Patent Publication Number: US-8989678-B2

Title: Transceiver and method thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of U.S. Provisional Application No. 61/503,273, filed on 30 Jun. 2011, and the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to wireless communication, and in particular relates to transceiver circuitry for wireless communication. 
     2. Description of the Related Art 
     Wireless communications systems operate over limited spectral bandwidths for providing quality service to all users. The wireless communication system includes a built-in radio transceiver, i.e., a receiver and a transmitter. The transmitter includes a power amplifier stage for amplifying the outgoing signal prior to transmission via an antenna and the receiver includes a low noise amplifier stage for amplifying the incoming signal picked up by the antenna. The transmitter and the receiver may share a common antenna through a transmit/receive (TR) switch. 
     As technology advances, the radio transceiver can be fabricated on an integrated circuit. Recently, amplifier technology has made tremendous progress in terms of device such as low noise and low power, circuit computer aided design (CAD) tools, circuit fabrication, packaging, and applications. Regarding the applications at millimeter wave frequencies, the design of silicon based TR switches is challenging due to the coupling of the radio frequency (RF) signals, which simultaneously increases insertion loss and decreases port to port isolation of the switch. As a consequence, the design of a CMOS TR switch at microwave frequencies requires a careful circuit design to meet the desired requirements for such as insertion loss, isolation, and signal sensitivity. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect of the invention, a transceiver is disclosed, comprising a transmitter, a receiver, and a three-port network. The transmitter is configured to transmit an outgoing RF signal. The receiver is configured to receive an incoming RF signal. The three-port network comprises a transmission line, configured to have a line length less than a quarter of a wavelength of the incoming RF signal; an antenna port, configured to connect to an antenna; a receiver port, configured to connect the receiver to the antenna port; and a transmitter port, configured to connect the transmitter to the antenna port and the receiver port through the transmission line. 
     In another aspect of the invention, a transceiver is provided, comprising a transmitter, a receiver, and a three-port network. The transmitter is configured to transmit an outgoing RF signal. The receiver is configured to receive an incoming RF signal. The three-port network comprises a transmission line, configured to have a line length less than a quarter of a wavelength of the outgoing RF signal; an antenna port, configured to connect to an antenna; a transmitter port, configured to connect the transmitter to the antenna port; and a receiver port, configured to connect the receiver to the antenna port and the transmitter port through the transmission line. 
     In yet another aspect of the invention, a method for a transceiver is revealed, comprising: turning on a transmitter amplifier of the transceiver, and turning off a receiver amplifier of the transceiver; and transmitting an outgoing RF signal from the transmitter amplifier to an antenna through a three-port network, wherein the three-port network comprises a transmission line, configured to have a line length less than a quarter of a wavelength of the incoming RF signal; an antenna port, configured to connect to the antenna; a receiver port, configured to connect the receiver to the antenna port; and a transmitter port, configured to connect the transmitter to the antenna port and the receiver port through the transmission line. 
     In still another aspect of the invention, a method for a transceiver is described, comprising: turning on a transmitter amplifier of the transceiver, and turning off a receiver amplifier of the transceiver; and transmitting an outgoing signal from the transmitter amplifier to an antenna through a three-port network, wherein the three-port network comprises: a transmission line, configured to have a line length less than a quarter of a wavelength of the outgoing RF signal; an antenna port, configured to connect to an antenna; a transmitter port, configured to connect the transmitter to the antenna port; and a receiver port, configured to connect the receiver to the antenna port and the transmitter port through the transmission line. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a system diagram of a wireless communication system  1  according to one embodiment of the invention; 
         FIG. 2  is a block diagram of a radio transceiver circuit  2  according to an embodiment of the invention; 
         FIG. 3  is a block diagram of a radio transceiver circuit  3  according to another embodiment of the invention; 
         FIGS. 4A , B, and C illustrate physical implementation, a block diagram, and an equivalent circuit of the transmission line; 
         FIG. 5  is a flowchart of a transmission and reception method  5  performed by the radio transceiver circuit  2  according to an embodiment of the invention; and 
         FIG. 6  is a flowchart of a transmission and reception method  6  performed by the radio transceiver circuit  3  according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
       FIG. 1  is a system diagram of a wireless communication system  1  according to one embodiment of the invention, comprising a service network and a plurality of User Equipment (UE) capable of receiving a network service therefrom. The service network may be a Wireless Local Area network (WLAN), a General Packet Service (GPRS) network, a Universal Mobile Telecommunication System (UMTS) network, a Long Term Evolution (LTE) network, or a combination thereof. The UEs  10   a ,  10   b , and  10   c  are any device used directly by an end-user for communication, e.g., handheld mobile phones, laptop or personal computers equipped with broadband network adaptors, or any other device capable of communication. The service network comprises a radio access network that provides wireless communication in radio frequencies and a core network that provides network services to the wireless devices. The radio access network comprises a base station (BS) or access point (AP)  12 . The core network/local network  14  provides various services including circuit-switched (CS) based services to the wireless devices by interfacing with a CS based network such as the Public Switched Telephone Network (PSTN), and Packet Switched (PS) based services by interfacing with a Internet Protocol (IP) based Network such as the Internet. The wireless communication system  1  is implemented using a time division duplexing (TDD) technique, where the UEs  10  and the BS/AP  12  communicate through uplink and downlink communications at different times, typically by asymmetrical uplink and downlink data rates. The Hardware construction of the wireless devices  10   a ,  10   b , and  10   c  and BS/AP  12  are further detailed in the communication devices disclosed in  FIG. 2  and  FIG. 3 . 
     Conventionally, a quarter wavelength transmission line is inserted between the transmitter and the receiver in a transceiver circuit as an isolation network. For a quarter wavelength transmission line when one end is attached to a zero load impedance such as by grounding, the other end which is a quarter wavelength away from the short circuited end becomes infinitely large or open circuited for a signal with a corresponding quarter wavelength equivalent to the transmission cable length. Consequently no signal with the frequency of the quarter wavelength cable can pass through, whereas a signal with a different wavelength can go through the transmission line. The quarter-wavelength transmission line property is applied in a conventional TR switch to isolate an LNA from a PA during a transmitter operation so that an outgoing RF signal does not go into the LNA. When the outgoing RF signal is applied by the transmitter, one end of the quarter-wavelength transmission line connected to the receiver is grounded so that the other end connected to the transmitter becomes an open line for the specific frequency of the outgoing RF signal; hence separating the receiver from the transmitter during transmission. Conversely, when an incoming RF signal is accepted by the receiver, one end of the quarter-wavelength transmission line connected to the transmitter is grounded, so that the other end connected to the receiver is opened, thus isolating the transmitter from the incoming RF signal during reception. In any case, the transmission line has the finite length of a quarter wavelength to provide the isolation between the transmitter and receiver, thus the transmitter or the receiver is at least the quarter wavelength away from the antenna, rendering a finite circuit area occupied by the transmission line, and unwanted signal loss or signal degradation. 
       FIG. 2  is a block diagram of a radio transceiver circuit  2  according to an embodiment of the invention, comprising a transmitter  20 , a receiver  22 , a transmitter-receiver (TR) switch  24 , and a baseband module  26 . The transceiver circuit  2  may be implemented in an integrated circuit (IC) or a discrete circuit comprising the illustrated blocks. The radio transceiver circuit  2  can be incorporated in a wireless communication device such as the UEs  10   a ,  10   b ,  10   c  and the BS/AP  12 , allowing uplink and downlink data transmission to be performed via a single antenna. The baseband module  26  is operable to generate outgoing digital signals for uplink transmission and to process incoming digital signals from downlink reception. The transmitter  20  carries out analog signal processing for the data transmission and the receiver  24  performs analog signal processing for the data reception. The TR switch  24  is a three-port device which allows the transmitter  20  and the receiver  22  to operate with a single antenna  28 , and is capable of connecting and disconnecting to the antenna  28  for the transmit and receive processes. The shared antenna  28  may be built-in or external to the radio transceiver circuit  2 , and shared by the transmission and reception path as controlled by the TR switch  24 . The implementation of the radio transceiver circuit  2  and the antenna  28  are compliant with a communication standard to which the wireless communication device adopts. 
     The transmitter  20  comprises a power amplifier (PA) (transmitter amplifier)  202  and a transmitter filter  204 . During the transmit process, the outgoing digital signals are outputted to a transmitter front end (not shown) for analog conversion, up-conversion, and other filtering processes, where the signal is transformed into an analog form, up-converted to a radio frequency (RF), and removed of unwanted signal components, to provide an outgoing radio frequency signal to the PA  202 . The radio frequency of the outgoing RF signal S out  is defined by the communication standard to which the wireless communication device adopts, and may be 60 GHz. The PA  202  is operable to increase transmission power of the outgoing RF signal S out  to a predetermined power range or a predetermined power level that may be assigned by the service network. The transmitter matching network  204  may comprise resistive, inductive and capacitive components, arranged to provide output impedance matching for the PA  202 , thereby increasing or maximizing power transfer of the outgoing RF signal S out  to the antenna  28 . The selection of the components for the transmitter matching network is determined by considering the data transmission condition, i.e., when the PA  202  is turned on and the LNA  222  is turned off. The transmitter matching network is constructed to transform turned-on output impedance of the PA  202  to match with the combined loading of the turned-off input impedance of the LNA  222  and antenna port loading of an antenna port  244  which is connected to the antenna  28 . The transmitter matching network  204  may further include a low pass filter or a bandpass filter to reduce or remove unwanted signal components. The TR switch  24  is operable to enable a transmission path to the PA  202  and disable the LNA  222  from the antenna  28  to pass the filtered outgoing RF signal S out  to the antenna  28  for the uplink transmission. 
     The receiver  22  comprises a receiver matching network  220  and a low noise amplifier (LNA) (receiver amplifier)  222 . The receiver  22  receives the incoming RF signal S in  via the antenna  28 . The TR switch  24  is adapted to enable the reception path to the LNA  222  and disable the transmission path of the PA  202  from the antenna  28  to deliver the incoming RF signal S in  for the data reception. The antenna  28  picks up and passes the incoming RF signal S in  from air interface to the receiver matching network  220  via the TR switch  24 . The receiver matching network  220  provides input impedance matching for the LNA  222 , thereby increasing power transfer and reducing signal reflection of the incoming RF signal S in . The selection of the components for the receiver matching network is determined by considering the data reception condition, i.e., when the LNA  222  is turned on and the PA  202  is turned off. The receiver matching network is constructed to transform turned-on input impedance of the LNA  222  to match with the combined loading of the turned-off output impedance of the PA  202  and the antenna port loading of the antenna port, and also take into account the transmission line  246  in the TR switch  24 . The receiver matching network  220  may further include a bandpass filter producing a filtered RF signal to the LNA  222 , which amplifies an incoming RF signal S in , while adding little or no noise and distortion to the amplified RF signal. The amplified incoming RF signal S in  is transferred to a receiver front end (not shown), where filtering processes, down-conversion, and analog to digital conversion is performed to output a baseband signal for processing by the baseband module  26 . 
     The TR switch  24  controls connection and disconnection of a transmit path to the transmitter  20  and a receive path to the receiver  22 , such that the transmitter  20  and receiver  22  can share the same antenna  28  for outgoing and incoming transmission. The TR switch  24  employs a transmission line  246  to isolate the input impedance of the LNA  222  and part of the pad and ESD capacitance from the PA  202 . Assumed in absence of the transmission line  246 , the antenna port loading at the antenna port  244  might include loading due to PA output, LNA input, ESD, pad, power detector, bump to bump capacitance, resulting in a small inductor with inductance L load . Given that the voltage V and inductance L load  is related by the expression V=IwL Load , the small inductance L load  renders increased current requirement to provide a voltage swing of 2V DD  with the voltage V DD  being a full swing of the voltage V, therefore efficiency of the PA  202  is reduced. In presence of the transmission line  246 , as illustrated in the embodiment, the antenna port loading at antenna port  244  is reduced, since the LNA input impedance and part of the pad and ESD capacitance are isolated by the transmission line  246 , leading to decreased current requirement and increased PA efficiency. 
     The TR switch  24  in the present invention employs a transmission line which can be of any length. In practice, longer transmission line introduces more loss. In some implementations, the transmission line has a length less than a quarter of a wavelength of the outgoing RF signal S out  to provide reduced circuit area, increased signal quality, and a more flexible circuit floor planning in comparison to the conventional TR switch. The TR switch  24  includes a network connection to couple the transmitter  20  to the antenna  28  for data transmission and to disable a communication path between the antenna  28  and the receiver  22  to prevent the LNA  222  from receiving unwanted outgoing RF signal S out , or, alternatively, to disable the PA  202  from producing the amplified outgoing RF signal to the antenna  28  while enabling the communications path from the antenna  28  to the receiver  22  for the data reception. The TR switch  24  comprises a transmitter port  240 , a receiver port  242 , an antenna port  244  and the transmission line  246 . A control switch (not shown in  FIG. 2 ) can be inserted between the transmission line  246  and the LNA  222 . For example, in one implementation, the control switch is implemented in the receiver matching network  220  or in the TR switch  24 ; in another implementation, the control switch is implemented on the path between the transmission line  246  and the receiver matching network  220 . 
     On the transmission line, the voltage and current vary along the line path.  FIGS. 4A , B, and C illustrate physical implementation, a block diagram, and an equivalent circuit of an example of the transmission line. The example of transmission line is regarded as an ideal loseless line, specialized to carry alternating current of a radio frequency. That is, currents with a frequency high enough that its wave nature must be taken into account. Refer to  FIG. 4A , the transmission line comprises signal line  400 , ground layers  402 , top metal  404 , vias  406 , and bottom metal  408 . The signal line  400  carries the RF signals to and from the antenna. The transmission line can be in the form of a coaxial cable, a microstrip, a stripline, a balanced line, a twisted pair, a combination thereof or other available types.  FIG. 4B  shows the transmission line modeled as a two-port network, comprising a transmission line  410  with a characteristic impedance Z o , Port A and Port B. The two-port network is assumed to be linear, or, the complex voltage across either port is proportional to the complex current flowing into the port when there are no reflections, and the two ports are assumed to be interchangeable. The transmission line  410  is uniform along the length thereof, and the behaviour is largely described by a single parameter called the characteristic impedance, symbol Z 0 , represented by a ratio of the complex voltage of a propogation wave to the complex current of the same wave at any point on the line  410 . Typical values of Z 0  are 50 or 75 ohms for a coaxial cable, about 100 ohms for a twisted pair of wires, and about 300 ohms for a common type of untwisted pair used in radio transmission. When sending a signal down a transmission line, it is usually desirable that as much power of the signal as possible will be absorbed by the load and as little as possible will be reflected back to the source. This can be ensured by making the load impedance equal to Z 0 , in which case the transmission line is said to be matched. 
     Refer to  FIG. 4C , showing an equivalent circuit of the transmission line in  FIG. 4A , comprising a resistance R and inductance L in Series with a capacitance C and conductance G in parallel. The resistance R and conductance C contribute to the loss of the transmission line. Some of the power fed into the transmission line is lost because of the resistance R, referred to as ohmic or resistive loss. At high frequencies, another effect called dielectric loss becomes significant, adding to the losses caused by resistance, arising from the insulating material inside the transmission line absorbs energy from the alternating electric field and converts it to heat. The voltage V(x) and current I(x) at each point x of the transmission line can be represented by the following expressions: 
     
       
         
           
             
               
                 
                   
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     In some implementations, another transmission line (not shown) can be inserted between the antenna port  244  and the antenna  28 . In further other implementations, the antenna port  244  is configured to directly connect to the antenna  28 . 
     The transmitter port  240  is configured to directly connect to the transmitter matching network  204 . The receiver port  242  is configured to directly connect to the receiver matching network  220 , and to the transmitter port  240  and the antenna port  244  through the transmission line  246  having a length less than a quarter of a wavelength of the outgoing RF signal S out . The control switch controls connection and disconnection of the transmit path and receive path to the antenna  28 , and may be realized by a transistor or a diode. When the control switch is closed, the TR switch  24  enables the transmit path between the transmitter  20  and the antenna  28  for the outgoing RF signal S out  and disables the receive path to prevent the transmit power from being absorbed by the LNA  222 . Conversely, when the control switch is opened, the TR switch  24  enables the receive path between the antenna  28  and receiver  22  for the incoming RF signal S in , and disables the transmit path to prevent the received signal from being absorbed by the PA  202 . 
     In the embodiment, the transmission line  246  has a length less than a quarter of a wavelength of the outgoing RF signal S out . Because the length of the transmission line is not one quarter wavelength long and the voltage and current vary with the line length, the design of the receiver matching network  220  needs to take the transmission line length into account, such that the turned-on input terminal of the LNA  222  in combination with the matching network filter  220  produces a matched impedance matching to the combined loading of the turned-off output impedance of the PA  202  and the antenna port loading of the antenna port, in the presence of the non-quarter-wavelength transmission line. 
     The TR switch  24  in the embodiment using the transmission line of any length, offering circuit layout flexibility, decreased insertion loss, reduce circuit area, and decreased manufacturing cost, while providing circuit isolation between the transmitter and receiver during data transmission and reception. 
       FIG. 3  is a block diagram of a radio transceiver circuit  3  according to another embodiment of the invention, comprising a transmitter  30 , a receiver  32 , a TR switch  34 , and a baseband module  36 . The transceiver circuit  3  may be implemented in an integrated circuit (IC) or a discrete circuit comprising the illustrated blocks. The transmitter  30 , the receiver  32 , and the baseband module  36  are identical to the transmitter  20 , the receiver  22 , and the baseband module  26 , thus explanations can be found in the preceding paragraphs. The TR switch  34  comprises a transmitter port  340 , a receiver port  342 , an antenna port  344 , and a transmission line  346 . A control switch (not shown in  FIG. 3 ) can be inserted between the transmission line  346  and the PA  302 . For example, in one implementation, the control switch is implemented in the transmitter matching network  304  or the TR switch  34 ; in another implementation the control switch is implemented on the path between the transmission line  346  and the transmitter matching network  304 . The TR switch  34  is different from the TR switch  24  on the connection of the transmission line  346  and the switch  340 . The transmission line  346  can be of any length. In one implementation, the transmission line  346  has the length less than one quarter wavelength of the incoming RF signal S in . In some implementations, another transmission line (not shown) is inserted between the antenna port  344  and the antenna  38 . In other implementations, the antenna port  344  is configured to directly connect to an antenna  38 . The receiver port  342  is configured to directly connect to the receiver filter  320 . The transmitter port  340  is configured to directly connect to the transmitter filter  304 , and to the receiver port  342  and the antenna port  344  through the transmission line  346 . The control switch controls connection and disconnection of the transmit path and receive path to the antenna  38 , and may be realized by a transistor or a diode. When the control switch is closed, the TR switch  34  enables the receive path between the antenna  38  and receiver  32  for the incoming transmission and disables the transmit path to prevent the received signal from being absorbed by the PA  302 . Conversely, when the control switch is opened, the TR switch  34  enables the transmit path between the transmitter  30  and the antenna  38  for the outgoing transmission and disables the receive path to prevent the transmit power from being absorbed by the LNA  322 . Because the length of the transmission line  346  is not one quarter wavelength long and the voltage and current vary with the line length, the design of the receiver filter  320  needs to take the transmission line length into account, such that the turned-on input terminal of the LNA  322  in combination with the receiver filter  320  produces a matched impedance matching to the combined loading of the turned-off output impedance of the PA  302  and the antenna port loading of the antenna port  344 , in the presence of the non-quarter-wavelength transmission line  346 . 
     Because the transmission line  346  is not placed on the receive path to the receiver, the configuration of the TR switch  34  provides enhanced receiver sensitivity comparing to the TR switch  24  in the radio transceiver circuit  2 . Since the transmission line  346  can be of any length, and in particularly, can be a length less than the quarter wavelength of the incoming RF signal S in , the TR switch  34  provides circuit layout flexibility, reduced circuit area, and decreased manufacturing cost, while maintaining circuit isolation between the transmitter and receiver in operation. 
     Although the transmission line is located on either the receive path or the transmit path in the radio transceiver ICs  2  and  3 , those skilled in the art will recognize that the transmission lines and the grounding switches may be incorporated on both the transmit and receive paths, using the principle of the invention. 
     Referring to  FIG. 2 , when considering the circuit design for the transmitter matching network  204  and receiving matching network  220 , the following procedure can be adopted. To begin, the transmitter matching network is designed to match the turned-on output impedance of the PA  202  to the combined loading of the port loading of the antenna port  244  and the turned-off input impedance of the LNA  222 . The line length of the transmission line  246  is determined according to the actual physical floor planning of the transmitter, the receiver, and the TR switch circuitry. A shortest distance between the antenna port  244  and the receiver  22  may be selected as the line length, which can be less than a quarter wavelength. The receiver matching network is the next to be designed to match the turn-on input impedance of the LNA  222  in accordance to the combined loading of the antenna port  244 , the turned-off output impedance of the PA  202 , and the effect of the line length of the transmission line  246 . 
     Referring to  FIG. 3 , when considering the circuit design for the transmitter matching network  304  and receiving matching network  320 , the following procedure can be adopted. To begin with, the transmitter matching network is designed to match the turned-on output impedance of the PA  302  to the combined loading of the port loading of the antenna port  344  and the turned-off input impedance of the LNA  322 . The line length of the transmission line  346  is determined according to the actual physical floor planning of the transmitter  30 , the receiver  32 , and the TR switch  34  circuitry. A shortest distance between the antenna port  344  and the receiver  32  may be selected as the line length, which can be less than a quarter wavelength. Having the transmission line  346  being inserted between the antenna port and the PA  302 , the transmitter matching network is then adjusted to accommodate the effect of the line length of the transmission line  346 . Lastly, the receiver matching network is designed to match the turn-on input impedance of the LNA  322  in accordance to the combined loading of the antenna port  244 , and the turned-off output impedance of the PA  302 . 
       FIG. 5  is a flowchart of a transmission and reception method  5  performed by the radio transceiver circuit  2  according to an embodiment of the invention. Upon startup, the radio transceiver circuit  2  is initialized for transmitting and receiving RF signals (S 500 ). During transmission, the PA  202  is turned on and the LNA  222  is turned off (S 502 ), so that the PA  202  can transmit the outgoing RF signal S out  to the antenna  28  through the three-port network  24  detailed in the preceding explanation (S 504 ). During reception, the PA  202  is turned off and the LNA  222  is turned on (S 506 ), so that the LNA is enabled to receive the incoming RF signal S in  to the antenna  28  through the three-port network  24 , as detailed  FIG. 2  (S 508 ). The three-port network  24  comprises the transmission line  246  located on the receive path, resulting in When the radio transceiver circuit  2  is no longer required to perform data communication, the transmission and reception method  5  is exited and completed (S 510 ). 
       FIG. 6  is a flowchart of a transmission and reception method  6  performed by the radio transceiver circuit  3  according to an embodiment of the invention. Upon startup, the radio transceiver circuit  3  is initialized for transmitting and receiving RF signals (S 600 ). During transmission, the PA  202  is turned on and the LNA  222  is turned off (S 602 ), so that the PA  202  can transmit the outgoing RF signal S out  to the antenna  28  through the three-port network  24  detailed in the preceding explanation (S 604 ). During reception, the PA  202  is turned off and the LNA  222  is turned on (S 606 ), so that the LNA is enabled to receive the incoming RF signal S in  to the antenna  28  through the three-port network  24 , as detailed  FIG. 2  (S 608 ). When the radio transceiver circuit  3  is no longer required to perform data communication, the transmission and reception method  6  is exited and completed (S 610 ). 
     As used herein, the term “determining” encompasses calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.