Abstract:
A transmitter in an RFID system, the transmitter includes a signal generator which has a PIN diode and generates a first signal, a directional unit connected to a cathode of the PIN diode; and an antenna connected to the directional unit, wherein the signal generator has a first terminal configured to receive a first control signal to control a frequency band of the first signal and a second terminal configured to receive a second control signal to control a modulation depth of the first signal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to a transmitter and, more particularly, to a transceiver having the same in a radio-frequency identification (RFID) system. 
         [0002]    RFID technology is prevalent and applied nowadays in various industries such as electronic payment, security and stock inventorying, etc.  FIG. 1  shows a structure of a conventional reader  1  in an RFID system. The reader  1  may include a directional coupler  10  having four ports ( 101 ,  102 ,  103  and  104 ), an antenna  11 , a transmitter portion  12  and a receiver portion  13 . The transmitter portion  12  includes an oscillator  121 , a surface acoustic wave (SAW) device  122 , an amplifier  123 , a first diode  124  and a forward power leveling controller  125 . The receiver portion  13  includes a second diode  131 , an amplifier  132  and a comparator  133 . 
         [0003]    A signal from the transmitter portion  12  may be sent to the antenna  11  through the directional coupler  10 . However, the four-port directional coupler  10  may largely attenuate signals from the transmitter portion  12  and therefore the attenuated signals transmitted from the antenna  11  may not have sufficient power to activate an electronic tag (not shown). 
         [0004]    Still referring to  FIG. 1 , the first diode  124  and the forward power leveling controller  125  form a feedback path to monitor output power and maintain an amplitude of transmitted RF signal at a desired level. Complex feedback mechanisms must be developed to help the first diode  124  and the forward power leveling controller  125  controlling the output power. Moreover, it may take lots of efforts to solve problems such as stability when designing the feedback mechanism. 
         [0005]    It may therefore desirable to have a cost efficient device with a simplified circuit. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    Examples of the present invention may provide a transmitter in an RFID system, the transmitter includes a signal generator which has a PIN diode and generates a first signal, a directional unit connected to a cathode of the PIN diode; and an antenna connected to the directional unit, wherein the signal generator has a first terminal configured to receive a first control signal to control a frequency band of the first signal and a second terminal configured to receive a second control signal to control a modulation depth of the first signal. 
         [0007]    Some examples of the present invention may also provide a transmitter in an RFID system, the transmitter includes a signal generator and a directional unit, the signal generator has a carrier generator, an amplifier to receive a carrier signal from the carrier generator, a PIN diode that includes an anode connected to an output of the amplifier and a bias circuit having a first terminal to receive a first control signal to control a frequency band of the carrier signal, a second terminal connected to an anode of the PIN diode and the output of the amplifier, and a third terminal connected to a cathode of the PIN diode, and the directional unit is connected to the cathode of the PIN diode. 
         [0008]    Some examples of the present invention may also provide a transceiver in an RFID system, the transceiver has a signal generator having a PIN diode and generating a first signal, a directional unit connected to a cathode of the PIN diode; and a receiving circuit connected to the directional unit, wherein the signal generator comprises a first terminal configured to receive a first control signal to control a frequency band of the first signal and a second terminal configured to receive a second control signal to control a modulation depth of the first signal. 
         [0009]    Additional features and advantages of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The features and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
         [0010]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0011]    The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings examples which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
           [0012]    In the drawings: 
           [0013]      FIG. 1  is a block diagram of a conventional reader  1  in an RFID system; 
           [0014]      FIG. 2A  is a block diagram of a transmitter  2  in an RFID system in accordance with an example of the present invention; 
           [0015]      FIG. 2B  is a block diagram further illustrating the transmitter  2  as shown in  FIG. 2A  in accordance with an example of the present invention; 
           [0016]      FIG. 3  is a block diagram of a transceiver  2 ′ in an RFID system in accordance with an example of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Reference will now be made in detail to the present examples of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
         [0018]      FIG. 2A  is a block diagram of a transmitter  2  in an RFID system in accordance with an example of the present invention. Referring to  FIG. 2A , the transmitter  2  may include a micro control unit (MCU)  3 , a digital processor  4 , a signal generator  20 , a directional unit  5  and an antenna  6 . 
         [0019]    The digital processor  4  may connect to the MCU  3 . The signal generator  20  may be connected between the digital processor  4  and the directional unit  5 . The directional unit  5  may connect to the antenna  6  by which a signal may be sent to a tag  7 . In another example, the digital processor  4  and the MCU  3  may be integrated into a control circuit (not shown). 
         [0020]    The signal generator  20  may include a carrier generator  201 , an amplifier  202 , a diode  203  and a bias circuit  204 . The digital processor  4  may connect to a first terminal of the bias circuit  204 . A second terminal of the bias circuit  204  may connect to the anode of the diode  203  and an output of the amplifier  202 . A third terminal of the bias circuit  204  may connect to the cathode of the diode  203 . The amplifier  202  may have an input terminal which may connect to the carrier generator  201 . The third terminal of the bias circuit  204  and the cathode of the diode  203  may connect to the directional unit  5 . 
         [0021]    The carrier generator  201  may generate a signal TS 1  at a frequency f ts1 , and the signal TS 1  may then be sent to the amplifier  202 . The amplifier  202  may receive the signal TS 1 , then amplify the voltage and/or power of signal TS 1  and in turn output an amplified signal TS 2 , which may be sent to the diode  203 . In another example, the frequency f ts1  may be but is not limited to approximately 433.92 mega hertz (MHz) and the amplifier  202  may linearly amplify the signal TS 1 . In yet another example, the frequency f ts1  may be but is not limited to approximately 915 MHz. 
         [0022]    The diode  203  may be but is not limited to a p-intrinsic-n (PIN) diode. The digital processor  4 , which may be subject to the MCU  3 , may send a control signal to the bias circuit  204  to change the voltage level across the diode  203 , which may further vary the impedance of the diode  203 . In this manner, the amplitude of signal TS 2  may be changed to perform an amplitude-shift-keying (ASK) modulation on signal TS 2 . The diode  203  may output and send an ASK modulated signal TS 3  to the directional unit  5 . The directional unit  5  may process the signal TS 3  and send a signal TS 4  to the antenna  6 . The signal TS 4  may be transmitted to the tag  7  by the antenna  6 . 
         [0023]    A fourth terminal of the bias circuit  204  may connect to a terminal VM, which may supply at least one voltage level to the fourth terminal of the bias circuit  204 . For example, the terminal VM may supply a relatively low voltage level to the bias circuit  204  such that the signal generator  20  may perform an ASK modulation with 75% modulation depth. In another example, the terminal VM may supply a relatively high voltage level to the bias circuit  204  such that the signal generator  20  perform an ASK modulation with 50% modulation depth. In another example, the terminal VM may be eliminated and the fourth terminal of the bias circuit  24  may connect to the digital processor  4 . 
         [0024]      FIG. 2B  is a block diagram further illustrating the transmitter  2  as shown in  FIG. 2A  in accordance with an example of the present invention. Referring to  FIG. 2B , the bias circuit  204  may include a variable resistor VR, two resistors R 1  and R 2 , two inductors L 1  and L 2 , a switch SW and a transistor Q 1 . 
         [0025]    The variable resistor VR may have a terminal connected to a voltage terminal VDD which may supply a direct current (DC) voltage level. Another terminal of the variable resistor VR may connect to the resistor R 1  and the switch SW, which are connected in parallel. The switch SW may connect to the digital processor  4 . The resistor R 2  may connect to the resistor R 1  and the inductor L 1  in series. The inductor L 1  may have a terminal connected to the output of the amplifier  202  and the anode of the diode  203 . The inductor L 2  may have a terminal connected to the cathode of the diode  203  and the directional unit  5  and another terminal which is grounded. The transistor Q 1  may have a first terminal connected to the terminal VM. The transistor Q 1  may further have a second terminal and a third terminal and the resistor R 2  may be connected between the second and third terminals of the transistor Q 1 . In one example, the transistor Q 1  may be but is not limited to a complementary metal-oxide-semiconductor (CMOS) transistor. In another example, the switch SW and the transistor Q 1  may be but is not limited to a transistor made by integrated circuit (IC) manufacture process. 
         [0026]    The control signal from the digital processor  4  may be used to turn on/off the switch SW. When the switch SW is off, the signal generator  20  may perform the ASK modulation. In other words, the digital processor  4  may determine whether or not the signal generator  20  is going to perform the ASK modulation. The terminal VM may supply a relatively low voltage level to the transistor Q 1  such that the signal generator  20  may perform an ASK modulation with 75% modulation depth. In another example, the terminal VM may supply a relatively high voltage level to the transistor Q 1  such that the signal generator  20  perform an ASK modulation with 50% modulation depth. In another example, the terminal VM may be eliminated and the transistor Q 1  may connect to the digital processor  4 . 
         [0027]    In one example, the variable resistor VR may have a resistance in the range of  100  to 50 kΩ, each of the resistors R 1  and R 2  may have a resistance of 10 kΩ, each of the inductors L 1  and L 2  may have an inductance of 100 Nano-Henry (nh). However, the values of the above resistance and inductance may be varied in another example to change the modulation depth. 
         [0028]      FIG. 3  is a block diagram of a transceiver  2 ′ in an RFID system in accordance with an example of the present invention. Referring to  FIG. 3 , the transceiver  2 ′ may include an MCU  3 ′, a digital processor  4 ′, a signal generator  20 ′, a directional unit  5 ′ and an antenna  6 ′ which may be similar to the MCU  3 , the digital processor  4 , the signal generator  20 , the directional unit  5  and the antenna  6  as illustrated and described with reference to  FIG. 2A , except that a memory  8  and a receiving circuit  30  may be added to the transceiver  2 ′. The three-port direction unit  5 ′ may not cause a huge signal attenuation as compared to the four-port directional coupler  10  of  FIG. 1 . 
         [0029]    The receiving circuit  30  may be connected between the directional unit  5 ′ and the MCU  3 ′. In one example, the receiving circuit  30  may be but is not limited to a detecting circuit, which may include a diode, an operational (OP) amplifier and a comparator (not shown). The diode, the OP amplifier and the comparator may be coupled in series to demodulate the received signal by the antenna  6 ′. 
         [0030]    The receiving circuit  30  may rectify the received signal from the antenna  6 ′ and remove the carrier from the rectified signal so as to obtain an envelope of the rectified signal. The receiving circuit  30  may further demodulate the envelope to generate a demodulated signal. Thereby, data contained in the received signal from the antenna  6 ′ may be retrieved by the MCU  3 ′. 
         [0031]    The memory  8  may be connected to the MCU  3 ′. In one example, the memory  8  may be but is not limited to a non-volatile memory and programmable. The memory  8  may include a first field that may contain a first set of identification information. The memory  8  may also have a second field that may contain a second set of identification information. The first and second sets of identification information may include but is not limited a series of numerals and/or symbols. The first set of identification information may be permanent and the second set of identification information may be changeable. In another example, the memory  8  may be replaced by two separate memories to respectively store the first set of identification information and the second set of identification information. In yet another example, the memory  8  may be integrated with the MCU  3 ′ or the digital processor  4 ′ into a single chip. 
         [0032]    In one example, the MCU  3 ′ may access the memory  8  and retrieve the first and second sets of identification information. The MCU  3 ′ and the digital processor  4 ′ control the signal generator  20 ′ to generate a signal TS 5  containing information relevant to the first and second sets of identification information. The directional unit  5 ′ may process the signal TS 5  and may further transmit a signal TS 6  to the server  9  through the antenna  6 ′. In another, the signal TS 5  may be transmitted to the server  9  by another interface such like Ethernet, universal serial bus (USB) or Bluetooth. In still another example, MCU  3 ′ retrieves the first and second sets of identification information and transmits to server  9  by wired or wireless link, such like an USB or Bluetooth interface. 
         [0033]    The server  9  may identify the first and/or second set of identification information. If the identification information is identified, the server  9  may use the first and/or second sets of identification information to generate a third set of identification information. The server  9  may send a signal containing the third set of identification information to the transceiver  2 ′, in which such signal may be demodulated by the receiving circuit  30  so that the MCU  3 ′ may retrieve the third set of identification information and store the said information in the second field of the memory  8 . The third set of identification information may be used to identify the transceiver  2 ′ in the next communication. By this manner, the transceiver  20 ′ is authenticated during information uploading or downloading process. 
         [0034]    The transmitter  2  shown in  FIGS. 2A and 2B  and the transceiver  2 ′ shown in  FIG. 3  both use an open-loop control to replace the complex feedback control circuit as illustrated with reference to  FIG. 1 . 
         [0035]    It will be appreciated by those skilled in the art that changes could be made to the examples described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular examples disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims. 
         [0036]    Further, in describing representative examples of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.