Switch bidirectional coupler structure based on on-chip slow-wave coplanar waveguide

Abstract

The invention relates to the technical field of millimeter waves, and discloses a switch bidirectional coupler structure based on an on-chip slow wave coplanar waveguide, which comprises a main transmission line and a coupling transmission line which are arranged in parallel to form a directional coupling structure, one end of the coupling transmission line is a forward coupling end, and the other end is a reverse coupling end; the forward coupling end is connected with a first control switch, the reverse coupling end is connected with a second control switch, the first control switch is connected with the first resistor or the output inductor, and the second control switch is connected with the second resistor or the output inductor; the end, not connected with the forward coupling end, of the first resistor is grounded, the end, not connected with the reverse coupling end, of the second resistor is grounded, and one end of the output inductor is a coupling output port. When the first control switch is connected with the first resistor, the second control switch is connected with the output inductor; when the first control switch is connected with the output inductor, the second control switch is connected with the second resistor; a shielding metal strip is arranged in a signal strip area or a grounding plane, so that the size of the bidirectional coupler is reduced.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of millimeter waves, and in particular to a switch bidirectional coupler structure based on an on-chip slow-wave coplanar waveguide. BACKGROUND

[0002] The millimeter wave frequency band is 30GHz-300GHz, and has become a core supporting technology in the fields of 5G / 6G communication, vehicle-mounted radar, satellite communication and precision measurement due to high bandwidth and low delay characteristics. With the rapid development of automatic driving vehicle-mounted radar and millimeter wave communication, a millimeter wave circuit in the 76GHz-81GHz frequency band has become one of the core technologies, which puts forward strict requirements on the integration, performance density and functional diversity of the radio frequency front end. As a core passive device, the directional coupler needs to realize functions such as power coupling, signal monitoring and standing wave measurement. The bidirectional coupler becomes a key component of the full-duplex system because it can support bidirectional signal transmission and bidirectional standing wave detection.

[0003] At present, the bidirectional coupler mostly adopts a scheme of cascading two one-way directional couplers, which directly leads to a sharp increase in the physical area and seriously occupies the chip integration space, which is contrary to the development trend of high-density integration corresponding to the millimeter wave system. In addition, multiple independent power detection circuits need to be matched to realize bidirectional standing wave measurement, which not only increases the chip area, but also needs complex control logic and wiring, introduces a large number of parasitic parameters such as parasitic capacitance and inductance, and further deteriorates the signal integrity in the millimeter wave frequency band.

[0004] On-chip integration is the core development direction of millimeter wave devices, and CMOS and other silicon-based processes have become the mainstream implementation scheme of on-chip devices due to low cost, high integration and strong compatibility. The coupler composed of traditional transmission lines such as microstrip lines and ordinary coplanar waveguides has a large physical size, although the wavelength of the W wave band is reduced to a size comparable to the chip, but the length of the lambda / 4 transmission line still limits the integration. In addition, the low resistivity substrate of the CMOS process leads to electromagnetic wave leakage and serious dielectric loss. SUMMARY

[0005] In order to reduce the size of the bidirectional coupler, the application provides a switch bidirectional coupler structure based on an on-chip slow-wave coplanar waveguide, which adopts the following technical scheme: A switch bidirectional coupler structure based on an on-chip slow-wave coplanar waveguide, comprising a main transmission line and a coupling transmission line arranged in parallel, the main transmission line and the coupling transmission line forming a directional coupling structure; one end of the main transmission line is a main port, and the other end is a through port; one end of the coupling transmission line is a forward coupling end, and the other end is a reverse coupling end; A first control switch is connected to the forward coupling terminal, and a second control switch is connected to the reverse coupling terminal. The first control switch is used to connect a first resistor or an output inductor, and the second control switch is used to connect a second resistor or an output inductor. The end of the first resistor not connected to the forward coupling terminal is grounded, the end of the second resistor not connected to the reverse coupling terminal is grounded, and the end of the output inductor not connected to the first or second control switch is the coupling output port. When the first control switch is connected to the first resistor, the second control switch is connected to the output inductor; when the first control switch is connected to the output inductor, the second control switch is connected to the second resistor. The main transmission line and the coupled transmission line are located in the signal strip area. The grounding of the first resistor and the second resistor is located in the ground plane. At least two parallel shielding metal strips are set in the signal strip area or the ground plane. The shielding metal strips form a periodically loaded transmission line to change the distributed inductance L and distributed capacitance C of the main transmission line and the coupled transmission line, thereby reducing the phase velocity v of the electromagnetic wave. p v p =ω / β, where ω is the angular frequency and β is the phase constant.

[0006] By employing the above technical solution, a bidirectional switching coupler structure based on an on-chip slow-wave coplanar waveguide is realized. This reduces the electromagnetic wave phase velocity and shortens the equivalent wavelength. While maintaining electrical performance such as coupling and phase shift, the physical size of the device is reduced by 30%-60% compared to traditional transmission lines, meeting the high-density integration requirements of millimeter-wave circuits. The slow-wave coplanar waveguide SW-CPW possesses advantages such as low radiation loss, flexible impedance matching, and strong process compatibility.

[0007] Optionally, both the first control switch and the second control switch are NMOS switches.

[0008] By adopting the above technical solution, NMOS transistors have high electron mobility and lower on-resistance in the on state compared with PMOS transistors of the same size. Therefore, under the condition that the on-resistance is the same as that of PMOS transistors, NMOS transistors are smaller in size and have a smaller equivalent capacitance in the off state, resulting in weaker side effects of the off-state capacitance.

[0009] Optionally, the capacitance of the NMOS switch in the off state is equivalent to C. off , , where C gd C is the equivalent capacitance between the gate and drain. gs C is the equivalent capacitance between the gate and the source. ds This is the equivalent capacitance between the drain and source. The resistance of an NMOS switch in the on state is equivalent to R. on , , where μ n It is electron mobility, Cox V is the capacitance per unit area of ​​the gate oxide layer, W is the channel width, L is the channel length, W / L is the channel width-to-length ratio, and V is the channel oxide capacitance per unit area. gs It is the gate-source voltage, V th It is the threshold voltage; The resistance of the first or second resistor is Z0-R on .

[0010] By adopting the above technical solution, a resistor matching the system characteristic impedance Z0 is cascaded outside the isolation port to ensure that all key performance parameters of the coupler, such as orientation, coupling degree, and matching of input and output ports, meet the design specifications.

[0011] Optionally, the first resistor and the second resistor have the same resistance value, and Z0 is 50 ohms.

[0012] Optionally, at least two parallel shielding metal strips are provided in both the signal strip area and the ground plane.

[0013] Optionally, multiple shielding metal strips are provided, with more than two strips at each location and all strips being evenly distributed at equal intervals.

[0014] Optionally, the shielding metal strips are provided in multiple locations, with at least one location having two strips distributed in parallel, and at least one location having more than two strips distributed at equal intervals.

[0015] Optionally, the shielding metal strips are provided in multiple locations, with two strips at each location, and both are evenly distributed at equal intervals. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a switched bidirectional coupler structure based on an on-chip slow-wave coplanar waveguide.

[0017] Figure 2 This is a layout of a switched bidirectional coupler structure based on an on-chip slow-wave coplanar waveguide.

[0018] Figure 3 It is a circuit diagram of the switching transistor and its equivalent circuit.

[0019] Reference numerals: 1. Main port; 2. Straight-through port; 3. Forward coupling terminal; 4. Reverse coupling terminal; 5. Coupled output port. Detailed Implementation

[0020] The embodiments of this application are described in detail below, and examples of the embodiments are shown in the accompanying drawings.

[0021] In the description of this specification, the references to "certain embodiments," "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples" refer to specific features, structures, materials, or characteristics described in connection with the described embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0022] In existing coupler designs, there is a trade-off between area and integration density. Existing bidirectional coupler structures lack support for slow-wave structures. Traditional coplanar waveguide / microstrip line structures, to achieve coupling phase and length, have large physical dimensions, making high-density integration with active circuits such as switches and detection circuits difficult. Bidirectional couplers use multiple independent power detection circuits, resulting in a large area and increased system complexity. Couplers exhibit poor RF performance, severe dielectric loss, and the long transmission lines further degrade RF insertion loss. Traditional unidirectional couplers have a single function, coupling signals in only one direction within the same area.

[0023] This application discloses a switched bidirectional coupler structure based on an on-chip slow-wave coplanar waveguide, referring to... Figure 1 It includes parallel main transmission lines and coupled transmission lines, forming a directional coupling structure. One end of the main transmission line is the main port, and the other end is a through port; one end of the coupled transmission line is the forward coupling end, and the other end is the reverse coupling end.

[0024] The forward coupling terminal is connected to a first control switch, and the reverse coupling terminal is connected to a second control switch. The first control switch is used to connect a first resistor or an output inductor, and the second control switch is used to connect a second resistor or an output inductor. The output inductor is a matching inductor.

[0025] The end of the first resistor not connected to the forward coupling terminal is grounded, the end of the second resistor not connected to the reverse coupling terminal is grounded, and the end of the output inductor not connected to the first or second control switch is the coupling output port. When the first control switch is connected to the first resistor, the second control switch is connected to the output inductor; when the first control switch is connected to the output inductor, the second control switch is connected to the second resistor.

[0026] like Figure 2 As shown, the main transmission line and the coupled transmission line are located in the signal strip area. The grounding of the first resistor and the second resistor is located in the ground plane. At least two parallel shielding metal strips are set in the signal strip area or the ground plane. The shielding metal strips are set as follows: At least two parallel shielding metal strips are provided in both the signal strip area and the ground plane; The shielding metal strips are installed in multiple locations, with more than two strips at each location, and all are evenly distributed at equal intervals. The shielding metal strips are installed in multiple locations, with at least one location having two strips arranged in parallel, and at least one location having more than two strips arranged at equal intervals. There are multiple shielding metal strips, with two strips at each location, and they are evenly distributed with equal spacing.

[0027] Strictly adhering to the requirement of symmetry, periodic shielding metal strips are introduced into the signal strips or ground plane of the coplanar waveguide to form a periodically loaded transmission line, thereby achieving the slow wave effect. This is used to change the distributed inductance L and distributed capacitance C of the main transmission line and the coupled transmission line, thus reducing the phase velocity v of the electromagnetic wave. p v p =ω / β, where ω is the angular frequency and β is the phase constant. The equivalent wavelength is shortened, thus significantly reducing the physical length for the same electrical length, achieving slow-wave miniaturization. Furthermore, the coplanar ground plane of the CPW effectively isolates surrounding electromagnetic interference sources.

[0028] CMOS transistors can be used as switches in circuits, adjusting the conduction or cutoff state of the channel by controlling the gate voltage to achieve switching functionality. In bidirectional coupler designs, the coupling direction can be switched by controlling the state of the CMOS transistor to switch between the coupled and isolated ports. Therefore, the performance of CMOS switches has a significant impact on circuit performance. Transistors typically exhibit non-ideal parasitic effects, which can limit circuit performance. Both the first and second control switches are NMOS switches. NMOS transistors have high electron mobility and, compared to PMOS transistors of the same size, have lower on-resistance in the on-state. Therefore, under the same on-resistance condition, NMOS transistors are smaller in size and have a smaller equivalent capacitance in the off-state, resulting in weaker off-capacitance side effects. The NMOS transistors form a single-pole double-throw (SPD) switch module. The common terminal of the SPD switch module can be connected to an external power detection circuit to detect the power of the NMOS transistor.

[0029] like Figure 3 As shown, the capacitance of an NMOS switch in the off state is equivalent to C. off , , where C gd C is the equivalent capacitance between the gate and drain. gs C is the equivalent capacitance between the gate and the source. ds It is the equivalent capacitance between the drain and the source.

[0030] The resistance of an NMOS switch in the on state is equivalent to R. on , , where μ n It is electron mobility, C ox V is the capacitance per unit area of ​​the gate oxide layer, W is the channel width, L is the channel length, W / L is the channel width-to-length ratio, and V is the channel oxide capacitance per unit area. gs It is the gate-source voltage, V th It is the threshold voltage.

[0031] The resistance of the first or second resistor is Z0-R on Preferably, the first resistor and the second resistor have the same resistance value, and Z0 is 50 ohms.

[0032] A resistor matching the system characteristic impedance Z0 is cascaded outside the isolation port to ensure that all key performance parameters of the coupler, such as orientation, coupling degree, and input / output port matching, meet the design specifications. The cascaded resistors are the first and second resistors with a resistance value of Z0-R. on Because a capacitor C is introduced when the switch is turned off. off The parasitic capacitance C of the branch off It will be directly connected in parallel to the main transmission line of the coupler, causing impedance offset. In order to solve the mismatch problem caused by the parallel capacitor, we connect the output inductor in series at the output port of the coupler to form an L-shaped matching network.

[0033] This paper presents a bidirectional switch-coupled structure based on an on-chip slow-wave coplanar waveguide. This structure reduces the electromagnetic wave phase velocity and shortens the equivalent wavelength, while maintaining electrical performance such as coupling and phase shift. The physical size of the device is reduced by 30%-60% compared to traditional transmission lines, meeting the high-density integration requirements of millimeter-wave circuits. The slow-wave coplanar waveguide (SW-CPW) offers advantages such as low radiation loss, flexible impedance matching, and strong process compatibility. Its structure effectively addresses the trade-off between area and integration density, reducing coupler size by over 60%. The SPDT switch replaces "two unidirectional couplers + two independent detection circuits," further reducing circuit area by 50% and enabling high-density integration with active circuits such as switches and amplifiers.

[0034] The structure improves RF performance; the slow-wave structure shortens the transmission line length, reducing insertion loss by more than 0.5dB. Return loss is better than -20dB, coupling fluctuation is ≤±0.8dB, and it covers the 76GHz-81GHz frequency band.

[0035] It facilitates expanded functionality and reduced system complexity by achieving bidirectional coupling through CMOS transistor switching. The same structure supports power coupling and VSWR measurement of forward and reverse signals, replacing the single-function unidirectional coupler. In terms of hardware configuration, only one detection circuit and simple level control logic are required, reducing the introduction of parasitic parameters and improving VSWR measurement accuracy by more than 5%.

[0036] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A switched bidirectional coupler structure based on an on-chip slow-wave coplanar waveguide, characterized in that, It includes parallel main transmission lines and coupled transmission lines, which form a directional coupling structure; one end of the main transmission line is the main port and the other end is the through port; one end of the coupled transmission line is the forward coupling end and the other end is the reverse coupling end. A first control switch is connected to the forward coupling terminal, and a second control switch is connected to the reverse coupling terminal. The first control switch is used to connect a first resistor or an output inductor, and the second control switch is used to connect a second resistor or an output inductor. The end of the first resistor not connected to the forward coupling terminal is grounded, the end of the second resistor not connected to the reverse coupling terminal is grounded, and the end of the output inductor not connected to the first or second control switch is the coupling output port. When the first control switch is connected to the first resistor, the second control switch is connected to the output inductor; when the first control switch is connected to the output inductor, the second control switch is connected to the second resistor. The main transmission line and the coupled transmission line are located in the signal strip area. The grounding of the first resistor and the second resistor is located in the ground plane. At least two parallel shielding metal strips are set in the signal strip area or the ground plane. The shielding metal strips form a periodically loaded transmission line to change the distributed inductance L and distributed capacitance C of the main transmission line and the coupled transmission line, thereby reducing the phase velocity v of the electromagnetic wave. p v p =ω / β, where ω is the angular frequency and β is the phase constant.

2. The switchable bidirectional coupler structure based on an on-chip slow-wave coplanar waveguide according to claim 1, characterized in that, Both the first control switch and the second control switch are NMOS switches.

3. The switchable bidirectional coupler structure based on an on-chip slow-wave coplanar waveguide according to claim 1, characterized in that, The capacitance of an NMOS switch in the off state is equivalent to C. off , , where C gd C is the equivalent capacitance between the gate and drain. gs C is the equivalent capacitance between the gate and the source. ds This is the equivalent capacitance between the drain and source. The resistance of an NMOS switch in the on state is equivalent to R. on , , where μ n It is electron mobility, C ox V is the capacitance per unit area of ​​the gate oxide layer, W is the channel width, L is the channel length, W / L is the channel width-to-length ratio, and V is the channel oxide capacitance per unit area. gs It is the gate-source voltage, V th It is the threshold voltage; The resistance of the first or second resistor is Z0-R on .

4. The switchable bidirectional coupler structure based on on-chip slow-wave coplanar waveguide according to claim 3, characterized in that, The first resistor and the second resistor have the same resistance value, Z0 is 50 ohms.

5. The switchable bidirectional coupler structure based on an on-chip slow-wave coplanar waveguide according to claim 1, characterized in that, At least two parallel shielding metal strips are provided in both the signal strip area and the ground plane.

6. The switchable bidirectional coupler structure based on an on-chip slow-wave coplanar waveguide according to claim 1, characterized in that, There are multiple shielding metal strips, with more than two strips at each location, and all of them are evenly distributed at equal intervals.

7. The switchable bidirectional coupler structure based on an on-chip slow-wave coplanar waveguide according to claim 1, characterized in that, The shielding metal strips are installed in multiple locations, with at least one location having two strips arranged in parallel, and at least one location having more than two strips arranged at equal intervals.

8. The switchable bidirectional coupler structure based on an on-chip slow-wave coplanar waveguide according to claim 1, characterized in that, There are multiple shielding metal strips, with two strips at each location, and they are evenly distributed with equal spacing.

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