Abstract:
The present invention provides a transceiver for a radio frequency identification (RFID) reader. The transceiver includes an RF front end, a transmitting component, a receiving component, a power divider and a micro control unit (MCU). The power divider has three terminals. The first terminal of the power divider is connected to the transmitting component. The second terminal of the power divider is connected to the receiving component. The third terminal is connected to the RF front end. Moreover, the MCU is connected to the transmitting component and the receiving component, and generates a transmitted signal and receives a retrieved data. According to the present invention, the transceiver further includes an RF switch, a matching circuit and a receiving circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of U.S. patent application No. 61/872,899, filed on Sep. 3, 2013, which is incorporated herewith by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a transceiver, and more specifically to a transceiver for a radio frequency identification (RFID) reader. 
     2. The Prior Arts 
     Nowadays, RFID has been widely used in various fields. In a traditional RFID reader of an RFID system, the analog front end (AFE) has a complex structure with a large circuit size, large power consumption and high cost.  FIG. 1  is a block diagram illustrating a transceiver  11  of a traditional RFID reader  1 . Referring to  FIG. 1 , the AFE  12  of the transceiver  11  of the traditional RFID reader  1  includes a pair of mixers  13  (i.e., an I-channel mixer  131  and a Q-channel mixer  132 ), a pair of dense reader mode (DRM) filters  14 , a pair of inputting gain circuits  15 , a pair of digitizers  16 , a received signal strength indication (RSSI) measuring means  17  and an outputting gain circuit  18 . 
     An RF signal RFS from an external device (such as an RFID tag) which is received by the RFID reader  1  is sent to a directional unit  19  and then sent to the pair of mixers  13 . The received RF signal RFS is down-converted to an I-channel baseband signal IBS and a Q-channel baseband signal QBS by the pair of mixers  13 , and the pair of DRM filters  14  eliminates undesired noise and harmonic components. Furthermore, the pair of inputting gain circuits  15  amplify the I-channel baseband signal IBS and the Q-channel baseband signal QBS. Subsequently, the amplified I-channel and Q-channel baseband signals are converted to digital signals IDS and QDS by the pair of digitizers  16 . The digital signals IDS and QDS are sent to an MCU for post processing. On the other hand, the amplified I-channel and Q-channel baseband signals are also sent to the RSSI measuring means so as to measure RSSI and thereby detect interference from other external devices. 
     However, the pair of mixers  13 , DRM filters  14  and inputting gain circuits  15  consume relatively large power, have large circuit size and high cost, which in turn results in a large overall size and high cost of the transceiver  11  of the RFID reader  1 . Further, in order to accommodate large power consumption, the RFID reader  1  may require an external power supply, such as a battery. Accordingly, such an RFID reader  1  is not suitable for a portable device. 
     It may therefore be desirable to have a transceiver for an RFID reader which has a simple structure, small size and low power consumption, which is suitable for a portable device. 
     SUMMARY OF THE INVENTION 
     In light of the foregoing drawbacks, an objective of the present invention is to provide a small-size low-power transceiver that is suitable for a portable device. 
     For achieving the foregoing objective, the present invention provides a transceiver for a radio frequency identification (RFID) reader. The transceiver of the present invention may include an RF front end, having an antenna and an RF filter connected to the antenna; a transmitting component, having a first matching circuit and a transmitting circuit connected to the first matching circuit; a receiving component, having a second matching circuit, a detecting circuit, an amplifier and an analog-to-digital (A/D) converter; a power divider, having a first terminal connected to the first matching circuit of the transmitting component, a second terminal connected to the second matching circuit of the receiving component and a third terminal connected to the RF filter of the RF front end; and a micro control unit (MCU), connected to the transmitting component and the receiving component, generating a transmitted signal and receiving a retrieved data. Moreover, the detecting circuit of the present invention may be connected between the second matching circuit and an input terminal of the amplifier, and the A/D converter of the present invention may be connected to an output terminal of the amplifier. 
     According to the present invention, the transceiver may further include an RF switch, a third matching circuit and a receiving circuit. The RF switch may have three terminals that are connected to the RF filter of the RF front end, the third matching circuit and the third terminal of the power divider, respectively. The receiving circuit and the transmitting component may be integrated and may perform long-distance duplex transmission. 
     Preferably, the third matching circuit of the present invention may provide impedance matching between the terminal of the RF switch and an input terminal of the receiving circuit. 
     Moreover, the first matching circuit of the present invention may provide impedance matching between the first terminal of the power divider and an output terminal of the transmitting circuit, and the second matching circuit of the present invention may also provide impedance matching between the second terminal of the power divider and an input terminal of the detecting circuit. 
     Preferably, the detecting circuit of the present invention may include a diode, a capacitor and a first resistor connected to the capacitor in parallel. In addition, the anode of the diode is connected to the second matching circuit, and the cathode of the diode is connected to a terminal of the capacitor and a terminal of the first resistor. 
     Preferably, the diode of the present invention may be a Shockley diode. In addition, the capacitor and the first resistor may form a low-pass filter. 
     Preferably, the amplifier of the present invention may include an operational (OP) amplifier and a plurality of second resistors. 
     Preferably, the amplifier may amplify a baseband signal. Additionally, the plurality of second resistors may form a bandpass filter. 
     Preferably, the A/D converter may be a discrete component or an integrated component, and the A/D converter is integrated into the MCU if the A/D converter is an integrated component. 
     Preferably, the power divider may be a Wilkinson power divider. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be apparent to those skilled in the art by reading the following detailed description of preferred exemplary embodiments thereof, with reference to the attached drawings, in which: 
         FIG. 1  is a block diagram illustrating a transceiver of a traditional RFID reader; 
         FIG. 2A  is a block diagram illustrating an RFID reader in accordance with an exemplary embodiment of the present invention; 
         FIG. 2B  is a block diagram illustrating the detecting circuit and the amplifier of  FIG. 2A  in accordance with an exemplary embodiment of the present invention; 
         FIG. 3A  is a block diagram illustrating an RFID reader in accordance with another exemplary embodiment of the present invention; and 
         FIG. 3B  is a block diagram illustrating the external devices and the RFID reader in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
     With regard to  FIGS. 1-3B , the drawings showing exemplary embodiments are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for clarity of presentation and are shown exaggerated in the drawings. Similarly, although the views in the drawings for ease of description generally show similar orientations, this depiction in the drawings is arbitrary for the most part. Generally, the present invention can be operated in any orientation. 
     In light of the foregoing drawings, an objective of the present invention is to provide a transceiver. Referring to  FIG. 2A ,  FIG. 2A  is a block diagram illustrating an RFID reader  2  in accordance with an exemplary embodiment of the present invention. Referring to  FIG. 2A , the RFID reader  2  may include an RF front end  21 , a power divider  22 , a transmitting component  23 , a receiving component  24  and a micro control unit (MCU)  25 . 
     The RF front end  21  may include an antenna  211  and an RF filter  212  connected to the antenna  211 . The transmitting component  23  may include a matching circuit  231  and a transmitting circuit  232  connected to the matching circuit  231 . The receiving component  24  may include a matching circuit  241 , a detecting circuit  242 , an amplifier  243  and an analog-to-digital (A/D) converter  244 . In this exemplary embodiment of the present invention, the detecting circuit  242  is connected between the matching circuit  241  and an input terminal  243   a  of the amplifier  243 . Furthermore, the A/D converter  244  is connected to the output terminal  243   b  of the amplifier  243 . 
     The power divider  22  has a terminal  22   a  connected to the RF filter  212  and two terminals  22   b  and  22   c  connected to the matching circuit  231  of the transmitting component  23  and the matching circuit  241  of the receiving component  24  respectively. 
     The matching circuit  231  may provide impedance matching between the terminal  22   b  of the power divider  22  and the output terminal  232   a  of the transmitting circuit  232 . Likewise, the matching circuit  241  may provide impedance matching between the terminal  22   c  of the power divider  22  and the input terminal  242   a  of the detecting circuit  242 . 
     In a transmitting mode that the reader  2  may transmit a signal to an external device (not shown) disposed away from the reader  2  with a relatively long distance (for example, in the range of 5 m), the transmitted signal (TS 1 ) may be generated by the MCU  25 . The signal TS 1  may then be modulated and up-converted to an RF signal TS 2  by the transmitting circuit  232 . The RF signal TS 2  may then be sent to the antenna  211  through the matching circuit  231 , the power divider  22  and the RF filter  212 . In one exemplary embodiment of the present invention, the power divider  22  may be but is not limited to a Wilkinson Power divider. Furthermore, the RF filter  212  may eliminate undesired noise and harmonic components of the RF signal TS 2 . The antenna  211  may then transmit the filtered RF signal TS 3  to the external device. 
     On the other hand, in a receiving mode that the reader  2  may receive signal from an external device  30  (such as an RFID tag) away from the reader  2  with a relatively short distance (such as in the range of 50 cm), an RF signal RS 1  from the external device  30  may be received by the antenna  211  and then be sent to the detecting circuit  242  through the RF filter  212 , the power divider  22  and the matching circuit  241 . Similarly, the RF filter  212  may eliminate undesired noise and harmonic components of the RF signal RS 1  (the filtered RF signal is termed as RS 2 ). 
     The detecting circuit  242 , the amplifier  243  and the A/D converter  244  operate as a whole may down-convert and demodulate the signal RS 2 , and data contained in the signal RS 2  may thus be retrieved. The retrieved data may then be sent to the MCU  25 . Furthermore, through the receiving component  24 , signals from other devices (not shown) at the same frequency band (or channel) as the signal RS 1  may be also received, and the RSSI may thus be measured. 
     Details of the structures and operations of the detecting circuit  242  and the amplifier  243  will be described in the exemplary embodiment of the present invention by reference to  FIG. 2B . 
       FIG. 2B  is a block diagram illustrating the detecting circuit  242  and the amplifier  243  of  FIG. 2A  in accordance with an exemplary embodiment of the present invention. Referring to  FIG. 2B , the detecting circuit  242  may include a diode  31 , a capacitor  32  and a resistor  33 . In one exemplary embodiment of the present invention, the diode  31  may be but is not limited to a Shockley diode. The anode  31   a  of the diode  31  may be connected to the matching circuit  241 , and the cathode  31   b  of the diode  31  may be connected to a terminal  32   a  of the capacitor  32  and a terminal  33   a  of the resistor  33 . The capacitor  32  and the resistor  33  may be connected in parallel. Furthermore, a terminal  32   b  of the capacitor  32  and a terminal  33   b  of the resistor  33  may be grounded. 
     The diode  31  may rectify the signal RS 2 . Furthermore, the capacitor  32  and the resistor  33  operating as a whole may function as a low pass filter to eliminate carrier of the signal RS 2 . Thereby, the RS 2  may be down-converted to a baseband signal RS 3 . 
     The amplifier  243  may include an operational amplifier (op-amp)  34  and four resistors  35 ,  36 ,  37  and  38 . The non-inverting input terminal  34   a  of the op-amp  34  may be connected to the cathode  31   b  of the diode  31  through the resistor  35  and receive the baseband signal RS 3  from the detecting circuit  242 . Furthermore, through the resistor  36 , the inverting input terminal  34   b  may be connected to a voltage source (not shown) supplying a bias voltage Vb. A terminal  37   a  of the resistor  37  may be connected to the inverting input terminal  34   b  of the op-amp  34 , and a terminal  37   b  of the resistor  37  may be grounded. The resistor  38  may be connected between the non-inverting input terminal  34   a  and the output terminal  34   c  of the op-amp  34 . The op-amp  34  may amplify the baseband signal RS 3 , and the four resistors  35 ,  36 ,  37  and  38  may function as a bandpass filter to eliminate undesired noise. 
     The amplified baseband signal RS 4  may then be sent to the A/D converter  244 , and the A/D converter  244  may convert the amplified baseband signal RS 4  to digital signal. The digital signal represents the data contained in the signal RS 2 . In one exemplary embodiment of the present invention, the A/D converter  244  may be a discrete component. In another exemplary embodiment of the present invention, the A/D converter  244  may be integrated into the MCU  25 . 
       FIG. 3A  is a block diagram illustrating a RFID reader  4  in accordance with another exemplary embodiment of the present invention. Referring to  FIG. 3A , the reader  4  may be similar to the reader  2  illustrated in  FIG. 2A  except that, the reader  4  may further include a receiving circuit  41 , a matching circuit  42  and a switch  43 . In this exemplary embodiment of the present invention, the receiving circuit  41  and the transmitting circuit  232  are parts of a transceiver chip  44  which is capable of performing long-distance duplex transmission. 
     In one exemplary embodiment of the present invention, the switch  43  may be but is not limited to a single pole double throw (SPDT) RF switch. The SPDT RF switch  43  has three terminals  43   a ,  43   b  and  43   c  which are connected to the RF filter  212 , the matching circuit  42  and the terminal  22   a  of the power divider  22  respectively. 
     In the transmitting mode, the SPDT RF switch  43  may be configured to connect the RF front end  21  to the terminal  22   a  of the power divider  22 , which may in turn connect the RF front end  21  to the transmitting circuit  232 . As described in the exemplary embodiment of the present invention by reference to  FIG. 2A , with the help of the transmitting circuit  232 , signal generated by the MCU  25  may be transmitted to an external device  51  which is located away from the reader  4  with a relatively long distance (as shown in  FIG. 3B  which illustrates the external device  51  and the RFID reader  4  in accordance with an exemplary embodiment of the present invention). Such an external device  51  may be but is not limited to a household appliance, for example, a television. 
     Referring back to  FIG. 3A , on the other hand, in the receiving mode, the SPDT RF switch  43  may be configured to connect the RF front end  21  to the matching circuit  42 , which may in turn connect the RF front end  21  to the receiving circuit  41 . With the help of the receiving circuit  41 , signal from the external device  51  may be received by the reader  4 . 
     Referring to  FIG. 3B , with the help of the transmitting circuit  232  and the receiving circuit  41 , the household appliance  51  may transmit and receive control signals to and from the reader  4 . Through the control signals, the household appliance  51  and a portable device  52  (such as a tablet computer or a smart phone) equipped with the reader  4  may be matched as a pair. In one exemplary embodiment of the present invention, the portable device  52  may function as a remote controller of the household appliance  51 . Furthermore, before receiving control signal from the household appliance  51 , the receiving circuit  41  of the reader  4  is capable of measuring RSSI so as to avoid interference from other household appliances  53  and  54 . 
     In this exemplary embodiment of the present invention, with the help of the receiving component  24 , the reader  4  may be still capable of receiving signal from the RFID tag  30 . 
     The above exemplary embodiments describe the principle and effect of the present invention, but are not limited to the present invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents. 
     Although the present invention has been described with reference to the preferred exemplary embodiments thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.