High-isolation radio frequency switch circuit

Abstract

The utility model discloses a high-isolation radio frequency switch circuit, and relates to the field of radio frequency switches. A radio frequency antenna is respectively connected with radio frequency interfaces of a first radio frequency circuit and a second radio frequency circuit; the first radio frequency circuit comprises a first equivalent mos transistor, a second equivalent mos transistor and a third mos transistor, the source electrode of the first equivalent mos transistor is connected with the first radio frequency end, and the drain electrode of the first equivalent mos transistor is cascaded with the source electrode of the second equivalent mos transistor; the drain electrode of the second equivalent mos transistor is connected with the radio frequency antenna; the drain electrode of the third mos transistor is connected with the drain electrode input end of the first equivalent mos transistor, and the source electrode output is grounded; grid electrodes of the first equivalent mos tube and the second equivalent mos tube are respectively connected with an R1 and an R2, the R1 and the R2 are jointly connected with a resistor Ra, grid voltage Vg1 is connected to the side of the resistor Ra, and grid voltage Vg3 is connected to a grid electrode of the third mos tube. The circuit adapts to various frequency band widths, the isolation of a specific frequency band is effectively improved, the insertion loss is not affected, and the isolation of the switch is greatly improved.

Description

Technical Field

[0001] The present application relates to the field of radio frequency switches, and in particular to a high-isolation radio frequency switch circuit. Background Art

[0002] In the transceiver of the wireless communication system, high-performance switches are used to select the signals of the transmitting and receiving paths. The insertion loss, linearity, isolation and other performance of the switch directly restrict the output power, noise coefficient and other performance of the entire system. Especially in today's 5G, which is widely used in mobile phone communications and navigation, the transceiver needs to select multiple frequency bands and multiple modes, so high-performance single-pole multi-throw switches are indispensable. Today, SOI technology is still the mainstream technology for RF switches. This process is widely used in wireless communication systems for its ultra-low cost and excellent RF performance (low insertion loss, high isolation and high linearity).

[0003] The isolation of an RF switch refers to the degree of interference of the input signal on the output when the switch is turned off. If the isolation is not enough, it will cause signal leakage, affect the normal operation of the system, and may even cause system performance degradation. In the field of military communications, it is also crucial to improve the isolation of RF switches. Military communication systems have extremely high requirements for signal security and stability, and any small interference may have serious consequences. Therefore, improving the isolation of RF switches has become an important requirement for the development of current communication technology.

[0004] In the related art, under standard process conditions, in order to improve the isolation of the RF switch, a T-type structure method is generally adopted. However, this method increases the complexity of the RF switch mechanism, which not only increases the layout area of ​​the circuit, but also increases the number of series transistors in the signal path, resulting in a series of problems such as increased insertion loss and narrower working bandwidth. Utility Model Content

[0005] The present application provides a high-isolation RF switch circuit to solve the problem of RF switch isolation performance and the problem of increased insertion loss and narrowed working bandwidth caused by series transistors. The high-isolation RF switch circuit includes a symmetrically arranged first RF circuit, a second RF circuit, and a RF antenna shared by the two RF circuits, wherein the RF antenna is respectively connected to the RF interfaces of the first RF circuit and the second RF circuit;

[0006] The first radio frequency circuit includes a first equivalent mos transistor, a second equivalent mos transistor and a third mos transistor, and the source of the first equivalent mos transistor is connected to the first radio frequency terminal, and the drain is cascaded to the source of the second equivalent mos transistor; the drain of the second equivalent mos transistor is connected to the radio frequency antenna; the drain of the third mos transistor is connected to the drain input terminal of the first equivalent mos transistor, and the source output is grounded;

[0007] The gates of the first equivalent MOS tube and the second equivalent MOS tube are connected to the first resistor R1 and the second resistor R2 respectively. The first resistor R1 and the second resistor R2 are connected to the resistor Ra together, and the gate voltage Vg1 is connected to the resistor Ra side. The gate of the third MOS tube is connected to the gate voltage Vg3.

[0008] Specifically, the first equivalent MOS tube has the same parameters as the second equivalent MOS tube, and the substrate of the first equivalent MOS tube is connected to the resistor R7, and the substrate of the second equivalent MOS tube is connected to the resistor R8. The resistors R7 and R8 are connected to the substrate voltage vb1; the first resistor R1 and the second resistor R2 have the same resistance value.

[0009] Specifically, the first equivalent MOS tube includes at least six NMOS tubes with cascaded sources and drains, the gate of each NMOS tube is respectively connected to a gate resistor Rx, and all gate resistors Rx are commonly connected to a first resistor R1; a resistor Ry is respectively connected between the source and drain of each NMOS tube; the substrate of each NMOS tube is connected to a substrate resistor Rx, and all substrate resistors Rx commonly input a substrate voltage vb1.

[0010] Specifically, the second RF circuit includes a fourth equivalent MOSFET and a fifth equivalent MOSFET, and the source of the fourth equivalent MOSFET is connected to the second RF terminal, the drain is cascaded to the source output of the fifth equivalent MOSFET, and the drain of the fifth equivalent MOSFET is connected to the RF antenna.

[0011] Specifically, the second radio frequency circuit further includes a sixth MOSFET, the drain of the sixth MOSFET is connected to the source output terminal of the fifth equivalent MOSFET, the source output of the sixth MOSFET is grounded, and the gate is connected to the gate voltage Vg4.

[0012] Specifically, the gates of the fourth equivalent MOS tube and the fifth equivalent MOS tube are respectively connected to the fourth resistor R4 and the fifth resistor R5, and the fourth resistor R4 and the fifth resistor R5 are connected in parallel to the resistor Rb, and the gate voltage Vg2 is connected to the resistor Rb side.

[0013] Specifically, the fourth equivalent MOS tube has the same parameters as the fifth equivalent MOS tube, and the substrate of the fourth equivalent MOS tube is connected to the resistor R10, and the substrate of the fifth equivalent MOS tube is connected to the resistor R9. The resistors R9 and R10 are connected to the substrate voltage vb2; the fourth resistor R4 and the fifth resistor R5 have the same resistance value.

[0014] Specifically, a third resistor R3 is connected to the gate of the third MOS tube, a substrate resistor R11 is connected to the substrate, and a substrate voltage vb3 is passed through the substrate;

[0015] The gate of the sixth MOS tube is connected with a sixth resistor R6, the substrate is connected with a substrate resistor R12, and a substrate voltage vb4 is passed through.

[0016] Specifically, when the RF path from the RF antenna to the first RF end is turned on, Vg1 inputs a positive voltage, Vb1 inputs a zero voltage, Vg2 and Vb2 input a zero voltage, Vg3 and Vb3 input a negative voltage, Vg4 inputs a positive voltage, and Vb4 inputs a zero voltage.

[0017] Specifically, when the RF path from the RF antenna to the first RF end is turned on, the fourth equivalent MOS tube and the fifth equivalent MOS tube are cut off to form two parasitic capacitors; the third MOS tube is turned on to form an equivalent resistor group; the parasitic capacitor and the resistors R4, R5 and Ra are combined to form a first high-pass filter, and the parasitic capacitor and the equivalent resistor are combined to form a second high-pass filter.

[0018] The beneficial effects brought about by the technical solution provided in the embodiment of the present application include at least: based on the high-isolation RF switch circuit provided in the embodiment of the present application, the parasitic capacitance formed in the off state of the transistor and the equivalent resistance formed in the on state can be utilized, and a notch filter structure can be formed by utilizing the resistor connected to the gate end of the transistor, so that the isolation of the RF switch in the selected frequency band is improved, and for two symmetrically designed RF circuits, the parameters and resistance values ​​of the tubes and resistors can be adjusted according to the target frequency band to adapt to various bandwidths, effectively improve the isolation of a specific frequency band, and will not affect the insertion loss, thereby greatly improving the isolation of the switch. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A double-throw high-isolation radio frequency switch circuit is provided in an embodiment of the application;

[0020] Figure 2 It is the circuit diagram of the equivalent MOS tube;

[0021] Figure 3 It is a simulation diagram of the isolation of a common radio frequency circuit in the related technology;

[0022] Figure 4 It is an insertion loss simulation diagram of a common radio frequency circuit in the related technology;

[0023] Figure 5 This is the isolation simulation diagram of the high isolation RF switch circuit;

[0024] Figure 6 This is the insertion loss simulation diagram of the high isolation RF switch circuit. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present application clearer, the implementation methods of the present application will be further described in detail below in conjunction with the accompanying drawings.

[0026] The term "multiple" as used herein refers to two or more than two. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the related objects are in an "or" relationship.

[0027] This application takes a double-throw RF circuit as an example. When one of the RF switches is working and the antenna receives the signal and transmits it to the RF input port, the other RF switch should be completely isolated and disconnected, and too many transistors and switch structure complexity should not be added, which would lead to increased insertion loss and narrower working bandwidth.

[0028] Figure 1 It is a double-throw high-isolation RF switch circuit provided in an embodiment of the present application, including a symmetrically arranged first RF circuit 10, a second RF circuit 20, and an RF antenna shared by the two RF circuits, and the RF antenna is respectively connected to the RF interfaces of the first RF circuit and the second RF circuit. Specifically, the first RF circuit includes a first equivalent MOSFET M1, a second equivalent MOSFET M2, and a third MOSFET M3, and the source of the first equivalent MOSFET is connected to the first RF terminal RF1, and the drain of M1 is cascaded to the source of the second equivalent MOSFET M2. The drain of the second equivalent MOSFET M2 serves as the RF interface of the first RF circuit 10 and is connected to the RF antenna ANT. The drain of the third MOSFET M3 is connected to the drain input terminal of the first equivalent MOSFET M1, and the source output is grounded.

[0029] Since the first RF circuit 10 and the second RF circuit 20 are designed symmetrically, the second RF circuit 20 includes a fourth equivalent MOS tube M4, a fifth equivalent MOS tube M5, and a sixth MOS tube M6. The source of the fourth equivalent MOS tube M4 is connected to the second RF terminal RF2, the drain of M4 is cascaded to the source output of the fifth equivalent MOS tube M5, and the drain of the fifth equivalent MOS tube M5 is used as the RF interface of the second RF circuit 20 and connected to the RF antenna ANT.

[0030] Specifically, in the first RF circuit 10, the gates of the first equivalent MOS tube and the second equivalent MOS tube are respectively connected to the first resistor R1 and the second resistor R2, the first resistor R1 and the second resistor R2 are connected in parallel to one end of the resistor Ra, the other end of the resistor Ra is connected to the gate voltage Vg1, and the gate of the third MOS tube is connected to the gate voltage Vg3. In some feasible implementation schemes, the resistance values ​​of R1 and R2 can also be kept consistent, while the parameters of M1 and M2 are kept consistent, that is, the two parallel branches composed of R1 and M1 and R2 and M2 are exactly the same. Similarly, in the second RF circuit, the gates of the fourth equivalent MOS tube and the fifth equivalent MOS tube are respectively connected to the fourth resistor R4 and the fifth resistor R5, and the fourth resistor R4 and the fifth resistor R5 are connected in parallel to one end of the resistor Rb, and the other end is connected in parallel to the gate voltage Vg2. Correspondingly, the resistance values ​​of R4 and R5 can also be designed to be consistent, while the parameters of M4 and M5 are kept consistent, that is, the two parallel branches composed of R4 and M4 and R5 and M5 are exactly the same.

[0031] In addition, a resistor R7 is connected to the substrate of the first equivalent MOS tube, a resistor R8 is connected to the substrate of the second equivalent MOS tube, and resistors R7 and R8 are connected to the substrate voltage vb1. Correspondingly, a resistor R10 is connected to the substrate of the fourth equivalent MOS tube, a resistor R9 is connected to the substrate of the fifth equivalent MOS tube, and resistors R9 and R10 are connected to the substrate voltage vb2.

[0032] In the above RF circuit structure, because it is transmitted from the RF antenna to the RF end, NMOS tubes are selected for connection in the two RF circuits. In some other embodiments, for the stability of the circuit, the third resistor R3 is connected to the gate of the third MOS tube M3, and the sixth resistor R6 is connected to the gate of the sixth MOS tube M6. Considering the substrate voltage, the substrate resistor R11 is connected to the substrate of the third MOS tube, and the substrate voltage vb3 is passed. The substrate resistor R12 is connected to the substrate of the sixth MOS tube, and the substrate voltage vb4 is passed.

[0033] See also Figure 2 , because the characteristic parameters of the equivalent MOS tube need to be set according to actual needs, several ordinary nmos tubes are actually formed in series. In some embodiments, the first equivalent MOS tube includes at least six nmos tubes with cascaded sources and drains, and the RFIN and RFOUT at both ends are cascaded with adjacent equivalent resistors. The gate of each nmos tube is respectively connected to a gate resistor Rx, and all gate resistors Rx are commonly connected (node ​​N1) to the first resistor R1. Resistors Ry are respectively connected between the source and drain of each nmos tube. The substrate of each nmos tube is connected to a substrate resistor Rx, and all substrate resistors Rx commonly input (node ​​N2) substrate voltage vb1.

[0034] In the above RF circuit structure, when the RF path from the RF antenna ANT to the first RF terminal RF1 is turned on, Vg1 inputs a positive voltage, Vb1 inputs a zero voltage, Vg2 and Vb2 input a negative voltage, Vg3 and Vb3 input a negative voltage, Vg4 inputs a positive voltage, and Vb4 inputs a zero voltage. Due to the characteristics of the MOS tube, when Vg1 is at a negative voltage, M3, M4, and M5 are cut off, and M4 and M5 are equivalent to two equivalent capacitors C. When Vb2 is at a positive voltage, M6 is turned on, and M6 is equivalent to an equivalent resistor R'. At this time, the equivalent capacitor C and the equivalent resistor R' structurally form a high-pass filter (second high-pass filter), and the two equivalent capacitors C and the corresponding R4, R5, and Rb structurally form a high-pass filter (first high-pass filter). When the signal is transmitted from ANT, it will first be filtered by the first high-pass filter, and then pass through the second high-pass filter. According to the cut-off frequency calculation formula Fo=1 / (2pi*R*C), when the capacitance is the same, the larger the R, the smaller the Fo. Therefore, part of the signal overflowing to the second RF circuit 20 will be consumed by the parasitic capacitance, Rb, R4 and R5, thereby improving the isolation of the second RF circuit. The resistance of R4 and R5 determines the degree of signal suppression at this frequency. The larger the resistance, the better the isolation. When the RF path from ANT to RF2 is turned on and RF1 is turned off, the same is true, which will not be repeated here.

[0035] In the above structure, according to the Fo calculation formula, the Ra and Rb resistors are particularly important for the isolation performance, and the resistance values ​​of Ra and Rb determine the frequency selection. In the comparative design experiment, it is assumed that the Ra and Rb resistors are removed, and then the RF circuit is directly simulated and tested to obtain Figure 3 The common isolation simulation diagram in Figure 4 In the comparative experiment, the Ra and Rb resistors are retained for simulation, that is, the isolation RF switch circuit of this embodiment is simulated and tested to obtain Figure 5 Isolation simulation diagrams for medium and high isolation, and Figure 6 Insertion loss simulation diagram under medium and high isolation.

[0036] contrast Figure 3 and Figure 4 In the design, it can be seen that at 1.9GHz, the isolation is 83dBm, and at Figure 5The test was conducted with Ra or Rb of 1k ohm in the figure, and the isolation was 101dBm at 1.9GHz. By comparison, it can be seen that the isolation of the RF switch circuit in this embodiment is improved by 18dBm at 1.9GHz, and the insertion loss is consistent with the traditional RF switch circuit in the passband. Through the above simulation and description, the RF switch circuit of this invention can effectively improve the isolation of a specific frequency band, achieve high-performance isolation without introducing transistors and circuit complexity, and will not affect the insertion loss, greatly improving the isolation of the switch.

[0037] In summary, based on the high-isolation RF switch circuit provided in the embodiment of the present application, the parasitic capacitance formed in the off state of the transistor and the equivalent resistance formed in the on state can be utilized, and a notch filter structure can be formed by using the resistor connected to the gate end of the transistor to improve the isolation of the RF switch in the selected frequency band. For two symmetrically designed RF circuits, the parameters and resistance values ​​of the tubes and resistors can be adjusted according to the target frequency band to adapt to various frequency bandwidths.

[0038] The preferred embodiments of the present invention are described above; it should be understood that the present invention is not limited to the above-mentioned specific implementation modes, and the devices and structures not described in detail should be understood to be implemented in a common manner in the art; any technician familiar with the art can make many possible changes and modifications without departing from the technical solution of the present invention, or modify them into equivalent embodiments with equivalent changes, which does not affect the essential content of the present invention; therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of protection of the technical solution of the present invention.

Claims

1. A high isolation radio frequency switch circuit, characterized in that: It includes a symmetrically arranged first radio frequency circuit, a second radio frequency circuit, and a radio frequency antenna shared by the two radio frequency circuits, wherein the radio frequency antenna is respectively connected to radio frequency interfaces of the first radio frequency circuit and the second radio frequency circuit; The first radio frequency circuit includes a first equivalent MOS tube, a second equivalent MOS tube and a third MOS tube, and the source of the first equivalent MOS tube is connected to the first radio frequency terminal, and the drain is cascaded to the source of the second equivalent MOS tube; The drain of the second equivalent MOS tube is connected to the radio frequency antenna; The drain of the third MOS tube is connected to the drain input terminal of the first equivalent MOS tube, and the source output is grounded; The gates of the first equivalent MOS tube and the second equivalent MOS tube are connected to the first resistor R1 and the second resistor R2 respectively. The first resistor R1 and the second resistor R2 are connected to the resistor Ra together, and the gate voltage Vg1 is connected to the resistor Ra side. The gate of the third MOS tube is connected to the gate voltage Vg3.

2. The high isolation radio frequency switch circuit according to claim 1, characterized in that: The first equivalent MOS tube has the same parameters as the second equivalent MOS tube, and the substrate of the first equivalent MOS tube is connected to the resistor R7, and the substrate of the second equivalent MOS tube is connected to the resistor R8. The resistors R7 and R8 are connected to the substrate voltage vb1; the first resistor R1 and the second resistor R2 have the same resistance value.

3. The high isolation radio frequency switch circuit according to claim 2, characterized in that: The first equivalent MOS tube includes at least six NMOS tubes with cascaded sources and drains, the gate of each NMOS tube is respectively connected to a gate resistor Rx, and all gate resistors Rx are commonly connected to a first resistor R1; a resistor Ry is respectively connected between the source and drain of each NMOS tube; a substrate resistor Rx is connected to the substrate of each NMOS tube, and all substrate resistors Rx commonly input a substrate voltage vb1.

4. The high isolation radio frequency switch circuit according to claim 3, characterized in that: The second RF circuit includes a fourth equivalent MOS tube and a fifth equivalent MOS tube, and the source of the fourth equivalent MOS tube is connected to the second RF terminal, the drain is cascaded to the source output of the fifth equivalent MOS tube, and the drain of the fifth equivalent MOS tube is connected to the RF antenna.

5. The high isolation radio frequency switch circuit according to claim 4, characterized in that: The second radio frequency circuit also includes a sixth MOSFET, the drain of the sixth MOSFET is connected to the source output end of the fifth equivalent MOSFET, the source output of the sixth MOSFET is grounded, and the gate is connected to the gate voltage Vg4.

6. The high isolation radio frequency switch circuit according to claim 5, characterized in that: The gates of the fourth equivalent MOS tube and the fifth equivalent MOS tube are connected to the fourth resistor R4 and the fifth resistor R5 respectively, and the fourth resistor R4 and the fifth resistor R5 are connected to the resistor Rb in parallel, and the gate voltage Vg2 is connected to the resistor Rb side.

7. The high isolation radio frequency switch circuit according to claim 6, characterized in that: The fourth equivalent MOS tube has the same parameters as the fifth equivalent MOS tube, and the substrate of the fourth equivalent MOS tube is connected to the resistor R10, and the substrate of the fifth equivalent MOS tube is connected to the resistor R9. The resistors R9 and R10 are connected to the substrate voltage vb2; the fourth resistor R4 and the fifth resistor R5 have the same resistance value.

8. The high isolation radio frequency switch circuit according to claim 7, characterized in that: The gate of the third MOS tube is also connected to a third resistor R3, the substrate is connected to a substrate resistor R11, and a substrate voltage vb3 is passed through; The gate of the sixth MOS tube is connected with a sixth resistor R6, the substrate is connected with a substrate resistor R12, and a substrate voltage vb4 is passed through.

9. The high isolation radio frequency switch circuit according to claim 7, characterized in that: When the RF path from the RF antenna to the first RF end is turned on, Vg1 inputs a positive voltage, Vb1 inputs a zero voltage, Vg2 and Vb2 input a negative voltage, Vg3 and Vb3 input a negative voltage, Vg4 inputs a positive voltage, and Vb4 inputs a zero voltage.

10. The high isolation radio frequency switch circuit according to claim 9, characterized in that: When the RF path from the RF antenna to the first RF end is turned on, the fourth equivalent MOS tube and the fifth equivalent MOS tube are cut off to form two parasitic capacitors; the third MOS tube is turned on to form an equivalent resistor group; the parasitic capacitor and the resistors R4, R5 and Ra are combined to form a first high-pass filter, and the parasitic capacitor and the equivalent resistor are combined to form a second high-pass filter.

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