Phase shifter

Abstract: A phase shifter, which can switch between a phase delay circuit and a phase leading circuit consisting of inductors and capacitors, is constituted by disposing FETs having inductors or capacitors arranged in parallel with the source and drain electrodes of each FET connected and controlling a bias voltage to be applied to the gate electrodes of the FETs to switch between the on and off conditions of the FETs. Thus, a phase shifter obtained has a small frequency characteristic.

Description: 1. Field of the Invention The invention relates to a phase shifter using, as a switching device, an FET (field-effect transistor) which operates at microwave and millimetric wave bands. 2. Description of the Related Art The FET-using phase shifter is commonly used for various transmission circuits and phased array antennas at microwave and millimetric wave bands. The conventional phase shifters include one having an equivalent circuit as shown in Fig. 14, which is known as a switched line type phase shifter. In Fig. 14 reference numeral 1 is a first FET, 3 a second FET, 5 a third FET, 6 a fourth FET, 25 a reference transmission line, and 26 a delay transmission line. A drain electrode 27a of the first FET 1 and a drain electrode 27b of the second FET 3 are connected to an input terminal 10, and a drain electrode 27c of the third FET 5 and a drain electrode 27d of the fourth FET 6 are connected to an output terminal 11. The reference transmission line 25 is connected between a source electrode 28b of the second FET 3 and a source electrode 28d of the fourth FET 6, and the delay transmission line 26 having an electrical length longer than the reference transmission line 25 is connected between a source electrode 28a of the first FET 1 and a source electrode 28c of the fourth FET 6. Reference numeral 29 is a gate electrode for each FET. Schindler et al. discloses in Microwave and Millimeter-Wave Monolithic Circuits Symposium, 1988 Digest of Papers, IEEE 1988, pages 95-98 a phase shifter with a first and a second serial circuit between a RF IN terminal an a RF OUT terminal and a third circuit between GND and a node between the first and the second serial circuit. A similar phase shifter is further disclosed in Lane et al. Electronically Scanned Antennas, IEE Colloquium 1988, pages 6-11. Takasu et al. discloses in Microwave Symposium Digest 1994, IEEE MTT-S International, vol. 3 pages 1413-1416 an X-band five-bit Ga As MMIC phase shifter using parasitic distributed-line effects of the FET. US 5,021,758 A discloses a microwave phase shifter including a switched spiral inductor and a MESFET for switching the inductor in and out of the circuit in order to reduce parasitic capacitance's. US 5,317,290 A discloses a phase shift network for a multi-bit phase shifter. This circuit provides in one switching state a band pass network of low insertion phase and in the other switching state a low pass network of high insertion phase. A. Sharma provides in Microwave Journal (1989), Suppl., no. 9, pages 95-112, an overview of phase shifters for microwave of millimeter wave systems known or in use in 1989. Summary of the Invention The invention aims to provide a phase shifter which is compact and has a small frequency characteristic. This aim is achieved by a phase shifter according to claim 1. Improvements of this phase shifter are provided in the dependent claims. In a phase shifter according to the invention both ends of an inductor line pattern connected in parallel with an FET may be connected to source electrode patterns and drain electrode patterns which are in a interdigital(comb teeth) form of the FET. Where interdigital(comb teeth) means "formed in an interlaced pattern". In a phase shifter according to the invention, line patterns forming the input and output terminals of a capacitor connected in parallel with an FET may be connected to source electrode patterns and drain electrode patterns which are in a interdigital(comb teeth) form of the FET. In a phase shifter according to the invention, gate electrode patterns may be formed in gaps between source electrode patterns and drain electrode patterns which are in a interdigital(comb teeth) form to form an FET, and remaining source electrode patterns and drain electrode patterns are connected to form an inductor. In a phase shifter according to the invention, gate electrode patterns may be formed in gaps between source electrode patterns and drain electrode patterns which are in a interdigital(comb teeth) form to form an FET, and a Metal insulator Metal capacitor (hereinafter referred to as "MIM capacitor") is formed between remaining source electrode patterns and drain electrode patterns. In a phase shifter according to the invention, gate electrode patterns may be formed in gaps between source electrode patterns and drain electrode patterns which are in a interdigital(comb teeth) form to form an FET, and an interdigital capacitor is formed between remaining source electrode patterns and drain electrode patterns. In a phase shifter according to the invention, grounding may be made through a source electrode or drain electrode capacitor of an FET. Brief Description of the Drawings Fig. 1 is a circuit diagram showing an embodiment of the invention. Fig. 2A, Fig. 2B and Fig. 2C are circuit diagrams illustrating the operations of the embodiment according to Fig. 1. Fig. 3 is a circuit diagram showing an embodiment of the invention. Fig. 4A and Fig. 4B are circuit diagrams describing the operations of the embodiment according to Fig. 3. Fig. 5 is a circuit diagram showing an embodiment of the invention. Fig. 6 is a circuit diagram showing an embodiment of the invention. Fig. 7A and Fig. 7B are circuit diagrams illustrating the operations of the embodiment according to Fig. 6. Fig. 8 is a circuit diagram showing of the invention. Fig. 9 is a structural diagram showing an embodiment of the invention. Fig. 10 is a structural diagram showing an embodiment of the invention. Fig. 11 is a structural diagram showing an embodiment of the invention. Fig. 12 is a structural diagram showing an embodiment of the invention. Fig. 13 is a structural diagram showing an embodiment of the invention. Fig. 14 is a circuit diagram showing a conventional phase shifter. Description of Preferred Embodiments Embodiment 1 Fig. 1 is a circuit diagram showing an embodiment of the invention. Embodiment 1 switches between the passing circuit and the T-type phase delay circuit. First, the first FET 1, the second FET 3 and the third FET 5 are turned on, and the fourth FET 6 is turned off to constitute a passing circuit. The equivalent circuit under this condition is as shown simply in Fig. 2A because the FETs have fully low impedance with the FETs on and a high-frequency signal passes through the FETs, while the FETs have high impedance with the FETs off and the high-frequency signal is cut off, and a resistance value is sufficiently low with the FETs on. At this time, when a constant of the third inductor 4c is set to provide high impedance for the high-frequency signal, the third inductor 4c works to cut off the high-frequency signal. Specifically, since the third FET 5 and the fourth FET 6, which are connected in parallel with the main line connecting the input terminal 10 and the output terminal 11, are regarded as open ends, the equivalent circuit of Fig. 2A can be regarded as the equivalent circuit of Fig. 2B and works as a passing circuit. Then, the first FET 1, the second FET 3 and the third FET 5 are turned off, and the fourth FET 6 is turned on to constitute a phase delay circuit. The equivalent circuit under this condition is as simply shown in Fig. 2A because a resistance value is sufficiently low with the FET on. At this time, the first capacitor 2a in Fig. 2C is a capacitive component with the third FET 5 off. Thus, the passing circuit and the T-type phase delay circuit are switched by controlling the on and off conditions of the FETs to effect a phase-shift difference between signals passing both of the above circuits. In Embodiment 1, since the number of FETs which are connected in parallel with the main line connecting the input terminal 10 and the output terminal 11 is decreased the phase shifter can decrease a passing loss and can be made compact. Embodiment 2 Fig. 3 is a circuit diagram showing Embodiment 2 of the invention. Embodiment 2 switches between the passing circuit and the T-type phase leading circuit. First, the first FET 1, the second FET 3 and the fourth FET 6 are turned on, and the third FET 5 is turned off to constitute a passing circuit. The equivalent circuit under this condition is as shown simply in Fig. 4A, because the FETs have fully low impedance with the ETETs on and a high-frequency signal passes through the FETs, the FETs have high impedance with the FETs off and the high-frequency signal is cut off, and a resistance value is sufficiently low with the FETs on. Thus, since the third FET 5 is regarded as an open end with respect to the main line which connects the input terminal 10 and the output terminal 11, it serves as a passing circuit. At this time, the fourth IFET 6 is on in order to prevent the high-frequency signal from being attenuated due to resonance of the capacitive component and the first inductor 4c with the FET 5 off. First, the first FET 1, the second FET 3 and the fourth FET 6 are turned off, and the third FET 5 is turned on to constitute a phase leading circuit. The equivalent circuit under this condition is a T-type phase leading circuit as shown simply in Fig. 4B because a resistance value is sufficiently low with the FET on. Thus, the passing circuit and the T-type phase leading circuit are switched by controlling the on and off conditions of the FETs to carry out different phase-shifting for signals passing through the above circuits. In Embodiment 2, since the number of FETs which are connected in parallel With the main line connecting the input terminal 10 and the output terminal 11 is decreased, the phase shifter can decrease a passing loss and can be made compact. Embodiment 3 Fig. 5 is a circuit diagram showing Embodiment 3 of the invention. Embodiment 3 switches between the passing circuit and the T-type phase leading circuit in the same way as in Embodiment 2 but is different from Embodiment 2 in that the first capacitor 2a and the second capacitor 2b are omitted from Fig. 3. Embodiment 2 uses the capacitor connected in parallel with the FET to constitute the T-type phase leading circuit, while Embodiment 3, instead of the first capacitor 2a and the second capacitor 2b of Embodiment 2, uses a capacitive component with the FETs off as a capacitor for constituting a T-type phase leading circuit. The operations are the same as in Embodiment 2 except that the capacitor constituting the T-type phase leading circuit is realized by a capacitance with the first FET 1 and the second FET 3 off. Differing from Embodiment 2, Embodiment 3 does not need a capacitor and can make the circuit small. Embodiment 4 Description will be given of Embodiment 4 with reference to Fig. 6 and Fig. 7. Fig. 6 is a circuit diagram showing Embodiment 4 of the invention. Embodiment 4 is configured to switch between an LC phase delay circuit and an LC phase leading circuit using an inductor L and a capacitor C. First, the second FET 3 and the fourth FET 6 are turned on, and the first FET 1 and the third FET 5 are turned off. Then, with the FETs on, the FETs have fully low impedance and a high-frequency signal passes through the FETs, and with the FETs off, the FETs have high impedance and the high-frequency signal passes through the circuit connected in parallel. The equivalent circuit of the phase shifter under this condition is as shown simply in Fig. 7A because a resistance value is sufficiently low with the FETs on. Thus, the first inductor 4a and the second capacitor 2b, together with a capacitive component with the third FET 5 off, constitute an LC low-pass filter to operate as a phase delay circuit. Then, the second FET 3 and the fourth FET 6 are turned off, and the first FET 1 and the third FET 5 are turned on. The equivalent circuit of the phase shifter under this condition is as shown simply in Fig. 7B because a resistance value is sufficiently low with the FETs on. Thus, the second inductor 4b and the first capacitor 2a constitute an LC high-pass filter to operate as a phase leading circuit. Thus, the LC phase leading circuit and the LC phase delay circuit are switched by controlling the on and off conditions of the FETs to effect different phase-shifting for signals passing through each of the above circuits. The phase shifter can be configured using concentrated constant elements. Since the number of FETs which are connected in series with the main line connecting the input terminal 10 and the output terminal 11 is decreased the phase shifter can decrease a passing loss and can be made compact. Embodiment 5 Fig. 8 is a circuit diagram showing Embodiment 5 of the invention. Embodiment 5 is different from Embodiment 4 in that the first capacitor 2a is omitted from Fig.6. In embodiment 4, a capacitive component produced between the drain electrode and the source electrode when a pinch-off voltage is applied to the gate electrodes of the FETs, is set to have high impedance or cut off with respect to a passing high frequency signal, and the capacitors connected in parallel with the FETs are used to constitute the LC phase leading circuit. Embodiment 5 uses a capacitive component with the FETs off as a capacitor constituting the LC phase leading circuit instead of the first capacitor 2a in embodiment 4. The operations are the same as in Embodiment 4 except that the capacitor constituting the LC phase leading circuit is realized by the capacity with the second FET 3 off. Differing from embodiment 4, embodiment 5 does not need a capacitor and can make the circuit smaller. Embodiment 6 Fig. 9 is a circuit diagram showing an aspect of the embodiments of the invention, showing a second FET connected to a first inductor. In Fig. 9 the second FET is formed by arranging strip-shaped drain electrode patterns 12 and strip-shaped source electrode patterns 13 in a form as if a plurality of comb teeth are interlaced with one another (interdigital) and a gate electrode pattern 14 is inserted between the drain electrode patterns 12 and the source electrode patterns 13. The gate electrode patterns 14 are connected together and to an external lead. The source electrode patterns 13 are connected to a connection pattern 19a for other FETs through air bridges 15a to avoid interference with the gate electrode pattern 14. Reference numeral 18 designates an inductor line pattern. One end of the inductor line pattern 18 is connected to the leading end of a drain electrode pattern 12a, and the other end to the leading end of a source electrode pattern 13a through an air bridge 16. The plurality of drain electrode patterns 12 formed like the teeth of a comb are mutually connected by an air bridge 17, and the source electrode patterns 13 are mutually connected by the air bridge 16. With the above configuration, the inductor line pattern 18 can have its area made smaller than when both its ends are extended from connection patterns 19a, 19b for adjacent FETs. Further, since electrical interference with adjacent circuits can be reduced, stable electrical characteristics are attained without being affected by the arrangement of the inductor line pattern 18. Generally, inductor capacity which is required to obtain a desired phase-shifting quantity has a smaller value as a frequency used is increased. Thus, when configured as shown in Fig. 9, the inductor line pattern 18 can be made shorter, so that a limitation on the inductor capacity being designed can be reduced, and a phase shifter obtained operates stably at a high frequency. Description has been made in connection with a certain structure, but all embodiments of the invention can be operated in the same way. In Fig. 9, the drain electrode patterns 12 are mutually connected by the air bridge 17 and the source electrode patterns 13 are mutually connected by the air bridge 16. To reduce a parasitic inductance component due to the air bridges 16, 17, both ends of the inductor line pattern 18 can be connected to not all but at least one of the drain electrode patterns 12 and to not all but at least one of the source electrode patterns 13. Embodiment 7 Fig. 10 is a structural diagram showing an aspect of Embodiment 6 showing the first FET connected to the first capacitor. In Fig. 10, the first FET has the same electrode structure as the second FET. Reference numeral 20 designates an MIM capacitor which corresponds to the first capacitor. The MIM capacitor 20 is connected to the second FET by means of terminal line patterns 21. A terminal line pattern 21a is connected to the leading end of the drain electrode pattern 12a and a terminal line pattern 21b to the leading end of the source electrode pattern 13a through the air bridge 16. The plurality of drain electrode patterns 12 formed like the teeth of a comb are mutually connected by the air bridge 17, and the source electrode patterns 13 are mutually connected by the air bridge 16. With the above configuration, the terminal line patterns 21 can be made as short as possible and made smaller than when they are extended from the connection patterns 19a, 19b for adjacent FETs. Further, a parasitic inductor component involved with the terminal line patterns 21 which deteriorates a frequency characteristic can be reduced, and electrical interference with circuits connected to adjacent FETs can also be reduced. Description has been given in connection with one specific capacitor, but other capacitors according to the embodiments of the invention which have the same configuration can be operated in the same way. In Fig. 10, the drain electrode patterns 12 are mutually connected by the air bridge 17 and the source electrode patterns 13 are mutually connected by the air bridge 16. To reduce a parasitic inductance component due to the air bridges 16, 17, the terminal line patterns 21 can be connected to at least one of the drain electrode patterns 12 and to at least one of the source electrode patterns 13. Embodiment 8 Fig. 11 is a circuit diagram showing Embodiment 8, showing the second FET connected to the first inductor. In Fig. 11 reference numeral 22a designates a first FET cell having a gate electrode pattern 14a formed between the drain electrode pattern 12a and the source electrode pattern 13a, and reference numeral 22b designates a second FET cell having a gate electrode pattern 14b formed between the drain electrode pattern 12c and the source electrode pattern 13b. An inductor line pattern 18 is formed between the above FET cells and also between the connection patterns 19a and 19b through an air bridge 15b. Thus, since the inductor line pattern 18 is disposed within the FET, the inductor line pattern can be made much shorter and the circuit can be made compact. Embodiment 9 Fig. 12 is a circuit diagram showing Embodiment 9, showing the first FET connected to the first capacitor. In Fig. 12 reference numeral 20 designates an MIM capacitor which is formed between the first FET cell 22a and the second FET cell 22b. The MIM capacitor 20 is connected to the connection patterns 19 through the terminal line patterns 21 and the air bridge 15b. Thus, since the MIM capacitor 20 is disposed within the FET, the terminal line patterns 21 can be made much shorter. Embodiment 10 Fig. 13 is a circuit diagram showing Embodiment 10 of the invention, showing the first FET connected to the first capacitor. In Fig. 13, reference numeral 23 designates an interdigital capacitor positioned between the first FET cell 22a and the second FET cell 22b and formed between the drain electrode pattern 12b and the source electrode patterns 13. Thus, the interdigital capacitor 23 is realized within the EET by virtue of the drain electrode pattern 12b and the source electrode patterns 13 of the FET, making it possible to constitute a compact capacitor without using an MIM capacitor. The invention configured as described above provides the following effects. Since configuration of the phase shifters of the invention switches between the T-type phase delay circuit and the T-type phase leading circuit depending on the lumped constant of the inductor and the capacitor, the phase shifter having a large phase-shifting quantity can be made compact, the phase shifter having a small frequency characteristic can be designed by providing the phase delay circuit and the phase leading circuit with opposite frequency characteristics. Since the invention switches between the T-type phase delay circuit and the T-type phase leading circuit depending on the lumped constant of the inductor and the capacitor, and the capacitor having a small capacitance required to attain a large phase-shifting quantity is realized by a capacitance with the FET off, the phase shifter obtained is compact and has only a small number of capacitor elements. Since the invention switches between the T-type phase delay circuit and the T-type phase leading circuit depending on the lumped constant of the inductor and the capacitor, and the capacitor having a small capacitance required to attain a small phase-shifting quantity is realized by a capacitance with the FET off, the phase shifter obtained is compact and has only a small number of capacitor elements. Since the invention switches between the T-type phase delay circuit and the T-type phase leading circuit depending on the lumped constant of the inductor and the capacitor and the capacitor having a small capacitance required to operate as the phase shifter in a high-frequency band is realized by a capacitance with the EET off, the phase shifter obtained is compact and has only a small number of capacitor elements. Since the invention switches between the passing circuit and the T-type phase delay circuit depending on the lumped constant of the inductor and a capacitance with the FET off, the phase shifter obtained is compact with less loss and has only a small number of circuit elements which constitute the phase shifter. Since the invention switches between the passing circuit and the T-type phase leading circuit by depending on the lumped constant of the inductor and the capacitor, the phase shifter obtained is compact with less loss and has only a small number of circuit elements which constitute the phase shifter. Since the invention switches between the passing circuit and the T-type phase leading circuit depending on the lumped constant of the inductor and a capacitance with the FET off, the phase shifter obtained is compact with less loss and has only a small number of circuit elements which constitute the phase shifter. Since the invention mounts the short inductor line pattern in parallel with an FET, the circuit can be made compact, the limitation of a small inductance is eased, and the phase shifter which stably operates in a high-frequency band can be designed easily. Since the invention disposes the short line pattern which forms the I/O terminals of the capacitor mounted in parallel with TET, the circuit can be made compact, the parasitic inductance due to the line pattern is decreased, and the phase shifter with a reduced frequency characteristic can be designed. Since the invention forms the inductor line pattern within the FET so as to be able to mount the inductor line pattern that is in parallel with the FET in a shorter form, the circuit can be made compact, the limitation of a small inductance is eased, and the phase shifter which stably operates in a high-frequency band can be designed easily. Since the invention forms the MIM capacitor within the FET so as to be able to dispose the line pattern which forms the I/O terminals of the capacitor mounted in parallel with the FET in a shorter manner, the circuit can be made compact, the parasitic inductance due to the line pattern is decreased, and the phase shifter with a reduced frequency characteristic can be designed. Since the invention forms the interdigital capacitor within the FET, the circuit can be made compact and the capacitor can be formed easily without using a circuit element such as an MIM capacitor. Since the invention can control the gate voltage to a given voltage, the limitation against the drive circuit of the FET can be eased, and the phase shifter including the external drive circuit can be made compact.

Claims: A phase shifter for shifting a phase of a signal entered through an input terminal and outputting the shifted signal from an output terminal comprising: (a) a first FET (1) with one end connected to the input terminal, (b) a second FET (3) connected between the other end of said first FET and the output terminal, a drain electrode and a source electrode being the connecting terminals of both the first FET (1) and the second FET (3), (c) a prescribed serial circuit (6,4c; 5) connected between a ground (9) and a node between said first FET (1) and said second FET (3), and (d) a prescribed control circuit for controlling said first FET, said second FET and said prescribed serial circuit; said prescribed serial circuit comprising (c1) a third FET (5), and (c2) a fourth FET (6) having a first inductor (4c) arranged across a drain electrode and a source electrode and being connected in series with said third FET with the drain electrode and the source electrode as connecting terminals. The phase shifter according to claim 1, wherein the first FET (1) has a second inductor (4a) arranged across a drain electrode and a source electrode, and wherein said prescribed control circuit being provided with means for applying a bias voltage to each gate electrode of said first through fourth FETs. The phase shifter according to claim 2, wherein said second FET (3) has a third inductor (4b) arranged across a drain electrode and a source electrode. The phase shifter according to claim 1, wherein said first FET (1) has a first capacitor (2a) arranged across a drain electrode and a source electrode, and said control circuit is provided with means for applying a bias voltage to a gate electrode of each of said first through fourth FETs. The phase shifter according to claim 4, wherein said second FET (3) has a second capacitor (2b) arranged across a drain electrode and a source electrode. The phase shifter according to claim 2, wherein said second FET (3) has a capacitor (2a) arranged across a drain electrode and a source electrode. The phase shifter according to one of claims 1 to 6 wherein the source electrode and the drain electrode of at least one FET among the FETs having said inductor or said capacitor arranged have a interdigital or comb teeth, shape which is formed by arranging at least one strip-shaped pattern in parallel, and an inductor line pattern, which forms said inductor or said capacitor arranged on the FED having the interdigital, or comb teeth, shaped electrodes, is formed by connecting at least one electrode pattern of either the source electrode pattern or the drain electrode pattern and at least one electrode pattern of the other electrode pattern. The phase shifter according to one of claims 1 to 6, wherein a part (13a, 13b) of the source electrode (13) and a part (12a, 12c) of the drain electrode (12) of at least one FET (3) among said FETs have a interdigital or comb teeth, shape which is formed by arranging at least one stripshaped pattern in parallel, a gate electrode pattern (14) is disposed in a gap part between source and drain electrode patterns having a interdigital or comb teeth, shape to form the FET, and remaining parts (18) of the source and drain electrode patterns (13, 12) are connected to form said inductor. The phase shifter according to one of claims 1 to 6, wherein the source electrode and the drain electrode of at least one FET among said FETs have a interdigital or comb teeth, shape which is formed by arranging at least one strip-shaped pattern in parallel, a gate electrode pattern is disposed in a gap part between source and drain electrode patterns having a interdigital or comb teeth, shape to form the FET, and a metal insulator metal capacitor is formed on part of remaining source and drain electrode patterns to form said capacitors. The phase shifter according to one of claims 1 to 6, wherein the source electrode and the drain electrode of at least one FET among said FETs have a interdigital or comb teeth, shape which is formed by arranging at least one strip-shaped pattern in parallel, a gate electrode pattern is disposed in a gap part between source and drain electrode patterns having a interdigital or comb teeth, shape to form the FET, and an interdigital capacitor is formed in a gap between remaining source and drain electrode patterns to form said capacitors.

Inventors: INAMI KAZUYOSHI, IYAMA YOSHITADA, KASAHARA MICHIAKI, KAWANO HAZIME, MUROI KOHICHI, INAMI, KAZUYOSHI, IYAMA, YOSHITADA, KASAHARA, MICHIAKI, KAWANO, HAZIME, MUROI, KOHICHI, INAMI, KAZUYOSHI C/O MITSUBISHI DENKI K.K., Iyama, Yoshitada, c/o Mitsubishi Denki K.K., KASAHARA, MICHIAKI, C/O MITSUBISHI DENKI K.K., KAWANO, HAZIME, C/O MITSUBISHI DENKI K.K., MUROI, KOHICHI, C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1996
Main classification: H03H11
IPC codes: H03H7, H03H11