Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present disclosure claims priority to U.S. Provisional App. No. 61/347,112 for filed May 21, 2010, and is incorporated herein by reference in its entirety for all purposes. 
     
    
     BACKGROUND 
       [0002]    The present invention relates generally to wireless communication circuits, and in particular to transmit and receive switches. 
         [0003]    Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
         [0004]    One of the more important components in present-day wireless communication equipment is the RF (radio frequency) switch. The purpose of an RF switch is to connect/disconnect an antenna between the transmitter circuitry and the receiver circuitry. Accordingly, such switches are commonly referred to as T/R switches (transmit/receive). T/R designs typically include impedance matching circuitry to direct the high power transmit signal to the antenna while at the same time preventing that signal from entering the sensitive front end of the local receiver (transmit mode), and also allowing a low-loss connection between the antenna and the receiver (receive mode). 
         [0005]    For wireless applications (e.g., mobile devices) it is desirable to reduce the size of the RF board and to lower the cost. These two goals can be achieved by fully integrate the T/R switch on-chip; in other words using integrated circuit techniques to form the T/R switch on an integrated circuit (IC) chip.  FIG. 6  shows a schematic illustration of a conventional fully integrated on-chip arrangement of a T/R switch circuit based on CMOS (complementary metal-oxide semiconductor) technology. 
         [0006]    The IC chip in  FIG. 6  includes a power amplifier which can output a transmit signal to be broadcast by an antenna. A low-noise amplifier can accept a receive signal that is sensed by the antenna to be amplified for further processing. The power amplifier and low-noise amplifier can be components which constitutes a transceiver circuit. The circuit arrangement that is between the power amplifier and the low-noise amplifier can be collectively referred to as the T/R switch. The T/R switch includes switch elements (e.g., transistors M T , M RS , and M RP ) and impedance matching components (e.g., inductors such as inductor L RS , and capacitors C C , C RS , and C S ). The IC chip includes a single tx/rx pin to output the transmit signal for transmission by an antenna and to input a receive signal sensed by the antenna. The switch elements (M T , M RS , and M RP ) control whether the transmit signal is output on the tx/rx pin or the signal sensed by the antenna is input via the tx/rx pin. The impedance matching components provide impedance matching between the power amplifier and the antenna, and between the low-noise amplifier and the antenna. 
         [0007]    The IC chip is typically assembled on a printed circuit board (PCB), and connected to an “off-chip” component. For example, a balun (balance-unbalance) filter is a typical off-chip component used with the antenna and is assembled on the PCB along with the IC chip. The single tx/rx pin of the IC chip can be connected to the balun filter via a trace formed on the PCB between the tx/rx pin and a pin on the balun filter. Alternatively, the tx/rx pin and balun pin can be connected to respective pads on the PCB, and a bonding wire can be soldered to the pads to make the connection. 
         [0008]    The quality factors of on-chip matching components, especially inductors, are usually quite poor due to metal resistance and lossy properties of silicon substrates. Poor quality factors result in limited transmit power and receive sensitivity performance. With on-chip matching components, there is loss of flexibility in fine tuning the RF switch. Since the inductors and capacitors are fabricated on-chip, it is not practical to vary their component values in case fine tuning is needed, for example, to accommodate for impedance variations in the antenna/balun filter assembly. In addition, component values of the on-chip matching elements are subject to process variations and thus may vary from one lot of chips to another. Also, there is loss of flexibility to accommodate different package designs. 
         [0009]    These and other issues are addressed by embodiments of the present invention, individually and collectively. 
       SUMMARY 
       [0010]    A circuit configuration in accordance with embodiments of the present invention includes an integrated circuit (IC) having first and second switching elements. The first switching element may provide a transmit signal to the antenna. The second switching element may receive a received signal sensed by the antenna. The IC includes a first pin and a second pin to respectively transmit and receive signals. An off-chip impedance matching circuit is separate from the IC, but electrically connected to the IC. The impedance matching circuit includes a single electrical connection to the antenna. 
         [0011]    In and embodiment, the impedance matching circuit comprises one or more capacitive or inductive components. 
         [0012]    In an embodiment, the impedance matching circuit can be affixed to a printed circuit board PCB) and the IC can affixed to the PCB or to separate PCB. 
         [0013]    In an embodiment, the IC includes an on-chip impedance matching network. 
         [0014]    In an embodiment, a method for a circuit includes receiving a transmit signal on an IC chip and outputting the transmit signal to a first pin of the IC chip. The transmit signal is received by an impedance matching network that is off-chip with respect to the IC chip. The transmit signal is then output to an antenna via a terminal of the impedance matching network. The method further includes receiving at the terminal of the impedance matching network a received signal sensed by the antenna and outputting the received signal to a second pin of the IC chip. In an embodiment, the received signal is received by a second amplifier of the IC chip. 
         [0015]    A circuit configuration in accordance with embodiments of the present invention includes a printed circuit board having disposed on it an antenna assembly, an impedance matching network, and a transceiver integrated circuit. The impedance matching network includes a single connection to the antenna assembly. The transceiver integrated circuit includes a first amplifier configured to output a transmit signal on a first pin, and a second amplifier configured to receive a received signal on a second pin. The impedance matching network provides impedance matching between the first pin and second pin of the transceiver integrated circuit and the single terminal connected to the antenna assembly. 
         [0016]    In an embodiment, the transceiver integrated circuit does not include any impedance matching network circuitry. 
         [0017]    In an embodiment, the transceiver integrated circuit includes on-chip impedance matching network circuitry. 
         [0018]    The following detailed description and accompanying drawings provide a better understanding of the nature and advantages of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1A  shows a high level block diagram of the present invention. 
           [0020]      FIG. 1B  shows an embodiment of the present invention. 
           [0021]      FIG. 2  shows alternate circuit configurations in accordance with the present invention. 
           [0022]      FIG. 3  shows an embodiment of the board matching network. 
           [0023]      FIG. 3A  shows a particular implementation of the board matching network. 
           [0024]      FIG. 4  shows a particular implementation of the board matching network and the on-chip matching network. 
           [0025]      FIG. 5  shows a wireless system incorporating the circuit configuration of the present invention. 
           [0026]      FIG. 6  shows a conventional arrangement of T/R switch circuitry. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Described herein are illustrative embodiments of a T/R switch circuit arrangement for an RF front-end. 
         [0028]    In the following description, for purposes of explanation, numerous examples and specific details are set forth in order to provide a thorough understanding of the present invention. It will be evident, however, to one skilled in the art that the present invention as defined by the claims may include some or all of the features in these examples alone or in combination with other features described below, and may further include modifications and equivalents of the features and concepts described herein. 
         [0029]      FIG. 1A  is a high level block diagram of a transmit/receive (T/R) circuit in accordance with the present invention. A transceiver circuit  2  may include a transmit circuit for producing a signal suitable for transmission by an antenna (in the antenna assembly  6 ) and receiver circuit for receiving a received signal sensed by the antenna. The transceiver circuit  2  may include a transmit/receive switch to switch between outputting a transmit signal or receiving a received signal. A matching network  4  provides impedance matching between the antenna assembly  6  and the transceiver circuit  2  in order to maximize power transfer, reduce reflection of signals and so on. The antenna assembly  6  may include the antenna itself and may include other supporting circuitry; for example, a balun filter. 
         [0030]    Referring to  FIG. 1B , a T/R (transmit/receive) circuit arrangement in accordance with the present invention includes an IC chip  108  comprising circuitry for transmitting signals and receiving signals and corresponding switching circuitry to switch between transmit mode and receive mode. In an embodiment, the matching network  4  ( FIG. 1A ) may comprise board matching network  124  for matching the impedance between an antenna  104  and the circuitry in IC chip  108 . Further in accordance with the present invention, the board matching network  124  is “off-chip” with respect to the IC chip  108 . In other words, the board matching network  124  is a component that is not fabricated on the IC chip  108 , but rather is a component that is physically separate from the IC chip. In an embodiment, the board matching network  124  is assembled on a printed circuit board (PCB)  102 . The IC chip  108  can be connected to the PCB  102 , for example, via bond wires  112 ,  114 . An antenna assembly comprising the antenna  104  and a balun filter  106  can be assembled on the PCB  102 . 
         [0031]    The board matching network  124  may include a terminal  124   a  configured to receive an incoming signal, a terminal  124   b  configured to output an outgoing signal, and terminal  124   c  configured to output a signal to be transmitted by the antenna  104  and to receive a signal sensed or otherwise received by the antenna. The bond wires  112 ,  114  may have inductive characteristics. Accordingly, in an embodiment, the bond wires  112 ,  114  can be considered part of the board matching network  124 . 
         [0032]    In embodiments, the IC chip  108  may include a power amplifier  132  and a low-noise amplifier (LNA)  134 . The amplifiers  132 ,  134  can be components of a transceiver circuit (not shown). The IC chip  108  may further include T/R switches  126 ,  128 . For example, the T/R switches  126 ,  128  shown in  FIG. 1B  are CMOS NPN transistors. A PA T/R switch  126  can be connected to an output of the power amplifier  132 . The PA T/R switch  126  can be configured to enable or prevent conduction of the transmit signal along signal path  116 . 
         [0033]    An LNA T/R switch  128  can be connected to an input of the amplifier  134 . In embodiments, the amplifier  134  can be a low-noise amplifier that receives and amplifies a signal sensed by the antenna  104 . The LNA T/R switch  128  can be configured to enable or prevent conduction, in response to a control signal (rx control), of the sensed signal appearing at an output  122   d  of an on-chip matching network  122  (discussed below) to an input of the amplifier  134 . 
         [0034]    In a transmit mode of operation, a signal to be transmitted (tx signal) is provided to the power amplifier  132 . The output of the power amplifier  132  constitutes a transmit signal that essentially follows signal path  116  toward the antenna  104 , where it is broadcast. In a receive mode of operation, signals sensed (i.e., received) by the antenna  104  essentially follows signal path  118  toward the amplifier  134 . The amplifier  134  amplifies the sensed signal to produce an output that constitutes a received signal (rx signal) which can be provided to downstream circuits (not shown) for further processing. 
         [0035]    As mentioned above, in accordance with the present invention, the matching network  4  comprises board matching network  124 . In embodiments, the matching network  4  may further comprise the on-chip impedance matching network  122  fabricated on the IC chip  108 . The on-chip matching network  122  may include a terminal  122   a  configured to receive via switch  126  the output (transmit signal) of the power amplifier  132 . Terminals  122   b  and  122   c  may be connected to respective external pins (not shown) of the IC chip  108 . The terminal  122   b  is configured to output the transmit signal to the external pin. The terminal  122   c  is configured to receive the signal sensed by the antenna  104 . A terminal  122   d  is configured to provide the signal sensed by the antenna  104  to amplifier  134 . The bond wires  112 ,  114  may have inductive characteristics. Accordingly, in an embodiment, the bond wires  112 ,  114  can be considered part of the board matching network  124 . 
         [0036]    Referring to  FIG. 2A , in embodiments, the IC chip  108  can be assembled on the same PCB  102  as the board matching network  122 , and connected together by traces  202  formed on the PCB  102 . The antenna  104  can be provided separate from the PCB  102 . In  FIG. 2B , an embodiment is shown wherein the IC chip  108  can be assembled on a PCB  102   a  different from the PCB  102 . A suitable connector  204  (e.g., flex connector) can be used to connect the PCB  102  and the PCB  102   a.  It will be appreciated that the matching network (either on-chip matching network  122  or board matching network  124 , or both) can be further configured to account of the impedance present in the connector  204 . A magnified area of  FIG. 2C  shows the bond wire  112 ,  114  connections to the traces  202 . 
         [0037]    Referring to  FIG. 3 , in an embodiment, all of the impedance matching components of the matching network  6  ( FIG. 1 ) can be provided by the board matching network  124 . In other words, all of the matching components are “off-chip” in that none of the matching components are fabricated on the IC chip  108 . In this embodiment, the on-chip matching network  122  in the IC chip  108  is effectively absent, comprising only traces  122   x  formed in a metal layer of the IC chip. The board matching network  124  comprises reactive elements X 1 -X 3 , and can be any suitable combination of inductors and/or capacitors. 
         [0038]    During receive mode operation, the PA T/R switch  126  and the LNA T/R switch  128  are OFF, so that signals sensed by the antenna  104  will essentially follow signal path  118 . Accordingly, the impedances that arise include the input impedance of the low-noise amplifier  134  seen at terminal  124   b  and some parasitic impedance seen at element X 2 . The X 1  and X 3  elements constitute an L-matching network and can be designed with element values based on the input impedance of the low-noise amplifier  134  and the parasitic impedance to transform those impedances to match the impedance of the antenna  104  and balun filter  106  assembly, for example  50 Ω. 
         [0039]    During transmit mode operation, the PA T/R switch  126  and the LNA T/R switch  128  are ON; the LNA T/R switch acts as a shunt to ground, thus bypassing the input to the low-noise amplifier  134 . Accordingly, the impedances that arise during include the low impedance path (e.g., several ohms) seen at terminal  124   b  due to the shunt. The X 1  element together with the X 2  and X 3  elements can be designed to be resonant with the balun filter  106  at the transmit frequency, thus maximizing the transmit output power delivered to the antenna  104 . 
         [0040]      FIG. 3A  shows an example of a more specific embodiment. Capacitors C 2  and C 3  and inductor L 1  are provided off-chip. For example, capacitors C 2  and C 3 , and inductor L 1  can be discrete components. Capacitors C 2  and C 3  can be IC components provided in discrete form and are assembled off-chip. The particular embodiment shown in  FIG. 3A  offers maximum flexibility in terms of accommodating changes to the matching network  6  because it is contained off-chip in board matching network  124 . However, the cost of having exclusively off-chip components may constitute an unacceptable cost in manufacture. For example, while low-cost discrete off-chip capacitors may be available, discrete inductors tend to be more expensive. 
         [0041]    In an embodiment, the matching network  6  ( FIG. 1 ) may comprise on-chip components, namely some of the components of the matching network may be integrated on the IC chip  108 . Accordingly, the embodiment shown in  FIG. 4  provides a board matching network  124  comprising capacitors C 2 , C 3  and an on-board matching network  12  comprising inductor L 1 . The inductor L 1  fabricated on the IC chip  108 ; i.e., it is on-chip as compared to the capacitors C 2 , C 3  which are off-chip. This configuration may be more acceptable in terms of manufacturing costs. For example, the inductor L 1  may be on the order of a few nano-Henries which lends itself to the possibility of integration. The cost of a discrete component vs. the degradation of performance of an integrated circuit version of the component may weigh in favor of integration. 
         [0042]      FIG. 5  illustrates a wireless communication system  502  incorporating an embodiment of the present invention. For example, wireless communication system  502  can be any handheld device such as a mobile communication device (e.g., cellular telephone), a computing device having wireless communication capability (e.g., laptop, notebook computer), a handheld gaming device having wireless communication capability (e.g., iPod Touch manufactured and sold by Apple Inc.), and so on. The wireless communication system  502  can use any communication standard such as the various IEEE 802 formats (e.g., Bluetooth, 802.11n, 802.11g and so on). 
         [0043]    As used in the description herein and throughout the claims that follow, “a”, “an”, and “the” includes plural references unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. 
         [0044]    The above description illustrates various embodiments of the present invention along with examples of how aspects of the present invention may be implemented. The above examples and embodiments should not be deemed to be the only embodiments, and are presented to illustrate the flexibility and advantages of the present invention as defined by the following claims. Based on the above disclosure and the following claims, other arrangements, embodiments, implementations and equivalents will be evident to those skilled in the art and may be employed without departing from the spirit and scope of the invention as defined by the claims.

Technology Category: h