Radio frequency switch system, radio frequency switch protective circuit, and protecting method thereof

A radio frequency (RF) switch system, an RF switch protective circuit, and a protecting method thereof are provided. The RF switch system may include an RF switch and a protective circuit. The RF switch may be connected between a port that receives an RF signal and a ground. The protective circuit may detect a first voltage that is a voltage that is generated when the first RF switch is turned off, and may transmit an impedance value that is varied based on the first voltage to the port.

CROSS-REFERENCE TO RELATED APPLICATIONS APPLICATION

This application claims the benefit under 35 USC 119(a) of Korean Patent Application No. 10-2020-0096227 filed on Jul. 31, 2020, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes.

BACKGROUND

The following description relates to a radio frequency switch system, a radio frequency switch protective circuit, and a protecting method thereof.

2. Description of Related Art

A radio frequency (RF) switch is an element that is generally used in a transmitting end and a receiving end of a communication module, and functions to allow an RF signal to pass through, or to bypass the RF signal to a ground. The RF switch may also be used to vary a use frequency of an antenna, and the RF switch may be connected between the antenna and an impedance component to switch connection of the impedance component to the antenna.

A withstand voltage characteristic of withstanding high power of the RF signal is an important aspect in the RF switch. When the RF switch is turned off, a high voltage is applied, accordingly, linearity of the RF switch may be affected and the RF switch may be damaged. The voltage that the turned-off switch should withstand is limited, accordingly a method for connecting transistors at various stages in series is implemented by the RF switch to prevent the RF switch from breaking down. When the RF switch is realized by implementing the transistors at many stages in series, the voltage distributed to one transistor may be reduced to prevent the RF switch from breaking down.

The RF switch may be broken down when a high voltage is distributed to a specific stage from among the transistors at many stages. To solve this issue, many more transistors may be coupled in series. However, when many transistors are used, the characteristic of the On stage of the RF switch may deteriorate. To counter this, a total width of the transistors may be increased, which may, however, increase a size of an integrated circuit.

SUMMARY

In a general aspect, a radio frequency (RF) switch system includes a first RF switch connected between a port which receives an RF signal and a ground; and a protective circuit, configured to detect a first voltage that is generated when the first RF switch is turned off, and transmit an impedance value to the port, wherein the impedance value is varied based on the detected first voltage.

The protective circuit may be connected between the port and the ground.

The impedance value may have a lower value at a second voltage, and the first voltage may be higher than a third voltage.

The first RF switch may include at least one transistor, and the first voltage may be transmitted to at least one of a gate and a body of the transistor.

The RF switch system may further include a voltage generator, configured to generate the first voltage and transmit the generated first voltage to at least one of the gate and the body of the transistor, wherein the first voltage is a negative voltage.

The RF switch system may further include a second RF switch connected between the port and an antenna, and may be configured to switch transmission of the RF signal to the antenna, wherein the second RF switch may be configured to turn off when the first RF switch is turned on.

A first end of the first RF switch may be connected to the port, an impedance component may be connected between a second end of the first RF switch and the ground, and the first RF switch may be configured to transmit the impedance component to tune an antenna.

The first RF switch may include a second RF switch and a third RF switch, a first end of the second RF switch may be connected to the port, an impedance component may be connected between a second end of the second RF switch and the ground, the third RF switch may be connected between the second end of the second RF switch and the ground, and the first voltage is generated when at least one of the second RF switch and the third RF switch is turned off.

The protective circuit may include a voltage detector, configured to receive the first voltage, and generate a second voltage corresponding to the first voltage; and an impedance variation unit, configured to transmit an impedance value that may be varied by the second voltage to the port.

The impedance variation unit may include at least one transistor comprising a first end connected to the port; and an impedance component, connected between the at least one transistor and the ground, and an impedance value of the at least one transistor changes based on a control of the second voltage.

The impedance variation unit may further include a voltage limiter connected between the port and the at least one transistor.

The impedance variation unit may include a voltage limiter comprising a first end connected to the port; a variable capacitor including a first end connected to a second end of the voltage limiter; and an impedance component connected between a second end of the variable capacitor and the ground, and an impedance value of the variable capacitor is changed based on a control of the second voltage.

The impedance variation unit may further include a variable capacitor connected between the port and a first end of the at least one transistor, and an impedance value of the variable capacitor is changed based on a control of the second voltage.

In a general aspect, a radio frequency (RF) switch protective circuit that protects an RF switch connected between a port that receives an RF signal includes a voltage detector, configured to detect a first voltage transmitted to the RF switch to turn off the RF switch; and an impedance variation unit, configured to transmit an impedance value that is varied by the first voltage between the port and the ground.

The impedance value may have a lower value when the first voltage becomes high.

The RF switch may include a plurality of transistors, the first voltage may be applied to bodies of the plurality of transistors, the first voltage may be predetermined with a negative voltage, and when a voltage at respective ends of the RF switch increases, the first voltage rises to a level that may be higher than the negative voltage.

The impedance variation unit may include at least one of a transistor with an impedance value that is varied based on the first voltage and a variable capacitor.

The impedance variation unit may further include a voltage limiter comprising at least one diode and is connected between the port and at least one element.

In a general aspect, a method to protect a radio frequency (RF) switch connected between a port that receives an RF signal and a ground includes detecting a first voltage applied to the RF switch to turn off the RF switch; transmitting a first impedance value between the port and the ground when the first voltage corresponds to a second voltage; and transmitting a second impedance value that is lower than the first impedance value between the port and the ground when the first voltage is a third voltage that is higher than the second voltage.

The second voltage may be a negative voltage, and the first voltage may rise to the third voltage when a voltage at respective ends of the RF switch increases.

DETAILED DESCRIPTION

Throughout the specification, when an element, such as a layer, region, or substrate, is described as being “on,” “connected to,” or “coupled to” another element, it may be directly “on,” “connected to,” or “coupled to” the other element, or there may be one or more other elements intervening therebetween. In contrast, when an element is described as being “directly on,” “directly connected to,” or “directly coupled to” another element, there can be no other elements intervening therebetween. As used herein “portion” of an element may include the whole element or less than the whole element.

The terminology used herein is for describing various examples only, and is not to be used to limit the disclosure. The articles “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms, “includes,” “comprises,” “is configured to,” “has,” etc. of the description specify the presence of stated features, numbers, steps, operations, members, elements, parts, and/or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, members, elements, parts, and/or combinations thereof.

FIG.1illustrates an example RF switch, in accordance with one or more embodiments.

Referring toFIG.1, the RF switch100amay be positioned in an RF signal line to transmit RF signals to an antenna200. The RF switch100amay be connected between a terminal (RFin) which receives the RF signal, and the antenna200, and may switch transmission of the RF signal between the terminal (RFin), which receives the RF signal, and the antenna200.

An RF switch100bmay be connected between the terminal (RFin), which receives the RF signal, and a ground so as to allow the RF signal to be bypassed to the ground. The RF switch100bmay allow the RF signal to be bypassed to the ground when it is turned on. In an example, when the RF switch100ais turned off, the RF switch100bmay be turned on to allow the RF signal to be bypassed to the ground. When the RF switch100ais turned on, the RF switch100bmay be turned off, and the RF signal may be transmitted to the antenna200. A node at which the RF switch100acontacts the RF switch100bis marked as N1inFIG.1, and, in an example, the node N1may be the terminal (RFin) which receives the RF signal.

FIG.2illustrates an example RF switch, in accordance with one or more embodiments.

Referring toFIG.2, an RF switch100cmay be connected between the antenna200and an impedance component300to vary an impedance of the antenna200. That is, a first end of the RF switch100cmay be connected to the terminal (RFin), which receives the RF signal, and the antenna200, and the impedance component300may be connected between a second end of the RF switch100cand the ground. The impedance component300may include, as non-limiting examples, at least one of a resistor, a capacitor, and an inductor. When the RF switch100cis turned on, the impedance of the antenna200may be changed by the impedance component300. Accordingly, the antenna200may support various frequency bands. That is, depending on whether the RF switch100cis turned on or turned off, the frequency bands supportable by the antenna200may be changed.

Referring toFIG.2, an RF switch100dmay be positioned between the second end of the RF switch100cand the ground. When the RF switch100cis turned on, the RF switch100dmay be turned off, and when the RF switch100cis turned off, the RF switch100dmay be turned on. Specifically, the antenna200may be tuned by alternately switching the RF switch100cand the RF switch100d. InFIG.2, a node at which the RF switch100ccontacts the antenna200is marked as N2, and a node at which the RF switch100ccontacts the RF switch100dis marked as N3.

For better understanding and ease of description, one RF switch100c, one RF switch100d, and one impedance component300are provided inFIG.2. However, the number of the RF switches100cand100dand the impedance component300may be plural in number so as to support various frequency bands.

From among the switches described with reference toFIG.1andFIG.2, the switch connected between a predetermined port (i.e., terminal (RFin)) and the ground may receive a high voltage of the RF signal when it is turned off, so a breakdown of the switch may occur. That is, the RF switch100b, the RF switch100c, and the RF switch100dmay be respectively connected between the predetermined port and the ground, and when they are turned off, a high voltage of the RF signal may be applied, so a function for protecting he RF switch100b, the RF switch100c, and the RF switch100dmay be beneficial. The RF switch100b, the RF switch100c, and the RF switch100dmay receive a further higher voltage by a voltage standing wave ratio (VSWR) as well as the voltage caused by the RF signal. The antenna impedance of the antenna200may vary by 50 ohms according to various use conditions, by which the voltage standing wave ratio (VSWR) increases. By a reflected wave generated in a high voltage standing wave ratio (VSWR) condition, a higher voltage may be applied to the turned-off RF switch100b, the RF switch100c, and the RF switch100d, by which a of the switch may occur. A circuit for protecting the switch from such a breakdown and an RF switch system including the same will now be described.

FIG.3illustrates an RF switch system1000, in accordance with one or more embodiments.

Referring toFIG.3, the RF switch system1000may include an RF switch1100, a an RF switch protective circuit1200, and a voltage generator1300.

The RF switch1100may be connected between a predetermined port P1and a ground. In an example, the RF switch1100may be one of the RF switch100b, the RF switch100c, and the RF switch100ddescribed with reference toFIG.1andFIG.2. Referring toFIG.3, a predetermined port P1may be one of the nodes N1, N2, and N3described with reference toFIG.1andFIG.2, and may be an RF common port in the RF circuit. The RF switch1100receives a turn-on voltage or a turn-off voltage from the voltage generator1300, and is switched on or off.

The voltage generator1300generates the turn-on voltage and the turn-off voltage of the RF switch1100, and supplies the generated turn-on voltage and turn-off voltage to the RF switch1100. Referring toFIG.3, a turn-on voltage of the RF switch1100is shown as VPOS, and a turn-off voltage of the RF switch1100is shown as VNEG. The turn-on voltage (VPOS) may be a positive (+) voltage, and the turn-off voltage (VNEG) may be a negative (−) voltage. In an example, the voltage generator1300may be implemented with a charge pump to supply the turn-off voltage (VNEG) to the RF switch1100. A method for the voltage generator1300to generate the turn-on voltage (VPOS) and the turn-off voltage (VNEG) will not be described herein.

FIG.4illustrates an example RF switch1100ofFIG.3.

Referring toFIG.4, the RF switch1100, in accordance with one or more embodiments, may include a plurality of transistors (M1, M2, . . . , Mn−1, Mn), and the transistors (M1, M2, . . . , Mn+1, Mn) may be coupled in series with each other. That is, the RF switch1100has a structure in which a plurality of transistors (M1, M2, . . . , Mn−1, Mn) are stacked. A drain of the transistor M1may be connected to a port P1, a drain of the transistor M2may be connected to a source of the transistor M1, and a drain of the transistor (Mn) may be connected to a source of the transistor Mn−1. Here, a plurality of transistors (M1, M2, . . . , Mn−1, Mn) may be a FET (Field Effect Transistor), a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), or a BJT (Bipolar Junction Transistor).

The turn-on voltage (VPOS) or the turn-off voltage (VNEG) may be applied to gates (G) of a plurality of transistors (M1, M2, . . . , Mn−1, Mn)

When the turn-on voltage (VPOS) is applied to the gate (G), a plurality of transistors (M1, M2, . . . , Mn−1, Mn) are turned on, and when the turn-off voltage (VNEG) is applied to the gates (G), a plurality of transistors (M1, M2, . . . , Mn−1, Mn) are turned off. When the switch1100is turned off, the turn-off voltage (VNEG) is applied to bodies (B) of a plurality of transistors (M1, M2, . . . , Mn−1, Mn).

When the switch1100is turned off and a high voltage is applied to respective ends of the switch1100, the turn-off voltage (VNEG) supplied by the voltage generator1300may become greater than a predetermined value. That is, the turn-off voltage (VNEG), that is a negative (—) voltage, becomes greater than the predetermined value. When the switch1100is turned off, a potential difference between the drain and the source of each of a plurality of transistors (M1, M2, . . . , Mn−1, Mn) increases. When the potential of the drain increases, a high leakage current flows to the body, and a leakage current that is greater than the current driven by the voltage generator1300that supplies a negative turn-off voltage (VNEG) supplied to the body (B) and the gate (G), is generated. Accordingly, the negative turn-off voltage (VNEG) supplied by the voltage generator1300becomes greater than a predetermined value. In an example, when the turn-off voltage (VNEG) is set to be −5 V, the turn-off voltage (VNEG) may increase to approximately the level of 0 V. This phenomenon will be referred to as a gate induced drain leakage (GIDL). When the negative turn-off voltage (VNEG) is applied to the gates (G) and the bodies (B) of a plurality of transistors (M1, M2, . . . , Mn−1, Mn), depletion regions may be formed in sections where the gates and the drains of a plurality of transistors (M1, M2, . . . , Mn−1, Mn) overlap each other. In this instance, when a high potential is applied to the drain, electrons and holes enter the depletion region. That is, the electrons enter toward the drain through tunneling by the high potential at the drain, which signifies a leakage current to the body. The negative turn-off voltage (VNEG) increases by the leakage current. In other words, when the RF switch1100is turned off and the voltage at the respective ends of the RF switch1100increases, the negative turn-off voltage (VNEG) supplied to the RF switch1100from the voltage generator1300becomes higher than the predetermined value. The RF switch protective circuit1200to be described detects the negative turn-off voltage (VNEG), and it may indirectly detect applying of a high voltage at the respective ends of the RF switch1100through the detected turn-off voltage (VNEG). That is, the RF switch protective circuit1200performs a protection operation according to the detected turn-off voltage (VNEG).

The RF switch protective circuit1200receives the turn-off voltage (VNEG) supplied by the voltage generator1300, detects the received turn-off voltage (VNEG), and changes an impedance value based on the detected turn-off voltage (VNEG). The RF switch protective circuit1200is connected between the port P1and the ground and protects the RF switch1100. The RF switch protective circuit1200may include an element having an impedance value that is internally changed, and changes the impedance value based on the detected turn-off voltage (VNEG). In an example, when the detected turn-off voltage (VNEG) increases, the RF switch protective circuit1200may lower the internal impedance value to allow the voltage (signal) at the RF switch1100to bypass the RF switch1100. Accordingly, the RF switch protective circuit1200may protect the RF switch1100from being broken down.

FIG.5illustrates a block diagram of an example RF switch protective circuit1200, in accordance with one or more embodiments.

As illustrated inFIG.5, the RF switch protective circuit1200may include a voltage detector1210and an impedance variation unit1220.

The voltage detector1210may detect the turn-off voltage (VNEG) supplied to the RF switch1100from the voltage generator1300. To turn off the RF switch1100, the voltage generator1300supplies the negative turn-off voltage (VNEG) to the gate and the body of the RF switch1100. The voltage detector1210may receive the negative turn-off voltage (VNEG) applied to at least one terminal of the gate and the body of the RF switch1100and may detect it. A method for the voltage detector1210to detect the negative turn-off voltage (VNEG) will be described in detail in a latter portion of the present specification. The voltage detector1210may detect the negative turn-off voltage (VNEG), and output a detection voltage (VDET) corresponding to the detected value to the impedance variation unit1220.

The impedance variation unit1220receives a detection voltage (VDET) from the voltage detector1210, and changes an internal impedance value according to the detection voltage (VDET). The impedance variation unit1220lowers the internal impedance value when the detection voltage (VDET) increases (or rises). The impedance lowered in this way may be applied to the respective ends of the RF switch1100, so the voltage (signal) at the respective ends of the RF switch1100may be bypassed through the RF switch protective circuit1200with a low impedance value.

FIG.6illustrates a conceptual graph of an operation of an example RF switch system1000, in accordance with one or more embodiments.

Referring toFIG.6, a horizontal axis represents an RF signal size at respective ends of the RF switch1100. The RF signal size may increase by internal design factors or external environment factors (e.g., a rise of the VSWR). S610indicates a turn-off voltage (VNEG) (the voltage applied to the gate or the body when the RF switch1100is turned off) according to the RF signal size. S620indicates an impedance value of the RF switch protective circuit1200according to the RF signal size.

Referring to S610ofFIG.6, when the RF signal size increases, the turn-off voltage (VNEG) of the RF switch1100increases. A rise of the turn-off voltage (VNEG) of the RF switch1100may be generated by the gate induced drain leakage (GIDL). When the turn-off voltage (VNEG) of the RF switch1100rises to be equal to, or greater than, a predetermined threshold value (Vth), the RF switch protective circuit1200decreases the internal impedance value. When the impedance value of the RF switch protective circuit1200decreases, a current l2flowing through the RF switch protective circuit1200from the port P1decreases. When the impedance value of the RF switch protective circuit1200decreases, a current l1flowing through the RF switch1100from the port P1decreases. Accordingly, RF power applied to the turned-off RF switch1100may be reduced, and a breakdown of the RF switch1100may be prevented.

Various examples of the RF switch protective circuit1200will now be described with reference toFIG.7AtoFIG.7D

FIG.7Aillustrates an example RF switch protective circuit1200a, in accordance with one or more embodiments.

As illustrated inFIG.7A, the RF switch protective circuit1200aincludes a voltage detector1210and an impedance variation unit1220a.

The voltage detector1210may include a plurality of resistors R1and R2. A first end of the resistor R1is connected to a power voltage VDD, and a first end of the resistor R2is connected to a second end of the resistor R1. A second end of the resistor R2is connected to the turn-off voltage (VNEG) of the RF switch1100. Specifically, the turn-off voltage (VNEG) of the RF switch1100is applied to the second end of the resistor R2. The resistor R1and the resistor R2are coupled in series to each other to form a resistor column, and a voltage at a node of the resistor R1and the resistor R2corresponds to the detection voltage (VDET).FIG.7Aillustrates the voltage detector1210configured with two resistors R1and R2, and the voltage detector1210may be configured with more resistor columns.

The detection voltage (VDET) satisfies Equation 1 below.

In Equation 1, resistance of the resistors R1and R2and the power voltage VDD may be fixed values, so the detection voltage (VDET) changes according to the turn-off voltage (VNEG) of the RF switch1100. That is, the voltage detector1210may generate a detection voltage (VDET) that is changed by the turn-off voltage (VNEG) of the RF switch1100.

The impedance variation unit1220amay include a buffer1221, a transistor unit1222, and an impedance component1223.

The buffer1221receives the detection voltage (VDET), and drives the transistor unit1222based on the detection voltage (VDET).

The transistor unit1222may include at least one transistor (T1to TN) coupled in series to each other.FIG.7Aillustrates the transistor unit1222including a plurality of transistors (T1to TN). However, in an example, the transistor unit1222may include a single transistor T1.

A plurality of transistors (T1to TN) may respectively receive an output of the buffer1221through a plurality of gate resistors (Rg). A drain of the transistor T1may be connected to the port P1, a drain of the transistor T2may be connected to a source of the transistor T1, and a drain of the transistor (Tn) may be connected to a source of the transistor Tn−1. A source of the transistor (Tn) is connected to the impedance component1223. The plurality of transistors (T1to TN) may be, as non-limiting examples, field effect transistors (FET), metal oxide semiconductor field effect transistors (MOSFET), or bipolar junction transistors (BJT).

The impedance component1223is connected between the transistor unit1222and the ground. That is, the impedance component1223may be connected between the source of the transistor (Tn) and the ground. The impedance component1223may include, as non-limiting examples, at least one of a resistor, a capacitor, and an inductor, and provides a predetermined impedance value according to a frequency of the RF signal.

When the detection voltage (VDET) increases (rises), the buffer1221drives (turns on) the transistor unit1222with a high voltage. When the transistor unit1222is turned on, the total impedance value (ZSUM_ON) of the impedance variation unit1220acorresponds to the sum of the impedance value corresponding to the turn-on of the transistor unit1222and the impedance value of the impedance component1223. When the impedance value corresponding to the turn-on of the transistor unit1222is given as ‘RON’ for convenience's sake, the total impedance value (ZSUM_ON) of the impedance variation unit1220ais expressed as Equation 2 below.
ZSUM_ON=RON+ZEquation 2:

In Equation 2, Z represents an impedance value of the impedance component1223.

When the detection voltage (VDET) falls (or is reduced), the buffer1221may not turn on the transistor unit1222. When the transistor unit1222is turned off, the total impedance value (ZSUM_OFF) of the impedance variation unit1220amay correspond to the sum of the impedance value corresponding to the turn-off of the transistor unit1222and the impedance value of the impedance component1223. When the impedance value corresponding to the turn-off of the transistor unit1222is given as ‘ZCoff’, the total impedance value (ZSUM_OFF) of the impedance variation unit1220ais expressed as Equation 3 below.
ZSUM_OFF=ZCoff+ZEquation 3:

The impedance value (RON) corresponding to the turn-on of the transistor unit1222has a value that is substantially lower than the impedance value (ZCoff) corresponding to the turn-off of the transistor unit1222. Accordingly, the impedance variation unit1220amay supply a low impedance value between the port P1and the ground when the turn-off voltage (VNEG) of the RF switch1100increases (or rises).

FIG.7Billustrates an example RF switch protective circuit1200b, in accordance with one or more embodiments.

Referring toFIG.7B, the RF switch protective circuit1200bmay include a voltage detector1210and an impedance variation unit1220b.

Referring toFIG.7BandFIG.7A, the impedance variation unit1220bcorresponds to the impedance variation unit1220aexcept that the impedance variation unit1220bmay further include a voltage limiter1224.

The voltage limiter1224is connected between the port P1and the transistor unit1222. The voltage limiter1224may be implemented by at least one diode. In an example, the voltage limiter1224may include a plurality of diodes coupled in series with each other. Further, the RF signal may be an AC signal, accordingly, the voltage limiter1224may include diodes connected back to back. A detailed configuration of the voltage limiter1224will be described with reference toFIG.8. When a voltage that is equal to or greater than the threshold voltage is applied at the respective ends of the voltage limiter1224, the voltage limiter1224is turned on, and a predetermined limiter voltage is applied at the respective ends. That is, the voltage limiter1224has a low impedance value at the voltage that is equal to or greater than the threshold voltage. The voltage limiter1224is turned off at the voltage that is less than the threshold voltage and has a high impedance value.

As described with reference toFIG.7A, when the detection voltage (VDET) increases (or rises), the transistor unit1222is turned on, and the transistor unit1222has a low impedance value. When the impedance value of the transistor unit1222is reduced, a voltage that is equal to or greater than the threshold voltage is applied to the voltage limiter1224, and the voltage limiter1224is accordingly turned on. The voltage limiter1224is turned on, so the voltage limiter1224has a low impedance value. That is, when the detection voltage (VDET) increases (or rises), the voltage limiter1224and the transistor unit1222have low impedance values.

As described with reference toFIG.7A, when the detection voltage (VDET) is low, the transistor unit1222is turned off, and the transistor unit1222has a high impedance value. When the impedance value of the transistor unit1222increases, a voltage that is less than a threshold voltage is applied to the voltage limiter1224, and the voltage limiter1224is accordingly turned off. The voltage limiter1224is turned off, so the voltage limiter1224has a high impedance value. That is, when the detection voltage (VDET) is reduced (or lowered), the voltage limiter1224and the transistor unit1222have high impedance values.

The impedance variation unit1220baccording to an example as described above may supply a low impedance value between the port P1and the ground when the turn-off voltage (VNEG) of the RF switch1100increases (or rises).

FIG.7Cillustrates an example RF switch protective circuit1200c, in accordance with one or more embodiments.

Referring toFIG.7C, the RF switch protective circuit1200cmay include a voltage detector1210and an impedance variation unit1220c.

Referring toFIG.7CandFIG.7B, the impedance variation unit1220ccorresponds to the impedance variation unit1220bexcept that the transistor unit1222of the impedance variation unit1220bis replaced with a variable capacitor1225.

A first end of the variable capacitor1225is connected to the voltage limiter1224, and a second end of the variable capacitor1225is connected to the impedance component1223. That is, the variable capacitor1225is connected between the voltage limiter1224and the impedance component1223. A control terminal of the variable capacitor1225is connected to an output end of the buffer1221. A capacitance of the variable capacitor1225may change according to the voltage input to the control terminal. That is, when the voltage input to the control terminal increases, the capacitance of the variable capacitor1225is increased, and the impedance value accordingly decreases. The variable capacitor1225may be realized with a varactor, which may control the capacitance of the variable capacitor1225.

When the detection voltage (VDET) increases, an output voltage of the buffer1221increases. The output voltage of the buffer1221is input to a control terminal of the variable capacitor1225, and accordingly, when the detection voltage (VDET) increases, the impedance value of the variable capacitor1225decreases. When the impedance value of the variable capacitor1225is decreases, a voltage that is equal to or greater than the threshold voltage is applied to the voltage limiter1224, and the voltage limiter1224is turned on. As the voltage limiter1224is turned on, the voltage limiter1224may have a low impedance value. That is, when the detection voltage (VDET) increases, the voltage limiter1224and the variable capacitor1225may have low impedance values.

When the detection voltage (VDET) decreases, the output voltage of the buffer1221decreases. The output voltage of the buffer1221is input to the control terminal of the variable capacitor1225, and accordingly, when the detection voltage (VDET) decreases, the impedance value of the variable capacitor1225increases. When the impedance value of the variable capacitor1225increases, a voltage that is less than the threshold voltage is applied to the voltage limiter1224, and the voltage limiter1224is then turned off. As the voltage limiter1224is turned off, the voltage limiter1224has a high impedance value. That is, when the detection voltage (VDET) decreases (or falls), the voltage limiter1224and the variable capacitor1225have high impedance values.

When the turn-off voltage (VNEG) of the RF switch1100increases (or rises), the impedance variation unit1220c, according to an example, may supply a low impedance value to the port P1and the ground.

FIG.7Dillustrates an example RF switch protective circuit1200d, in accordance with one or more embodiments.

Referring toFIG.7D, the RF switch protective circuit1200dmay include a voltage detector1210and an impedance variation unit1220d.

Referring toFIG.7DandFIG.7B, the impedance variation unit1220dcorresponds to the impedance variation unit1220bexcept that the voltage limiter1224of the impedance variation unit1220bis replaced with the variable capacitor1226.

A first end of the variable capacitor1226is connected to the port P1, and a second end of the variable capacitor1226is connected to the transistor unit1222. That is, the variable capacitor1226is connected between the port P1and the transistor unit1222. A control terminal of the variable capacitor1226is connected to the output end of the buffer1221. The capacitance of the variable capacitor1226changes according to the voltage input to the control terminal. That is, when the voltage input to the control terminal increases, the capacitance of the variable capacitor1226increases, and the impedance value accordingly decreases.

As described with reference toFIG.7AandFIG.7B, when the detection voltage (VDET) increases (or rises), the transistor unit1222is turned on, so the transistor unit1222has a low impedance value. When the detection voltage (VDET) increases (or rises), the impedance value of the variable capacitor1226decreases. That is, when the detection voltage (VDET) increases (or rises), the transistor unit1222and the variable capacitor1226have low impedance values.

As described with reference toFIG.7AandFIG.7B, when the detection voltage (VDET) decreases (or falls), the transistor unit1222is turned off, so the transistor unit1222has a high impedance value. When the detection voltage (VDET) decreases, the impedance value of the variable capacitor1226increases. That is, when the detection voltage (VDET) decreases (or falls), the transistor unit1222and the variable capacitor1226have high impedance values.

The impedance variation unit1220d, in accordance with one or more embodiments, may supply a low impedance value between the predetermined port P1and the ground when the turn-off voltage (VNEG) of the RF switch1100increases (or rises).

FIG.8illustrates an example voltage limiter1224, in accordance with one or more embodiments. That is,FIG.8illustrates the example voltage limiter1224described with reference toFIG.7BandFIG.7C.

Referring to element810ofFIG.8, the voltage limiter1224may include at least one diode. Referring to element810ofFIG.8, the voltage limiter1224may be configured with a plurality of diodes coupled in series with each other, and the voltage limiter1224may be implemented with a single diode.

Referring to element820ofFIG.8, the voltage limiter1224may include diodes821and822connected back to back. The diode821may include a plurality of diodes coupled in series with each other. The diode822may include a plurality of diodes that are provided in an opposite direction to the diode821and are coupled in series with each other. That is, the diode821and the diode822may be connected to each other back to back. When the RF signal has a positive (+) value, the diode821functions as a voltage limiter, and when the RF signal has a negative (−) value, the diode822functions as a voltage limiter. The diode821and the diode821are shown to respectively include a plurality of diodes, but may respectively include at least one diode.