FIELD OF THE INVENTION 
       [0001]    The invention relates generally to antenna switches, and more particularly, to CMOS (complementary metal oxide semiconductor) antenna switches. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the past decade, the wireless communication industry has experienced explosive growth, which has in turn accelerated the development of integrated circuit (IC) industry. In particular, in the IC industry, many mobile application systems like low noise amplifiers (LNAs), mixers, and voltage-controlled oscillators (VCOs) have been integrated into CMOS technology. Two significant mobile application components—power amplifiers (PAs) and radio frequency (RF) switches—have not yet been commercially integrated into CMOS technology. 
         [0003]    However, IC industry research is quickly moving towards power amplifier integrated into CMOS technology. For example, current research indicates that a CMOS power amplifier may be feasible and be able to provide a significant amount of power, perhaps up to 2 W, for mobile communications. Accordingly, when the power amplifier becomes integrated into CMOS technology, there will be a need for an RF switch integrated into CMOS technology. 
         [0004]    However, current CMOS technology presents a variety of difficulties for its application to RF switches. In particular, CMOS material characteristics, including lossy substrates due to low mobility of electrons and low breakdown voltages due to p-n junction, hot carrier effects, have prevented CMOS technology from being used for RF switches that require multi-band operation, high power levels, and/or integration with other devices and circuits. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    Embodiments of the invention may provide for CMOS RF switches, which may be referred to as a CMOS SPDT switch. According to an embodiment of the invention, the CMOS RF switch may be fabricated using a standard 0.18 um process, although other processes may be utilized without departing from the embodiments of the invention. In order to provide high-power handling capability in a multi-band operation (e.g., about 900 MHz, 1.9 GHz and 2.1 GHz) of the CMOS RF switch, a multi-stacked transistor with substrate body switching may be applied to the receiver switch. According to an embodiment of the invention, the CMOS RF switch may provide higher power blocking capability and lower leakage current toward the receiver switch at the transmission (Tx) mode as well as low insertion loss at the reception (Rx) mode at multi-band (e.g., 900 MHz, 1.9 GHz and 2.1 GHz). 
         [0006]    According to an example embodiment of the invention, there is a CMOS antenna switch. The CMOS antenna switch may include an antenna operative at a plurality of radio frequency (RF) bands, a transmit switch in communication with the antenna, and a receiver switch in communication with the antenna, where the receiver switch comprises a plurality of transistors. The CMOS antenna switch may also include a first external component provided for a first transistor of the plurality of transistors, where the first transistor includes a first source and a first gate, and wherein the first external component connects the first source and the first gate, and a second external component provided for a second transistor of the plurality of transistors, where the second transistor includes a second gate, a second drain, and a second body substrate, where the second external component connects the second gate and the second drain, and where the second body substrate is selectively connectable between a resistance and ground. 
         [0007]    According to another example embodiment of the invention, there is a method for a CMOS antenna switch. The method may include providing an antenna operative at a plurality of radio frequency (RF) bands, electrically connecting a transmit switch and a receiver switch to the antenna, where the receiver switch comprises a plurality transistors, and providing a first external component for a first transistor of the plurality of transistors, where the first transistor includes a first source and a first gate, and wherein the first external component connects the first source and the first gate. The method may also include providing a second external component for a second transistor of the plurality of transistors, where the second transistor includes a second gate, a second drain, and a second body substrate, where the second external component connects the second gate and the second drain, and where the second body substrate is selectively connectable between a resistance and ground. 
         [0008]    According to yet another embodiment of the invention, there is a CMOS antenna switch. The CMOS antenna switch may include an antenna operative at a plurality of radio frequency (RF) bands, a transmit switch in communication with the antenna, and a receiver switch in communication with the antenna, where the receiver switch includes a plurality of transistors, including a first transistor having a first source and a first gate, and a second transistor having a second gate, a second drain, and a second body substrate. The CMOS antenna switch may also include means for electrically connecting the first source and the first gate, means for electrically connecting the second gate and the second drain, and means for selectively connecting the second body substrate between a resistance and ground. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0009]    Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
           [0010]      FIGS. 1A ,  1 B and  1 C illustrate simplified example operations of a receiver switch utilizing an example body switching technique in accordance with an example embodiment of the invention. 
           [0011]      FIG. 2A  illustrates an equivalent lumped model of a body floating transistor at an OFF state, according to an example embodiment of the invention. 
           [0012]      FIG. 2B  illustrates an equivalent lumped model of a body grounded transistor at OFF state, according to an example embodiment of the invention. 
           [0013]      FIG. 3  illustrates an equivalent lumped model of body floating transistor at ON state, according to an example embodiment of the invention. 
           [0014]      FIGS. 4A ,  4 B and  4 C illustrate simplified example operations of a receiver switch in accordance with example embodiments of the invention. 
           [0015]      FIG. 5  illustrates an equivalent lumped model of a multi-stack structure of a receiver switch utilizing a body switching technique and external components such as capacitors, according to an example embodiment of the invention. 
           [0016]      FIG. 6  illustrates a turn-on mechanism of a switch in the OFF state when a high-power signal is applied, according to an example embodiment of the invention. 
           [0017]      FIG. 7  illustrates an example of receiver switch simulation results in terms of capacitance of OFF state device as a function of input power level, according to an example embodiment of the invention. 
           [0018]      FIG. 8A  illustrates an example of receiver switch simulation results in terms of impedance of OFF state device, according to an example embodiment of the invention. 
           [0019]      FIG. 8B  illustrates an example of receiver switch simulation results in terms of impedance of OFF state device, according to an example embodiment of the invention. 
           [0020]      FIG. 9  illustrates an example of receiver switch simulation results in terms of leakage current toward receiver, according to an example embodiment of the invention. 
           [0021]      FIG. 10  illustrates an example of transmit switch simulation results in terms of power handling capability, according to an example embodiment of the invention. 
           [0022]      FIG. 11  illustrates an example of transmit switch simulation results in terms of second harmonic performance, according to an example embodiment of the invention. 
           [0023]      FIG. 12  illustrates an example of transmit switch simulation results in terms of third harmonic performance, according to an example embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Embodiments of the invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
         [0025]    Embodiments of the invention may provide for CMOS RF antenna switches, which may also be referred to as SPDT CMOS switches. The CMOS RF antenna switches in accordance with embodiments of the invention may provide for one or more of multi-band operation, high power handling, and integration with other devices and circuits. Generally, the CMOS RF antenna switch may include a receiver switch and a transmit switch. The receiver switch may utilize one or more switching substrate bodies and external components such as capacitors between drain-gate and source-gate in a multi-stack structure, which will be described in further detail below. In addition, the transmit switch may utilize a substrate body tuning technique, as will also be described in further detail below. 
         [0026]    I. A First Embodiment of CMOS RF Antenna Switch 
         [0027]    A CMOS RF antenna switch in accordance with an embodiment of the invention will be now be described with reference to  FIGS. 1-3 . It will be appreciated that while a particular embodiment of the CMOS RF antenna switch is illustrated in  FIGS. 1-3 , other variations of the illustrated CMOS RF antenna switch are available without departing from an embodiment of the invention. 
         [0028]      FIG. 1A  illustrates a simplified CMOS RF antenna switch and its operation in accordance with an example embodiment of the invention. The CMOS RF antenna switch may include a transmit switch  102  and a receiver switch  104 , in accordance with an example embodiment of the invention. Additionally, CMOS RF antenna switch may include an antenna  100  that is in communication with at least one of the transmit switch  102  and the receiver switch  104 . According to an example embodiment of the invention, the antenna  100  may be a single multi-mode (e.g., RX and TX), multi-band antenna, although a plurality of distinct antennas may be utilized according to other embodiments of the invention. The receiver switch  104  may be comprised of cascaded or stacked transistors  108 ,  110 ,  112 , and  106 , which may be Complementary Metal Oxide Semiconductor (CMOS) transistors, according to an example embodiment of the invention. The transistor  108  may include a source  108   a , a gate  108   b , a drain  108   c , and a body substrate  108   d . The transistor  110  may include a source  110   a , a gate  110   b , a drain  110   c , and a body substrate  110   d . The transistor  112  may include a source  112   a , a gate  112   b , a drain  112   c , and a body substrate  112   d . The transistor  106 , may include a source  106   a , a gate  106   b , a drain  106   c , and a body substrate (not shown). 
         [0029]    The transistor  108  may have its drain  108   c  connected to the source  110   a  of transistor  110 . In addition, the transistor  110  may have its drain  110   c  connected to the source of transistor  112   a . The drain  112   c  of transistor  104  may be connected to the receive (RX) block to processes received signals from the antenna  100 . Additionally, the body substrate  112   a  of the transistor  112  may be connected to the source  106   a  of the transistor  106 . The drain  106   c  of the transistor  106  may be connected to ground. As will be described in further detail, at least one transistor  106 , which may operate as a substrate body switch for transistor  112 , may be provided at the substrate body  112   d  in accordance with an example body switching technique. In particular, the at least one transistor  106  may be switched to an ON state or an OFF state, depending on whether depending on whether a respective transmit (Tx) mode or receive (Rx) mode is in operation. As will be described in further detail below in accordance with an example embodiment of the invention, the receiver switch  104  of  FIG. 1A  may yield different equivalent circuits depending on whether the receiver switch  104  is in an OFF state, as illustrated in  FIG. 1B , or an ON state, as illustrated in  FIG. 1C . 
         [0030]    A. Transmit Mode 
         [0031]      FIG. 1B  illustrates an equivalent circuit of the receiver switch  104  in an OFF (e.g., disabled, block, etc.) state, according to an example embodiment of the invention. In  FIG. 1B , the receiver switch  104  may be placed in the OFF state in order to provide isolation from the transmit switch  102 . With the receiver switch  104  in the OFF state, a transmit signal may be provided from a transmit (Tx) block to the antenna  100 . As shown in  FIG. 1B , when the receiver switch  104  is in an OFF state, the stacked transistors  108 ,  110 ,  112  may then be placed in an OFF state (e.g., opened), thereby providing a higher impedance. The stacked transistor  106  may placed in an ON state  114  (e.g., closed), thereby shorting the substrate body  112   d  of transistor  112  to ground, and reducing the signal paths for leakage current to travel from source  112   a  to drain  112   c.    
         [0032]    In the configuration of  FIG. 1B , the power of the transmit (Tx) signal may be maximized (and maximizing the power handling capability of the Tx block). The power handling capability of the transmit switch  102  may be determined by controlling leakage current directed towards the OFF-state receiver switch  104  as well as the source-to-drain breakdown voltage of cascaded switches  108 ,  110 , and  112  of the receiver switch  104 . Thus, the maximum transmit power of the transmit switch  102  may be dependent upon the characteristics of the receiver switch  104 . 
         [0033]    It will be appreciated that in order to increase the power handling capability of the Tx switch  102 , the number of multi-stacked transistors  108 ,  110 ,  112  may be increased to reduce the breakdown burden of each transistor  108 ,  110 ,  112 . For example, more than three transistors  108 ,  110 , and  112  may be cascaded, according to another embodiment of the invention. Furthermore, it will be appreciated that the last transistor  112  from the antenna  112  can control leakage current at the receiver switch  104 . If the leakage current toward OFF-state switches  108 ,  110 , and  112  in the Rx path is minimized, then maximum power may be delivered from the Tx block to the antenna  100 . As described above, the body switching transistor  106  that is connected between ground and the body substrate  112   d  of transistor  112  may be used to control leakage current at the receiver switch  104 . More particularly, by placing the body switching transistor  106  in the ON state  114 , the substrate body  112   d  of the last transistor  112  from the antenna  100  to the Rx block can be grounded, thereby reducing the signal paths for leakage current to travel from source  112   a  to drain  112   c.    
         [0034]    Still referring to  FIG. 1B , when the receiver switch  104  is in the OFF position, the stacked transistors  108 ,  110  may be body-floating transistors while stacked transistor  112  may be a body-grounded transistor.  FIG. 2A  illustrates an equivalent lumped model of a body floating transistor at an OFF state  200  such as transistors  108 ,  110  in  FIG. 1B , according to an example embodiment of the invention.  FIG. 2B  illustrates an equivalent lumped model of a body grounded transistor at an OFF state  202  such as transistor  112  in  FIG. 1B , according to an example embodiment of the invention. The equivalent models in  FIGS. 2A and 2B  include capacitors  212 ,  214 ,  216 ,  218  as well as p-n junction diodes  204 ,  206 , according to an example embodiment of the invention. 
         [0035]    When a voltage swing at the antenna  100  is received by the receiver switch  104 , the voltage swing may be divided among stacked transistors  108 ,  110 , and  112 . Accordingly, the last transistor  112  may only experience only one third of the full voltage swing at the antenna, thereby reducing the possibility of a source-to-drain breakdown voltage occurring for transistor  112 . It will be appreciated, however, that the voltage swing at the last transistor  112  may be different, and perhaps smaller, if additional preceding transistors are provided according to other embodiments of the invention to reduce the burden of the stacked transistors  108 ,  110 ,  112 . 
         [0036]    The transistors  108 ,  110  may be body floating transistors, as illustrated in  FIG. 2A . However, in order to reduce the leakage current towards the Rx block and maximize the power handling of the Tx block to the antenna  100 , the body switching transistor  106  can be put in the ON position  114  to connect the substrate body  112   d  to ground. Accordingly, the transistor  112  may be a body grounded transistor, as illustrated in  FIG. 2B , which reduces the signal paths for leakage current to travel from source  112   a  to drain  112   c.    
         [0037]    When a negative voltage swing is applied to the receiver switch  104 , the p-n junction diodes  204 ,  206  of the transistor  112  may turn on so that leakage current may occur by the current passing through the p-n junction diodes  204 ,  206 . An issue with the p-n junction diode  204 ,  206  turning on may be the possible clipping of the negative voltage swing so that power handling capability of the Tx block to the antenna  100  can be limited. However, this leakage current generated by channel formation of the device  112  in OFF state is prevented because the voltage level at  112   a  is fixed by the turning on voltage of the p-n junction diode  204 . Indeed, the multi-stacked transistors  108 ,  110 , and  112  at OFF-state can divide the voltage swing at antenna port so that the last OFF-state transistor  112 , and thus, p-n junction diodes  204 ,  206 , may experience only one third of voltage swing at antenna  100 . Thus, the overall voltage swing at antenna port may not be sufficient to turn the p-n junction diodes  204 ,  206  on at the last transistor  112 . 
         [0038]    B. Receive Mode 
         [0039]      FIG. 1C  illustrates an equivalent circuit of the receiver switch  104  in an ON (e.g., enable, receive, etc.) state, according to an example embodiment of the invention. In  FIG. 1C , the receiver switch  104  may be placed in the ON position in order for the receive (RX) block to receive a signal from the antenna  100 . With the receiver switch  104  in the ON state, the transmit switch  102  may be placed in the OFF (e.g., disabled, block) state to isolate the transmit switch  102  from the receiver switch  104 . As shown in  FIG. 1C , when the receiver switch  104  is in an ON state, the stacked transistor  106  may be placed in an OFF state  116 , thereby providing an equivalent resistor between the body substrate  112   d  of transistor  112  and ground (i.e., body floating). In this way, the insertion loss at the receive (Rx) path from the antenna  100  to the RX block may be minimized. 
         [0040]      FIG. 3  illustrates an equivalent lumped model of body floating transistor at ON state  300 , according to an example embodiment of the invention. As described above, the transistor  106  may be provided in an OFF position  116  to provide a body floating transistor, as illustrated by the equivalent lumped model of  FIG. 3 . In  FIG. 3 , as the size of the transistor  112  increases, the parasitic capacitors  304 ,  306 ,  308 ,  310  may provide another signal path at the ON  300  state. More specifically, the ON state transistor of  FIG. 3  may have an ON-resistor  302 , a gate-drain capacitor  308  to gate-source capacitor  310 , and a drain-body capacitor  304 , and body-source capacitor  306  as signal paths. If the body substrate were grounded, then one of these signal paths through capacitors  304 ,  306  may be lost, thereby increasing the insertion loss. Accordingly, when the receiver switch  104  is in the ON state, the last transistor  112  need to be in body floating state (e.g., with transistor  106  in the ON state  116 ) to ensure minimized insertion loss. 
         [0041]    II. A Second Embodiment of a CMOS RF Antenna Switch 
         [0042]    An alternative embodiment of a CMOS RF antenna switch with additional power handling capability will now be discussed with reference to  FIGS. 4A-6 . Generally, the CMOS RF antenna switch with improved power handling capability may include external components such as capacitors for improving the power handling of the CMOS antenna switch. 
         [0043]    Referring to  FIG. 4A , the CMOS RF antenna switch may include a transmit switch  402  and a receiver switch  404 . Further, an antenna  400  may be provided that is in communication with at least one of the transmit switch  402  and the receiver switch  404 . The receiver switch  404  may include stacked transistors  408 ,  410 ,  412 , and  406 , which may be complementary metal oxide semiconductor (CMOS) transistors, according to an example embodiment of the invention. The receiver switch  404  may further include capacitors  418 ,  420 . The transistor  408  may include a source  408   a , a gate  408   b , a drain  408   c , and a body substrate  408   d . The transistor  410  may include a source  410   a , a gate  410   b , a drain  410   c , and a body substrate  410   d . The transistor  412  may include a source  412   a , a gate  412   b , a drain  412   c , and a body substrate  412   d . The transistor  406  may include a source  406   a , a gate  406   b , a drain  406   c , and a body substrate (not shown). 
         [0044]    As shown in  FIG. 4A , a external component such as a capacitor  418  may be provided between the source  408   a  and the gate  408   b  of the transistor  408 . Likewise, the source  408   a  (or drain  408   c ) of the transistor  408  may be connected to its body substrate  408   d . The drain  408   c  of transistor  408  may be connected to the source  410   a  of transistor  410 . In addition, the source  410   a  (or drain  410   c ) of transistor  410  may be connected to its body substrate  410   d . The drain  410   c  of transistor  410  may be connected to the source  412   a  of transistor  412 . Another external component such as a capacitor  420  may be positioned between the gate  412   b  and the drain  412   c  of transistor  412 . Further, the body substrate  412   a  of the transistor  412  may be connected to the source  406   a  of the transistor  406 . The drain  406   c  of the transistor  406  may be connected to ground. As similarly described above, the transistor  406  may operate as a substrate body switch for transistor  412 . 
         [0045]    A. Transmit Mode 
         [0046]      FIG. 4B  illustrates an equivalent circuit of the receiver switch  404  in an OFF (e.g., disabled, block, etc) state, according to an example embodiment. In  FIG. 1B , the receiver switch  404  may be placed in the OFF state in order to provide isolation from the transmit switch  402 . With the receiver switch  404  in the OFF state, a transmit signal may be provided from a transmit (Tx) block to the antenna  400 . As shown in  FIG. 4B , when the receiver switch  404  is in an OFF state, the stacked transistors  408 ,  410 ,  412  may then be placed in an OFF state (e.g., opened), thereby providing a higher impedance. The stacked transistor  406  may placed in an ON state  414  (e.g., closed), thereby shorting the substrate body  412   d  of transistor  412  to ground, and reducing the signal paths for leakage current to travel from source  412   a  to drain  412   c.    
         [0047]    The power handling capability of the transmit switch transit switch  402  may be dependent upon the performance of the receiver switch  404  in the OFF state. The allowance of a large voltage swing at the antenna  400  port, maintenance of high impedance of OFF-state receiver switch  404 , and disabling the substrate junction diodes in the receiver switch  404  for negative voltage swings may provide for high power handling capability of the CMOS antenna switch. 
         [0048]    According to an example embodiment of the invention, large voltages swings at the antenna  400  port may be partially resolved using stacked transistors  408 ,  410 ,  412 , as provided for receiver switch  404 . Indeed, as similarly described above, the large voltage swings may be divided among the stacked transistors  408 ,  410 ,  412 . It will be appreciated that more than three stacked transistors may be utilized without departing from embodiments of the invention. Likewise, the impedance of the OFF-state receiver switch  404  may be improved by using the body switching technique described above. More specifically, with the body switching technique, the transistor  406  may be provided in an ON state, thereby connecting the body substrate  412   d  of transistor  412  to ground, and reducing the signal paths for leakage current to travel from source  112   a  to drain  112   c.    
         [0049]    With respect to negative voltage swings experienced at the negative port, the CMOS RF antenna switch may utilize external components such as capacitors  418 ,  420  to reduce leakage current by preventing channel formation of a transistor (e.g., transistors  408 ,  412 ) in the OFF state. The use of these external components such as capacitors  418 ,  420  to reduce leakage currents in the OFF-state receiver switch  404  will now be discussed in further detail with respect to  FIGS. 5 and 6 . 
         [0050]      FIG. 5  illustrates an equivalent lumped model of a multi-stack structure of the receiver switch  404  of  FIG. 4B , according to an example embodiment of the invention. In  FIG. 5 , the equivalent lumped model is provided for transistors  408 ,  410 ,  412  being in an OFF state with transistor  406  being in an ON state. As shown in  FIG. 5 , the equivalent lumped model for transistor  408   a  includes capacitors  502   a ,  504   a ,  506   a , and p-n junction diode  508   a . The equivalent lumped model for transistor  410  includes capacitors  502   b ,  504   b ,  506   b , and p-n junction diode  508   b . Likewise, the equivalent lumped model for transistor  412  includes capacitors  502   c ,  504   c ,  506   c ,  510 , and p-n junction diodes  508 ,  512 . 
         [0051]    It should be appreciated that the capacitances for capacitors  502   a - c ,  504   a - c , and  506   a - c  for the OFF-state transistors  408 ,  410 ,  412  may vary depending on the applied voltage swing, according to an example embodiment of the invention. Further, without the use of the external components such as capacitors  418 ,  412 , it is possible that the OFF-state transistors  408 ,  410 ,  412  may not actually stay in the OFF state for all voltage swings at the antenna  400  port. Instead, when a high power signal is delivered from the Tx switch  402  to the antenna  400  port, the OFF-state switches transistors  408 ,  410 ,  412  may experience a large voltage swing at the antenna  400  port. In this situation, the OFF-state transistors  408 ,  410 ,  412  may turn ON, thereby causing undesirable leakage current may start to flow in the receiver switch  404 . This undesirable leakage current may deteriorate the performance of the transmit signal as well as destroy the LNAs and Mixers in the receiver (Rx) block. However, as will be described in further detail below with respect to  FIG. 6 , the use of the external components such as capacitors  418 ,  420  may prevent one or more of the OFF-state transistors  408 ,  410 ,  412  from turning ON. 
         [0052]      FIG. 6  illustrates an equivalent circuit on an OFF-state CMOS transistor  600  such as OFF-state transistor  408 ,  410 , according to an example embodiment of the invention. The OFF-state transistor  600  may be depicted using parasitic capacitors such as gate-drain capacitor C gd    602 , gate-source capacitor C gs    604 , body-source capacitor C bs    606  and body-drain capacitor C bd    608 . According to an embodiment of the invention, the OFF-state CMOS transistor  600  requires a zero bias  614  for the gate, drain, and source to stay in the OFF state. When a small signal  616  voltage swing is applied to the drain, the source and drain remain at about a zero bias so that the OFF-state transistor  600  does not turn on. However, if a large signal  618  voltage swing is applied to the drain, the negative cycle  620  of the large signal  618  voltage swing may result in the drain having a lower voltage potential than the gate so that a current  624  may flow from the source to the drain. 
         [0000]    During the positive cycle  622  of the large signal  618  voltage swing, the potential of the gate may be determined based upon the capacitances of the gate-drain capacitor C gd    602  and the gate-source capacitor C gs  according to 
         [0000]    
       
         
           
             
               V 
               g 
             
             = 
             
               
                 
                   V 
                   d 
                 
                  
                 
                   ( 
                   
                     
                       C 
                       gd 
                     
                     
                       
                         C 
                         gd 
                       
                       + 
                       
                         C 
                         gs 
                       
                     
                   
                   ) 
                 
               
               . 
             
           
         
       
     
         [0000]    With a voltage potential at the gate, a current  626  may flow from the drain to source. 
         [0053]    In accordance with example embodiments of the invention, external components such as one or both of external capacitors  418 ,  420  may used to prevent undesirable currents  624 ,  626  during the respective negative cycle  620  and positive cycle  622  of the voltage swings. In particular, according to an embodiment of the invention, an external component such as external capacitor  420  may be connected between gate and drain such that the potential of gate is almost same as the drain so that the OFF-state transistor  600  does not turn on during the negative cycle  620  voltage swing. Likewise, an external component such as an external capacitor  418  may be connected between gate and source such that the potential of gate is almost same as the source so that OFF-state transistor  600  does not turn on during the positive cycle of voltage swing. Accordingly, by utilizing external components such as external capacitors  418 ,  420 , the receiver switch  404  in accordance with an embodiment of the invention may resolve this conflict demand for both negative  620  and positive cycle  622  of the voltage swing in the drain from the antenna  400  port. 
         [0054]    In summary, the receiver switch  404  in the OFF-state may include stacked transistors  408 ,  410 ,  412  for dividing the voltage burden of each transistor for large voltage swings at the antenna  400  port. Additionally, the OFF-state receiver switch  404  may utilize a body switching technique  406  for stacked transistor  412  in order to maximize the OFF-state impedance and reduce the leakage currents. Finally, the external components such as external capacitors  418 ,  420  may be added between either the source and gate or the drain and gate to prevent OFF-state devices of the receiver switch  404  from turning ON during a negative or positive voltage swing at the antenna  400  port. 
         [0055]    B. Receive Mode 
         [0056]      FIG. 4C  illustrates an equivalent circuit of the receiver switch  404  in an OFF (e.g., disable, block, etc.) state, according to an example embodiment of the invention. In  FIG. 4C , the receiver switch  404  may be placed in the ON position in order for the receive (RX) block to receive a signal from the antenna  400 . With the receiver switch  404  in the ON state, the transmit switch  402  may be placed in the OFF (e.g., disabled, block) state to isolate the transmit switch  402  from the receiver switch  404 . As shown in  FIG. 4C , when the receiver switch  404  is in an ON state, the stacked transistor  406  may be placed in an OFF state  416 , thereby providing an equivalent resistor between the body substrate  112   d  of transistor  412  and ground (i.e., body floating). In this way, the insertion loss at the receive (Rx) path from the antenna  400  to the RX block may be minimized. 
         [0057]    C. Variations of Capacitances/Impedances 
         [0058]      FIG. 7  illustrates the variation of the overall capacitance in multi-stack structure as the input power increases in the drain port. The parasitic capacitor values (e.g., C gd    602 , C gs    604 , C bs    606  and C bd    608 ) may vary depending on whether a transistor is in ON state or OFF state. If an OFF-state transistor in a receiver switch starts to turn ON by a large voltage swing supplied to the drain, then overall capacitance value of the OFF-state transistor may increase accordingly. As shown by capacitance  702  in  FIG. 7 , a receiver switch that only utilizes body switching (e.g.,  FIG. 1B ), but not external components such as capacitors  418 ,  420  in  FIG. 4B , may result in the receiver switch having a high capacitance  702  at a high input power. The is high capacitance  702  may be indicative of OFF-state transistors in the receiver switch inadvertently turning ON. By contrast, by using body-switching and external components such as capacitors  418 ,  420  in accordance with  FIG. 4B , a low capacitance  704  may be achieved even for a high input power. Accordingly, the low capacitance  704  at high input power means that the OFF-state transistors remain OFF even for a high input power. Accordingly, an OFF-state multi-stack receiver switch using both a body-switching technique and external components may be more stable than an OFF-state multi-stack receiver switch using only a body-switching technique. 
         [0059]      FIG. 8A  and  FIG. 8B  illustrates OFF-state impedance differences between a multi-stack receiver switch using a body-switching technique and a receiver switch using both the body-switching techniques and external components such as capacitors  418 ,  420 . The variation of OFF-state impedance of a transistor switch of an OFF-state receiver switch may depend on the operating frequency as well as the level of input power. In particular, the operating frequency may change vary the impedance of parasitic capacitors (e.g., parasitic capacitors  602 ,  604 ,  608 ,  610 ) of the OFF-state transistor. The variation of the OFF state impedance of a receiver switch may affect power handling capability and the harmonic performance at Tx switch.  FIG. 8A  illustrates OFF-state impedances based upon a small signal simulation that is performed by sweeping frequencies with fixed input power. As shown in  FIG. 8 , for a small signal simulation, the impedance  802  for a receiver switch using only a body-switching technique may be similar to the impedance  804  for a receiver switch using both the body-switching technique. However, the OFF-state impedances may be different from for a large signal simulation that sweeps input powers at a fixed frequency. In particular, as shown in  FIG. 5B , the impedance  806  of an OFF-state receiver switch using only body-switching may be lower at a higher input power than the impedance  808  of an OFF-state receiver switch using body-switching and external components. Accordingly, the receiver switch using body-switching and external components may have higher power handling capability and better harmonic performance. 
         [0060]    III. Simulation Results 
         [0061]      FIG. 9  illustrates simulation results for leakage currents in multi-band (e.g., 900 MHz, 1.9 GHz, 2.1 GHz) receiver switches in accordance with an example embodiment of the invention. As shown in  FIG. 9 , the leakage current  902  of a multi-stack receiver switch using only body-switching may be significantly higher than the leakage current  904  of a multi-stack receiver switch using both body-switching and external components. 
         [0062]      FIG. 10  illustrates simulation results for power handling capabilities for the for multi-band transmit switches in accordance with an example embodiment of the invention. As shown in  FIG. 10 , the power handling capability  1002  for a multi-stack receiver switch using only body-switching may be significantly worse for higher input powers than then the power handling capability  1004  for a multi-stack receiver switch using both body-switching and external components. 
         [0063]      FIG. 11  illustrates simulation results for the second harmonic performance for multi-band transmit switches in accordance with an example embodiment of the invention. As shown in  FIG. 11 , the second harmonic performance  1102  for a multi-stack receiver switch using only body-switching may be worse than the second harmonic performance  1104  for a multi-stack receiver switch using both body-switching and external components. 
         [0064]      FIG. 12  illustrates simulation results for the third harmonic performance for multi-band transmit switches in accordance with an example embodiment of the invention. As shown in  FIG. 12 , the third harmonic performance  1102  for a multi-stack receiver switch using only body-switching may be worse than the third harmonic performance  1104  for a multi-stack receiver switch using both body-switching and external components. 
         [0065]    Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Embodiments of the invention may provide for a CMOS antenna switch, which may be referred to as a CMOS SPDT switch. The CMOS antenna switch may operate at a plurality of frequencies, perhaps around 900 MHz, 1.9 GHz and 2.1 GHz according to an embodiment of the invention. The CMOS antenna switch may include both a receiver switch and a transmit switch. The receiver switch may utilize a multi-stack transistor with body substrate switching and attachment of external capacitor between drain and gate to block high power signals from the transmit path as well as to maintain low insertion loss at the receiver path. Exemplary embodiments of the CMOS antenna switch may provide for 38 dBm P 0.1 dB at multi bands (e.g., 900 MHz, 1.8 GHz, and 2.1 GHz). In addition, -60 dBc second and third harmonic performance up to 30 dBm input, may be obtained according to example embodiments of the invention.