Abstract:
A circuit comprises a transmitter port; a receiver port; an antenna port configured to transmit a signal from the transmitter port to antenna port and receive a signal at antenna port and pass to the receiver port; and a switch configured to switch whether the transmitter port or the receiver port is communicatively coupled to the antenna port. The switch comprises a plurality of NMOS FETs configured to switch between the transmitter port and the receiver port.

Description:
CLAIM OF PRIORITY 
     This application claims priority to Chinese Application No. 201410108599.0 entitled “A switch configured to control a transceiver, a radio frequency system and a method for operating the same,” filed on Mar. 21, 2014 by Beken Corporation, which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present application relates to circuits, and more particularly but not exclusive to a switch configured to switch an RF port (ANT) between a transmitter (TX) and a receiver (RX). 
     BACKGROUND 
     Conventionally, diodes are used to switch an RF port (ANT) between the transmitter (TX) port and the receiver (RX) port. However, a diode needs direct current (DC) for operation, which introduces DC power dissipation. Further, inductors are used along with the diodes to provide a DC operating point for the diodes. The large size of inductors limits the application of the diodes in the switch for the transceiver. Therefore, it is desirable that a device can be designed to reduce DC power consumption as well as with reduced size. 
     SUMMARY 
     According to an embodiment of the invention, a switch and a circuit including the switch use Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) and are configured to work with a transceiver. 
     In an embodiment, the switch comprises a first device, a first NMOS FET, a second device, a second NMOS FET, a receiver enabling node, a transmitter enabling node, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, a voltage source, a first capacitor and a second capacitor. A first terminal of the first device is connected to a transmitter port, a second terminal of the first device is connected to a receiver enabling node via the first resistor, a third terminal of the first device is connected to ground via the first capacitor, a fourth terminal of the first device is connected to ground via the second resistor, the third terminal of the first device is further connected to the voltage source via the ninth resistor. A drain of the first NMOS FET is connected to an antenna port, a gate of the first NMOS FET is connected to a transmitter enabling node via the third resistor, a source of the first NMOS FET is connected to a transmitter port, a body of the first NMOS FET is connected to ground via the fourth resistor. A first terminal of the second device is connected to the antenna port, a second terminal of the second device is connected to the receiver enabling node via the fifth resistor, a third terminal of the second device is connected to a receiver port, a fourth terminal of the second device is connected to ground via the sixth resistor. A drain of the second NMOS FET is connected to the receiver port, a gate of the second NMOS FET is connected to the transmitter enabling node via the seventh resistor, a source of the second NMOS FET is connected to ground via the second capacitor, a body of the second NMOS FET is connected to ground via the eighth resistor, the source of the second NMOS FET is further connected to the voltage source via the tenth resistor. 
     In another embodiment, a radio frequency system comprises a transmitter; a receiver; an antenna configured to transmit a signal from the transmitter and receive a signal and pass to the receiver; a switch configured to switch whether the transmitter or the receiver is communicatively coupled to the antenna. The switch comprises a plurality of NMOS FETs configured to switching between the transmitter and the receiver, wherein the switch further comprises a first device, a first NMOS FET, a second device, a second NMOS FET, a receiver enabling node, a transmitter enabling node, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, a voltage source, a first capacitor and a second capacitor. A first terminal of the first device is connected to the transmitter port which is communicatively connected to the transmitter, a second terminal of the first device is connected to the receiver enabling node via the first resistor, a third terminal of the first device is connected to ground via the first capacitor, a fourth terminal of the first device is connected to ground via the second resistor, the third terminal of the first device is further connected to the voltage source via the ninth resistor. A drain of the first NMOS FET is connected to an antenna port which is communicatively connected to the antenna, a gate of the first NMOS FET is connected to the transmitter enabling node via the third resistor, a source of the first NMOS FET is connected to the transmitter port, a body of the first NMOS FET is connected to ground via the fourth resistor. A first terminal of the second device is connected to the antenna port, a second terminal of the second device is connected to the receiver enabling node via the fifth resistor, a third terminal of the second device is connected to the receiver port, a fourth terminal of the second device is connected to ground via the sixth resistor. A drain of the second NMOS FET is connected to the receiver port, a gate of the second NMOS FET is connected to the transmitter enabling node via the seventh resistor, a source of the second NMOS FET is connected to ground via the second capacitor, a body of the second NMOS FET is connected to ground via the eighth resistor, the source of the second NMOS FET is further connected to the voltage source via the tenth resistor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. 
         FIG. 1  is a diagram illustrating a block diagram of a radio frequency system  10  according to an embodiment of the invention. 
         FIG. 2A  is a circuit diagram illustrating a switch according to an embodiment of the invention. 
         FIG. 2B  is a circuit diagram illustrating a switch according to an embodiment of the invention. 
         FIG. 3  is a circuit diagram illustrating a switch according to another embodiment of the invention. 
         FIG. 4  is a flowchart illustrating a method of operating a switch according to an embodiment of the invention. 
         FIG. 5  is a cross section view illustrating a structure of a NMOS FET in a Deep-Nwell according to an embodiment of the invention. 
         FIG. 6  is an equivalent circuit diagram of the structure shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Various aspects and examples of the invention will now be described. The following description provides specific details for a thorough understanding and enabling description of these examples. Those skilled in the art will understand, however, that the invention may be practiced without many of these details. Additionally, some well-known structures or functions may not be shown or described in detail, so as to avoid unnecessarily obscuring the relevant description. 
       FIG. 1  is a diagram illustrating a block diagram of a radio frequency system according to an embodiment of the invention. 
     The radio frequency system  10  comprises a transmitter (TX), a receiver (RX), a switch  120  and an antenna (ANT). The transmitter TX and the receiver RX can be included in a RF transceiver  100 . The transmitter TX and the receiver RX may be combined in the transceiver  100  and share common circuitry and/or a single housing. The antenna ANT transmits a signal from the transmitter TX, or receives a signal and passes the signal to the receiver RX. The switch  120  switches between a first mode (also called a transmitting mode) where the transmitter TX is communicatively coupled to the antenna ANT and the receiver RX is disconnected from the antenna ANT and a second mode (also called a receiving mode) where the receiver RX is communicatively coupled to the antenna ANT and the transmitter TX is disconnected from the antenna ANT. The switch  120  shown in  FIG. 1  is a single pole, double throw switch, and can changeover between connecting the transmitter TX and the receiver RX. Embodiments of the switch  120  can be implemented as switch  20 A,  20 B, or  30 , as will be discussed further below. 
     Alternatively, the system  10  may further comprises a power amplifier (PA)  110  that communicatively couples the transmitter TX with the switch  120  and amplifies signals outputted by the transmitter TX. 
       FIG. 2A  is a circuit diagram illustrating a switch  20 A according to an embodiment of the invention. As shown in  FIG. 2A , the switch  20 A comprises a first device  200 , a first NMOS FET M 22 , a second device  210 , a second NMOS FET M 26 , a receiver enabling node RXEN, a transmitter enabling node TXEN, a first resistor R 20 , a second resistor R 21 , a third resistor R 22 , a fourth resistor R 23 , a fifth resistor R 24 , a sixth resistor R 25 , a seventh resistor R 26 , an eighth resistor R 27 , a ninth resistor R 28 , a tenth resistor R 29 , a voltage source VC, a first capacitor C 20  and a second capacitor C 22 . The switch  20 A may further comprise a transmitter TX PORT, a receiver port RX PORT, and an antenna port ANT PORT. Note that the antenna port can also be referred as RF port, as radio frequency signal is transmitted from the antenna port. 
     A first terminal of the first device  200  is connected to a transmitter TX PORT which is communicatively connected to the transmitter TX also shown in  FIG. 1 . A second terminal of the first device  200  is connected to the receiver enabling node RXEN via the first resistor R 20 . A third terminal of the first device  200  is connected to ground via the first capacitor C 20 . A fourth terminal of the first device  200  is connected to ground via the second resistor R 21 . The third terminal of the first device  200  is further connected to the voltage source VC via the ninth resistor R 28 . 
     A drain of the first NMOS FET M 22  is connected to an antenna port ANT PORT which is communicatively connected to the antenna ANT also shown in  FIG. 1 . A gate of the first NMOS FET M 22  is connected to the transmitter enabling node TXEN via the third resistor R 22 . A source of the first NMOS FET M 22  is connected to the transmitter port TX PORT. A body of the first NMOS FET M 22  is connected to ground via the fourth resistor R 23 . 
     A first terminal of the second device  210  is connected to the antenna port ANT PORT. A second terminal of the second device  210  is connected to the receiver enabling node RXEN via the fifth resistor R 24 . A third terminal of the second device  210  is connected to a receiver port RX PORT. A fourth terminal of the second device  210  is connected to ground via the sixth resistor R 25 . 
     A drain of the second NMOS FET M 26  is connected to the receiver port RX PORT which is communicatively connected to the receiver RX also shown in  FIG. 1 . A gate of the second NMOS FET M 26  is connected to the transmitter enabling node TXEN via the seventh resistor R 26 . A source of the second NMOS FET M 26  is connected to ground via the second capacitor C 22 . A body of the second NMOS FET M 26  is connected to ground via the eighth resistor R 27 . The source of the second NMOS FET M 26  is further connected to the voltage source VC via the tenth resistor R 29 . 
       FIG. 4  is a flowchart illustrating a method  400  of operating the switch according to an embodiment of the invention. The method  400  comprises in a transmitting mode, turning on the transmitter TX (in block  410 A); turning off the receiver RX (in block  420 A); placing the TXEN to high (H) voltage (in block  430 A); placing the RXEN to low (L) voltage (in block  440 A); turning off the first device  200  and the second device  210  (in block  450 A); and turning on the first NMOS FET M 22  and the second NMOS FET M 26  (in block  460 A). Or, the method  400  comprises in a receiving mode, turning off the transmitter TX (in block  410 B); turning on the receiver RX (in block  40 B); placing the TXEN to low voltage (in block  430 B); placing the RXEN to high voltage (in block  440 B); turning on the first device  200  and the second device  210  (in block  450 B); and turning off the first NMOS FET M 22  and the second NMOS FET M 26  (in block  460 B). 
       FIG. 2B  is a diagram illustrating a switch  20 B according to an embodiment of the invention. Same or similar reference signs represent same or similar circuit elements as  FIG. 2A , such as the first device  200 , the second device  210 , the first NMOS FET M 22 , the second NMOS FET M 26 , the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth resistors R 20 , R 21 , R 22 , R 23 , R 24 , R 25 , R 26 , R 27 , R 28  and R 29 , the first capacitor C 20 , the second capacitor C 22 , the details of which are omitted for simplicity. The switch  20 B further comprises a third capacitor C 24 , a fourth capacitor C 26 , a fifth capacitor C 27  and a sixth capacitor C 28 . 
     The third capacitor C 24  is disposed between the first terminal and the second terminal of the first device  200 . The fourth capacitor C 26  is disposed between the fourth terminal and the first terminal of the first device  200 . The fifth capacitor C 27  is disposed between the first terminal and the second terminal of the second device  210 . The sixth capacitor C 28  is disposed between the fourth terminal and the first terminal of the second device  210 . 
     Alternatively, the first device  200  comprises a third NMOS FET M 20 . The first terminal of the first device  200  comprises a drain of the third NMOS FET M 20 . The second terminal of the first device  200  comprises a gate of the third NMOS FET M 20 . The third terminal of the first device  200  comprises a source of the third NMOS FET M 20 . The fourth terminal of the first device  200  comprises a body of the third NMOS FET M 20 . 
     Alternatively, the second device  210  comprises a fourth NMOS FET M 24 . The first terminal of the second device  210  comprises a drain of the fourth NMOS FET M 24 . The second terminal of the second device  210  comprises a gate of the fourth NMOS FET M 24 . The third terminal of the second device  210  comprises a source of the fourth NMOS FET M 24 . The fourth terminal of the second device  210  comprises a body of the fourth NMOS FET M 24 . 
       FIG. 4  is a flowchart illustrating a method  400  of operating the switch according to an embodiment of the invention. The method  400  comprises in a transmitting mode, turning on the transmitter port TX PORT (in block  410 A); turning off the receiver port RX PORT (in block  420 A); placing the transmitter enabling node TXEN to high (H) voltage (in block  430 A); placing the receiver enabling node RXEN to low (L) voltage (in block  440 A); turning off the first device  200  and the second device  210  (in block  450 A); and turning on the first NMOS FET M 22  and the second NMOS FET M 26  (in block  460 A). Or, the method  400  comprises in a receiving mode, turning off the transmitter port TX PORT (in block  410 B); turning on the receiver port RX PORT (in block  420 B); placing the transmitter enabling node TXEN to low voltage (in block  430 B); placing the receiver enabling node RXEN to high voltage (in block  440 B); turning on the first device  200  and the second device  210  (in block  450 B); and turning off the first NMOS FET M 22  and the second NMOS FET M 26  (in block  460 B). 
     Referring back to  FIG. 3 ,  FIG. 3  is a circuit diagram illustrating a switch  30  according to an embodiment of the invention. The switch  30  comprises a first device  300 , a first NMOS FET M 34 , a second device  310 , a second NMOS FET M 38 , a receiver enabling node RXEN, a transmitter enabling node TXEN, a first resistor R 310 , a second resistor R 315 , a third resistor R 340 , a fourth resistor R 345 , a fifth resistor R 350 , a sixth resistor R 355 , a seventh resistor R 380 , an eighth resistor R 385 , a ninth resistor R 390 , a tenth resistor R 395 , a voltage source VC, a first capacitor C 30  and a second capacitor C 32 . 
     The first device  300  comprises a third NMOS FET M 31 , a fifth NMOS FET M 32  and a sixth NMOS FET M 33 . The first terminal of the first device  300  comprises a drain of the third NMOS FET M 31 . The second terminal of the first device  300  comprises a gate of the third NMOS FET M 31 . The third terminal of the first device  300  comprises a source of the sixth NMOS FET M 33 . The fourth terminal of the first device  300  comprises a body of the third NMOS FET M 31 . 
     The drain of the third NMOS FET M 31  is connected to the transmitter port TX PORT. The gate of the third NMOS FET M 31  is connected to the receiver enabling node RXEN via the first resistor R 310 . A source of the third NMOS FET M 31  is connected to a drain of the fifth NMOS FET M 32 . The body of the third NMOS FET is connected to ground via the second resistor R 315 . 
     The drain of the fifth NMOS FET M 32  is connected to the source of the third NMOS FET M 31 . A gate of the fifth NMOS FET M 32  is connected to the receiver enabling node RXEN via an eleventh resistor R 320 . A source of the fifth NMOS FET M 32  is connected to a drain of the sixth NMOS FET M 33 . A body of the fifth NMOS FET M 32  is connected to ground via a twelfth resistor R 325 . 
     The drain of the sixth NMOS FET M 33  is connected to the source of the fifth NMOS FET M 32 . A gate of the sixth NMOS FET M 33  is connected to the receiver enabling node RXEN via a thirteenth resistor R 330 . A body of the sixth NMOS FET M 33  is connected to ground via a fourteenth resistor R 335 . The source of the sixth NMOS FET M 33  is connected to ground via the first capacitor C 30 , and the source of the sixth NMOS FET M 33  is also connected to the voltage source VC via the ninth resistor R 390 . 
     Alternatively, the second device  310  comprises a fourth NMOS FET M 35 , a seventh NMOS FET M 36  and an eighth NMOS FET M 37 . The first terminal of the second device  310  comprises a drain of the fourth NMOS FET M 35 . The second terminal of the second device  310  comprises a gate of the fourth NMOS FET M 35 . The third terminal of the second device  310  comprises a source of the eighth NMOS FET M 37 . The fourth terminal of the second device  310  comprises a body of the fourth NMOS FET M 35 . 
     The drain of the fourth NMOS FET M 35  is connected to the antenna port ANT PORT. The gate of the fourth NMOS FET M 35  is connected to the receiver enabling node RXEN via the fifth resistor R 350 . A source of the fourth NMOS FET M 35  is connected to a drain of the seventh NMOS FET M 36 . The body of the fourth NMOS FET M 35  is connected to ground via the sixth resistor R 355 . 
     The drain of the seventh NMOS FET M 36  is connected to the source of the fourth NMOS FET M 35 . A gate of the seventh NMOS FET M 36  is connected to the receiver enabling node RXEN via a fifteenth resistor R 360 . A source of the seventh NMOS FET M 36  is connected to a drain of the eighth NMOS FET M 37 . A body of the seventh NMOS FET M 36  is connected to ground via a sixteenth resistor R 365 . 
     The drain of the eighth NMOS FET M 37  is connected to the source of the seventh NMOS FET M 36 . A gate of the eighth NMOS FET M 37  is connected to the receiver enabling node RXEN via a seventeenth resistor R 370 . A source of the eighth NMOS FET M 37  is connected to the receiver RX, and a body of the eighth NMOS FET M 37  is connected to ground via an eighteenth resistor R 375 . 
     The switch  30  further comprises a third capacitor C 34 , a fourth capacitor C 36 , a fifth capacitor C 37  and a sixth capacitor C 38 . 
     The third capacitor C 34  is disposed between the drain and the gate of the third NMOS FET M 31 . The fourth capacitor C 36  is disposed between the body and the drain of the third NMOS FET M 31 . The fifth capacitor C 37  is disposed between the drain and the gate of the seventh NMOS FET M 36 . The sixth capacitor C 38  is disposed between the body and the drain of the seventh NMOS FET M 36 . 
     The first capacitor C 30  provides an alternate current path for the NMOS FETs M 31 , M 32  and M 33 . The first resistor R 310 , the eleventh resistor R 320 , the thirteenth resistor R 330  reduce power leakage, since when the switch  30  is operating in high frequency, these resistors R 310 , R 320  and R 330  prevent the formation of a high frequency path. Current through these resistors R 310 , R 320  and R 330  results in voltage drops, therefore the voltages on the gates of M 31 , M 32  and M 33  are variable instead of being constant to the voltage of RXEN. The third capacitor C 34  provides an alternating current path between the gate of the third NMOS FET M 31  and the transmitter port TX PORT, so as to enable the voltage of the gate of the third NMOS FET M 31  to quickly follow the voltage of the transmitter port TX PORT. The fourth capacitor C 36  provides an alternating current path between the drain of the third NMOS FET M 31  and the body of the third NMOS FET M 31 , so as to enable the voltage of the body of the third NMOS FET M 31  to quickly follow the voltage of the drain of the third NMOS FET M 31 . 
     An operation process of the circuit  30  will be described briefly as follows. When the transceiver  100  is operating in the transmitting mode, transmitter port TX PORT is ON and receiver port RX PORT is OFF, the transmitter enabling node TXEN is placed to high (H) voltage and the RXEN is placed to low (L) voltage. The first NMOS FET M 34  and second NMOS FET M 38  are ON. The third NMOS FET M 31 , a fifth NMOS FET M 32  and a sixth NMOS FET M 33 , and the fourth NMOS FET M 35 , the seventh NMOS FET M 36  and the eighth NMOS FET M 37  are OFF. Therefore, the transmitting signal from the transmitter port TX PORT can be provided to the antenna port ANT PORT via the first NMOS FET M 34 , and the leakage signal from the antenna port ANT PORT to the receiver port RX PORT can be shunt to the ground via the second NMOS FET M 38 . Further, as the fourth NMOS FET M 35 , the seventh NMOS FET M 36  and the eighth NMOS FET M 37  are OFF, the receiver port RX PORT will be isolated from the antenna port ANT PORT. 
     Alternatively, when the transceiver  100  is operating in the receiving mode, the transmitter port TX PORT is OFF and receiver port RX PORT is ON, the transmitter enabling node TXEN is placed to low (L) voltage and the receiver enabling node RXEN is placed to high (H) voltage. The first NMOS FET M 34  and second NMOS FET M 38  are OFF. The third NMOS FET M 31 , a fifth NMOS FET M 32  and a sixth NMOS FET M 33 , and the fourth NMOS FET M 35 , the seventh NMOS FET M 36  and the eighth NMOS FET M 37  are ON. Therefore, the receiving signal from antenna port ANT PORT can be provided to the receiver port RX PORT via the fourth NMOS FET M 35 , the seventh NMOS FET M 36  and the eighth NMOS FET M 37 , and any signal or noise from the transmitter port TX PORT can be shunt to the ground via the third NMOS FET M 31 , the fifth NMOS FET M 32  and the sixth NMOS FET M 33 . Further, as the first NMOS FET M 34  is OFF, the transmitting signal from the transmitter port TX PORT will be isolated from the antenna port ANT PORT. As the second NMOS FET M 38  is OFF, the receiving signal to the receiver port RX PORT will not be shunt to ground. 
       FIG. 4  is a flowchart illustrating a method  400  of operating the switch according to an embodiment of the invention. The method  400  comprises in a transmitting mode, turning on the transmitter port TX PORT (in block  410 A); turning off the receiver port RX PORT (in block  420 A); placing the transmitter enabling node TXEN to high (H) voltage (in block  430 A); placing the RXEN to low (L) voltage (in block  440 A); turning off the first device  300  and the second device  310  (in block  450 A); and turning on the first NMOS FET M 34  and the second NMOS FET M 38  (in block  460 A). Or, the method  400  comprises in a receiving mode, turning off the transmitter port TX PORT (in block  410 B); turning on the receiver port RX PORT (in block  420 B); placing the transmitter enabling node TXEN to low voltage (in block  430 B); placing the receiver enabling node RXEN to high voltage (in block  440 B); turning on the first device  300  and the second device  310  (in block  450 B); and turning off the first NMOS FET M 34  and the second NMOS FET M 38  (in block  460 B). 
       FIG. 5  is a cross section view illustrating a structure of the NMOS FET in deep n-well (DNW) discussed above, such as NMOS FETs M 20 , M 22 , M 24 , M 26 , M 31 , M 32 , M 33 , M 34 , M 35 , M 36 , M 37  and M 38 , according to an embodiment of the invention. In additional to the four terminals discussed above, such as the first terminal-drain (D), the second terminal-gate (G), the third terminal-source (S), and the fourth terminal-body, each of the plurality of NMOS FETs comprises a deep N-well located between a P-well which holds two N plus regions and a P-substrate. 
       FIG. 6  is an equivalent circuit diagram of the structure shown in  FIG. 5 . As shown in  FIG. 6 , a first parasitic diode DN 1  is located between the drain and the P-well. An anode of the first parasitic diode DN 1  is connected to the P-well, and a cathode of the first parasitic diode DN 1  is connected to the drain. A second parasitic diode DN 2  is located between the source to the P-well. An anode of the second parasitic diode DN 2  is connected to the P-well, and a cathode of the second parasitic diode DN 2  is connected to the source. A third parasitic diode DN 3  and a fourth parasitic diode DN 4  are located between the P-well and the P-substrate in a back-to-back manner. To be specific, both a cathode of the third parasitic diode DN 3  and a cathode of the fourth parasitic diode DN 4  are connected to the deep N-well. An anode of the third parasitic diode DN 3  is connected to the P-well. An anode of the fourth parasitic diode DN 4  is connected to the P-substrate. The third parasitic diode DN 3  between the P-well and DNW and the fourth parasitic diode DN 4  between the DNW and the P-sub form a good isolation between the P-well and the P-sub. Further, the P-well is connected to ground via a resistor, and the DNW is floating. In this circuit configuration, no matter how large the amplitude of input signal, a signal path between ground and the source or between ground and drain cannot be formed. 
     When NMOS FETs in DNW are used in the switched circuit, no inductance is introduced, thus reducing the size of integrated circuit. Further, NMOS FET does not require direct current (DC) during operation, thus reducing DC power dissipation. Further the NMOS FET can be integrated in a circuit instead of designing in a standalone circuit. Further, the circuit has good linearity before reaching the gain compression point of the NMOS FET. 
     It should be appreciated by those skilled in the art that components from different embodiments may be combined to yield another technical solution. This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.