) And a coplanar line-like propagation mode.

A range 30 indicates a portion of the line having a propagation mode like the coplanar line, a range 31 indicates a coplanar line formed on the thin film 27 on the upper part of the air layer, and a range 32 is formed on the silicon substrate 28. The created coplanar track is shown.
The operation of turning on the RF-MEMS switch is such that another electrode (not shown) is provided opposite to the thin film 27 and the bottom surface 282, and a voltage is applied to these to attract the thin film 27 serving as a movable part to the bottom surface 282 side. The contact 24, 25 on the thin film side is brought into contact with the conductor layer 26 on the bottom side. The structure of the coplanar line and the electrode structure for turning on / off the RF-MEMS switch are the same as those shown in Non-Patent Document 2.

FIG. 3 shows a configuration of a line length switching type phase shift circuit according to the second embodiment of the present invention. In the figure, parts corresponding to those in FIG.
In this phase shift circuit, as in FIG. 1, the RF-MEMS switches 12 and 15 are provided on the two branch circuits divided by the branch unit 11. The same basic structure as described in FIG. 2 is used. The constituent parts of the RF-MEMS switches 12 and 15 that correspond to the parts in FIG. 2 are shown by attaching the reference numerals used in FIG. 2 to the two digits after the numeral “12” or “15”. .
The RF-MEMS switches 12 and 15 used here have the contact distance and the length of the conductor layers 1226 and 1526 so that the difference in electrical length between the two contacts of both switches is 360 / n degrees (n is a natural number). Although different, each of the cavity 281 (FIG. 2) and the thin film 27 (FIG. 2) is the same size in both switches. 3, when the outer frame of the RF-MEMS switches 12 and 15 is viewed as a cavity, the distance between the input terminal 1220 and the contact 1224, the distance between the contact 1224 and the contact 1225, the contact 1225 and the output in the MEMS switch 12 The sum of the distances of the terminals 1223 is equal to the sum of the distance between the input terminal 1520 and the contact 1524, the distance between the contact 1524 and the contact 1525, and the distance between the contact 1525 and the output terminal 1523 in the MEMS switch 15. Thus, since the length of the movable part is the same in the RF-MEMS switches 12 and 15, the voltage for driving the movable part can be the same value, and the control circuit therefor can be simplified. it can. In addition, since switches having the same outer shape can be used, it is possible to avoid a complicated layout of peripheral circuit patterns. The line length switching type phase shift circuit may be manufactured on a single substrate together with the RF-MEMS switches 12 and 15.

Next, the operation will be described.
When the RF-MEMS switch 12 is in the off state and the RF-MEMS switch 15 is in the on state, the contacts 1224 and 1225 of the RF-MEMS switch 12 are open and separated, so the impedance becomes infinite. When the sum of the electrical length from the branching section 11 to the input terminal 1220 of the RF-MEMS switch 12 and the electrical length from the input terminal 1220 to the contact 1224 is set to a half wavelength of the operating frequency, the branching section 11 transmits the RF-MEMS. Since the impedance viewed from the direction of the switch 12 is infinite, nothing is connected. Therefore, all signals incident on the input terminal 10 are transmitted to the RF-MEMS switch 15. Further, if the distance between the branch portion 18 and the contact point 1225 is the same as the distance from the branch portion 11 to the contact point 1224, all signals appearing at the branch portion 18 after passing through the RF-MEMS switch 15 are output from the output terminal 19. It is transmitted to people.

  On the other hand, when the RF-MEMS switch 15 is in an off state and the RF-MEMS switch 12 is in an on state, the contacts 1524 and 1525 are open and separated, so that the impedance becomes infinite. When the sum of the electrical length from the branching unit 11 to the input terminal 1520 of the RF-MEMS switch 15 and the electrical length from the input terminal 1520 to the contact 1524 is set to a half wavelength of the operating frequency, the branching unit 11 transmits the RF-MEMS. Since the impedance viewed from the direction of the switch 15 is infinite, nothing is connected. Accordingly, all signals incident on the input terminal 10 are transmitted to the RF-MEMS switch 12. If the distance between the branch portion 18 and the contact point 1525 is the same as the distance from the branch portion 11 to the contact point 1524, all signals appearing at the branch portion 18 after passing through the RF-MEMS switch 12 are output from the output terminal 19. It is transmitted to people.

  Here, for example, the passing phase from the contact 1524 to the contact 1525 when the RF-MEMS switch 15 is turned on is 45 degrees larger than the passing phase from the contact 1224 to the contact 1225 when the RF-MEMS switch 12 is turned on. Set the distance between the contacts of each switch. Then, the RF-MEMS switch 12 is turned on and the RF-MEMS switch 15 is turned off, and the RF-MEMS switch 12 is turned off and the MEMS switch 15 is turned on. Can be different.

  As described above, according to the second embodiment, since the switches 12 and 15 are RF-MEMS switches manufactured by micromachining technology and using an insulating thin film as a movable part that opens and closes contacts, millimeters are used. A miniaturized phase shifter suitable for a frequency with a short wavelength such as a waveband can be realized. Moreover, since the size of the movable part is made the same by the switches 12 and 15, the drive voltage can be made the same value, and the control circuit for that purpose can be simplified. In addition, since switches having the same outer shape can be used, it is possible to avoid a complicated layout of peripheral circuit patterns.

It is explanatory drawing which shows the basic composition of the line length switching type phase shift circuit by Embodiment 1 of this invention. It is sectional drawing which shows the structure of the MEMS switch which concerns on Embodiment 2 of this invention. 2 shows a configuration of a line length switching type phase shift circuit according to a second embodiment of the present invention.

Explanation of symbols

  10, 20, 1220, 1520 input terminal, 11, 18 branching section, 12, 15 switch (RF-MEMS switch), 13, 14, 16, 17, 24, 25, 1224, 1225, 1524, 1525 contact, 19, 23, 1223, 1523 output terminal, 21, 22 coplanar line, 26, 1226, 1526 conductor, 27 thin film (insulator thin film), 28 silicon substrate (insulating substrate), 281 cavity.

Claims (4)

A branch section provided on each of the input side and the output side;
Two paths formed between the branch parts;
Each having two contacts for switching the line length provided in the two paths,
The difference between the electrical lengths of the two contacts of the switches is 360 / n degrees (n is a natural number), and the contact of the switch that is open from the branch on the input side when any of the switches is open Line length switching type phase shift circuit, characterized in that the electrical length up to is half the operating frequency.   2. The line length switching type phase shift circuit according to claim 1, wherein each switch is an RF-MEMS switch having an insulating thin film as a movable part that opens and closes a contact. Each RF-MEMS switch
An insulating substrate having a cavity dug by etching;
An insulator thin film stretched over the hollow layer of the cavity;
The input terminal and the output terminal formed on the upper surface of the insulating substrate across the cavity extend above the insulator thin film above the cavity, and each end protrudes from the insulator thin film toward the cavity and has two contacts. Each line forming
A conductor layer formed on the bottom surface of the cavity so as to face the two contacts;
3. The line length switching type phase shift circuit according to claim 2, wherein the two contact points are in contact with the conductor layer when the insulator thin film is drawn toward the bottom surface of the cavity.   4. The line length switching type phase shift circuit according to claim 3, wherein in the RF-MEMS switch, the sizes of the cavity and the insulator thin film are the same in both switches.

Images