Abstract:
Systems and methods may be provided for a CMOS RF antenna switch. The systems and methods for the CMOS RF antenna switch may include an antenna that is operative to transmit and receive signals over at least one radio frequency (RF) band, and a transmit switch coupled to the antenna, where the transmit switch is enabled to transmit a respective first signal to the antenna and disabled to prevent transmission of the first signal to the antenna. the systems and methods for the CMOS RF antenna switch may further include a receiver switch coupled to the antenna, where the receiver switch forms a filter when enabled and a resonant circuit when disabled, where the filter provides for reception of a second signal received by the antenna, and where the resonant circuit blocks reception of at least the first signal.

Description:
RELATED APPLICATION 
     This application claims priority to U.S. Provisional Ser. No. 60/803,873, entitled “Systems, Methods, and Apparatuses for Complementary Metal Oxide Semiconductor (CMOS) Antenna Switches Using Switched Resonators,” filed on Jun. 4, 2006, which is incorporated by referenced as if fully set forth herein. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to antenna switches, and more particularly, to CMOS (complementary metal oxide semiconductor) antenna switches. 
     BACKGROUND OF THE INVENTION 
     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. 
     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. 
     However, current CMOS technology presents a variety of difficulties for its application to RF switches. For example, CMOS material characteristics, including lossy substrates and low breakdown voltages due to low mobility of electrons, 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 
     Embodiments of the invention may provide for CMOS RF switches, which may be referred to as a CMOS SP4T switch. According to an embodiment of the invention, the CMOS RF switch may be fabricated using a variety of processes, including a 0.18 μm process. Indeed, 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 and 1.9 Hz) of the CMOS RF switch, an LC switched resonator scheme may be applied to the receiver switch. According to an embodiment of the invention, the CMOS RF switch may provide higher blocking capability at the transmission (TX) mode as well as low insertion loss at the reception (RX) mode at one or more bands, including multi-band (e.g., 900 MHz and 1.9 GHz). As an illustrative example, the CMOS RF switch may achieve a P1 dB watt level power handling capability at 900 MHz and 1.90 Hz respectively with −1.4 dB insertion loss at both bands (900 MHz and 1.9 Gz) in the TX mode. Likewise, in the RX mode, the CMOS RF switch may also achieve an insertion loss of −0.9 dB and −1.4 dB at around 900 MHz and 1.9 GHz, respectively. 
     According to an embodiment of the invention, there is a method for providing a CMOS antenna switch. The method may include providing an antenna operative to transmit and receive signals over at least one radio frequency (RF) band, and coupling the antenna to a transmit switch, where the transmit switch is enabled to transmit a first signal to the antenna and disabled to prevent transmission of the first signal to the antenna. The method may further include coupling the antenna to a receiver switch that forms a filter when enabled and a resonant circuit when disabled, where the filter provides for reception of a second signal received by the antenna and where the resonant circuit blocks reception of at least the first signal. 
     According to an embodiment of the invention, there is a system for a CMOS antenna switch. The system may include an antenna that is operative to transmit and receive signals over at least one radio frequency (RF) band, and a transmit switch coupled to the antenna, where the transmit switch is enabled to transmit a respective first signal to the antenna and disabled to prevent transmission of the first signal to the antenna, and a receiver switch coupled to the antenna, where the receiver switch forms a filter when enabled and a resonant circuit when disabled, where the filter provides for reception of a second signal received by the antenna, and where the resonant circuit blocks reception of at least the first signal. 
     According to yet another embodiment of the invention, there is a system for a CMOS antenna switch. The system may include an antenna operative at a plurality of radio frequency (RF) bands. The system may further include means for transmitting first signals to the antenna, and means for receiving second signals from the antenna, where the means for receiving forms a filter when the means for receiving is operative, and wherein the means for receiving forms a resonant circuit when the means for transmitting is operative. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       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: 
         FIGS. 1A and 1B  illustrate simplified operations of a receiver switch in accordance with an embodiment of the invention. 
         FIG. 2  illustrates a CMOS switch using a switched resonator at a TX mode, in accordance with an embodiment of the invention. 
         FIG. 3  illustrates a CMOS switch using a switched resonator at RX mode, in accordance with an embodiment of the invention. 
         FIG. 4A  illustrates a multi-stacked switch at a TX path, in accordance with an embodiment of the invention. 
         FIG. 4B  illustrates a simplified equivalent model of on state switch using a body floating technique switch with signal flow, in accordance with an embodiment of the invention. 
         FIG. 5  illustrates exemplary receiver switch simulation results, in accordance with an embodiment of the invention. 
         FIGS. 6A and 6B  illustrate exemplary transmit switch simulation results, in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. 
     Embodiments of the invention may provide for CMOS RF antenna switches, which may also be referred to as SP4T 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 level handling, and integration with other devices and circuits. Generally, the CMOS RF antenna switch may include at least one receiver switch and at least one transmit switch. The receiver switch may utilize one or more switched resonators, as will be described in further detail below. The transmit switch may utilize or otherwise employ a body substrate tuning technique, as will also be described in further detail below. 
     Description of a Receiver Switch 
     In accordance with an embodiment of the invention, the CMOS RF antenna switch, and in particular, the receiver switch component of the RF antenna switch will be now be described in further detail with reference to  FIGS. 1-3 .  FIGS. 1A and 1B  provide an illustrative example of an operation of a simplified CMOS RF antenna switch having a transmit switch  102  and a receiver switch  104 , in accordance with an embodiment of the invention. As shown in  FIGS. 1A and 1B , a CMOS RF antenna switch may comprise an antenna  100  in communication with at least one transmit switch  102  and at least one receiver switch  104 . As shown in  FIG. 1A , when the transmit switch  102  is ON (e.g., enabled), thereby providing a transmit signal to the antenna  100 , the receiver switch  104  is OFF (e.g., disabled). Likewise, as shown in  FIG. 1B , when the receiver switch  104  is ON (e.g., enabled), thereby allowing reception of a receive signal from the antenna  100 , the transmit switch  102  is OFF (e.g., disabled). According to an 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. 
     Still referring to  FIGS. 1A and 1B , the receiver switch  104  may be in the form of a switched resonator, according to an embodiment of the invention. This switched resonator may provide distinctly different equivalent circuits, depending on whether the receiver switch  102  is ON or OFF, respectively. In  FIG. 1A , when the receiver switch  104  is OFF, an LC resonant circuit may be formed in accordance with an embodiment of the invention. The LC resonant circuit may block the transmit signal provided from the transmit switch  102  in the ON state, thereby maximizing the power of the signal transmitted via antenna  100 . According to an embodiment of the invention, the LC resonant circuit may include at least one inductor  106  in parallel with at least one capacitor  108 . The value of the inductor  106  may be sufficiently large, perhaps over 5 nH, depending on the desired operating frequency of the resonant circuit. It will be appreciated that while the LC resonant circuit is illustrated as a parallel resonant circuit in  FIG. 1A , other embodiments of the invention may utilize a series resonant circuit as well (e.g., an RLC resonant circuit). 
     On the other hand, in  FIG. 1B , when the receiver switch  104  is ON, a filter may be formed, according to an embodiment of the invention. The filter may be a low-pass filter, with a certain cutoff frequency characteristics according to an embodiment of the invention. In addition, the filter may include a very small inductor  110  value at the desired operating frequency in order to provide for a low insertion loss. Accordingly, the filter  104  may provide for the reception, with low insertion loss, of at least a portion of the receive signal provided from the antenna  100 . While the above-described filter is illustrated as a low-pass filter, it will be appreciated that other embodiments of the filter may be a bandpass filter, a high-pass filter, or the like. 
       FIG. 2  illustrates an illustrative example of an operation of an RF antenna switch  200  in transmit (TX) mode. In particular,  FIG. 2  includes an antenna  100  in communication with the transmit switch  102  and the receiver switch  104 . According to an embodiment of the invention, the transmit switch  102  may comprise signal paths for one or more transmit signals. For example, as shown in  FIG. 2A , there may be two signal paths—that is, signal paths TX 1  and TX 2  controlled by switches M 1   204  and M 2   206 , respectively. The switches M 1   204  and M 2   206  may comprise one or more CMOS switches. Likewise, the receiver switch  104  may include signal paths RX 1  and RX 2 , as controlled by switches M 3   208 , M 4   210 , M 5   212 , M 6   214 , M 7   216 , M 8   218 , and M 9   220 , which may each comprise one or more CMOS switches. 
     In  FIG. 2 , according to an embodiment of the invention, the RF antenna switch  200  is illustrated as operating in TX mode for signal path TX 1 . With this TX mode configuration for transmit switch  102 , switch M 1   204  is closed and switch M 2   206  is open. In addition, the receiver switch  104  forms an resonant circuit, described in further detail below, by closing switches M 3   208 , M 4   210  while opening switches M 5   212 , M 6   214 , and M 7   216  to provide a high impedance point at node  232 . In addition, although not illustrated as such in  FIG. 2 , switches M 8   218  and M 9   220  may also be closed to bypass leakage signals to ground ion order to protect the low-noise amplifier (LNA) from such leakage signals. One of ordinary skill in the art will recognize that in  FIG. 2 , signal path TX 2  could have been enabled instead of signal path TX 1  without departing from embodiments of the invention. It will also be appreciated that the configuration of the transmit switch  102  and receiver switch  104 , including the numbers of transmit and receive signal paths, may be varied without departing from embodiments of the invention. 
     In the configuration illustrated in  FIG. 2 , the power handling capability of the transmit switch  102  may be based upon the impedance of the resonant circuit and the source-to-drain breakdown voltage of cascaded switches M 5   212 , M 6   214  M 7   216  of the receiver switch  104 . In other words, the maximum transmit power of the transmit switch  102  may be dependent upon the impedance and breakdown characteristics of the receiver switch  104 . 
     According to an embodiment of the invention, the resonant circuit may be an LC parallel resonant circuit formed by inductors L 1   222 , L 2   224  in parallel with capacitor C 1   226 . In order to provide the desired blocking during the TX mode configuration to maximize the transmit signal power, the inductance value of inductor L 2   224  may be sufficiently large. However, the ratio of the value of inductors L 1   222  and L 2   224  may be related to the power handling of the transmit switch  102 . Accordingly, if the value of L 1   222  is too small, then a large voltage swing may be above the source-to-drain breakdown voltage of switches M 5   212 , M 6   214 , and/or M 7   216 , which are intended to be open to provide a high impedance point at node  232 . Therefore, the value of the inductor L 1   222  may be selected to yield the optimum voltage swing for the TX mode and low insertion loss for the RX mode. 
     In accordance with an embodiment of the invention,  FIG. 3  provides an illustrative operation of an RF antenna switch  300  in transmit (RX) mode. As shown in  FIG. 3 , both switch M 1   204  and switch M 2   206  of the transmit switch  102  are open to isolate antenna  100  from transmit signal paths TX 1  and TX 2 , respectively. However, in enabling receive signal path RX 1 , switches M 3   208 , M 4   210 , and MS  218  are open, while switches M 5   212  and M 6   214  are closed. Further, to bypass leakage signal to ground to protect the low noise amplifier (LNA), switch M 9   220  may be closed. One of ordinary skill in the art will recognize that signal path RX 2  could have been enabled instead of signal path RX 1  without departing from embodiments of the invention. 
     Still referring to  FIG. 3 , a low-pass filter may be formed using inductor L 1   222  and capacitor C 2   228 . If low insertion loss is a primary consideration, then the inductor L 1   222  value may be as small as possible. However, as described above with respect to  FIG. 2 , the value of inductor L 1   222  impacts the voltage swing of the TX mode, and thus, the value of inductor L 1   222  may be selected to provide the optimum voltage swing for the TX mode and low insertion loss for the RX mode. 
     Dual Band operation 
     As described with reference to  FIGS. 1-3 , the receiver switch  104  (e.g., switched resonator) may provide for an LC resonator in the TX mode and an LC lowpass filter for the RX mode. In addition, as shown in  FIGS. 2 and 3 , there may be two transmit signal paths TX 1  and TX 2  and two receive signal paths RX 1  and RX 2 . It will be appreciated, however, that fewer transmit or receive paths may be included as desired without departing from embodiments of the invention. In accordance with an embodiment of the invention, TX 1  and RX 1  may be provided for GSM band (e.g., 900 MHz) communications and TX 2  and RX 2  may be provided for DCS/PCS band (e.g., 1.9 GHz) communications, although different bands may be utilized as well. In addition, more than two bands—perhaps three or four bands—may also be supported without departing from embodiments of the invention. 
     As the number of signal paths at the antenna  100  increases, however, the power handling capability of the transmit switch  102  may drop. Accordingly, in a single-pole multi-throw switch, it may be desirable to decrease the number of signal paths at the antenna  100 . For instance, as shown in  FIGS. 2 and 3 , RX 1  and RX 2  of the receiver switch  104  may share one LC parallel resonator at the antenna  100  front end, where the LC parallel resonator is comprised of inductors L 1   222 , L 2   224  and capacitor C 1   226 . As described above, the LC parallel resonator may block the transmit signals from TX 1  and TX 2  at either band. Instead of having a switched resonator with two switched transmission zeros at dual bands, the LC parallel resonator described above may have only one transmission zero, which may be at 1.5 GHz with a wide band, according to an embodiment of the invention. In addition, the LC parallel resonator may provide for −13 dB, −25 dB and −14 dB return loss at 900 MHz, 1.5 GHz, and 1.9 GHz, respectively. 
     Description of a Transmit Switch 
     The transmit switch  102  in  FIGS. 2 and 3  will now be described in further detail with reference to  FIGS. 4A and 4B . In particular,  FIG. 4A  illustrates a transmit switch  102  structure for switch M 1   204  at TX 1  and switch M 2   206  at TX 2  according to an exemplary embodiment of the invention. As shown in  FIG. 4A , switches M 1   204  and M 2   206  may include stacked transistors such as CMOS transistors  402 ,  404 , and  406  stacked (e.g., cascaded) from source to drain. By stacking transistors  402 ,  404 , and  406  from source to drain, the cumulative breakdown voltage can be increased since it is split among the transistors  402 ,  404 , and  406 , thereby providing for a higher power blocking capability. Such a high power blocking capability may be necessary, for example, at switch M 2   206  at TX 2  when switch M 1   204  at TX 1  is closed to transmit a signal. While  FIG. 4  illustrates three stacked transistors, it will be appreciated that fewer or more stacked can be cascaded as well. 
     However, by stacking the transistors  402 ,  404 , and  406 , the insertion loss of the transmit switch  102  may be increased. Accordingly, as shown in  FIG. 4A , a body floating technique, which includes connecting high resistor  408 ,  410 , and  412  values at the body substrate, may be applied to the transmit switch  102  in accordance with an embodiment of the invention With such a body floating technique, the transistors  402 ,  404 , and  406  may use a deep N-well structure, perhaps of a 0.18-um CMOS process, which may be immune to potential latch ups due to connecting high resistor  408 ,  410 ,  412  values at the body substrate. The resistors  408 ,  410 ,  412 , which may also be referred to as body floating resistors, may reduce the insertion loss by blocking leakage current to the substrate ground. 
       FIG. 4B  illustrates signal flow at on single stage switch—for example, transistor  402 ,  404 , or  406 . As the size of a transistor  402 ,  404 ,  406  increases, the parasitic capacitance value becomes high enough so that source-to-body  452  and drain-to-body  454  parasitic capacitor with body floating resistor  456  may be used as signal path c at the ON state. However, if the body is grounded, signal path c in  FIG. 4B  is bypassed to the ground, which results in degraded insertion loss. 
     Simulation results 
       FIG. 5  illustrates simulation results for the operation of an exemplary multi-band (e.g., 900 MHz, 1.9 GHz) receiver switch  104  in accordance with an embodiment of the invention. These simulation results illustrate the insertion loss  502 , the isolation  504  from the antenna  100  to the TX, and the isolation  506  between RX 1  and RX 2 . In particular, the insertion loss  502  is illustrated by the top solid line. The isolation  504  measured between the antenna  100  and the TX is illustrated by the middle line. Likewise, the isolation  506  between RX 1  and RX 2  is illustrated by the bottom line. 
       FIG. 6  illustrates simulation results for the operation of an exemplary multi-band transmit switch  102 . In particular, the simulation results in  FIGS. 6A  illustrate the power handling capability while  FIG. 6B  illustrates the isolation from the antenna  100  to the RX. In both  FIGS. 6A and 6B , the solid lines represent simulations at the first band of 1.9 GHz while the circled lines represent simulations at the second band of 900 MHz. 
     One of ordinary skill in the art will recognize that the simulation results are provided by way of example only. Indeed, the transmit switch  102  and the receiver switch  104  may be configured for other bands of operation as well. Accordingly, the simulation results may likewise be provided for other bands of operations without departing from embodiments of the invention. 
     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.