Patent Application
20050093646
1. Field of the Invention
The present invention relates to a high frequency switch, and particularly to a high frequency switch used for switching of an RF signal used for a radar and a communication device operated in a millimeter wave band.
2. Description of the Related Art
The application of a microwave device has been increasingly advanced with the progression of computerization. A microwave device of a cellular phone using a relatively low frequency, a microwave device used in information communication by a high frequency much higher than the low frequency of the cellular phone, a microwave device used in communication apparatuses such as a radar for automobile use, an observation satellite, etc. each of which uses a high frequency much higher than the above frequency in information communication, etc. have been applied in many fields.
Of these, the radar using the millimeter wave-band microwave device is used to recognize a forward vehicle or automobile and constitutes part of a system for performing automobile's collision avoidance.
A system for scanning nine directions has been used in a millimeter wave-band radar for detecting a forward automobile to carry out automobile's collision avoidance. This is used assuming that an automobile runs along three lanes. This system needs to perform the scanning of nine directions with a view toward scanning three directions for each lane. Therefore, there is a need to provide a nine-channel switch which switches an RF signal over to the nine directions.
As a high-speed switch, a small-sized and high-speed high frequency switch using a microwave IC (MIC) has been realized in recent years. Further, it is configured as an MMIC (Monolithic Microwave IC) in which connecting lines and switching elements are integrally formed on a semiconductor substrate, thereby enabling further speeding-up and miniaturization of the switch.
When the nine-channel high frequency switch is configured, the most basic configuration is proposed wherein nine SPST (Single Pole Single Throw) switches formed on a GaAs substrate are used. That is, a signal line that branches into nine branch lines from one input terminal via a branch point is formed on a dielectric substrate, and SPST switches are respectively provided in the individual branch lines of the signal line to thereby configure a nine-channel switch.
Alternatively, a nine-channel switch is configured wherein four SP3T (Single Pole 3 Throw) switches formed on a GaAs substrate are provided on a dielectric substrate, an input end of the first SP3T switch is connected to input signal lines on the dielectric substrate, and input terminals of the three other SP3T switches are respectively connected to three output terminals of the first SP3T switch to thereby set nine output ends.
As a known example of a conventional high frequency switch, there has been disclosed a configuration wherein by adopting a switch circuit using a distributed constant FET for SPDT, a less passage loss can be obtained in the case of switch ON and high isolation can be expected in the case of switch OFF (see, for example, Japanese Patent Laid-open No. 2002-33602, paragraph numbers [0013] and [0014] and
Further, as a known example of another high frequency switch, there has been disclosed a high frequency switch which includes a plurality of tristate switches which are connected in tournament form by strip lines and wherein the lengths of strip lines from branch points of adjacent lines connected to the individual switches to their corresponding switches are so adjusted that real parts of impedance obtained by viewing the turned-off switches from the branch points of the adjacent lines connected to the individual switches become maximum and imaginary parts thereof reach 0, and the lengths thereof from branch points of roots of the adjacent lines connected to the respective branch points to their corresponding branch points are adjusted to integral multiples of a ½ wavelength (see, for example, Japanese Patent Laid-open No. 2000-261218, paragraph number [0006] and
Furthermore, as a known example of a further high frequency switch, there has been disclosed one wherein when four or more receiving antennas are switched in a holographic radar, single pole 2 throw (SPDT) or single pole 3 throw (SP3T) unit switches, e.g., planar circuit type high frequency switches like an MMIC and an HIC are utilized and combined in the form of a tournament to thereby realize multi-switching (see, for example, Japanese Patent Laid-open No.2000-155171, paragraph number [0005] and
Still further, as a known example of yet another high frequency switch, there has been disclosed an example wherein one transmission line is provided in the direction of the input of a signal and the remaining two transmission lines are provided in the directions of 90°, 180° and 270° with respect to the input direction of the signal to make equal distances to respective output terminals, thereby forming 3-distributed switches low in loss and equal in loss (see, for example, Japanese Patent Laid-open No. 2000-294568, paragraph number [0031] and
However, the nine channel switches respectively having such a configuration that the nine SPST switches are used and such a configuration that the four SP3T switches are used, are hard to achieve a size reduction because the dielectric substrates become large. Further, since the characteristics of the respective SPST and SP3T switches to be used are hard to match and the number of parts increases, the electrical characteristics of individual channels are apt to vary due to variations in bonding wire at their packaging. It was also difficult to constitute the high frequency switch having the nine channels uniform in electrical characteristic. It is thus considered that in order to constitute the nine-channel switch uniform in electrical characteristic, the MMIC configured by the one-chip GaAs substrate constitutes switches that branch into nine.
Isolation is considered as one of major parameters indicative of switch performance of a high speed switch. Since, however, the branch lines can be laid out at intervals of 90° with respect to the input signal line in the SP3T switch, it was easy to ensure the isolation between the respective branch lines. However, when the nine-branched switches are constituted by the MMIC simply configured of the one-chip GaAs substrate to configure the high frequency switch having the nine channels uniform in electrical characteristic, the branch angle formed between the respective branch lines becomes an acute angle.
Therefore, a problem arose in that isolation between respective terminals for the nine channels was hard to obtain.
The present invention has been made to solve the foregoing problems. A first object of the present invention is to configure a high frequency switch which is small in size and reduced in the number of parts and which has four or more branch lines and provides an isolation ranging more than or equal to 25 dB and less than or equal to 35 dB between the branch lines.
According to one aspect of the invention, there is provided a high frequency switch comprising: a first semiconductor substrate; a first signal line provided on the first semiconductor substrate and having a first main line, and first branch lines that branch into four or more from the first main line via a first branch point and first transmission lines each having a length of a ¼ wavelength of a signal propagated over the first branch lines, each first transmission line being contained in part of said each first branch line; and first switching elements each of which is shunt-connected between the first branch line on the end side of the first transmission line as viewed from the first branch point of the first signal line, and a ground end and electrically connects or shuts off the first branch line and the ground end in accordance with a control signal; wherein mutual connecting points of the first switching elements at the two first branch lines are provided with being spaced such a distance that isolation corresponding to the frequency of the signal reaches more than or equal to 25 dB and less than or equal to 35 dB at the ends of the adjacent first branch lines.
Accordingly, even when four or more branch lines that branch at the acute angle as viewed from a branch point are provided, a high frequency switch according to the present invention can be configured which has predetermined isolation and which is small in size and reduced in the number of parts.
Hence, the high frequency switch can be provided at low cost.
Other objects and advantages of the invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific embodiments are given by way of illustration only since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.
In all figures, the substantially same elements are given the same reference numbers.
First Embodiment
Referring to
Referring to
The FET 14d is connected between the connecting point 14g and a ground end through its source and drain. The gate thereof is provided as a control electrode, and a control terminal 14k is provided via a gate resistor 14i and a connecting line 14j as viewed from the gate electrode.
In the high frequency switch 10, an RF signal is inputted to the input terminal 16 and a control voltage is applied to the control terminal 14k connected to the gate electrode of the FET 14d of each unit switch 14X so that the unit switch 14X is turned on and off to output the RF signal from the output terminal 14e.
That is, when a gate voltage Vg=0V is applied to the control terminal 14k, the FET 14d is brought to an on state so that the connecting point 14g of the FET 14d is grounded. Therefore, the connecting point 14g is brought to an open end. Thus, the RF signal is reflected by the λ/4 transmission line 14f and hence the unit switch 14X is held off.
On the other hand, when a gate voltage Vg less than or equal to a pinch off voltage Vp, e.g., a gate voltage Vg=−5V is applied to the control terminal 14k, the FET 14d is brought to an off state so that an RF signal is propagated to the output terminal 14e via the branch signal line 14c.
In order to definitely identify signals among the respective unit switches 14X in the high frequency switch 10, the isolation between the two unit switches 14X is set to 25 dB or more, for example, 30 dB in the present embodiment.
Since it is normally difficult to ensure the isolation between the adjacent respective unit switches 14X, e.g., between 141 and 142 or 144 and 145, the isolation between the respective unit switches 14X is ensured if the isolation between the adjacent unit switches 14X is 25 dB or more. However, the present invention is not necessarily limited to the isolation between the adjacent unit switches 14X. The isolation between the arbitrary two unit switches 14X is also set to 25 dB or more.
This isolation corresponds to isolation measured between the output terminals 14e provided at the ends of the two unit switches 14X. The value of the isolation is determined according to the distance (corresponding to an interval indicated by L in
In
If an attempt is made to use the high frequency switch 10 as, for example, a 77 GHz-band switch and ensure an isolation of 30 dB, then 310 μm is needed as the line-to-line distance. In the case of a 60 GHz-band switch, the line-to-line distance needs 270 μm. When a 90 GHz-band switch is used, the line-to-line distance needs 330 μm.
In the sight of the isolation, the longer the distance L between the connecting points 14g and the line-to-line distance M between the connecting lines 14h, the better. As, however, the distance L between the connecting points 14g and the line-to-line distance M between the connecting lines 14h increase, the size of the GaAs substrate 12 becomes large and hence the MMIC becomes large in chip size.
Further, since the loss increases and a power loss becomes great with the increase in the chip size, large power is needed. The magnitude of isolation necessary and enough for it exists. If its magnitude ranges more than or equal to 25 dB and less than or equal to 35 dB, more preferably, it falls within a value ranging more than or equal to 29 dB and less than or equal to 31 dB, for example, then the signals among the unit switches 14X can be definitely identified. That is, sufficient resolution is obtained and a high frequency switch whose substrate is small and power loss is less reduced, can be configured.
That is, in the high frequency switch 10, the distance L between the connecting points 14g and the line-to-line distance M between the connecting lines 14h are set in such a manner that the isolation measured between the output terminals of the two unit switches 14X falls within a range more than or equal to 25 dB and less than or equal to 35 dB, more desirably, a value more than or equal to 29 dB and less than or equal to 31 dB.
Although the unit switch 14X shown in
In the unit switch 14X shown in
When a forward bias voltage is applied to the output terminal 14e, the diode 14m is brought into conduction so that the connecting point 14g is grounded so as to assume an open end. Thus, the RF signal is reflected by the λ/4 transmission line 14f so that the unit switch 14X is brought to an off state.
When a reverse bias voltage is applied to the output terminal, the diode 14m is brought into non-conduction. Thus, the diode 14m is brought to an off state so that the RF signal is propagated to the output terminal 14e via the branch signal line 14c.
As described above, the high frequency switch 10 according to the first embodiment includes the signal line 14, which is provided on the semiconductor substrate 12 and which branches into four or more from the connecting line 14a on the input side via the branch point 14b and has the λ/4 transmission lines 14f contained in parts of their branch signal lines 14c, and the FETs 14d each connected in shunt with the branch signal line 14c between the connecting point 14g on the output terminal 14e side as viewed from the λ/4 transmission line 14f provided in the branch signal line 14c, and the ground end. The mutual connecting points of the FETs 14d or the connecting lines 14h in the two branch signal lines 14c are arranged with being spaced therebetween such a distance that the isolation corresponding to the RF signal reaches over 25 dB and under 35 dB at the ends of these branch signal lines 14c. Owing to such a configuration, necessary isolation between the respective unit units 14X of the high frequency switch 10 can be ensured. It is also possible to bring the semiconductor substrate 12 into less size and cost and reduce a power loss. Further, the high frequency switch 10 is configured as the MMIC and variations in the characteristic between the unit switches 14X can be less reduced. By extension, a high frequency switch, which is uniform in electrical characteristic and which is small in size and low in loss, can be configured. The high frequency switch can be provided at low cost.
Modification 1
In the high frequency switch 10 shown in
On the other hand, in the high frequency switch 20 shown in
Further, a resistor 22b and a capacitor 22c for blocking a DC component are connected in series between a connecting point 22a provided between these gate resistor 14i and connecting line 14j and a ground end.
In microwave devices, since the layout of circuit elements influences the electric characteristics of a microwave device, the layout of the high frequency switch 20 might preferably be rather than the layout of the high frequency switch 10 as the case may be. When the resistors 22b and the capacitors 22c are not respectively provided between the connecting points 22a and the ground ends in the layout of the high frequency switch 20, the connecting lines 14j and the control terminals 14k are interposed in the unit switch 141 and the unit switch 142 or the unit switch 144 and the unit switch 145. Thus, the line-to-line distance M between the adjacent connecting lines 14h becomes equivalent to be short, and isolation is degraded depending on load impedance externally connected to each of the control terminals 14k.
Therefore, a resistor 22b of 50 Ω or more and a capacitor 22c for blocking a DC component are connected in series between the connecting point 22a and the ground end to thereby enable prevention of degradation of isolation due to a variation in load.
Referring to
Judging from the graphs, an isolation of 35 dB is ensured in the high frequency switch 10 and the high frequency switch 20.
Although each of the high frequency switch 10 and the high frequency switch 20 is not placed under the influence of a variation in external load, the isolation is greatly degraded due to the external load where no resistors 22b and capacitors 22c are connected.
Modification 2
In the high frequency switch 20 according to the modification 1, the resistor 22b of 50 Ω or more and the capacitor 22c for blocking the DC component are connected in series between the connecting point 22a and the ground end to thereby prevent degradation of the isolation due to the variation in load. In the high frequency switch 26 shown in
Incidentally, if the length of the connecting line 14j is not equal to λ/4, then the length thereof may be either longer or shorter than λ/4.
Even in the case of such a configuration, an effect similar to the high frequency switch 20 according to the modification 1 is obtained, and the degradation of isolation due to a variation in load can be prevented. As the isolation, an isolation of 35 dB similar to the diagrammatic diagram A shown in
Modification 3
The high frequency switch 30 shown in
The amplifier 32 is capable of compensating for a passage loss.
Modification 4
The high frequency switch 36 shown in
Modification 5
A passage loss occurs during a period in which the signal propagates from the input terminal 16 to an output terminal 14e of each unit switch 14X. The amplifier 42 is capable of compensating for the passage loss in advance.
Second Embodiment
Referring to
The high frequency switch 50 has a configuration wherein an output terminal 14e of a unit switch 143 of a high frequency switch 10a used as a first high frequency switch, and an input terminal 16 of a high frequency switch 10b used as a second high frequency switch are connected to each other by a bonding wire 52.
Thus, the nine branch switch equipped with the nine unit switches 50X (where X=1, 2, 3, . . . , 9) is configured, which is disposed on a dielectric substrate 54. The unit switches 50X are identical in configuration to the unit switches 14X.
The present nine-branch high frequency switch 50 is used to recognize a forward automobile, as, for example, a millimeter wave radar for automobile use and constitutes part of a system for performing automobile collision avoidance.
The system for carrying out automobile collision avoidance scans three directions one-lane assuming that the automobile is being driven along three lanes. Therefore, the millimeter wave radar for detecting the forward automobile needs to scan nine directions and requires a nine branch high frequency switch which switches an RF signal over to the nine directions.
The high frequency switches 10a and 10b that constitute the high frequency switch 50 are configured as MMICs and respectively have isolations of, for example, 30 dB between the respective unit switches 50X. Therefore, high resolution in the adjacent two directions can be ensured and variations in characteristic between the unit switches 50X are less reduced.
Since the high frequency switch 50 is provided only with the high frequency switches 10a and 10b and the bonding wires 52 for connecting the high frequency switches 10a and 10b, as parts, the number of parts can be reduced and variations in electrical characteristic between the unit switches 50X can be lessened.
As described above, the high frequency switch according to the present embodiment is equivalent to one wherein two each corresponding to the high frequency switch 10 having the five branch switches described in the first embodiment are selected and the output terminal 14e of the unit switch 143 of the high frequency switch 10a and the input terminal 16 of the high frequency switch 10b used as a second high frequency switch are connected by the bonding wire. Owing to such a configuration, the high frequency switch reduced in the number of parts and uniform in terms of the electrical characteristics of the switches for the respective branch lines can be configured while maintaining predetermined isolation between the adjacent unit switches 50X. This high frequency switch can be provided at low cost.
Incidentally, although the present embodiment has explained, as one example, the two series-connected high frequency switches, the number of the high frequency switches is not necessarily limited to two. Much more high frequency switches may be connected.
Modification 1
The high frequency switch 60 shown in
That is, the high frequency switch 60 has a configuration wherein the output terminal 14e of the unit switch 143 of the high frequency switch 30 and the input terminal 16 of the high frequency switch 10 are connected by a bonding wire 52.
In the high frequency switch 60, an RF signal inputted to the input terminal 16 is reduced in signal output due to a passage loss. Therefore, when the RF signal is inputted from the output terminal 14e of the unit switch 143 to the input terminal 16 of the high frequency switch 30 in case of no amplifier 32, a difference occurs between each of outputs of unit switches 501, 502, 503 and 504 of the high frequency switch 30 and each of outputs of unit switches 505, 506, 507, 508 and 509 of the high frequency switch 10. In order to prevent it, the amplifier 32 temporarily amplifies the RF signal and thereby compensates for the passage loss, before the RF signal is outputted from the output terminal 14e of the unit switch 143 of the high frequency switch 30, and inputs the so-processed signal to the input terminal 16 of the high frequency switch 10.
Thus, the outputs of the RF signals of the respective unit switches 50X can be uniformized. By extension, a high frequency switch can be configured which is uniform in terms of electrical characteristics of the switches of the respective branch lines.
This high frequency switch can be provided at low cost.
Modification 2
The high frequency switch 70 shown in
That is, the high frequency switch 70 has a configuration wherein the output terminal 14e of the unit switch 143 of the high frequency switch 36 and the input terminal 16 of the high frequency switch 10 are connected to each other by a bonding wire 52.
In the high frequency switch 70, an RF signal inputted to the input terminal 16 is reduced in signal output due to a passage loss. Therefore, when the RF signal is inputted from the output terminal 14e of the unit switch 143 to the input terminal 16 of the high frequency switch 30 in case of no attenuators 38, a difference occurs between each of outputs of unit switches 501, 502, 503 and 504 of the high frequency switch 36 and each of outputs of unit switches 505, 506, 507, 508 and 509 of the high frequency switch 10. In order to prevent it, the attenuators 38 are respectively inserted immediately before the output terminals 14e of the unit switches 501, 502, 503 and 504, whereby the outputs of the unit switches 501, 502, 503 and 504 and the outputs of the unit switches 505, 506, 507, 508 and 509 can be uniformized.
Thus, the outputs of the RF signals of the respective unit switches 50X can be uniformized. By extension, a high frequency switch can be configured which is uniform in terms of electrical characteristics of the switches of the respective branch lines. This high frequency switch can be provided at low cost.
Modification 3
In
The high frequency switch 80 has a configuration wherein the output terminal 14e of the unit switch 143 of the high frequency switch 40a used as a first high frequency switch, and the input terminal 16 of the high frequency switch 40b used as a second high frequency switch are connected to each other by a bonding wire 52.
Since each of the high frequency switches 40a and 40b has a passage loss, an RF signal inputted to the input terminal 16 of the high frequency switch 40a is reduced in signal output due to the passage loss when it is inputted from the output terminal 14e of the unit switch 143 to the input terminal 16 of the high frequency switch 40b in case of no amplifiers 42. Therefore, a difference occurs between each of outputs of unit switches 501, 502, 503 and 504 of the high frequency switch 30 and each of outputs of unit switches 505, 506, 507, 508 and 509 of the high frequency switch 10. In order to prevent it, the amplifiers 42 are respectively provided immediately following the input terminals 16 of the high frequency switches 40a and 40b. Each of the amplifiers 42 effects beforehand compensation corresponding to the passage loss on the input RF signal and transmits the so-processed signal to each of the unit switches 50X.
Thus, the outputs of the RF signals of the unit switches 50X can be uniformized. By extension, a high frequency switch can be configured which is uniform in terms of electrical characteristics of the switches of the respective branch lines. This high frequency switch can be offered at low cost.
Although the second embodiment has explained, as an example, the case in which some of the high frequency switches described in the first embodiment are combined together, other high frequency switches described in the first embodiment may be utilized in combination.
As described above, the high frequency switch according to the present invention is suitable for a high frequency switch used for switching of an RF signal employed in each of a radar and a communication device operated in a millimeter wave band.
While the presently preferred embodiments of the present invention have been shown and described. It is to be understood these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-369377 | Oct 2003 | JP | national |
