Broadband switched capacitor CMOS circulator adopting transformer for isolation improvement

Abstract

The broadband switched capacitor CMOS circulator comprises a switched capacitor network structure with N paths of same branches, a switch group on each side is controlled by a non-overlapping square wave modulation signal, and an inductor L is arranged on each side of the switched capacitor network structure; a group of switches are arranged at a central capacitor node of a switched capacitor network structure to form a three-port circulator, each layer of switch of the three-port circulator is controlled in a rotating mode, a central capacitor of each layer is charged from one port, and then charges are released to the next port; when the central capacitor of the first layer discharges through the port 3, the central capacitor of the second layer discharges through the port 2; a part of the discharge current of the second-layer center capacitor is fed into the first-layer center capacitor through the transformer in a reverse-phase mode, and the isolation degree from the first port to the third port is improved. The isolation degree and the working bandwidth can be improved, and the noise coefficient, the circuit complexity and the chip power consumption can be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of radio frequency integrated circuit design, and in particular relates to a broadband switched capacitor CMOS circulator using a transformer as an isolation enhancement device and a method thereof. Background Art

[0002] Currently, existing commercial standards such as WCDMA and WiFi can provide 80 MHz of accessible bandwidth and provide a data transmission rate of 100~1000 Mbit / s for each user. 5G systems require higher accessible bandwidth and higher data rates. Compared with the previous generation of communication systems, 5G is expected to support 1000 times or more data volume per area and provide 10~100 times the data transmission rate (10~100 Gbit / s) for each user. The future 6G system will require higher bandwidth and data rate than 5G. This requires that the active (quasi) circulator as a full-duplex wireless communication system, Massive MIMO and software-defined radio antenna module of future wireless communication systems should have broadband working capabilities. At the same time, the operating frequency band of FMCW radar is relatively wide, and the active quasi-circulator is also required to work in a broadband range. In addition, in order to minimize the impact of the transmitted signal on the received signal, and to improve the transmit power and receiving sensitivity of the wireless communication system, the active (quasi) circulator must have a high degree of isolation (ISO) from the transmitting port to the receiving port in the wireless communication system. Since the active (quasi) circulator is located at the front end of the receiving link as the antenna interface, its noise level directly affects the noise figure (NF) of the entire receiving link. Therefore, in order to ensure the receiving sensitivity of the receiving link, the NF from the active (quasi) circulator antenna port to the receiving port must be reduced.

[0003] Although passive circulators have the advantages of low noise figure and low insertion loss, their disadvantages of large size, heavy weight and high cost make them difficult to use in RFIC systems. CMOS integrated circulators are used as passive alternatives in RFIC systems due to their small size, low cost and easy integration. Although active (quasi) circulators can be integrated with CMOS, their noise and isolation performance are limited. Achieving high isolation and low noise in a broadband operating range is the most important challenge in the design of silicon-based shared antenna interfaces (circulators).

[0004] Currently, a variety of technologies have been used to improve the isolation, bandwidth, and noise performance of CMOS circulators. For example, the paper "A Tunable 5–7 GHz Distributed Active Quasi-Circulator With 18-dBm OutputPower in CMOS SOI," (K. Fang and JF Buckwalter, IEEE Microwave and Wireless Components Letters, vol. 27, no. 11, pp. 998-1000, Nov. 2017) proposes a monolithic integrated active quasi-circulator based on tunable capacitor technology. This technology can operate in the frequency range of 5.3~7.3 GHz by adjusting the effective value of the capacitor, and the isolation from the transmitting port to the receiving port is greater than 30 dB, but its effective bandwidth at each frequency is only 100 MHz (relative bandwidth is 0.8%), while the NF from the antenna port to the receiving port is as high as 20 dB. The paper "A 1.5-mW, 2.4 GHz Quasi-Circulator With High Transmitter-to- Receiver Isolation in CMOS Technology," (J. -Y. Hsieh, T. Wang and S. -S. Lu, IEEE Microwave and Wireless Components Letters, vol. 24, no. 12, pp. 872-874, Dec. 2014) uses current multiplexing and adjustable technology to design a monolithic integrated active quasi-circulator operating at 2.4 GHz. Although the active quasi-circulator achieves an isolation of more than 65 dB from the transmitter port to the receiver port, its corresponding operating bandwidth is only 10 MHz (relative bandwidth is 0.4%).The paper “A 30 GHz Active Quasi-Circulator With Current-Reuse Technique in 0.18 μm CMOS Technology,” (C. -H. Chang, Y. -T. Loand J. -F. Kiang, IEEE Microwave and Wireless Components Letters, vol. 20, no.12, pp. 693-695, Dec. 2010) proposed a monolithic integrated active quasi-circulator with current reuse technology. In the frequency range of 29~31 GHz (relative bandwidth of 6.7%), the isolation from the transmitting port to the receiving port is only 12 dB. The paper “A Dual Interference-Canceling Active Quasi-Circulator Achieving 36-dBIsolation Over 6-GHz Bandwidth,” (B. Tang, X. Gui, J. Xu, Q. Xia and L. Geng, IEEE Microwave and Wireless Components Letters, vol. 29, no. 6, pp. 409-411, June 2019) developed a monolithic integrated active quasi-circulator with dual-path cancellation technology. The bandwidth of the active quasi-circulator reaches 6 GHz, the relative bandwidth is 150%, the isolation from the transmit port to the receive port exceeds 36 dB, and the NF from the antenna port to the receive port is as high as 16 dB. Reference [5] “A Wideband Active Quasi-Circulator With 34-dBIsolation and Insertion Loss of 2.5 dB,” (B. Tang, X. Gui, J. Xu, Q. Xia, H.Yang and L. Geng, IEEE Microwave and Wireless Components Letters, vol. 30, no. 7, pp. 693-696, July 2020) proposed an improved dual-path cancellation technology and added noise cancellation technology, which extended the bandwidth of the monolithic integrated active quasi-circulator to 7 GHz, with a relative bandwidth of 155.6%, an isolation from the transmit port to the receive port higher than 34 dB, and a NF from the antenna port to the receive port lower than 10 dB.The paper “Low NF and High P1dB Wideband Quasi-Circulator With Unequal Power Split and Reconfigurable Inter-Stage Matching,” (W. Chen, Z. Deng, Y. Shu, HJ Qian and X. Luo, IEEE Transactions on Microwave Theory and Techniques, vol. 69, no. 4, pp. 2241-2252, April 2021) designs an active quasi-circulator based on the reconfigurable inter-stage matching method. The active quasi-circulator can operate in the frequency range of 1.75~2.9 GHz (relative bandwidth is 49.5%), with an isolation of 27 dB from the transmitting port to the receiving port, and a NF of only 4.6 dB from the antenna port to the receiving port, but the overall power consumption is as high as 224 mW. In addition, a circulator based on a switched capacitor network is presented in the literature [7] "Ultra-Wideband Switched-Capacitor Delays and Circulators— Theory and Implementation," (A. Nagulu, A. Mekkawy, M. Tymchenko, D. Sounas, A. Alù and H. Krishnaswamy, IEEE Journal of Solid-State Circuits, vol. 56, no. 5, pp. 1412-1424, May 2021). The circulator can operate in the DC~1GHz range (relative bandwidth is 200%), and the NF from the antenna port to the receiving port is as low as 4.1 dB, but the isolation from the transmitting port to the receiving port is only 18 dB, and the complexity of the modulation signal generation circuit is increased.

[0005] There are two main deficiencies in the existing technology and structure: 1. It is not possible to obtain high isolation within a broadband range; 2. Even if a high degree of isolation is achieved within a wide bandwidth, the noise figure is high or the overall power consumption increases dramatically.

[0006] The above two shortcomings make the current technology less suitable for future broadband full-duplex, FMCW radar and multi-band wireless communication systems. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a broadband switched capacitor CMOS circulator and a method thereof using a transformer to improve isolation in view of the deficiencies in the above-mentioned prior art. The transformer-based isolation improvement technology is adopted, so that the CMOS circulator not only obtains broadband, high isolation and low noise coefficient, but also has low circuit complexity and low chip power consumption in the switched capacitor structure, and is used to solve the technical problems of excessive influence of the transmitted signal on the received signal and reduced receiving sensitivity of the receiving link in future broadband full-duplex, FMCW radar and multi-band wireless communication systems.

[0008] The present invention adopts the following technical solutions: A broadband switched capacitor CMOS circulator using a transformer as an isolation enhancer includes a switched capacitor network structure having N identical branches. N The switch group on each side is controlled by a non-overlapping square wave modulation signal, and the period of each non-overlapping square wave modulation signal is T S , the duty cycle is T S / N , an inductor is set on each side of the switched capacitor network structure L A set of switches is set at the central capacitor node of the switched capacitor network structure to form a three-port circulator. The switches of each layer of the three-port circulator are controlled in a rotating manner. The central capacitor of each layer is charged from one port and then released to the next port. When the central capacitor of the first layer is discharged through port 3, the central capacitor of the second layer is discharged through port 2 at this moment; part of the discharge current of the central capacitor of the second layer is fed into the central capacitor of the first layer in an inverted form through the transformer, thereby improving the isolation from port 1 to port 3.

[0009] Preferably, when R S C ≈ T S / 2 N When the capacitor follows the input voltage, it then releases that voltage to the output port.

[0010] Preferably, the switched capacitor network structure exhibits a low-loss broadband response, and its time delay is determined by the modulation signal delay. The delay times generated by the forward signal transmission and the reverse signal transmission process are respectively MT S / N and( N–M ) T S / N .

[0011] Preferably, the time delay of the output switch group relative to the modulation signal of the input switch group is MT S / N , M =1, 2, 3, ..., N −1.

[0012] Preferably, the inductor L Equal to 2 R S T S / π 2 N .

[0013] Preferably, the frequency of the modulation signal f S Equal to 1 / T S .

[0014] Preferably, the switch uses a deep N-well MOS transistor.

[0015] Preferably, the body terminal of the deep N-well MOS transistor is grounded through a resistor.

[0016] Preferably, two center-tapped inductors are used instead of a transformer.

[0017] Another technical solution of the present invention is to use a transformer as a working method of a broadband switched capacitor CMOS circulator with improved isolation, a single-ended clock signal with a frequency of 2 GHz is fed into a modulation signal generation circuit; the single-ended clock signal is passed through a single-ended differential conversion circuit to generate a pair of differential clock signals; the differential clock signal is amplified into a square wave signal after passing through a differential buffer; then, an orthogonal signal generator composed of two latches generates four-way orthogonal square wave signals; the four-way orthogonal square wave signals are fed into a non-overlapping signal generator to generate a four-phase non-overlapping modulation signal with a frequency of 1 GHz and a duty cycle of 25%. Compared with the prior art, the present invention has at least the following beneficial effects: A broadband switched capacitor CMOS circulator using a transformer to improve isolation, in which a MOS transistor M 1a 、M 2a 、M 3a 、M 4a 、M 1b 、M 2b 、M 3b 、M 4b 、M 1c 、M 2c 、M 3c 、M 4cAll work in the switch mode. The centers of the four-way switch network structure are connected to capacitors C1, C2, C3, and C4 respectively. At the same time, these switches are controlled by control signals LO1, LO2, LO3, and LO4 to control their on and off states, thereby realizing the basic functions of the circulator.

[0018] Furthermore, when R S C ≈ T S / 2 N When , the capacitor follows the input voltage and then releases this voltage to the output port, making the switching network exhibit low loss broadband response characteristics.

[0019] Furthermore, the switch network structure exhibits the characteristics of low-loss broadband response, so that the entire switched capacitor CMOS circulator has broadband and low insertion loss characteristics.

[0020] Furthermore, the time delay of the output switch group relative to the modulation signal of the input switch group is MT S / N , M =1,2,3,..., N −1. This arrangement makes the switched capacitor network structure similar to that of a transmission line, providing only delay and phase shift.

[0021] Furthermore, the advantage of using deep N-well MOS transistors for the switches is that the bias of the MOS transistor body can be set independently.

[0022] Furthermore, the body terminal of the deep N-well MOS transistor is grounded through a resistor, so that the transistor has a floating body function, thereby increasing the linearity of the transistor.

[0023] Furthermore, two center-tapped inductors are used to replace the transformer, thereby reducing the chip area of ​​the circulator and saving costs.

[0024] The working method of the broadband switched capacitor CMOS circulator with improved isolation using a transformer is shown in Figure 1. A single-ended clock signal with a frequency of 2GHz is fed into the modulation signal generation circuit; the single-ended clock signal is first connected to a 50Ω resistor and a series capacitor C inThe impedance matching circuit formed by the single-ended to differential circuit (STD) reduces the attenuation and reflection of the input signal, and generates a pair of differential clock signals through the single-ended to differential circuit (STD), which is convenient for the subsequent differential circuit to use; the differential clock signal is amplified into a square wave signal after passing through the differential buffer chain; then the orthogonal signal generator composed of two latches generates four orthogonal square wave signals; the four orthogonal square wave signals are fed into the non-overlapping signal generator (NOLAP) to generate a four-phase frequency of 1 GHz and a duty cycle of 25% non-overlapping modulation signal. The above four-phase frequency of 1 GHz and duty cycle of 25% non-overlapping modulation signals LO1, LO2, LO3, LO4 are used to control the conduction and disconnection state of the MOS transistor in the switch capacitor structure, thereby realizing the function of the circulator.

[0025] In summary, the present invention can improve isolation and operating bandwidth, and reduce noise coefficient, circuit complexity and chip power consumption.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings to be used in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 Schematic diagram of a two-port delay module based on an N-way switched capacitor network, where (a) the circuit diagram of the two-port N-way switched capacitor network, (b) the modulation signal of the switch; Figure 2 The structure diagram of the circulator based on the three-port switched capacitor network layer, where (a) is the principle diagram and (b) is the modulation signal timing diagram; Figure 3 ,where, (a) the change of the center capacitor voltage with time when there is excitation at port 1, (b) the schematic diagram of improving isolation; Figure 4 The structure diagram of the present invention, wherein (a) is the overall structure of the circulator, (b) is the modulation signal timing diagram, and (c) is the S parameter simulation result; Figure 5 is the overall circuit topology of the circulator; Figure 6Where, (a) is the chip photo of the circulator, (b) is the S parameter from port 1 to port 2, (c) is the S parameter from port 2 to port 3, (d) is the S parameter from port 3 to port 1, (e) is the noise figure (NF), and (f) is the input 1dB compression point (IP 1dB ). DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "one side", "one end", "one side" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0031] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0033] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0034] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0035] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0036] The present invention provides a broadband switched capacitor CMOS circulator, which applies transformer-based isolation enhancement technology to radio frequency integrated circuit design to improve the isolation performance of radio frequency integrated circuits within a broadband operating range. As a non-reciprocal device, it is generally used in radio frequency communications, radar / imaging sensors, quantum computing and quantum communication systems. It also serves as an important shared antenna interface to achieve decoupling of incident waves and reflected waves and is used in full-duplex, frequency modulated continuous wave radars (FMCW-based radars) and multi-band wireless communication systems.

[0037] See also Figure 1 , is a two-port delay module based on an N-way switched capacitor network with N identical branches. The switch groups on each side are controlled by non-overlapping square wave modulation signals, and the period of each square wave modulation signal is T S , and the duty cycle is T S / N ,like Figure 1 (b) The time delay of the modulation signal of the output switch group (right side) relative to the input switch group (left side) is MT S / N ,in M =1,2,3,..., N −1. R S C ≈ TS / 2 N When the capacitor weakly follows the input voltage, it then weakly releases the voltage to the output port. The switched capacitor network structure exhibits a low-loss broadband response, and its time delay is determined by the modulation signal delay, and the delay time generated by the forward signal transmission and reverse signal transmission process is respectively MT S / N and( N–M ) T S / N , that is, the forward signal transmission and reverse signal transmission processes are non-reciprocal. In order to improve the port impedance R S To achieve the desired matching, an inductor can be added on each side of the switched capacitor network to further improve insertion loss and reduce harmonic conversion losses. L Equal to 2 R S T S / π 2 N .

[0038] See also Figure 2 On the basis of the above two-port delay module structure, an additional set of switches is added at the central capacitor node to form a three-port circulator. The switches of each layer of the circulator are controlled in a rotating manner. Therefore, at any time, only one switch in each layer is connected to the central capacitor. The control timing of the switch is as follows: Figure 2 (b) The central capacitor of each layer is charged from one port and then releases most of the charge to the next port. This rotational exchange enables low-loss transmission of signals from port 1 to port 2 and from port 2 to port 3, as well as isolation from any other port.

[0039] The existing three-port circulator based on an 8-way switched capacitor network has 8 identical layers. Since the structure requires 8 non-overlapping modulation signals to control the switching of the above 8-way switched capacitor network, the design complexity and power consumption of the modulation signal generation circuit are increased. In order to simplify the modulation signal generation circuit, the present invention adopts a 4-way switched capacitor network structure to reduce the number of switches. At the same time, in order to ensure similar low-loss transmission performance as the existing structure, the circuit structure of the present invention must have the same non-aliasing bandwidth as the existing structure, that is, both are equal to Nf S / 2, where f S is the frequency of the modulating signal, equal to 1 / T S Therefore, the modulation signal frequency of the present invention must be twice that of the existing structure.

[0040] Bundle Figure 2 (a) The corresponding schematic diagram N When the voltage of the central capacitor of the first layer changes with time, the voltage of the central capacitor of the first layer changes with time. Figure 3 (a). According to Figure 3 As shown in (a), due to the presence of the inductor on the port, the charging and discharging performance of the central capacitor is improved, thereby reducing the signal transmission loss from port 1 to port 2 and improving the signal isolation from port 1 to port 3. T S / 4 At the moment, the voltage on the central capacitor changes from V 6 Increase to V 6a, that is, reducing the discharge speed of port 3, the signal isolation from port 1 to port 3 can be further improved, such as Figure 3 Although the isolation can be improved by reducing the inductance of port 3, it will also lead to an increase in the transmission loss from port 2 to port 3.

[0041] In order to improve the isolation without increasing the transmission loss, the present invention adopts an isolation improvement technology based on a transformer structure. The overall structure of the circulator is as follows: Figure 4 (a). When there is excitation at port 1, according to Figure 4 From the modulation signal timing diagram shown in (b), it can be seen that when the central capacitor of the first layer is discharged through port 3, the central capacitor of the second layer is discharged through port 2 at this moment. A part of the discharge current of the central capacitor of the second layer is fed into the central capacitor of the first layer in reverse form through the transformer, thereby reducing the current discharge speed of the central capacitor of the first layer, thereby slowing down the voltage drop on the capacitor, and finally achieving an improvement in isolation from port 1 to port 3.

[0042] See also Figure 5 The present invention discloses a broadband switched capacitor CMOS circulator using a transformer as an isolation-enhanced device, comprising a switched capacitor network structure with four identical branches.

[0043] Among them, MOS transistor M 1a 、M 2a 、M 3a 、M 4a 、M 1b 、M 2b 、M 3b 、M 4b 、M 1c 、M 2c 、M 3c 、M 4cAll work in the switch mode; the center of the four-way switch network structure is connected to the capacitors C1, C2, C3, and C4 respectively, and the on and off states of these switches are controlled by control signals LO1, LO2, LO3, and LO4 respectively.

[0044] The above four control signals LO1, LO2, LO3, and LO4 are all generated by the modulation signal generation circuit, and its working process is as follows: a single-ended clock signal with a frequency of 2 GHz is fed into the modulation signal generation circuit; The single-ended clock signal is first connected to the 50Ω resistor and series capacitor C in The impedance matching circuit formed by the single-ended differential converter (STD) can reduce the attenuation and reflection of the input signal, and generate a pair of differential clock signals to facilitate the use of subsequent differential circuits. The differential clock signal is amplified into a square wave signal after passing through a differential buffer chain; then, an orthogonal signal generator composed of two latches generates four orthogonal square wave signals, and each latch adopts an SDTC structure; The four orthogonal square wave signals are fed into a non-overlapping signal generator (NOLAP) to generate four non-overlapping modulation signals LO1, LO2, LO3, LO4 with a frequency of 1 GHz and a duty cycle of 25%. 4。

[0045] The non-overlapping signal generator is composed of four NAND gates (NAND), and each NAND gate adopts the most basic CMOS structure.

[0046] In the broadband switched capacitor CMOS circulator, all switches are implemented using deep N-well MOS transistors, and the body terminals of all transistors are connected through resistors R 1a , R 2a , R 3a , R 4a , R 1b , R 2b , R 3b , R 4b , R 1c , R 2c , R 3c , R 4c Grounding, i.e. floating body technology, improves linearity.

[0047] In order to reduce the area, the present invention uses two center-tapped inductors to replace the transformer.

[0048] The working principle of a broadband switched capacitor CMOS circulator of the present invention is as follows: A single-ended clock signal with a frequency of 2 GHz is fed into the modulation signal generation circuit; First, the single-ended clock signal passes through a single-ended to differential conversion circuit to generate a pair of differential clock signals; Then, the differential clock signal is amplified into a square wave signal after passing through a differential buffer; Then, an orthogonal signal generator composed of two latches generates four orthogonal square wave signals; Finally, the four orthogonal square wave signals are fed into a non-overlapping (NOLAP) signal generator to generate a four-phase non-overlapping modulation signal with a frequency of 1 GHz and a duty cycle of 25%.

[0049] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0050] The S parameter simulation results of the CMOS circulator of the present invention without and with a transformer are as follows: Figure 4 (c) It can be seen that when a transformer is installed, the isolation of the circulator |S 31 |It is increased by more than 2 dB compared to the case without a transformer, and the insertion loss is almost unchanged, which verifies the effectiveness of the transformer structure in improving the isolation performance of the circulator.

[0051] The circulator of the present invention is designed using 55 nm CMOS technology, and the chip photo is shown in FIG. Figure 6 As shown in (a), the inductance at the port is realized by using off-chip bonding wire inductors. The size of the chip including the pad is 0.45 mm × 0.5 mm.

[0052] The overall power consumption of the circulator is only 4.1 mW when powered by a 1.2 V supply.

[0053] Circulator S parameters, noise figure NF and input 1dB compression point (Input 1dB Compression Point, IP 1dB ) The test results are as follows Figure 6 (b) ~ Figure 6 (f) shown.

[0054] In the frequency range of DC~1.4 GHz, the transmission loss of the circulator (|S 21 | and |S 32 |) is 3.9~5.3dB, isolation |S 31 |>19.6 dB, return loss (|S 11 |、|S 22 | and |S 33 |) are all greater than 9 dB, and the noise figure NF from the antenna port (ANT port / port 2) to the receiving port (RX port / port 3) is 3.9~7.1 dB.

[0055] IP from transmit port (TX port / port 1) to ANT port and ANT port to RX port at 500 MHz 1dB 2.6 dBm and 2.5 dBm respectively.

[0056] In summary, the broadband switched capacitor CMOS circulator and method thereof of the present invention effectively improve the isolation of the circulator by adopting a transformer-based isolation enhancement technology, and at the same time reduce the circuit complexity and noise factor by adopting a 4-way switched capacitor structure, and improve the bandwidth and reduce the chip power consumption, so that the circulator is more suitable for future broadband full-duplex, FMCW radar and multi-band wireless communication systems.

[0057] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A broadband switched capacitor CMOS circulator using a transformer as an isolation enhancer, characterized in that: A switched capacitor network structure having N identical branches, N The switch group on each side is controlled by a non-overlapping square wave modulation signal, and the period of each non-overlapping square wave modulation signal is T S , the duty cycle is T S / N , an inductor is set on each side of the switched capacitor network structure L A set of switches is set at the central capacitor node of the switched capacitor network structure to form a three-port circulator. The switches of each layer of the three-port circulator are controlled in a rotating manner. The central capacitor of each layer is charged from one port and then released to the next port. When the central capacitor of the first layer is discharged through port 3, the central capacitor of the second layer is discharged through port 2 at this moment; part of the discharge current of the central capacitor of the second layer is fed into the central capacitor of the first layer in an inverted form through the transformer, thereby improving the isolation from port 1 to port 3.

2. The broadband switched capacitor CMOS circulator with improved isolation using a transformer according to claim 1, characterized in that: when R S C ≈ T S / 2 N , the capacitor follows the input voltage and then releases that voltage to the output port.

3. The broadband switched capacitor CMOS circulator with improved isolation using a transformer according to claim 2, characterized in that: The switched capacitor network structure exhibits a low-loss broadband response, and its time delay is determined by the modulation signal delay. The delay times generated by the forward signal transmission and the reverse signal transmission process are MT S / N and( N–M ) T S / N .

4. The broadband switched capacitor CMOS circulator with improved isolation using a transformer according to claim 1, characterized in that: The time delay of the output switch group relative to the modulation signal of the input switch group is MT S / N , M =1,2,3,..., N −1.

5. The broadband switched capacitor CMOS circulator with improved isolation using a transformer according to claim 1, characterized in that: inductance L Equal to 2 R S T S / π 2 N .

6. The broadband switched capacitor CMOS circulator with improved isolation using a transformer according to claim 1, characterized in that: The frequency of the modulating signal f S Equal to 1 / T S .

7. The broadband switched capacitor CMOS circulator with improved isolation using a transformer according to claim 1, characterized in that: The switches use deep N-well MOS transistors.

8. The broadband switched capacitor CMOS circulator with improved isolation using a transformer according to claim 7, characterized in that: The body terminal of the deep N-well MOS transistor is grounded through a resistor.

9. The broadband switched capacitor CMOS circulator with improved isolation using a transformer according to claim 1, characterized in that: Two center-tapped inductors are used instead of a transformer.

10. The working method of any one of claims 1 to 9 using a transformer as a broadband switched capacitor CMOS circulator with improved isolation, characterized in that: A single-ended clock signal with a frequency of 2 GHz is fed into the modulation signal generation circuit; the single-ended clock signal is converted to a differential clock signal through a single-ended to differential circuit to generate a pair of differential clock signals; the differential clock signal is amplified into a square wave signal after passing through a differential buffer; then, an orthogonal signal generator composed of two latches generates four orthogonal square wave signals; the four orthogonal square wave signals are fed into a non-overlapping signal generator to generate a four-phase non-overlapping modulation signal with a frequency of 1 GHz and a duty cycle of 25%.

Images