Radio frequency switching module and control method thereof

The present application is based on, and claims priority from, Taiwan Application Serial Number 103114415, filed on Apr. 21, 2014, the disclosure of which is hereby incorporated by reference herein in its entirety.

1. Field of the Invention

The embodiment relates to a radio frequency (RF) switching module and a control method thereof, and particularly to an RF switching module and a control method that can decrease RF signal leakage.

2. Description of the Prior Art

With popularity of wireless communication, setting RF circuits in various devices has become a trend, wherein an RF switching module is one of the RF circuits.

When the RF switching module transmits RF signals, a switch located at a transmitting port of the RF switching module is turned on to transmit the RF signals through an antenna, and a switch located at a receiving port of the RF switching module is turned off to prevent the RF signals of the transmitting port from leaking to the receiving port. RF signal leakage not only decreases quality of the RF signals when the RF switching module transmits/receives the RF signals, but also damages low voltage devices of the receiving port. In addition, the RF signal leakage also increases additional power consumption to further decrease usage time of a battery applied to a mobile device. Therefore, an effective and adjustable control method for decreasing the RF signal leakage of the RF switching module is necessary.

An embodiment provides a control method of an RF switching module, wherein the RF switching module includes a first switch coupled between a common port and a first port, and a second switch coupled between the common port and a second port, wherein the RF switching module is applied to switch between a first mode and a second mode, the first switch is turned on and the second switch is turned off in the first mode, and the first switch is turned off and the second switch is turned on in the second mode. The control method includes providing a first turning-off signal to the first switch when the RF switching module is in the first mode; providing a first turning-on signal to the second switch after the first turning-off signal is provided for a first predetermined time; and switching the RF switching module from the first mode to the second mode according to the first turning-on signal.

Another embodiment provides an RF switching module. The RF switching module includes a first switch, a second switch, and a control signal generation module for providing a first turning-off signal and a first turning-on signal. The first switch is coupled between a common port and a first port. The second switch is coupled between the common port and a second port. The control signal generation module is used for providing a first turning-off signal and a first turning-on signal. The RF switching module is applied to switch between a first mode and a second mode, the first switch is turned on and the second switch is turned off in the first mode, and the first switch is turned off and the second switch is turned on in the second mode. The first turning-off signal is provided to the first switch when the RF switching module is in the first mode, and the first turning-on signal is provided to the second switch after the first turning-off signal is provided for a first predetermined time to make the RF switching module be switched from the first mode to the second mode.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

FIG. 1 is a diagram illustrating an RF switching module 100 according to an embodiment.

FIG. 2 is a timing diagram illustrating the control signals of the RF switching module.

FIG. 3 is a timing diagram illustrating the control signals of the RF switching module according to another embodiment.

FIG. 4 is diagram illustrating a control signal generation module for generating the control signals shown in FIG. 2 .

FIG. 5 is a timing diagram of the signals IN, INB, SWD 2 , SW, SWD 1 , SWD 1 B and SWB shown in FIG. 4 .

FIG. 6 is a diagram illustrating an RF switching module according to another embodiment.

FIG. 7 is a flowchart illustrating a control method of the RF switching module according to another embodiment.

FIG. 8 is a timing diagram illustrating the gate voltages of the switches.

FIG. 9 is a flowchart illustrating a control method of the RF switching module according to another embodiment.

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.

Please refer to FIG. 1 . FIG. 1 is a diagram illustrating an RF switching module 100 according to an embodiment. The RF switching module 100 includes switches S 1 ˜S 4 , resistors R 1 ˜R 9 , and capacitors C 1 ˜C 5 , wherein each of the switches S 1 ˜S 4 has a first terminal, a second terminal, and a control terminal. In the embodiment of FIG. 1 , the switches S 1 ˜S 4 are metal-oxide-semiconductor field effect transistors (MOSFET). A control terminal and a first terminal/second terminal of each of the switches S 1 ˜S 4 can be a gate and a source/drain of a MOSFET, respectively.

The resistors R 1 ˜R 4 are coupled to first terminals and second terminals of the switches S 1 ˜S 4 respectively for making direct current (DC) biases at the first terminals of the switches S 1 ˜S 4 be equal to DC biases at the second terminals of the switches S 1 ˜S 4 . Resistors R 5 ˜R 8 are coupled to control terminals of the switches S 1 ˜S 4 , respectively. Resistor R 9 is coupled between a bias VBIAS and the capacitor C 1 to set DC biases of terminals of the switches S 1 , S 3 adjacent to the resistor R 9 . The resistors R 1 ˜R 9 are designed to have high impedance, and the resistors R 5 ˜R 9 are used for preventing RF signals from leaking to terminals corresponding to control signals SW, SWB, and the bias VBIAS through switch channels (that is, the switches S 1 ˜S 4 ) to prevent from signal loss or signal distortion.

When the RF switching module 100 is in a first mode (e.g. a transmitting mode), the control signal SW is high to make the switch S 1 turning-on, resulting in the RF signals being transmitted from a port TX (a first port) to a port ANT (a common port) to emit through the switch S 1 , and also make the switch S 2 turning-on to let signals of a port RX (a second port) bypass to ground GND to prevent from interfering with the RF signals transmitted to the port ANT. Meanwhile, the control signal SWB is low to make the switch S 3 turning-off to prevent the RF signals transmitted to the port ANT from entering the port RX, and also make the switch S 4 turning-off to prevent the RF signals of the port TX from bypassing to the ground GND. Similarly, when the RF switching module 100 is in a second mode (e.g. a receiving mode), turning-on/turning-off states of the switches S 1 ˜S 4 are just opposite to those of the switches S 1 ˜S 4 in the transmitting mode, wherein RF signals are received by the port ANT and transmitted to the port RX through the switch S 3 .

FIG. 2 is a timing diagram illustrating the control signals SW, SWB of the RF switching module 100 , wherein a solid line represents the control signal SW, a dashed line represents the control signal SWB, t represents a time axis, v represents a voltage axis, VH represents a high voltage, and VL represents a low voltage. The control signal SW is used for controlling turning-on and turning-off of the switches S 1 , S 2 , and the control signal SWB is used for controlling turning-on and turning-off of the switches S 3 , S 4 . When the control signals SW, SWB are switched, a high impedance gate resistor and an equivalent gate capacitor of each of the switches S 1 ˜S 4 can cause a time delay (that is, an RC-delay) between a gate voltage and a control signal thereof.

In addition, when the RF switching module 100 is switched between the transmission mode and the receiving mode, the capacitors C 1 ˜C 5 need to be charged or discharged, wherein the capacitors C 1 ˜C 5 are charged or discharged after an sufficient charging/discharging time, source/drain biases of the switches S 1 ˜S 4 just achieve a design value, resulting in the switches S 1 ˜S 4 being completely turned on or turned off. Adding charging/discharging circuits at the sources/drains of the switches S 1 ˜S 4 can accelerate turning-on or turning-off of the switches S 1 ˜S 4 , but need additional chip area and power consumption.

When the control signal SWB is switched from the high voltage (VH) to the low voltage (VL), the switch S 3 is not immediately turned off because of a gate voltage time delay caused by the gate resistor and the equivalent gate capacitor of the switch S 3 , and the charging/discharging time for the source/drain bias of the switch S 3 reaching the design value. Meanwhile, if the switch S 1 is already turned on, the RF signals of the port TX can leak to the port RX through the switch S 3 . The RF signal leakage not only decreases quality of the RF signals of the port TX, but also interferes with signals of the port RX or damages low voltage devices of the port RX.

To prevent from the RF signal leakage of the port TX, the control signal SW can be designed to switch from low to high after the control signal SWB is switched from high to low for a predetermined time D 2 ; and on the other hand, the control signal SWB is switched from low to high after the control signal SW is switched from high to low for a predetermined time D 1 . For example, after the RF switching module 100 completes the transmitting mode, the control signal SW is switched from high to low to early turn off the switches S 1 , S 2 for the predetermined time D 1 , and then the control signal SWB is switched from low to high to turn on the switches S 3 , S 4 to make the RF switching module 100 enter the receiving mode; and vice versa. Thus, the RF switching module 100 can prevent from simultaneously switching the control signals SW, SWB to cause the RF signal leakage. Optimal values of the predetermined times D 1 , D 2 can be determined according to the gate voltage time delay, the charging/discharging time, and a requirement of a communication specification to prevent from the above mentioned RF signal leakage and the RF switching module 100 operates effectively in time domain.

FIG. 3 is a timing diagram illustrating the control signals SW, SWB of the RF switching module 100 according to another embodiment, wherein a solid line represents the control signal SW, and a dashed line represents the control signal SWB. When the control signal SWB is switched from high to low, the control signal SWB has a switching delay time thereof because of parasitic effects of a system where the RF switching module 100 is applied to or an environment surrounding the RF switching module 100 . In FIG. 3 , the control signal SWB can be set to start to decrease from the high voltage (VH) for the predetermined time D 2 , then the control signal SW starts to increase from the low voltage (VL). That is to say, after the control signal SWB starts to decrease from the high voltage (VH) and is lower than a predetermined voltage, the control signal SW starts to increase from the low voltage (VL) to prevent the RF signals of the port TX from leaking to the port RX through the switch S 3 to avoid the above mentioned RF signal leakage. Similarly, the control signal SW can be set to start to decrease from the high voltage (VH) for the predetermined time D 1 , then the control signal SWB starts to increase from the low voltage (VL). That is to say, after the control signal SW starts to decrease from the high voltage (VH) and is lower than a predetermined voltage, the control signal SWB starts to increase from the low voltage (VL) to prevent the RF signals of the port RX from leaking to the port TX through the switch S 1 to avoid the above mentioned RF signal leakage. Further, in one embodiment of the present invention, the predetermined time D 1 is greater than the predetermined time D 2 .

FIG. 4 is a diagram illustrating a control signal generation module 500 for generating the control signals SW, SWB shown in FIG. 2 . In the control signal generation module 500 , an AND gate 506 is coupled to the switches S 1 , S 2 (not shown in FIG. 4 ), and an AND gate 512 is coupled to the switches S 3 , S 4 (not shown in FIG. 4 ). A delay unit 504 can generate and output a delay signal SWD 2 to the AND gate 506 according to an input signal IN and the predetermined time D 2 ; and then the AND gate 506 can generate and output the control signal SW to the switches S 1 , S 2 according to the input signal IN and the delay signal SWD 2 . In addition, an inverter 510 can generate and output an inverse signal INB to the AND gate 512 according to the input signal IN; and a delay unit 514 can generate and output a delay signal SWD 1 to an inverter 516 according to the input signal IN and the predetermined time D 1 , wherein an inverter 516 can generate and output an inverse delay signal SWD 1 B to the AND gate 512 according to the delay signal SWD 1 ; and then the AND gate 512 can generate and output the control signal SWB to the switches S 3 , S 4 according to the inverse delay signal SWD 1 B and the inverse signal INB. FIG. 5 is a timing diagram of the input signal IN, the inverse signal INB, the delay signal SWD 2 , the control signal SW, the delay signal SWD 1 , the inverse delay signal SWD 1 B, and the control signal SWB shown in FIG. 4 illustrating that the design of the control signal generation module 500 can generate the predetermined times D 1 , D 2 shown in FIG. 2 when the control signals SW, SWB are switched.

In addition, please refer to FIG. 6 . FIG. 6 is a diagram illustrating an RF switching module 600 according to another embodiment. As shown in FIG. 6 , a difference between the RF switching module 100 and the RF switching module 600 is that the RF switching module 600 does not include the switch channels corresponding to the switches S 2 , S 4 . Further, subsequent operational principles of the RF switching module 600 are the same as those of the RF switching module 100 , so further description thereof is omitted for simplicity.

FIG. 7 is a flowchart illustrating a control method of the RF switching module 100 according to another embodiment. Detailed steps of the control method 700 are as follows:

Step 702 : When the RF switching module 100 is in the first mode, a first turning-off signal is provided to the switches S 1 , S 2 . For example, a control signal SW is switched from a high voltage (VH) to a low voltage (VL), resulting in the switches S 1 , S 2 starting to be turned off.

Step 704 : After the first turning-off signal is provided to the switches S 1 , S 2 for a predetermined time D 1 (that is, the switches S 1 , S 2 start to be turned off for the predetermined time D 1 ), a first turning-on signal is provided to the switches S 3 , S 4 . For example, a control signal SWB is switched from the low voltage (VL) to the high voltage (VH), resulting in the switches S 3 , S 4 starting to be turned on to switch the first mode to the second mode.

Step 706 : A second turning-off signal is provided to the switches S 3 , S 4 . For example, the control signal SWB is switched from the high voltage (VH) to the low voltage (VL), resulting in the switches S 3 , S 4 starting to be turned off.

Step 708 : After the second turning-off signal is provided to the switches S 3 , S 4 for a predetermined time D 2 (that is, the switches S 3 , S 4 start to be turned off for the predetermined time D 2 ), a second turning-on signal is provided to the switches S 1 , S 2 . For example, the control signal SW is switched from the low voltage (VL) to the high voltage (VH), resulting in the switches S 1 , S 2 starting to be turned on to switch the second mode to the first mode.

According to the above mentioned steps, the control signal SW includes the first turning-off signal and the second turning-on signal; and the control signal SWB includes the first turning-on signal and the second turning-off signal.

In Step 702 , when the control signal SW is switched from the high voltage (VH) to the low voltage (VL), the switch S 1 is not immediately turned off, wherein a time for decrease of the gate voltage of the switch S 1 is determined by equation (1). In equation (1), t represents time, exp represents an exponential function, RR 5 represents a resistance of the gate resistor R 5 , Cg 5 represents a capacitance of an equivalent gate capacitor of the switch S 1 , and Vg(t) represents the gate voltage of the switch S 1 at the time t.

Vg ( t )=( VH−VL )*exp(− t /( RR 5 *Cg 5))+ VL   (1)

FIG. 8 is a timing diagram illustrating the gate voltages of the switches S 1 , S 3 . If the control signal SW starts to be switched from high to low at the time T 1 , change of the gate voltage of the switch S 1 with time is shown as Vg. After the predetermined time D 1 (that is, at the time T 1 +D 1 ), the control signal SWB just starts to be switched from low to high. Meanwhile, change of the gate voltage of the switch S 3 with time is shown as Vg′. At the time T 2 , the switch S 1 is almost turned off and the gate voltage of the switch S 3 is not increased to a high voltage which is not enough to turn on the switch S 3 completely, so RF signal leakage from the port TX to the port RX through the switches S 1 , S 3 can be decreased significantly, and power consumption of the RF switching module 100 , low voltage device damage of the port RX, or unexpected results can also be decreased.

The time T 1 +D 1 can be set after the switch S 1 is completely turned off, or after the gate voltage Vg of the switch S 1 is lower than the threshold voltage of the switch S 1 or a voltage (VH+VL)/2. The time D 1 can be set to be equal to or greater than a product of RR 5 *Cg 5 .

Similarly, the above mentioned principles can also be applied to Steps 706 , 708 to utilize the predetermined time D 2 to reduce the RF signal leakage from the port RX to the port TX, so further description thereof is omitted for simplicity.

FIG. 9 is a flowchart illustrating a control method of the RF switching module 600 according to another embodiment. Detailed steps of the control method 900 are as follows:

Step 902 : When the RF switching module 600 is in the first mode, a first turning-off signal is provided to the switch S 1 . For example, a control signal SW is switched from a high voltage (VH) to a low voltage (VL), resulting in the switch S 1 starting to be turned off.

Step 904 : After the first turning-off signal is provided to the switch S 1 for a predetermined time D 1 (that is, the switch S 1 starts to be turned off for the predetermined time D 1 ), a first turning-on signal is provided to the switch S 3 . For example, a control signal SWB is switched from the low voltage (VL) to the high voltage (VH), resulting in the switch S 3 starting to be turned on to switch the first mode to the second mode.

Step 906 : A second turning-off signal is provided to the switch S 3 . For example, the control signal SWB is switched from the high voltage (VH) to the low voltage (VL), resulting in the switch S 3 starting to be turned off.

Step 908 : After the second turning-off signal is provided to the switch S 3 for a predetermined time D 2 (that is, the switch S 3 start to be turned off for the predetermined time D 2 ), a second turning-on signal is provided to the switch S 1 . For example, the control signal SW is switched from the low voltage (VL) to the high voltage (VH), resulting in the switch S 1 starting to be turned on to switch the second mode to the first mode.

Subsequent operational principles of the control method 900 are the same as those of the control method 700 , so further description thereof is omitted for simplicity.

In one embodiment, the first turning-off signal, the first turning-on signal, the second turning-off signal, and the second turning-on signal control turning-on and turning-off of the switches S 1 ˜S 4 by adjusting the biases of the gates of the switches S 1 ˜S 4 . In another embodiment, the first turning-off signal, the first turning-on signal, the second turning-off signal, and the second turning-on signal control turning-on and turning-off of the switches S 1 ˜S 4 by adjusting voltage drops between the gates and the source/drains of the switches S 1 ˜S 4 .

To sum up, the RF switching module and the control method thereof turn off all switches during the RF switching module being switched between the transmitting mode and the receiving mode, and then turn on required switches after the all switches are turned off for a predetermined time to switch to a next mode (the transmitting mode or the receiving mode). Thus, the embodiment could significantly reduce RF signal leakage, RF signal interference each other, power consumption of the RF switching module, low voltage device damage of the receiving port, or unexpected results, and could also increase RF signal quality. In addition, the RF switching module provided by the embodiment can be implemented on a monolithic chip by a silicon on insulator (SOI) process, a high-electron-mobility transistor (HEMT) process, or a metal-oxide-semiconductor (MOS) process.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.