Radio frequency switch

Abstract

A radio frequency switch includes a signal terminal, a reference voltage terminal, and a shunt switch path. The shunt switch path is coupled to the signal terminal and the reference voltage terminal and includes a first shunt sub-circuit and a second shunt sub-circuit. The second shunt sub-circuit includes a first transistor and a second transistor in parallel. The radio frequency switch has a first impedance when switched to a first state, a second impedance when switched to a second state, and a third impedance when switched to a third state. The first impedance, the second impedance, and the third impedance are different.

Description

Technical Field

[0001] This invention relates to radio frequency circuits, and more particularly to a radio frequency switch in a radio frequency circuit. Background Technology

[0002] Radio frequency (RF) switches can guide radio frequency signals through one or more transmission paths and are widely used in televisions, mobile phones, wireless communication devices, wireless networks (Wi-Fi), Bluetooth, and global positioning systems (GPS).

[0003] However, in related technologies, when the RF switch is turned off, the RF signal will be reflected, causing the RF switch to malfunction. Summary of the Invention

[0004] This invention provides a radio frequency (RF) switch, comprising a signal terminal, a reference voltage terminal, and a shunt switch path coupled to the signal terminal and the reference voltage terminal. The shunt switch path includes a first shunt sub-circuit and a second shunt sub-circuit. The second shunt sub-circuit includes a first transistor and a second transistor connected in parallel. When the RF switch is switched to a first state, it has a first impedance; when the RF switch is switched to a second state, it has a second impedance; and when the RF switch is switched to a third state, it has a third impedance. The first impedance, the second impedance, and the third impedance are different. Attached Figure Description

[0005] Figure 1 This is a circuit diagram of a radio frequency switch according to an embodiment of the present invention.

[0006] Figure 2 This is a circuit diagram of another radio frequency switch in an embodiment of the present invention.

[0007] Figure 3 This is a circuit diagram of another radio frequency switch in an embodiment of the present invention.

[0008] Figure 4 This is a circuit diagram of another radio frequency switch in an embodiment of the present invention.

[0009] Figure 5 This is a circuit diagram of another radio frequency switch in an embodiment of the present invention.

[0010] Figure 6 This is a circuit diagram of another radio frequency switch in an embodiment of the present invention.

[0011] Figure 7 This is a circuit diagram of another radio frequency switch in an embodiment of the present invention.

[0012] Symbol Explanation

[0013] 1 to 7: Radio Frequency Switches

[0014] 10,18,181,182: Signal end

[0015] 12,22,32,221,222: Shunt switch path

[0016] 14, 16, 26, 261, 141, 262, 142: Shunt circuits

[0017] 40, 401, 402: Series switch paths

[0018] 42: Antenna

[0019] 44: Radio Frequency Circuits

[0020] GND: Reference voltage terminal

[0021] Srf: Radio frequency signal

[0022] Tsh, T1, T2, Tsr: Transistors

[0023] Rsh, Rsr, R1, R2: Resistors

[0024] Vcsh, Vc1, Vc2, Vsr, Vc11, Vc21, Vcsh1, Vcsr1, Vc12, Vc22, Vcsh2, Vcsr2: Control voltage Detailed Implementation

[0025] Figure 1 This is a circuit diagram of a radio frequency switch 1 according to an embodiment of the present invention. The radio frequency switch 1 can transmit or receive radio frequency signals Srf.

[0026] The RF switch 1 includes a signal terminal 10, a reference voltage terminal GND, a shunt switch path 12, and a signal terminal 18. The shunt switch path 12 is coupled to the signal terminal 10 and the reference voltage terminal GND. The signal terminal 10 can be coupled to either an antenna or an RF circuit, and the signal terminal 18 can be coupled to the other. The reference voltage terminal GND can provide a reference voltage, such as 0V. When the RF switch 1 is turned on, the shunt switch path 12 is turned off, and the shunt switch path 12 can disconnect the coupling between the signal terminal 10 and the reference voltage terminal GND to transmit the RF signal Srf between the signal terminal 10 and the signal terminal 18. When the RF switch 1 is turned off, the shunt switch path 12 is turned on, and the shunt switch path 12 can establish the coupling between the signal terminal 10 and the reference voltage terminal GND to guide the RF signal Srf to the reference voltage terminal GND. The RF switch 1 of the present invention can selectively provide an equivalent resistance substantially equal to the load resistance in a corresponding state. The load resistance can be the equivalent resistance of the antenna and RF circuit, such as 50 ohms or 75 ohms.

[0027] Shunt switch path 12 includes shunt sub-circuit 14 and shunt sub-circuit 16. Shunt sub-circuit 14 includes a first terminal coupled to signal terminals 10 and 18, a second terminal, and a control terminal for receiving a control voltage Vcsh to control the shunt sub-circuit 14. Shunt sub-circuit 16 includes a first terminal coupled to a second terminal of shunt sub-circuit 14, and a second terminal coupled to a reference voltage terminal GND. Shunt sub-circuit 14 may include N stacked transistors Tsh, where N is a positive integer. Each transistor Tsh may have the same size and its conduction state may be controlled by the control voltage Vcsh. The number N of transistors Tsh in shunt sub-circuit 14 may be determined by the power of the radio frequency signal Srf. For example, the higher the power of the radio frequency signal Srf, the more transistors Tsh need to be configured in shunt sub-circuit 14 to provide sufficient isolation when transmitting or receiving the radio frequency signal Srf. In some embodiments, the number N of transistors Tsh may be 24. The shunt circuit 14 may further include N resistors Rsh, each Rsh coupled to the first and second terminals of a corresponding stacked transistor Tsh, and the resistance values ​​of each Rsh may be equal. When the shunt switch path 12 is off, all N stacked transistors Tsh are off, and each transistor Tsh can be equivalent to a capacitor. When the shunt switch path 12 is on, all N stacked transistors Tsh are on, and each transistor Tsh can be equivalent to a resistor when on, with a resistance value very small, approaching 0 ohms. When 24 transistors Tsh are on, this is equal to 48 ohms, and the shunt switch path 12 can be equivalent to a 50-ohm resistor. For example, when the shunt switch path 12 is on, the resistor Rsh can be used as a bias resistor to fix the potential between the first and second terminals of the transistor Tsh, and the resistance value of the resistor Rsh can be between 10K ohms and 50K ohms. In some embodiments, a selected resistor Rsh may be used such that the impedance of the equivalent capacitance of the shunt circuit 14 transistor Tsh is much smaller than the impedance of the resistor Rsh when the transistor is turned off.

[0028] The shunt circuit 16 includes transistors T1 and T2 connected in parallel. Transistor T1 may include a first terminal coupled to a first terminal of the shunt circuit 16, a second terminal coupled to a second terminal of the shunt circuit 16, and a control terminal for receiving a control voltage Vc1 to control the conduction state of transistor T1. Transistor T2 may include a first terminal coupled to a first terminal of the shunt circuit 16, a second terminal coupled to a second terminal of the shunt circuit 16, and a control terminal for receiving a control voltage Vc2 to control the conduction state of transistor T2. The dimensions of transistors T1, T2, and Tsh may be different. For example, in some embodiments, the dimension of transistor Tsh may be larger than the dimension of transistor T1, and the dimension of transistor T1 may be larger than the dimension of transistor T2. In some embodiments, the dimension of transistor Tsh may be equal to the sum of the dimensions of transistors T1 and T2. In some embodiments, the size of transistor T2 can be selected such that when transistor T2 is turned on, the equivalent resistance of shunt switch path 12 is close to the on-resistance of the load resistor. For example, the on-resistance of transistor T2 can be selected between 30 ohms and 48 ohms, such that the equivalent resistance of shunt switch path 12 is approximately 50 ohms. In some embodiments, the size ratio of transistor T1 to transistor T2 can be between 70:30 and 99:1. For example, the size ratio of transistor Tsh, transistor T1, and transistor T2 can be 100:99:1. Since the size of transistor Tsh and transistor T1 is much larger than that of transistor T2, they can be considered as a short circuit when transistor Tsh or transistor T1 is turned on. In some embodiments, when shunt switch path 12 is turned on, the RF signal Srf can be guided to the reference voltage terminal GND via 24 transistors Tsh (0 ohms) and transistor T2 (50 ohms), thus preventing signal reflection and degrading signal quality. In other embodiments, when the shunt switch path 12 is turned on, the radio frequency signal Srf can be guided to the reference voltage terminal GND via 24 transistors Tsh (0 ohms) and transistor T1 (0 ohms). Transistors Tsh, T1, and T2 can all be N-type metal-oxide-semiconductor field-effect transistors (MOSFETs).

[0029] In some embodiments, the dimensions of transistors Tsh, T1, and T2 can be directly proportional to the finger width of each transistor Tsh, T1, and T2. For example, in an embodiment where the size ratio of transistors Tsh, T1, and T2 is 100:99:1, the finger width of transistor Tsh can be 10 micrometers and the number of fingers can be 100; the finger width of transistor T1 can be 9.9 micrometers and the number of fingers can be 100; and the finger width of transistor T2 can be 0.1 micrometers and the number of fingers can be 100. Therefore, the size of transistor Tsh can be 10 micrometers * 100 fingers, the size of transistor T1 can be 9.9 micrometers * 100 fingers, and the size of transistor T2 can be 0.1 micrometers * 100 fingers. In other embodiments, the dimensions of transistors Tsh, T1, and T2 can be directly proportional to the number of fingers in each transistor, thereby providing a simple circuit layout and better electrostatic discharge (ESD) characteristics. For example, transistor Tsh has a finger width of 10 micrometers and 100 fingers, transistor T1 has a finger width of 10 micrometers and 99 fingers, and transistor T2 has a finger width of 10 micrometers and 1 finger. Therefore, the dimensions of transistor Tsh can be 10 micrometers * 100 fingers, transistor T1 can be 10 micrometers * 99 fingers, and transistor T2 can be 10 micrometers * 1 finger.

[0030] RF switch 1 can be switched to one of states S0 to S3, as shown in Table 1:

[0031] Table 1

[0032] state Vcsh(V) Vc1(V) Vc2(V) Impedance (ohms) S0 -2.5 2.5 2.5 1 / jw(Coff / N) S1 -2.5 -2.5 -2.5 1 / jw(Coff / (N+1)) S2 2.5 2.5 2.5 0 S3 2.5 -2.5 2.5 50

[0033] As shown in Table 1, when RF switch 1 switches to state S0, shunt circuit 14 receives -2.5V and is cut off, while transistors T1 and T2 also receive 2.5V and are turned on, so that RF switch 1 has an impedance Z0, which can be equal to 1 / jw(Coff / N), where Coff is the equivalent capacitance value of each transistor Tsh when it is cut off, and N is the number of transistors Tsh. When RF switch 1 switches to state S1, shunt circuit 14 receives -2.5V and is cut off, while transistors T1 and T2 also receive -2.5V and are turned off, so that RF switch 1 has an impedance Z1, which can be equal to 1 / jw(Coff / (N+1)). When RF switch 1 switches to state S2, shunt circuit 14 receives 2.5V and is turned on, while transistors T1 and T2 receive 2.5V and are turned on, so that RF switch 1 has an impedance Z2, which can be equal to 0 ohms. When RF switch 1 switches to state S3, shunt circuit 14 receives 2.5V to be turned on, transistor T1 receives -2.5V to be turned off, and transistor T2 receives 2.5V to be turned on, so that RF switch 1 has an impedance Z3, which can be equal to 50 ohms. That is, impedances Z0 to Z3 are all different, and one of them can be equal to 50 ohms. Impedance Z3 can be matched with the load resistance. For example, impedance Z3 can be close to 50 ohms or 75 ohms. Impedance Z1 can be greater than impedance Z3, and impedance Z3 can be greater than impedance Z2. States S0 and S1 are applicable when RF switch 1 is on, and states S2 and S3 are applicable when RF switch 1 is off. When RF switch 1 switches to state S3 to be off, since the RF signal Srf is guided to the reference voltage terminal GND through the impedance Z3 matched with the load resistance, no signal reflection will occur, thus preventing signal quality degradation.

[0034] Although Table 1 shows -2.5V for cutting off shunt circuit 14, transistor T1, and / or transistor T2, those skilled in the art will know that other voltages less than -2.5V can be used to cut off shunt circuit 14, transistor T1, and / or transistor T2. Furthermore, although Table 1 shows 2.5V for turning on shunt circuit 14, transistor T1, and / or transistor T2, those skilled in the art will know that other voltages exceeding the corresponding threshold voltages of transistors Tsh, T1, and / or T2 can be used to turn on shunt circuit 14, transistor T1, and / or transistor T2. In some embodiments, transistors T1 and T2 can also be made to produce impedances in states S0 to S3 by changing control voltages Vc1 and Vc2.

[0035] The RF switch 1 can provide an equivalent resistance that is substantially equal to the load resistance when it is turned on or off, thereby improving signal quality without increasing the circuit area.

[0036] Figure 2This is a circuit diagram of another radio frequency switch 2 according to an embodiment of the present invention. The difference between radio frequency switch 2 and radio frequency switch 1 is that transistors T1 and T2 in the shunt sub-circuit 26 of the shunt switch path 22 are each connected in parallel with resistors R1 and R2. When the shunt switch path 22 is off, resistor 1 can be used as a bias resistor to fix the potential of the first and second terminals of transistor T1, and resistor 2 can be used as a bias resistor to fix the potential of the first and second terminals of transistor T2. The operation of radio frequency switch 2 is similar to that of radio frequency switch 1, and will not be described again here.

[0037] Figure 3 This is a circuit diagram of another radio frequency switch 3 according to an embodiment of the present invention. The difference between radio frequency switch 3 and radio frequency switch 1 is that the positions of shunt sub-circuit 14 and shunt sub-circuit 16 in shunt switch path 32 are interchanged. The first terminal of shunt sub-circuit 16 is coupled to signal terminal 10 and signal terminal 18. The first terminal of shunt sub-circuit 14 is coupled to the second terminal of shunt sub-circuit 16, and the second terminal of shunt sub-circuit 14 is coupled to reference voltage terminal GND. The operation mode of radio frequency switch 3 is similar to that of radio frequency switch 1, and will not be described again here.

[0038] Figure 4 This is a circuit diagram of another radio frequency switch 4 according to an embodiment of the present invention. The difference between radio frequency switch 4 and radio frequency switch 2 is that radio frequency switch 4 further includes a series switch path 40. The series switch path 40 includes a first end coupled to signal terminal 10 and a second end coupled to signal terminal 18. Signal terminal 10 is coupled to antenna 42, and signal terminal 18 is coupled to radio frequency circuit 44. Radio frequency circuit 44 may be a matching circuit, a power amplifier, or other circuit. When the series switch path 40 is turned on, the series switch path 40 can establish coupling between signal terminal 10 and signal terminal 18 to transmit the radio frequency signal Srf between signal terminal 10 and signal terminal 18; when the series switch path 40 is turned off, the series switch path 40 can disconnect the coupling between signal terminal 10 and signal terminal 18 to prevent the transmission of the radio frequency signal Srf between signal terminal 10 and signal terminal 18. The equivalent resistance of antenna 42 and the equivalent resistance of radio frequency circuit 44 may be substantially equal. The series switching path 40 may include a transistor Tsr and a resistor Rsr connected in parallel. The transistor Tsr includes a first terminal coupled to signal terminal 10 and a second terminal coupled to shunt switching path 22, signal terminal 18, and a control terminal, used to receive a control voltage Vcsr to control the transistor Tsr. The resistor Rsh includes a first terminal coupled to the first terminal of the transistor Tsr and a second terminal coupled to the second terminal of the transistor Tsr. The transistor Tsr may be an N-type MOSFET. Although... Figure 4The series switch path 40 shows only one transistor Tsr and one resistor Rsr. In other embodiments, the series switch path 40 may also include M transistors Tsr and M resistors Rsr, with the M transistors Tsr stacked sequentially, and each resistor Rsr coupled to the first and second terminals of the corresponding stacked transistor Tsr, where M is a positive integer. The operation of RF switch 4 is similar to that of RF switch 2, and will not be described again here.

[0039] Figure 5 This is a circuit diagram of another radio frequency switch 5 according to an embodiment of the present invention. The difference between radio frequency switch 5 and radio frequency switch 4 is that the first end of the series switch path 40 is coupled to the signal terminal 18, and the second end of the series switch path 40 is coupled to the signal terminal 10. The operation mode of radio frequency switch 5 is similar to that of radio frequency switch 4, and will not be described again here.

[0040] Figure 6 This is a circuit diagram of another radio frequency switch 6 in an embodiment of the present invention. Radio frequency switch 6 is a single-pole double-throw (SPDT) switch. The difference between radio frequency switch 6 and radio frequency switch 4 is that radio frequency switch 6 includes series switch paths 401 and 402, shunt switch paths 221 and 222, and signal terminals 181 and 182. The circuit setup and operation of series switch paths 401 and 402 are similar to those of series switch path 40, and the circuit setup and operation of shunt switch paths 221 and 222 are similar to those of shunt switch path 22, which will not be described again here. Radio frequency switch 6 can receive control voltages Vc11, Vc21, Vcsh1, Vcsr1, Vc12, Vc22, Vcsh2, and Vcsr2 to form a path between signal terminal 10 and one of signal terminals 181 and 182 to transmit or receive radio frequency signal Srf. When RF switch 6 forms a path between signal terminal 10 and signal terminal 181, series switch path 401 is turned on, shunt switch path 221 is turned off, series switch path 402 is turned off, and shunt switch path 222 is turned on. When RF switch 6 forms a path between signal terminal 10 and signal terminal 182, series switch path 401 is turned off, shunt switch path 221 is turned on, series switch path 402 is turned on, and shunt switch path 222 is turned off.

[0041] Figure 7This is a circuit diagram of another radio frequency switch 7 according to an embodiment of the present invention. The difference between radio frequency switch 7 and radio frequency switch 5 is that radio frequency switch 7 includes series switch paths 401 and 402, and signal terminals 181 and 182. The circuit setup and operation of series switch paths 401 and 402 are similar to those of series switch path 40, and will not be described again here. Radio frequency switch 7 can receive control voltages Vc1, Vc2, Vcsh, Vcsr1, and Vcsr2 to form a path between signal terminal 10 and one of signal terminals 181 and 182 to transmit or receive radio frequency signal Srf, or disable radio frequency switch 7 to interrupt the coupling between signal terminal 10 and signal terminal 181, and interrupt the coupling between signal terminal 10 and signal terminal 182. When radio frequency switch 7 forms a path between signal terminal 10 and signal terminal 181, series switch path 401 is turned on, series switch path 402 is turned off, and shunt switch path 22 is turned off. When RF switch 7 forms a path between signal terminal 10 and signal terminal 182, series switch path 401 is cut off, series switch path 402 is turned on, and shunt switch path 22 is cut off. When RF switch 7 is disabled, series switch path 401 is cut off, series switch path 402 is cut off, and shunt switch path 22 is turned on.

[0042] RF switches 1 to 7 can provide an equivalent resistance that is substantially equal to the load resistance when they are turned on or off, thereby improving signal quality without increasing circuit area.

[0043] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made in accordance with the scope of the claims of the present invention shall be covered by the present invention.

Claims

1. A radio frequency switch, characterized by It includes: a signal terminal; A reference voltage terminal; and A shunt switch path, coupled to the signal terminal and the reference voltage terminal, includes: A first shunt circuit; and A second shunt circuit includes a first transistor and a second transistor connected in parallel; When the RF switch is switched to a first state, it has a first impedance; when the RF switch is switched to a second state, it has a second impedance; and when the RF switch is switched to a third state, it has a third impedance. The first impedance, the second impedance, and the third impedance are different.

2. The radio frequency switch of claim 1, wherein, The first shunt circuit contains a plurality of stacked transistors.

3. The radio frequency switch of claim 2, wherein, The dimensions of the plurality of stacked transistors, the dimensions of the first transistor, and the dimensions of the second transistor are different.

4. The radio frequency switch of claim 3, wherein, The size of the plurality of stacked transistors is larger than the size of the first transistor, and the size of the first transistor is larger than the size of the second transistor.

5. The radio frequency switch of claim 3, wherein, The size of the plurality of stacked transistors is equal to the sum of the size of the first transistor and the size of the second transistor.

6. The radio frequency switch of claim 2, wherein, The first shunt circuit further includes a plurality of resistors, each resistor being coupled to a first terminal and a second terminal of a corresponding stacked transistor among the plurality of stacked transistors.

7. The radio frequency switch of claim 1, wherein, The dimensions of the first transistor and the second transistor are different.

8. The radio frequency switch of claim 7, wherein, The size of the first transistor is larger than the size of the second transistor.

9. The radio frequency switch of claim 1, wherein, The size ratio of the first transistor to the second transistor is 99:

1.

10. The radio frequency switch of claim 1, wherein, When the second transistor is turned on, it has an on-resistance that is close to a load resistance.

11. The radio frequency switch of claim 10, wherein, The on-resistance is 50 ohms.

12. The radio frequency switch of claim 1, wherein, One of the first impedance, the second impedance, and the third impedance is equal to 50 ohms.

13. The radio frequency switch of claim 1, wherein, The third impedance is matched with a load resistor.

14. The radio frequency switch of claim 1, wherein, The third impedance is approximately 50 ohms or 75 ohms.

15. The radio frequency switch of claim 1, wherein, It also includes a series switch path coupled to the signal terminal and an radio frequency circuit.

16. The radio frequency switch of claim 1, wherein, The signal terminal is coupled to an antenna.

17. The radio frequency switch of claim 1, wherein, When the RF switch is switched to the first state, the first shunt circuit is turned off, and the first transistor and the second transistor are also turned off.

18. The radio frequency switch of claim 1, wherein, When the RF switch is switched to the second state, the first shunt circuit is turned on, and the first transistor and the second transistor are turned on.

19. The radio frequency switch of claim 1, wherein, When the RF switch is switched to the third state, the first shunt circuit is turned on, the first transistor is turned off, and the second transistor is turned on.

20. The radio frequency switch of claim 1, wherein, The first impedance is greater than the third impedance, and the third impedance is greater than the second impedance.

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