JP7610220B2 - Radio and phased array radio - Google Patents

Description

The present invention relates to a radio and a phased array radio.

Wideband radio waves of 300 GHz or more, for example, THz waves from 300 GHz to 30 THz, are being considered for application to ultra-high-speed wireless communications such as next-generation wireless communications (beyond 5G). In particular, the 300 GHz band has been actively researched and developed because it is the frequency band that has the least absorption attenuation during atmospheric propagation among the THz bands and can be used in wireless transceivers (hereinafter also referred to as TRX) formed with a CMOS (Complementary Metal Oxide Semiconductor) structure on a Si substrate such as SiGe (see Non-Patent Documents 1 and 2).

In the 300 GHz band TRX, as in the millimeter wave band TRX for 5G, a phased array that controls the directivity of radio waves is an important technology. One of the 300 GHz band phased arrays reported so far is shown in Non-Patent Document 3. In Non-Patent Document 3, a transceiver circuit formed with a CMOS structure on a Si substrate is connected to a Vivaldi antenna fabricated on a dielectric substrate to produce one antenna-equipped TRX. The transceiver circuit consists of a bidirectional IF (Intermediate Frequency) amplifier, LO (Local Oscillator), LO amplifier, bidirectional mixer, and digital circuit. In Non-Patent Document 3, an active antenna array phased array radio is realized by arranging four antenna-equipped TRXs in an array, and wireless communication and beam directivity control at a distance of 2.5 cm are realized. This active antenna array can be realized with a small size and low power consumption using low-cost CMOS, making it suitable for ultra-high-speed wireless communication over short distances (several centimeters to several meters).

S. Lee et al., “An 80-Gb/s 300-GHz-Band Single-Chip CMOS Transceiver,” IEEE Journal of Solid-State Circuits (JSSC), vol. 54, no. 12, Oct. 2019, pp .3577-3588. P. Rodriguez-Vazquez et al., “A 16-QAM 100-Gb/s 1-M wireless link with an EVM of 17% at 230 GHz in an SiGe technology,” IEEE Microwave and Wireless Components Letters (MWCL), vol. 29, no. 4, Apr. 2019, pp. 297-299. I. Abdo et al., “A 300GHz-Band Phased-Array Transceiver Using Bi-Directional Outphasing and Hartley Architecture in 65nm CMOS,” International Solid-State Circuits Conference (ISSCC),” Feb. 2021.

In order to achieve long-distance (tens to hundreds of meters) wireless communication with the configuration of Non-Patent Document 3, there is a problem that the number of active antenna arrays must be quite large. For example, in order to obtain the same communication quality (signal-to-noise ratio) at a communication distance of 25 m as when it is 2.5 cm with the TRX configuration of Non-Patent Document 3, a gain improvement of +60 dB must be achieved by using active arrays. This requires expanding the number of arrays to a huge value of 1000. It is not impossible to achieve such a large number of active arrays using CMOS technology, which has high yield and integration. However, considering power consumption and inspection costs, it is preferable to suppress the increase in the number of arrays as much as possible, and as a result, it is difficult to perform long-distance wireless communication when using only CMOS.

The configuration in Non-Patent Document 3 uses a Vivaldi antenna, which is a type of endfire antenna. This antenna has a wider bandwidth and higher gain than patch antennas and the like. It is therefore suitable for high-speed wireless communications that take advantage of the broadband nature of the THz band. However, the feeder line of the endfire antenna is a differential line, and a reduction in antenna gain can be an issue.

For example, when designing a single-ended transmission/reception circuit, a balun, which is a single-differential conversion circuit, is required between the transmission/reception circuit and the endfire antenna. It is generally difficult to widen the bandwidth of this balun. Therefore, when using an endfire antenna, even if the transmission/reception circuit and the antenna are designed to be sufficiently wideband, the communication bandwidth may be limited by the bandwidth of the balun. In addition, strictly speaking, not only the differential mode but also the common mode exists at the differential output port of the balun when viewed from the transmission/reception circuit. This is because the signal output from the differential output port of the balun contains an amplitude error and a phase error from 180 degrees. However, the signal radiated in the form of an electromagnetic wave from the endfire antenna into space is only the signal propagating in the above-mentioned feeder line in differential mode. Therefore, the common mode output from the balun and input to the feeder line is not radiated into space but is reflected to the transmission/reception circuit side. This means that the power radiated from the antenna is reduced, which equivalently causes a reduction in antenna gain. In addition, the signal returned to the transmission/reception circuit side may have a negative effect on the operation of the transmission/reception circuit. This makes it difficult to fully utilize the wideband and high-gain characteristics of endfire antennas, making it difficult to achieve high-speed, long-distance wireless communications.

The problem of reduced antenna gain can also occur when using other antennas that convert differential signals into electromagnetic waves or convert electromagnetic waves into differential signals, such as waveguide antennas other than endfire antennas.

The objective of the present invention is to obtain high antenna gain while reducing the number of arrays in a phased array.

In order to solve the above-mentioned problems, the radio according to the first aspect of the present invention is a radio configured to be arranged in an array as a phased array radio, and includes a transmission circuit that frequency converts an electrical signal representing information to be wirelessly transmitted into a high-frequency signal having a frequency of 300 GHz or more, which is higher than the electrical signal, a differential amplifier that amplifies the high-frequency signal and outputs it as a differentially amplified signal, and an antenna that converts the differentially amplified signal into an electromagnetic wave and radiates it, the transmission circuit being integrated in a CMOS (Complementary Metal Oxide Semiconductor) structure on a Si substrate, and the differential amplifier being integrated on an InP substrate.

In order to solve the above-mentioned problems, a radio according to a second aspect of the present invention is a phased array radio configured to be arranged in an array, and includes an antenna that converts electromagnetic waves of 300 GHz or more into a high-frequency signal that is a high-frequency electrical signal, a differential amplifier that amplifies the high-frequency signal and outputs it as an amplified signal, and a receiving circuit that frequency-converts the amplified signal into a signal having a lower frequency than the amplified signal and outputs it, the receiving circuit being integrated on a Si substrate in a complementary metal oxide semiconductor (CMOS) structure, and the differential amplifier being integrated on an InP substrate.

A phased array radio according to a third aspect of the present invention comprises a plurality of radios, each of which is the radio described above, arranged in a one-dimensional or two-dimensional array.

The present invention makes it possible to obtain high antenna gain while reducing the number of arrays in a phased array.

FIG. 1 is a diagram showing a schematic configuration of a phased array radio (transmitter) according to a first embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration of a phased array radio (receiver) according to a second embodiment of the present invention. FIG. 3 is a diagram showing a schematic configuration of a phased array radio (transmitter) according to a third embodiment of the present invention. FIG. 4 is a diagram showing a schematic configuration of a phased array radio (receiver) according to a third embodiment of the present invention. FIG. 5 is a diagram showing a schematic configuration of a phased array radio (transmitter) according to a fourth embodiment of the present invention. FIG. 6 is a diagram showing a schematic configuration of a phased array radio (receiver) according to a fourth embodiment of the present invention.

Below, a phased array radio according to an embodiment of the present invention will be described with reference to the drawings.

First Embodiment
As shown in Fig. 1, a phased array radio 1 according to the first embodiment of the present invention is configured as a radio transmitter and includes a plurality of radio devices 10 arranged in a one-dimensional array. The radio device 10 includes a Si substrate 20, which is a silicon semiconductor substrate, and an InP substrate 30, which is an indium phosphide semiconductor substrate. The plurality of radio devices 10 may be arranged in a two-dimensional array. The spacing between the plurality of radio devices 10 when arranged in an array is about half a wavelength to one wavelength, similar to a normal phased array.

A transmission circuit 21 with a complementary metal oxide semiconductor (CMOS) structure is integrated on the silicon substrate 20 by a semiconductor process. The transmission circuit 21 converts an intermediate frequency (IF) signal, which is an electrical signal representing information to be wirelessly transmitted, into a high-frequency signal having a frequency of 300 GHz or higher, which is higher than the frequency of the IF signal. The transmission circuit 21 is configured to handle single-ended signals.

A balun 31, a differential amplifier 32, and an antenna 33 are integrated on the InP substrate 30 by a semiconductor process. The InP substrate 30 is a differential amplifier chip with an antenna on which an on-chip antenna 33 is integrated, and is connected to the Si substrate 20, which is a CMOS transmitter chip. The antenna 33 is an end-fire antenna. The differential amplifier 32 is connected to the single-end output of the transmission circuit 21 via the balun 31, which is a single-differential conversion circuit. As a result, the single-end 300 GHz band high-frequency signal output by the transmission circuit 21 is converted into a differential high-frequency signal by the balun 31 and input to the differential amplifier 32. The differential amplifier 32 amplifies the input differential high-frequency signal and outputs it to the antenna 33 as a differential amplified signal. The antenna 33 converts the differential amplified signal into an electromagnetic wave (radio wave) and radiates it.

The phased array radio 1 described above can achieve high antenna gain while limiting the number of phased array elements. Below, we will explain this point first, and then explain the details of the phased array radio 1.

First, suppression of the number of arrays will be described. Increasing the transmission power of each radio 10 can be considered as one means of suppressing the number of arrays. If the transmission power per array is increased by N times, the number of arrays required to obtain the same signal-to-noise ratio at a certain communication distance can be reduced to 1/√N, assuming that the same receiver is used. Usually, the component that determines the transmission power of the antenna array is a power amplifier circuit (power amplifier) arranged at the final stage of the TX, that is, the transmitter. However, in general, in frequency bands of 300 GHz or more, it is difficult to form a power amplifier circuit with a CMOS structure on a Si substrate. This is because the maximum oscillation frequency of a Si substrate on which CMOS is configured is at most about 300 GHz, and it is difficult to realize an amplifier circuit with a high gain in frequency bands of 300 GHz or more. As a result, in conventional CMOS transmitters, a mixer-first configuration is adopted in which a mixer, which is a circuit that can be realized by CMOS, is used at the final stage of the transmission circuit. In general, the output power of the mixer is lower than that of the amplifier circuit, about -10 dBm. Therefore, in this embodiment, the differential amplifier 32 is formed using an InP substrate 30, which has better high frequency characteristics than a Si substrate. This differential amplifier 32 has a high gain in a frequency band of 300 GHz or more. In particular, the InP substrate 30 can realize a 300 GHz band differential amplifier 32 having an output of 10 dBm or more (for example, Non-Patent Document 4 below). Therefore, compared to the conventional case in which the radio device 10 is formed only with CMOS on a Si substrate, the output can be improved by 20 dB. Therefore, the number of arrays can be reduced to 1/10.
[Non-Patent Document 4] H. Hamada et al., “300-GHz-band 120-Gb/s Wireless Front-End Based on InP-HEMT PAs and Mixers,” IEEE Journal of Solid-State Circuits (JSSC), vol. 55, no. 9, Sep. 2020, pp. 2316-2335.

Next, the high antenna gain will be explained. The differential amplifier 32 formed on the InP substrate 30 can amplify only the differential signal and attenuate the common-mode signal (common-mode rejection). For example, as described in Non-Patent Document 5, an amplifier that can secure a common-mode rejection ratio (ratio of gain for a differential signal to gain for a common-mode signal) of up to 50 dB or more in the 300 GHz band has been reported. By using such a differential amplifier 32 with high common-mode rejection, the common-mode included in the output of the balun 31 integrated on the InP substrate 30 in FIG. 1 is sufficiently suppressed, and only the differential signal (fully differential signal) exists in the antenna 33. Therefore, the end-fire type antenna 33 is driven in an ideal state, and if the impedance matching between the differential amplifier 32 and the antenna 33 is properly performed, many signals input to the antenna 33, or more preferably all signals, can be radiated into space as radio waves. In other words, the decrease in antenna gain due to the common-mode signal is suppressed, and high antenna gain is secured.
[Non-Patent Document 5] H. Hamada et al., “220-325 GHz 25-dB-Gain Differential Amplifier With High Common-Mode-Rejection Circuit in 60-nm InP-HEMT Technology,” IEEE Microwave and Wireless Components Letters (MWCL), Early Access.

Next, the configuration of the phased array radio 1 will be described in more detail. The thickness of the InP substrate 30 is not about 600 μm, which is commercially available, but is thinner, about 50 μm. If a 600 μm InP substrate 30 is used, the high dielectric constant (about 12.4) of the InP substrate 30 causes the direction of radiation of the electromagnetic waves radiated from the antenna 33 formed on the InP substrate 30 to be biased toward the thickness direction of the InP substrate 30 (the depth direction of the paper in FIG. 1), making it difficult to form a beam in the appropriate direction during phased array. Therefore, by thinning the InP substrate 30 to 50 μm, which is sufficiently shorter than the free space propagation wavelength (1 mm) of the 300 GHz electromagnetic wave, the electromagnetic waves radiated from the antenna 33 can be directed in the appropriate direction (to the right in FIG. 1), and the above problem can be avoided. In addition, thinning the InP substrate 30 also serves to reduce unnecessary substrate modes propagating within the InP substrate 30, which can also prevent oscillation or unstable operation of the differential amplifier 32.

The Si substrate 20 and the InP substrate 30 are connected by a bonding wire connection or a flip chip connection or other connection method that connects the single-ended output of the transmission circuit 21 of the Si substrate 20 to the input wiring of the balun 31 of the InP substrate 30.

The transmission circuit 21 on the Si substrate 20 includes a multiplier 22, an LO amplifier 23, an IF amplifier 24, and a mixer 25. The multiplier 22 multiplies an LO signal from an LO (Local Oscillator) (not shown). The LO amplifier 23 amplifies the LO signal multiplied by the multiplier 22 and inputs it to the mixer 25. The IF amplifier 24 amplifies an IF signal representing information to be wirelessly transmitted by an antenna 33 from a circuit (not shown) and inputs it to the mixer 25. The mixer 25 mixes the LO signal from the LO amplifier 23 and the IF signal from the IF amplifier 24, and frequency converts the IF signal into a high-frequency signal in a frequency band of 300 GHz or more. Each circuit constituting the transmission circuit 21 has a single-ended configuration that handles single-ended signals.

The balun 31 is integrated on the InP substrate 30. It is also possible to integrate the balun 31 on the Si substrate 20, but in this case, it is necessary to connect the differential input lines of the differential amplifier 32 on the InP substrate 30 side to the differential output lines of the balun on the Si substrate 20 side by the above-mentioned connection means. For this reason, two wires or bumps must be used per radio 10. In other words, there are two connection points. On the other hand, the radio 10 has one connection point. Since loss at the connection points is large in the frequency band of 300 GHz or more, the configuration of the radio 10 of this embodiment, which has fewer connection points, is preferable.

Second Embodiment
The second embodiment will be described below, but the explanation of elements with the same names will be the same as that of the first embodiment regardless of whether the reference numerals are the same or different. As shown in Fig. 2, a phased array radio device 5 according to the second embodiment of the present invention is configured as a radio receiver, and includes a plurality of radio devices 50 arranged in a one-dimensional array. The radio device 50 includes a Si substrate 60 and an InP substrate 70.

The Si substrate 60 has a CMOS-structured receiving circuit 61 integrated by a semiconductor process. The InP substrate 70 has a balun 71, a differential amplifier 72, and an antenna 73 integrated by a semiconductor process. The InP substrate 70 is an antenna-equipped differential amplifier chip with an on-chip antenna 73 integrated therein, and is connected to the Si substrate 60, which is a CMOS transmitter chip. The antenna 73 is an end-fire antenna that converts electromagnetic waves (radio waves) of 300 GHz or more into high-frequency signals, which are high-frequency electrical signals. The differential amplifier 72 amplifies the high-frequency signal from the antenna 73 and outputs it as an amplified signal. This amplified signal is a differential signal. The balun 71 is interposed between the differential amplifier 72 and the single-end input of the receiving circuit 61, and converts the differential amplified signal from the differential amplifier 72 to a single-end and outputs it to the receiving circuit 61. The receiving circuit 61 frequency-converts the single-end amplified signal from the balun 71 to an IF signal with a lower frequency than this amplified signal and outputs it.

The receiving circuit 61 on the Si substrate 60 includes a multiplier 22, an LO amplifier 23, an IF amplifier 64, and a mixer 65. The mixer 65 mixes the single-ended amplified signal from the balun 71 with the IF signal from the IF amplifier 24, and converts the amplified signal to an intermediate frequency IF signal. The IF signal is amplified by the IF amplifier 64 and output to the outside of the radio 50.

As described above, the radio 50 is a receiver obtained by inverting the orientation of the IF amplifier 24 and the differential amplifier 32 of the radio 10, which is the transmitter of the first embodiment. Other explanations of the radio 50 are the same as those of the radio 10. Although there is a difference between transmission and reception, this radio 50 also has the same effect as the radio 10. In other words, the radio 50 can also amplify the high-frequency signal received by the antenna 73 and before being input to the receiving circuit 61 with the differential amplifier 72 provided on the InP substrate 70 side, so that the phased array radio 5 can receive electromagnetic waves well even if the number of arrays is small. In addition, the antenna gain seen from the receiving circuit 61 (the antenna gain of the InP substrate 70) is also secured. Therefore, a high antenna gain can be obtained while suppressing the number of arrays of the phased array. In addition, the differential amplifier 72 provided on the InP substrate 70 side can be used as a low noise amplifier (LNA), which improves the noise figure (NF).

Third Embodiment
3 and 4 show phased array radios 101 and 105 according to the third embodiment. In the phased array radios 101 and 105, the single-ended transmission circuit 21 in FIG. 1 or the reception circuit 41 in FIG. 2 is changed to a differential transmission circuit 121 or reception circuit 161. This change allows the balun 31 or 71 to be omitted. The rest of the description is the same as in the above embodiment. Each element of the third embodiment corresponds to an element of the first or second embodiment with a reference number obtained by subtracting 100 from the reference number given to the above element.

In this embodiment, two connecting parts such as wires or bumps must be used per radio 110 or 150. Ideally, the electrical length or impedance of these two connecting points should be the same, but in reality, they are different due to manufacturing errors. This causes a common mode to be input to the InP substrate 130 or 170, but this common mode is removed by the common mode removal effect of the differential amplifier 132 or 172, so there is no problem with the antenna operation. Therefore, even with this configuration, the same effect as in the first or second embodiment can be obtained. The transmission circuit 121 and the reception circuit 161 in Figures 3 and 4 are double-balanced types with a differential configuration. They may be single-balanced types in which either the IF amplifier 124 or 164 and the LO amplifier 123 have a single-ended configuration.

Fourth Embodiment
5 and 6 show phased array radios 201 and 205 according to the fourth embodiment. Each of the multiple radios 210 and 250 includes a hollow waveguide antenna 233 or 237 instead of the antenna 33 or 73 in FIG. 1 and FIG. 2. The waveguide antennas 233 and 273 are formed in the same shape. The waveguide antenna 233 or 273 includes a first end 233A or 273A connected to the differential amplifier 32 or 72 via a dipole coupler 234, and a second end 233B or 273B on the opposite side of the first end 233A or 273A and having an opening facing free space. The waveguide antenna 233 or 273 contains an InP substrate 230 or 270. The waveguide antenna 233 may also contain a Si substrate 20 or 60. The waveguide antenna 233 or 273 is, for example, a rectangular or cylindrical metal antenna. Since the waveguide antenna 233 or 273 operates with a differential signal, the present embodiment can provide the same effects as the embodiment using the endfire antenna. The rest of the description of the fourth embodiment is similar to the above embodiment.

The waveguide antenna 233 or 273, which is used as a transmission medium for high-frequency signals such as the 300 GHz band, radiates electromagnetic waves from its opening with good directionality. The waveguide antenna 233 or 273 has a high value of 6 to 8 dBi. Therefore, if the second end 233B is arrayed at intervals of about half the wavelength of the electromagnetic waves transmitted and received by the antenna as shown in Figures 5 and 6, a phased array similar to the above is formed. Since the Si substrate 220 or 260 and the InP substrate 230 or 270 are mounted in a package of the waveguide antenna 233, which is made of a robust metal and easy to handle, handling of the phased array is easier than in the above embodiment. Since the intervals between the waveguide openings can be formed with an error of several microns by metal processing, the array can also be arranged two-dimensionally at approximately equal intervals.

The waveguide antenna 233 or 273 and the differential amplifier 32 or 72 may be connected using a dipole coupler 234 or a ridge coupler (Non-Patent Document 4). Unlike the antenna 33, these couplers do not require a tapered structure (a flared shape) on the InP substrate 230 or 270 as shown in Figures 1 to 4, so the chip area of the InP substrate 230 or 270 can be made smaller than in the above embodiment.

The waveguide antenna 233 or 273 may be applied to the radio 110 or 150 of the third embodiment.

(Modification)
Various modifications are possible to the above embodiment. Each transmission circuit such as the transmission circuit 21 may have the function of a reception circuit. In other words, the transmission circuit may operate as a transmission/reception circuit. In this case, various amplifiers, baluns, mixers, etc. are bidirectional circuits. Any antenna that converts a differential signal into an electromagnetic wave may be used as the antenna.

(Scope of the present invention)
Although the present invention has been described above with reference to the embodiment and the modified examples, the present invention is not limited to the above embodiment and the modified examples. For example, the present invention includes various modifications to the above embodiment and the modified examples that can be understood by a person skilled in the art within the scope of the technical idea of the present invention. The configurations listed in the above embodiment and the modified examples can be appropriately combined within a range without contradiction.

1,5,101,105,201,205...phased array radio, 10,50,110,150,210,250...radio, 20,60,120,160...Si substrate, 21,121...transmitting circuit, 61,161...receiving circuit, 30,70,130,170,230,270...InP substrate, 31,71...balun, 32,72,132,172...differential amplifier, 33,73...antenna, 233,273...waveguide antenna, 233A,273A...first end, 233B,273B...second end, 234...dipole coupler.

Claims (9)

A radio configured to be arrayed in a phased array radio,
a transmission circuit that converts an electrical signal representing information to be wirelessly transmitted into a high-frequency signal having a frequency of 300 GHz or higher, which is higher than the frequency of the electrical signal;
a differential amplifier that amplifies the high frequency signal and outputs it as a differential amplified signal;
an antenna that converts the differentially amplified signal into an electromagnetic wave and radiates the electromagnetic wave,
The transmission circuit is integrated on a silicon substrate in a complementary metal oxide semiconductor (CMOS) structure,
The differential amplifier is integrated on an InP substrate.
Radio. The output of the transmitter circuit is single-ended;
a single-to-differential conversion circuit interposed between the differential amplifier and an output of the transmission circuit is integrated on the InP substrate;
2. A radio according to claim 1. The output of the transmission circuit is a differential output and is connected to the differential amplifier.
2. A radio according to claim 1. A radio configured to be arrayed in a phased array radio,
An antenna that converts electromagnetic waves of 300 GHz or more into a high-frequency signal that is a high-frequency electrical signal;
a differential amplifier that amplifies the high frequency signal and outputs it as an amplified signal;
a receiving circuit that converts the amplified signal into a signal having a lower frequency than the amplified signal and outputs the converted signal;
The receiving circuit is integrated on a silicon substrate in a complementary metal oxide semiconductor (CMOS) structure.
The differential amplifier is integrated on an InP substrate.
Radio. The input of the receiver circuit is single-ended,
a single-to-differential conversion circuit is integrated on the InP substrate and is interposed between the differential amplifier and an input of the receiving circuit;
5. A radio according to claim 4 . The input of the receiving circuit is a differential input and is connected to the differential amplifier.
5. A radio according to claim 4 . the antenna is an end-fire type antenna integrated on the InP substrate together with the differential amplifier;
A radio device according to any one of claims 1 to 6. the antenna is a waveguide antenna containing the InP substrate, the waveguide antenna having a first end connected to the differential amplifier and a second end opposite the first end and having an opening facing free space;
A radio device according to any one of claims 1 to 6. a plurality of radio units arranged in a one-dimensional or two-dimensional array, each of the radio units being the radio unit according to any one of claims 1 to 8 ;
Phased array radio.

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