High-isolation radio frequency single-pole double-throw switch
By introducing a bridged T coil into the RF single-pole double-throw switch for signal cancellation, the signal leakage and crosstalk problems are solved, and a high isolation and miniaturized RF switch design is achieved, which improves the performance and integration of the communication system.
Patent Information
- Application Number
- CN202510616615.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-14
- Publication Date
- 2025-08-29
AI Technical Summary
The existing RF single-pole double-throw switches have severe signal leakage and crosstalk at high frequencies, resulting in a reduced signal-to-noise ratio and a large area of land, which cannot meet the design needs of miniaturization of devices.
The high isolation RF single-pole double-throw switch structure is adopted, including the first and second series parallel switch groups and signal cancellation units. The bridge T coil is used to shift the signal by 180° phase, so that the leakage signal and the reverse signal are phased opposite and cancel each other. Combined with the optimization of the matching of inductor and capacitor parameters, the isolation performance is improved and the loss is reduced.
Without adding additional transistors, the isolation between the transmitter and receiver is significantly improved, signal transmission loss is reduced, and circuit layout area is reduced, which is suitable for high-density RF front-end design of high-frequency communication systems.
Smart Images
Figure CN120567211A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of millimeter wave radio frequency front-end architecture, and in particular relates to a high-isolation radio frequency single-pole double-throw switch. Background Art
[0002] The RF front-end system is a core module in wireless communication systems. Consisting primarily of key components such as power amplifiers, low-noise amplifiers (LNAs), and switches, the RF front-end system determines the overall performance of the communication system and directly impacts the user experience. The single-pole double-throw (SPDT) switch, which directly connects to the PA, LNA, and antenna, significantly impacts the performance of both the transmit and receive links. In transmit mode, the switch is located after the PA's output port. The switch's insertion loss directly reduces the transmit link's output power and efficiency. In receive mode, the switch is located before the LNA. Degraded switch isolation leads to increased signal leakage. Increased signal leakage and crosstalk increase the noise component in the received signal, reducing the signal-to-noise ratio. Furthermore, partial signal leakage from the transmit branch into the receive path impacts signal quality, increasing insertion loss in the conduction branch.
[0003] RF circuits typically use inductor-capacitor-inductor (LCL) or microstrip structures to transform impedance and mitigate signal leakage. However, microstrip lines are too large to be suitable at high frequencies, and the isolation provided by LCL circuits is limited, failing to meet the requirements of highly integrated designs. In short, existing methods for mitigating signal leakage offer poor isolation and occupy a large footprint, making them inadequate for miniaturized device designs. Therefore, a new single-pole, double-throw (SPDT) switch structure is needed to address these issues. Summary of the Invention
[0004] In order to solve the above problems existing in the prior art, the present invention provides a high-isolation radio frequency single-pole double-throw switch. The technical problem to be solved by the present invention is achieved through the following technical solutions:
[0005] The present invention provides a high-isolation radio frequency single-pole double-throw switch, comprising: a first series-parallel switch group, a second series-parallel switch group and a signal cancellation unit; the first input end of the first series-parallel switch group is connected to the output end of the transmitter, the second input end is connected to a power supply, the first output end is respectively connected to the first input end and the antenna port of the second series-parallel switch group, and the second output end is connected to the first input end of the signal cancellation unit; the second input end of the second series-parallel switch group is connected to the power supply, the first output end is connected to the input end of the receiver, and the second output end is connected to the second input end of the signal cancellation unit; the output end of the signal cancellation unit is grounded; the signal cancellation unit is used to perform a 180° phase shift on a signal leaked into the second series-parallel switch group to obtain a phase-shifted signal, and to cause a signal leaked from the first series-parallel switch group to cancel each other with the phase-shifted signal.
[0006] Optimally, the first series-parallel switch group includes a first symmetrical HEMT switch and a second symmetrical HEMT switch; and the second series-parallel switch group includes a third symmetrical HEMT switch and a fourth symmetrical HEMT switch; wherein the gates of the first, second, third, and fourth symmetrical HEMT switches are all connected to a power supply; the source / drain of the first symmetrical HEMT switch is respectively connected to the output of the transmitter and the source / drain of the second symmetrical HEMT switch; the drain / source of the first symmetrical HEMT switch is respectively connected to the source / drain of the third symmetrical HEMT switch and the antenna port; the drain / source of the third symmetrical HEMT switch is respectively connected to the input of the receiver and the source / drain of the fourth symmetrical HEMT switch; the drain / source of the second symmetrical HEMT switch is connected to the first input of the signal cancellation unit, and the drain / source of the fourth symmetrical HEMT switch is connected to the second input of the signal cancellation unit.
[0007] Optimally, the signal cancellation unit is a bridge T-coil comprising: a first capacitor, a second capacitor, a first inductor, and a second inductor; wherein the first end of the first capacitor and the first end of the first inductor are both connected to the drain / source of the second symmetrical HEMT switch, the second end of the first capacitor and the second end of the second inductor are both connected to the drain / source of the fourth symmetrical HEMT switch; the second end of the first inductor is connected to the first end of the second inductor; the second end of the first inductor is also connected to the first end of the second capacitor, and the second end of the second capacitor is grounded.
[0008] Optimally, the inductance values of the first inductor and the second inductor are equal, and the first inductor and the second inductor are coupled to each other.
[0009] Optimally, the calculation formulas for the capacitances of the first capacitor and the second capacitor satisfy:
[0010]
[0011] Among them, C p is the capacitance of the first capacitor, C s is the capacitance of the second capacitor, f1, f2, Z1, θ1, Z2 and θ2 are all values of the two equivalent microstrip lines, f1 is the lowest frequency of the working frequency band of the microstrip line, f2 is the highest frequency of the working frequency band of the microstrip line, Z1 is the first characteristic impedance of the microstrip line, θ1 is the first electrical length of the microstrip line, Z2 is the second characteristic impedance of the microstrip line, and θ2 is the second electrical length of the microstrip line.
[0012] Optimally, the calculation formula of the inductance value of the first inductor satisfies:
[0013]
[0014] Among them, L s is the inductance value of the first inductor.
[0015] Optimally, the coupling coefficient between the first inductor and the second inductor satisfies:
[0016]
[0017] Among them, L m is the coupling coefficient between the first inductor and the second inductor.
[0018] Compared with the prior art, the present invention has the following beneficial effects:
[0019] To address the problems of existing methods for mitigating signal leakage, which suffer from poor signal isolation and occupy a large layout area, failing to meet the design requirements for device miniaturization, this invention proposes a high-isolation RF single-pole double-throw switch. Based on the traditional symmetrical transistor switch group, this invention innovatively introduces a bridged T-coil composed of symmetrically coupled inductors and compensation capacitors as a signal cancellation unit. This solution utilizes the phase-shifting characteristics of the bridged T-coil to cause the signal leaking into the receiving path to be in opposite phase to the signal leaking from the reverse branch, thereby canceling each other out. Simultaneously, by optimizing the inductor and capacitor parameters to match the equivalent microstrip line characteristics, this solution significantly improves the isolation performance between the transmitting and receiving ends, significantly reduces signal transmission loss, and reduces the circuit layout area without adding additional transistors. This solution is suitable for high-density RF front-end designs in high-frequency communication systems, balancing performance and integration requirements. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 This is a circuit structure diagram of an existing single-pole double-throw switch;
[0021] Figure 2 Schematic diagram of signal flow in a conventional single-pole double-throw switch in transmit mode;
[0022] Figure 3 This is a circuit connection diagram of a high-isolation radio frequency single-pole double-throw switch provided by an embodiment of the present invention;
[0023] Figure 4 is an equivalent circuit diagram of a bridge T-coil provided by an embodiment of the present invention;
[0024] Figure 5 The embodiment of the present invention provides Figure 4 is a working principle diagram of an equivalent circuit diagram of a bridge T-coil provided by an embodiment of the present invention;
[0025] Figure 6 is an equivalent diagram between a bridge T-coil and a microstrip line provided by an embodiment of the present invention;
[0026] Figure 7 The embodiment of the present invention provides Figure 1 The single-pole double-throw switch in Figure 3 The switching loss comparison simulation diagram of the single-pole double-throw switch in the figure;
[0027] Figure 8 The embodiment of the present invention provides Figure 1 The single-pole double-throw switch in Figure 3 The isolation comparison simulation diagram of the single-pole double-throw switch in . DETAILED DESCRIPTION
[0028] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.
[0029] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.
[0030] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.
[0031] Figure 1 This is the circuit structure diagram of the existing single-pole double-throw switch. Figure 2 This is a schematic diagram of the signal flow in an existing single-pole double-throw switch in the transmitting mode. Figure 1 As shown, the gates of the symmetrical HEMT switch M1, the symmetrical HEMT switch M2, the symmetrical HEMT switch M3, and the symmetrical HEMT switch M4 are all connected to a power supply; the source / drain of the symmetrical HEMT switch M1 is connected to the output of the transmitter and the source / drain of the symmetrical HEMT switch M3, respectively; the drain / source of the symmetrical HEMT switch M1 is connected to the source / drain of the symmetrical HEMT switch M2 and the antenna port, respectively; the drain / source of the symmetrical HEMT switch M2 is connected to the input of the receiver and the source / drain of the symmetrical HEMT switch M4, respectively; the drain / source of the symmetrical HEMT switch M3 and the drain / source of the symmetrical HEMT switch M4 are grounded.
[0032] like Figure 2 As shown, the transmission signal path is marked with a dashed line, while the leakage signal path is marked with a dashed line. In transmit mode, symmetrical HEMT switch M1 is on and symmetrical HEMT switch M3 is off. The RF signal from the transmitter is transmitted to the antenna via symmetrical HEMT switch M1, forming a transmit branch. Simultaneously, symmetrical HEMT switch M2 is off and symmetrical HEMT switch M4 is on. A portion of the leakage signal is connected to ground via symmetrical HEMT switch M4, while a portion of the signal enters the receiver via symmetrical HEMT switches M1 and M2 and is then connected to ground via symmetrical HEMT switch M4. This leakage signal not only affects the transmission signal quality of the transmit branch but also increases crosstalk between different channels, affecting signal purity and overall performance.
[0033] In view of the above problems, the present invention proposes a high-isolation radio frequency single-pole double-throw switch. The high-isolation radio frequency single-pole double-throw switch proposed by the present invention is now described in detail with reference to the accompanying drawings.
[0034] Figure 3FIG. 1 is a circuit connection diagram of a high-isolation radio frequency single-pole double-throw switch provided by an embodiment of the present invention. Figure 3 As shown, the high-isolation radio frequency single-pole double-throw switch includes: a first series-parallel switch group, a second series-parallel switch group and a signal cancellation unit; the first input end of the first series-parallel switch group is connected to the output end of the transmitter, the second input end is connected to the power supply, the first output end is respectively connected to the first input end and the antenna port of the second series-parallel switch group, and the second output end is connected to the first input end of the signal cancellation unit; the second input end of the second series-parallel switch group is connected to the power supply, the first output end is connected to the input end of the receiver, and the second output end is connected to the second input end of the signal cancellation unit; the output end of the signal cancellation unit is grounded; the signal cancellation unit is used to perform a 180° phase shift on the signal leaked into the second series-parallel switch group to obtain a phase-shifted signal, and to make the signal leaked from the first series-parallel switch group and the phase-shifted signal cancel each other.
[0035] Please continue to refer to Figure 3 The first series-parallel switch group includes a first symmetrical HEMT switch and a second symmetrical HEMT switch; the second series-parallel switch group includes a third symmetrical HEMT switch and a fourth symmetrical HEMT switch. The gates of the first, second, third, and fourth symmetrical HEMT switches are all connected to a power supply. The source / drain of the first symmetrical HEMT switch is connected to the output of the transmitter and the source / drain of the second symmetrical HEMT switch, respectively. The drain / source of the first symmetrical HEMT switch is connected to the source / drain of the third symmetrical HEMT switch and the antenna port, respectively. The drain / source of the third symmetrical HEMT switch is connected to the input of the receiver and the source / drain of the fourth symmetrical HEMT switch, respectively. The drain / source of the second symmetrical HEMT switch is connected to the first input of the signal cancellation unit, and the drain / source of the fourth symmetrical HEMT switch is connected to the second input of the signal cancellation unit.
[0036] It should be noted that the antenna port can receive the signal sent by the transmitter, acting as an input end, and can also be used to send the received signal to the receiver, acting as an output end.
[0037] It should be noted that a symmetric HEMT switch refers to a switch in which the source (S) and drain (D) are completely symmetrical in terms of geometry, metal contact area, and electric field distribution. This means that, during operation, other devices can be connected to either electrode (except the gate) of the symmetric HEMT switch, acting as either the source or drain. For example, when one electrode of a second symmetric HEMT switch is connected as the source to the source of the first symmetric HEMT switch, the other electrode of the second symmetric HEMT switch is connected as the drain to the first input of the signal cancellation unit.
[0038] Here, the signal cancellation unit is a bridge T-coil, which includes: a first capacitor, a second capacitor, a first inductor, and a second inductor; wherein the first end of the first capacitor and the first end of the first inductor are both connected to the drain / source of the second symmetrical HEMT switch, the second end of the first capacitor and the second end of the second inductor are both connected to the drain / source of the fourth symmetrical HEMT switch; the second end of the first inductor is connected to the first end of the second inductor; the second end of the first inductor is also connected to the first end of the second capacitor, and the second end of the second capacitor is grounded.
[0039] Here, the inductance values of the first inductor and the second inductor are equal, and the first inductor and the second inductor are coupled to each other. Figure 4 : is an equivalent circuit diagram of the bridge T coil provided by the embodiment of the present invention. Figure 4 As shown, the circuit before equivalent can be expressed as the first end of the capacitor Cp and the inductor L S1 The first end of the capacitor Cp is connected to the second end of the inductor L S2 The second end of the inductor L S1 The second end and the inductor L S2 The first end of the capacitor Cs is connected to the inductor L S1 and inductor L S2 The other end is grounded; the equivalent circuit can be expressed as the first end of the capacitor Cp and the equivalent inductor L S1 -L M The first end of the capacitor Cp is connected to the second end of the equivalent inductor L S2 -L M The second end is connected to the equivalent inductor L S1 -L M The second end and the equivalent inductance L S2 -L M The first end of the coupled inductor L M One end is set at the equivalent inductor L S1 -L M and equivalent inductance L S2 -L M The other end is connected to one end of the capacitor Cs, and the other end of the capacitor Cs is grounded.
[0040] Here, a bridged T-coil is used to replace the inductor-capacitor-inductor (LCL) or microstrip line structure, without adding additional transistors, and can effectively reduce signal leakage in a very small layout area. Its specific working principle is as follows Figure 5After adding the bridge-T coil, the signals originally leaking through the third and fourth symmetrical HEMT switches are phase-shifted by 180° and enter the bridge-T coil. Because the direction of the phase-shifted signal is opposite to the direction of the signal leaking through the second symmetrical HEMT switch, the signals entering from the two input terminals of the bridge-T coil cancel each other out, achieving the effect of improving the isolation between the transmitter and receiver ports without adding additional switches.
[0041] In one possible implementation, Figure 6 As shown, when the microstrip line length is λ / 2, pure phase reversal can be achieved. Here, by using the microstrip line with a length of λ / 2 to calculate the parameter matrix of the bridged T coil, the bridged T coil can be used to replace the microstrip line with a length of λ / 2. The Y parameter matrix can be obtained by inverting the Z parameter matrix. The Z parameter matrix only needs to be equal to the Z parameter matrix of the microstrip line with a length of λ / 2.
[0042] For example, the Z parameter matrix of the bridged T-coil is equal to the Z parameter matrix of the microstrip line with a length of λ / 2: Here, TL refers to a microstrip line with a length of λ / 2, and BTC refers to a bridged T-coil.
[0043] Furthermore, in a possible implementation, the calculation formulas for the capacitances of the first capacitor and the second capacitor satisfy:
[0044]
[0045] Among them, C p is the capacitance of the first capacitor, C s is the capacitance of the second capacitor, f1, f2, Z1, θ1, Z2 and θ2 are the values of the two equivalent microstrip lines, f1 is the lowest frequency of the working band of the microstrip line, f2 is the highest frequency of the working band of the microstrip line, Z1 is the first characteristic impedance of the microstrip line, θ1 is the first electrical length of the microstrip line, Z2 is the second characteristic impedance of the microstrip line, and θ2 is the second electrical length of the microstrip line.
[0046] Where f1 corresponds to the first characteristic impedance Z1 of the microstrip line and the first electrical length θ1 of the microstrip line, and f2 corresponds to the second characteristic impedance Z2 of the microstrip line and the second electrical length θ2 of the microstrip line. Z1 and Z2 are generally set to 50Ω.
[0047] And, the coupling coefficient between the first inductor and the second inductor satisfies:
[0048]
[0049] Among them, L m is the coupling coefficient between the first inductor and the second inductor.
[0050] In one possible implementation, the calculation formula of the inductance value of the first inductor satisfies:
[0051]
[0052] Among them, L s is the inductance value of the first inductor.
[0053] It should be noted that the number of bridge T coils provided in the embodiments of the present invention can be increased as needed. The number of bridge T coils is determined by the number of parallel switches in the series-parallel switch group, with one bridge T coil provided between two parallel switches. If the series-parallel switch group consists of one series switch and two parallel switches, the corresponding number of bridge T coils is two.
[0054] After introducing the high-isolation radio frequency single-pole double-throw switch provided by the present invention, simulation software is used to verify the technical effect of the high-isolation radio frequency single-pole double-throw switch provided by the present invention. Figure 7 The embodiment of the present invention provides Figure 1 The single-pole double-throw switch in Figure 3 The switching loss comparison simulation diagram of the single-pole double-throw switch in Figure 8 The embodiment of the present invention provides Figure 1 The single-pole double-throw switch in Figure 3 The isolation comparison simulation diagram of the single-pole double-throw switch in Figure 7 and Figure 8 In the context of "traditional single-pole double-throw switch", Figure 1 The SPDT switch in the "Specific Implementation Example Switch" refers to Figure 3 The single-pole double-throw switch in.
[0055] like Figure 7 As shown, Figure 1 The switching loss of the SPDT switch is greater than Figure 3 The single-pole double-throw switch in Figure 8 As shown, Figure 1 The isolation of the single-pole double-throw switch is much greater than Figure 3 In combination with the SPDT switch Figure 7 and Figure 8 It can be seen that the high-isolation radio frequency single-pole double-throw switch provided by the present invention is conducive to offsetting the leakage signal in the loop without adding additional switching transistors, and achieves a balance between low insertion loss and high isolation.
[0056] To address the problems of existing methods for mitigating signal leakage, which suffer from poor signal isolation and occupy a large layout area, failing to meet the design requirements for device miniaturization, this invention proposes a high-isolation RF single-pole double-throw switch. Based on the traditional symmetrical transistor switch group, this invention innovatively introduces a bridged T-coil composed of symmetrically coupled inductors and compensation capacitors as a signal cancellation unit. This solution utilizes the phase-shifting characteristics of the bridged T-coil to cause the signal leaking into the receiving path to be in opposite phase to the signal leaking from the reverse branch, thereby canceling each other out. Simultaneously, by optimizing the inductor and capacitor parameters to match the equivalent microstrip line characteristics, this solution significantly improves the isolation performance between the transmitting and receiving ends, significantly reduces signal transmission loss, and reduces the circuit layout area without adding additional transistors. This solution is suitable for high-density RF front-end designs in high-frequency communication systems, balancing performance and integration requirements.
[0057] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.
Claims
1. A high-isolation radio frequency single-pole double-throw switch, characterized in that: include: A first series parallel switch group, a second series parallel switch group and a signal offset unit; The first input end of the first series-parallel switch group is connected to the output end of the transmitter, the second input end is connected to the power supply, the first output end is connected to the first input end and the antenna port of the second series-parallel switch group respectively, and the second output end is connected to the first input end of the signal cancellation unit; The second input end of the second series-parallel switch group is connected to a power supply, the first output end is connected to the input end of the receiver, and the second output end is connected to the second input end of the signal cancellation unit; the output end of the signal cancellation unit is grounded; The signal cancellation unit is used to perform a 180° phase shift on the signal leaked into the second series-parallel switch group to obtain a phase-shifted signal, and to cancel the signal leaked from the first series-parallel switch group with the phase-shifted signal.
2. The high-isolation radio frequency single-pole double-throw switch according to claim 1, characterized in that: The first series-parallel switch group includes: a first symmetrical HEMT switch and a second symmetrical HEMT switch; the second series-parallel switch group includes: a third symmetrical HEMT switch and a fourth symmetrical HEMT switch; The gates of the first symmetrical HEMT switch, the second symmetrical HEMT switch, the third symmetrical HEMT switch, and the fourth symmetrical HEMT switch are all connected to a power supply; The source / drain of the first symmetrical HEMT switch is connected to the output terminal of the transmitter and the source / drain of the second symmetrical HEMT switch, respectively. The drain / source of the first symmetrical HEMT switch is connected to the source / drain of the third symmetrical HEMT switch and the antenna port, respectively. The drain / source of the third symmetrical HEMT switch is connected to the input terminal of the receiver and the source / drain of the fourth symmetrical HEMT switch, respectively. The drain / source of the second symmetrical HEMT switch is connected to the first input terminal of the signal cancellation unit, and the drain / source of the fourth symmetrical HEMT switch is connected to the second input terminal of the signal cancellation unit.
3. The high-isolation radio frequency single-pole double-throw switch according to claim 2, characterized in that: The signal cancellation unit is a bridge T coil, and the bridge T coil includes: a first capacitor, a second capacitor, a first inductor and a second inductor; The first end of the first capacitor and the first end of the first inductor are both connected to the drain / source of the second symmetrical HEMT switch, and the second end of the first capacitor and the second end of the second inductor are both connected to the drain / source of the fourth symmetrical HEMT switch. a connection between the second end of the first inductor and the first end of the second inductor; The second end of the first inductor is also connected to the first end of the second capacitor, and the second end of the second capacitor is grounded.
4. The high-isolation radio frequency single-pole double-throw switch according to claim 3, characterized in that: The first inductor and the second inductor have equal inductance values, and the first inductor and the second inductor are coupled to each other.
5. The high-isolation radio frequency single-pole double-throw switch according to claim 3, characterized in that: The calculation formulas for the capacitance of the first capacitor and the second capacitor satisfy: Among them, C p is the capacitance of the first capacitor, C s is the capacitance of the second capacitor, f1, f2, Z1, θ1, Z2 and θ2 are all values of the two equivalent microstrip lines, f1 is the lowest frequency of the working frequency band of the microstrip line, f2 is the highest frequency of the working frequency band of the microstrip line, Z1 is the first characteristic impedance of the microstrip line, θ1 is the first electrical length of the microstrip line, Z2 is the second characteristic impedance of the microstrip line, and θ2 is the second electrical length of the microstrip line.
6. The high-isolation radio frequency single-pole double-throw switch according to claim 3, characterized in that: The calculation formula of the inductance value of the first inductor satisfies: Among them, L s is the inductance value of the first inductor.
7. The high-isolation radio frequency single-pole double-throw switch according to claim 5, characterized in that: The coupling coefficient between the first inductor and the second inductor satisfies: Among them, L m is the coupling coefficient between the first inductor and the second inductor.