Abstract:
An RF switch includes a transistor and a compensation capacitor circuit. The compensation capacitor circuit includes a first compensation capacitor and a second compensation capacitor of the same capacitance. The compensation capacitor circuit is used to improve voltage distribution between a control node and a first node of the transistor and between the control node and a second node of the transistor.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is related to a capacitance compensation circuit of an RF (radio frequency) switch, and more particularly, to a capacitance compensation circuit which improves voltage distribution of the RF switch. 
         [0003]    2. Description of the Prior Art 
         [0004]    Please refer to  FIG. 1  and  FIG. 2 .  FIG. 1  is a diagram illustrating a prior art RF switch  100 . The RF switch  100  includes a transistor  102  having a first parasitic capacitor Cgd coupled between a gate and a drain of the transistor  102 , a second parasitic capacitor Cgs coupled between the gate and a source of the transistor  102 , a third parasitic capacitor Cdb coupled between a well and the drain of the transistor  102 , and a fourth parasitic capacitor coupled between the well and the source of the transistor  102 . 
         [0005]      FIG. 2  is a timing diagram illustrating voltage signals on the prior art RF switch  100  when the RF switch  100  is turned off. In  FIG. 2 , −VR_DC is a DC (direct current) voltage difference between the source and the drain of the transistor  102 , BVdss is source-to-drain breakdown voltage of the transistor  102 , Vth is threshold voltage of the transistor  102 , Vgs is a voltage difference between the gate and the source of the transistor  102  illustrated by a solid line, and Vgd is a voltage difference between the gate and the source of the transistor  102  illustrated by a dashed line. Voltage having variable amplitude relative to the DC voltage difference is superimposed on the DC voltage difference. 
         [0006]      FIG. 2  illustrates an ideal condition where capacitance of the first parasitic capacitor Cgd is equal to capacitance of the second parasitic capacitor Cgs when the RF switch  100  is turned off. Thus impedance between the gate and the source of the transistor  102  is equal to impedance between the gate and the drain of the transistor  102  and voltage amplitude of an RF voltage signal across the source and the drain of the transistor  102  is distributed evenly to Vgs and Vgd. That is, voltage amplitude of Vgs at point A of  FIG. 2  is equal to that of Vgd at point B of  FIG. 2 . For example, supposing −VR_DC is −3V and voltage amplitude between the source and the drain of the transistor  102  is ±3V, if the voltage amplitude between the source and the drain of the transistor  102  is evenly distributed to Vgs and Vgd, the voltage amplitude of Vgs will be ±1.5V and the voltage amplitude Vgd will also be ±1.5V. Besides, a phase difference of 180 degrees exists between Vgs and Vgd. Thus the voltage of Vgs is −1.5V and the voltage of Vgd is −4.5V at point A of  FIG. 2 , and the voltage of Vgs is −4.5V and the voltage of Vgd is −1.5V at point B of  FIG. 2 . As long as the voltage amplitudes of both Vgs and Vgd are smaller than Vth or BVdss, the transistor  102  remains turned off. 
         [0007]    However in the real world the capacitance of the first parasitic capacitor Cgd is related to bias voltage between the gate and the drain of the transistor  102  and the capacitance of the second parasitic capacitor Cgs is related to bias voltage between the gate and the source of the transistor  102 . For example, the bias voltage between the gate and the drain of the transistor  102  is −4.5V and the bias voltage between the gate and the source of the transistor  102  is −1.5V at point A of  FIG. 2 , thus the capacitance of the first parasitic capacitor Cgd is different from the capacitance of the second parasitic capacitor Cgs. In addition, the voltage amplitude between the source and the drain of the transistor  102  is distributed to Vgd and Vgs inversely proportional to the capacitance of the first parasitic capacitor Cgd and the capacitance of the second parasitic capacitor Cgs respectively. As a result, the voltage amplitude between the source and the drain of the transistor  102  is distributed according to a capacitance ratio of Cgd to Cgs, unlike in the ideal condition. If the capacitance ratio of Cgd to Cgs is too big or too small, the voltage amplitude of either Vgs or Vgd may be bigger than Vth or BVdss, which may cause the transistor  102  to turn on falsely. 
         [0008]    The third parasitic capacitor Cdb and the fourth parasitic capacitor Csb apply the same aforementioned principles. Under ideal conditions, capacitance of the third parasitic capacitor Cdb is equal to capacitance of the fourth parasitic capacitor Csb of the transistor  102 , thus impedance between the well and the source of the transistor  102  is equal to impedance between the well and the drain of the transistor  102  and the voltage amplitude of the RF voltage signal is distributed evenly to Vdb and Vsb, where Vdb is a voltage difference between the well and the drain of the transistor  102  and Vsb is a voltage difference between the well and the source of the transistor  102 . However in the real world the capacitance of the third parasitic capacitor Cdb is different from the capacitance of the fourth parasitic capacitor Csb, thus the voltage amplitude of the RF voltage signal is distributed unevenly to Vdb and Vsb. If the voltage amplitude distributed to either Vdb or Vsb is bigger than Vth or BVdss, the transistor  102  will also be turned on falsely. 
       SUMMARY OF THE INVENTION 
       [0009]    An embodiment of the present invention discloses an RF switch. The RF switch comprises a transistor, a first compensation capacitor, and a second compensation capacitor. The first compensation capacitor is coupled between a control node and a first node of the transistor, and the second compensation capacitor is coupled between the control node and a second node of the transistor. Capacitance of the first compensation capacitor is substantially equal to capacitance of the second compensation capacitor. 
         [0010]    Another embodiment of the present invention discloses an RF switch system. The RF switch system comprises a plurality of transistors, a first compensation capacitor, and a second compensation capacitor. The first compensation capacitor is coupled between a control node of a transistor of the plurality of transistors and a first node of the transistor. The second compensation capacitor is coupled between the control node and a second node of the transistor. Capacitance of the first compensation capacitor is substantially equal to capacitance of the second compensation capacitor. 
         [0011]    Another embodiment of the present invention discloses an RF switch system. The RF switch system comprises at least one transistors, a first compensation capacitor, and a second compensation capacitor. The first compensation capacitor is coupled between a well and a first node of the at least one transistor. The second compensation capacitor is coupled between the well and a second node of the at least one transistor. Capacitance of the first compensation capacitor is substantially equal to capacitance of the second compensation capacitor. 
         [0012]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a diagram illustrating a prior art RF switch. 
           [0014]      FIG. 2  is a timing diagram illustrating voltage signals on the prior art RF switch when the RF switch is turned off. 
           [0015]      FIG. 3  is a diagram illustrating an RF switch according to a first embodiment of the present invention. 
           [0016]      FIG. 4A  and  FIG. 4B  are diagrams illustrating an RF switch according to a second embodiment of the present invention. 
           [0017]      FIG. 5  is a diagram illustrating an RF switch according to a third embodiment of the present invention. 
           [0018]      FIG. 6A  and  FIG. 6B  are diagrams illustrating an RF switch according to a fourth embodiment of the present invention. 
           [0019]      FIG. 7  is a diagram illustrating an RF switch according to a fifth embodiment of the present invention. 
           [0020]      FIG. 8  is a diagram illustrating an RF switch according to a sixth embodiment of the present invention. 
           [0021]      FIG. 9  is a diagram illustrating an RF device according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Please refer to  FIG. 3  that is a diagram illustrating an RF switch  300  according to a first embodiment of the present invention. The RF switch  300  includes an NMOS (N-type metal-oxide-semiconductor) transistor  302 , a first compensation capacitor C1, and a second compensation capacitor C2. The first compensation capacitor C1 is coupled between a gate and a drain of the NMOS transistor  302 , and the second compensation capacitor C2 is coupled between the gate and a source of the NMOS transistor  302 . Capacitance of the first compensation capacitor C1 is substantially equal to capacitance of the second compensation capacitor C2. The first compensation capacitor C1 and the second compensation capacitor C2 may be MIM (metal-insulator-metal) capacitors suitable for radio frequency usage. Not only a first parasitic capacitor Cgd but also the first compensation capacitor C1 is coupled between the gate and the drain of the NMOS transistor  302 , and not only a second parasitic capacitor Cgs but also the second compensation capacitor C2 is coupled between the gate and the source of the NMOS transistor  302 . 
         [0023]    When the RF switch  300  is turned off, capacitance of the first parasitic capacitor Cgd is different from that of the second parasitic capacitor Cgs. By paralleling the first compensation capacitor C1 to the first parasitic capacitor Cgd and paralleling the second compensation capacitor C2, of which the capacitance is substantially equal to the capacitance the first compensation capacitor C1, to the second parasitic capacitor Cgs, capacitance of an equivalent capacitor (Cgd+C1) between the gate and the drain of the NMOS transistor  302  and capacitance of an equivalent capacitor (Cgs+C2) between the gate and the source of the NMOS transistor  302  can be adjusted to predetermined ranges respectively so as to better distribute voltage amplitude between the drain and the source to Vgd and Vgs and keep voltage amplitudes of both Vgs and Vgd smaller than Vth or BVdss, in order that the NMOS transistor  302  remains turned off for ensuring that the RF switch  300  is in off state. 
         [0024]    For example, supposing the capacitance of the first parasitic capacitor Cgd is 0.5 pF, the capacitance of the second parasitic capacitor Cgs is 0.1 pF, and a capacitance ratio of Cgd to Cgs is 0.5 pF/0.1 pF=5:1. Thus the voltage amplitude ratio of Vgd to Vgs is 1:5. If the first compensation capacitor C1 and the second compensation capacitor C2 both having the capacitance of 0.1 pF are respectively coupled in parallel to the first parasitic capacitor Cgd and the second parasitic capacitor Cgs, the capacitance ratio of the equivalent capacitor between the gate and the drain to the equivalent capacitor between the gate and the source becomes (0.5+0.1)pF/(0.1+0.1)pF=3:1, thus the voltage amplitude ratio of Vgd to Vgs becomes 1:3, which is smaller than 1:5. In so doing, it is easier to adjust the voltage amplitudes of Vgd and Vgs to be within predetermined ranges respectively, thereby preventing the NMOS transistor  302  from being turned on falsely. 
         [0025]    Please refer to  FIG. 4A  and  FIG. 4B .  FIG. 4A  and  FIG. 4B  are diagrams illustrating an RF switch  400  according to a second embodiment of the present invention. The RF switch  400  further includes a third compensation capacitor C3, and a fourth compensation capacitor C4. The third compensation capacitor C3 is coupled between a well and the drain of the NMOS transistor  302 , and the fourth compensation capacitor C4 is coupled between the well and the source of the NMOS transistor  302 . Capacitance of the third compensation capacitor C3 is substantially equal to capacitance of the fourth compensation capacitor C4. The third compensation capacitor C3 and the fourth compensation capacitor C4 may be MIM capacitors suitable for radio frequency usage. Besides, a third parasitic capacitor Cdb exists between the well and the drain of the NMOS transistor  302  and a fourth parasitic capacitor Csb exists between the well and the source of the NMOS transistor  302 . Thus, not only the third parasitic capacitor Cdb but also the third compensation capacitor C3 is coupled between the well and the drain of the NMOS transistor  302 , and not only the fourth parasitic capacitor Csb but also the fourth compensation capacitor C4 is coupled between the well and the source of the NMOS transistor  302 . 
         [0026]    When the RF switch  400  is turned off, capacitance of the third parasitic capacitor Cdb is different from that of the fourth parasitic capacitor Csb. By paralleling the third compensation capacitor C3 to the third parasitic capacitor Cdb and paralleling the fourth compensation capacitor C4, of which the capacitance is substantially equal to the capacitance the third compensation capacitor C3, to the fourth parasitic capacitor Csb, capacitance of an equivalent capacitor (Cdb+C3) between the well and the drain of the NMOS transistor  302  and capacitance of an equivalent capacitor (Csb+C4) between the well and the source of the NMOS transistor  302  can be adjusted to a predetermined range respectively so as to better distribute the voltage amplitude between the drain and the source to Vdb and Vsb and keep voltage amplitudes of both Vsb and Vdb smaller than Vth or BVdss, in order that the NMOS transistor  302  remains turned off for ensuring that the RF switch  400  is in off state. 
         [0027]    For example, supposing the capacitance of the third parasitic capacitor Cdb is 0.5 pF, the capacitance of the fourth parasitic capacitor Cgs is 0.1 pF, and a capacitance ratio of Cdb to Csb is 0.5 pF/0.1 pF=5:1. Thus the voltage amplitude ratio of Vdb to Vsb is 1:5. If the third compensation capacitor C3 and the fourth compensation capacitor C4 both having the capacitance of 0.1 pF are respectively coupled in parallel to the third parasitic capacitor Cdb and the fourth parasitic capacitor Csb, the capacitance ratio of the equivalent capacitor between the well and the drain to the equivalent capacitor between the well and the source becomes (0.5+0.1)pF/(0.1+0.1)pF=3:1, thus the voltage amplitude ratio of Vdb to Vsb becomes 1:3, which is smaller than 1:5. In so doing, it is easier to adjust the voltage amplitudes of Vdb and Vsb to be within predetermined ranges respectively, thereby preventing the NMOS transistor  302  from being turned on falsely. 
         [0028]    In the aforementioned second embodiment, the first compensation capacitor C1, the second compensation capacitor C2, the third compensation capacitor C3, and the fourth compensation capacitor C4 may all be coupled to the NMOS transistor  302  in order to better adjust the voltage amplitudes of Vgd, Vgs, Vdb, and Vsb. Or, as shown in  FIG. 4B , only the third compensation capacitor C3 and the fourth compensation capacitor C4 may be coupled to the NMOS transistor  302  in order to better adjust the voltage amplitudes of Vdb and Vsb, thereby keeping the voltage amplitudes of both Vsb and Vdb smaller than Vth or BVdss, so that the NMOS transistor  302  remains turned off for ensuring that the RF switch  400  is in off state. 
         [0029]    Please refer to  FIG. 5  that is a diagram illustrating an RF switch  500  according to a third embodiment of the present invention. The RF switch  500  includes a PMOS (P-type metal-oxide-semiconductor) transistor  502 , a first compensation capacitor C1, and a second compensation capacitor C2. The first compensation capacitor C1 is coupled between a gate and a drain of the PMOS transistor  502 , and the second compensation capacitor C2 is coupled between the gate and a source of the PMOS transistor  502 . Capacitance of the first compensation capacitor C1 is substantially equal to capacitance of the second compensation capacitor C2. The first compensation capacitor C1 and the second compensation capacitor C2 may be MIM capacitors suitable for radio frequency usage. Not only a first parasitic capacitor Cgd but also the first compensation capacitor C1 is coupled between the gate and the drain of the PMOS transistor  502 , and not only a second parasitic capacitor Cgs but also the second compensation capacitor C2 is coupled between the gate and the source of the PMOS transistor  502 . 
         [0030]    When the RF switch  500  is turned off, capacitance of the first parasitic capacitor Cgd is different from that of the second parasitic capacitor Cgs. By paralleling the first compensation capacitor C1 to the first parasitic capacitor Cgd and paralleling the second compensation capacitor C2, of which the capacitance is substantially equal to the capacitance the first compensation capacitor C1, to the second parasitic capacitor Cgs, capacitance of an equivalent capacitor (Cgd+C1) between the gate and the drain of the PMOS transistor  502  and capacitance of an equivalent capacitor (Cgs+C2) between the gate and the source of the PMOS transistor  502  can be adjusted to a predetermined range respectively so as to better distribute voltage amplitude between the drain and the source to Vgd and Vgs and keep voltage amplitudes of both Vgs and Vgd smaller than Vth or BVdss, in order that the PMOS transistor  502  remains turned off for ensuring that the RF switch  500  is in off state. 
         [0031]    Please refer to  FIG. 6A  and  FIG. 6B .  FIG. 6A  and  FIG. 6B  are diagrams illustrating an RF switch  600  according to a fourth embodiment of the present invention. The RF switch  600  further includes a third compensation capacitor C3, and a fourth compensation capacitor C4. The third compensation capacitor C3 is coupled between a well and the drain of the PMOS transistor  502 , and the fourth compensation capacitor C4 is coupled between the well and the source of the PMOS transistor  502 . Capacitance of the third compensation capacitor C3 is substantially equal to capacitance of the fourth compensation capacitor C4. The third compensation capacitor C3 and the fourth compensation capacitor C4 may be MIM capacitors suitable for radio frequency usage. Besides, a third parasitic capacitor Cdb exists between the well and the drain of the PMOS transistor  502  and a fourth parasitic capacitor Csb exists between the well and the source of the PMOS transistor  502 . Thus, not only the third parasitic capacitor Cdb but also the third compensation capacitor C3 is coupled between the well and the drain of the PMOS transistor  502 , and not only the fourth parasitic capacitor Csb but also the fourth compensation capacitor C4 is coupled between the well and the source of the PMOS transistor  502 . 
         [0032]    When the RF switch  600  is turned off, capacitance of the third parasitic capacitor Cdb is different from that of the fourth parasitic capacitor Csb. By paralleling the third compensation capacitor C3 to the third parasitic capacitor Cdb and paralleling the fourth compensation capacitor C4, of which the capacitance is substantially equal to the capacitance the third compensation capacitor C3, to the fourth parasitic capacitor Csb, capacitance of an equivalent capacitor (Cdb+C3) between the well and the drain of the PMOS transistor  502  and capacitance of an equivalent capacitor (Csb+C4) between the well and the source of the PMOS transistor  502  can be adjusted to a predetermined range respectively so as to better distribute the voltage amplitude between the drain and the source to Vdb and Vsb and keep voltage amplitudes of both Vsb and Vdb smaller than Vth or BVdss, in order that the PMOS transistor  502  remains turned off for ensuring that the RF switch  600  is in off state. 
         [0033]    In the aforementioned fourth embodiment, the first compensation capacitor C1, the second compensation capacitor C2, the third compensation capacitor C3, and the fourth compensation capacitor C4 may all be coupled to the PMOS transistor  502  in order to better adjust the voltage amplitudes of Vgd, Vgs, Vdb, and Vsb. Or, as shown in  FIG. 6B , only the third compensation capacitor C3 and the fourth compensation capacitor C4 may be coupled to the NMOS transistor  302  in order to better adjust the voltage amplitudes of Vdb and Vsb, thereby keeping the voltage amplitudes of both Vsb and Vdb smaller than Vth or BVdss, so that the PMOS transistor  502  remains turned off for ensuring that the RF switch  600  is in off state. 
         [0034]    Please refer to  FIG. 7  that is a diagram illustrating an RF switch  700  according to a fifth embodiment of the present invention. The RF switch  700  includes an NPN (N-type P-type N-type) BJT (bipolar junction transistor)  702 , a first compensation capacitor C1, and a second compensation capacitor C2. The first compensation capacitor C1 is coupled between a base and a collector of the BJT  702 , and the second compensation capacitor C2 is coupled between the base and an emitter of the BJT  702 . Capacitance of the first compensation capacitor C1 is substantially equal to capacitance of the second compensation capacitor C2. The first compensation capacitor C1 and the second compensation capacitor C2 may be MIM capacitors suitable for radio frequency usage. Not only a first parasitic capacitor Cbc but also the first compensation capacitor C1 is coupled between the base and the collector of the BJT  702 , and not only a second parasitic capacitor Cbe but also the second compensation capacitor C2 is coupled between the base and the emitter of the BJT  702 . 
         [0035]    When the RF switch  700  is turned off, capacitance of the first parasitic capacitor Cbc is different from that of the second parasitic capacitor Cbe. By paralleling the first compensation capacitor C1 to the first parasitic capacitor Cbc and paralleling the second compensation capacitor C2, of which the capacitance is substantially equal to the capacitance the first compensation capacitor C1, to the second parasitic capacitor Cbe, capacitance of an equivalent capacitor (Cbc+C1) between the base and the collector of the BJT  702  and capacitance of an equivalent capacitor (Cbe+C2) between the base and the emitter of the BJT  702  can be adjusted to a predetermined range respectively so as to better distribute voltage amplitude between the collector and the emitter to Vbc and Vbe, where Vbc is a voltage difference between the base and the collector of the BJT  702  and Vbe is a voltage difference between the base and the emitter of the BJT  702 , and keep the voltage amplitudes of both Vbc and Vbe within predetermined voltage amplitude ranges respectively, in order that the BJT  702  remains turned off for ensuring that the RF switch  700  is in off state. 
         [0036]    Please refer to  FIG. 8  that is a diagram illustrating an RF switch  800  according to a sixth embodiment of the present invention. The RF switch  800  includes a PNP (P-type N-type P-type) BJT (bipolar junction transistor)  802 , a first compensation capacitor C1, and a second compensation capacitor C2. The first compensation capacitor C1 is coupled between a base and a collector of the BJT  802 , and the second compensation capacitor C2 is coupled between the base and an emitter of the BJT  802 . Capacitance of the first compensation capacitor C1 is substantially equal to capacitance of the second compensation capacitor C2. The first compensation capacitor C1 and the second compensation capacitor C2 may be MIM capacitors suitable for radio frequency usage. Not only a first parasitic capacitor Cbc but also the first compensation capacitor C1 is coupled between the base and the collector of the BJT  802 , and not only a second parasitic capacitor Cbe but also the second compensation capacitor C2 is coupled between the base and the emitter of the BJT  802 . 
         [0037]    When the RF switch  800  is turned off, capacitance of the first parasitic capacitor Cbc is different from that of the second parasitic capacitor Cbe. By paralleling the first compensation capacitor C1 to the first parasitic capacitor Cbc and paralleling the second compensation capacitor C2, of which the capacitance is substantially equal to the capacitance the first compensation capacitor C1, to the second parasitic capacitor Cbe, capacitance of an equivalent capacitor (Cbc+C1) between the base and the collector of the BJT  802  and capacitance of an equivalent capacitor (Cbe+C2) between the base and the emitter of the BJT  802  can be adjusted to a predetermined range respectively so as to better distribute voltage amplitude between the collector and the emitter to Vbc and Vbe, where Vbc is a voltage difference between the base and the collector of the BJT  802  and Vbe is a voltage difference between the base and the emitter of the BJT  802 , and keep the voltage amplitudes of both Vbc and Vbe within predetermined voltage amplitude ranges respectively, in order that the BJT  802  remains turned off for ensuring that the RF switch  800  is in off state. 
         [0038]    Please refer to  FIG. 9  that is a diagram illustrating an RF device  900 . The RF switch device includes two RF switch systems  902  and  904  and an RF antenna  906 . When the RF device  900  is receiving signals, the RF switch system  902 , containing a first set of serial connected RF switches, coupled between the RF antenna  906  and a receiving end Rx is turned on for receiving the signals, whereas the RF switch system  904 , containing a second set of serial connected RF switches, coupled between the RF antenna  906  and a transmitting end Tx is turned off for stopping transmitting signals. 
         [0039]    In  FIG. 9 , the first set and the second set of serial connected RF switches of the RF switch system  902  and  904  may be any combination of RF switches selected from the RF switches  300 ,  400 ,  500 ,  600 ,  700 ,  800  in the aforementioned embodiments. Utilizing the RF switches  300 ,  400 ,  500 ,  600 ,  700 ,  800  in the RF switch system  902  and  904  not only improves the capacitance ratio of the equivalent capacitors and the voltage amplitude distribution of each RF switch but also improves capacitance ratio of equivalent capacitors and voltage amplitude distribution among the serial connected RF switches. Due to voltage amplitude distributed to each RF switch in the RF switch system  902  being related to a capacitance ratio of a parasitic capacitor Cprx between the receiving end Rx and a ground to the equivalent capacitors of each RF switch, and the voltage amplitude distributed to each RF switch in the RF switch system  904  is related to a capacitance ratio of a parasitic capacitor Cptx between the transmitting end Tx and the ground to the equivalent capacitors of each RF switch, connecting the compensation capacitors to each RF switch as in aforementioned embodiments may increase the equivalent capacitors of each RF switch for decreasing the capacitance ratio of the parasitic capacitor Cprx to the equivalent capacitors of the RF switch and the capacitance ratio of the parasitic capacitor Cptx to the equivalent capacitors of the RF switch such that the voltage amplitude of the RF switch system  902  or  904  is more evenly distributed to each RF switch for ensuring that each RF switch and the RF switch systems are in off states. 
         [0040]    To sum up, adjusting the capacitance of equivalent capacitors by paralleling the compensation capacitors to the RF switch can improve the voltage amplitude distribution of the RF switch and further improve the voltage amplitude distribution of the RF switch system, so as to ensure that the RF switch remains turned off and preventing the RF switch from being turned on falsely, and thereby increasing design efficiency and accuracy. 
         [0041]    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.