Patent Abstract:
A proximity sensing method employed by a wireless communications device includes the steps of: performing a first predetermined operation to detect a presence of at least a transponder in the proximity of the wireless communications device; when the presence of a transponder in the proximity of the wireless communications device is not detected by the first predetermined operation, performing a second predetermined operation to obtain a first characteristic value and after a period of time, performing the second predetermined operation to obtain a second characteristic value sequentially; checking if the first characteristic value and the second characteristic value satisfy a predetermined criteria; and when the predetermined criterion is satisfied, performing the first predetermined operation again to check the presence of the transponder in the proximity of the wireless communications device.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/748,764 (filed Jan. 4, 2013). The entire content of this related application is incorporated herein by reference. 
    
    
     BACKGROUND 
     Near field communication, or NFC, is a set of short-range wireless technologies, typically requiring a distance of 4 cm or less. NFC generally operates at 13.56 MHz and at rates ranging typically from about 106 kbits/s to 848 kbits/s. NFC requires that NFC devices be present within a relatively close proximity to each other so that their corresponding magnetic fields can couple and the devices can exchange information. 
     An NFC device is required to sense proximity of a target (usually a card) in order to initiate communication. One way to do this is for the NFC device to constantly initiate communications for all possible card types (A, B and F) until it receives a response. This approach has the disadvantage of draining the battery because of the continuous polling (tens of mA). 
     Therefore, there is a need for a better proximity sensing mechanism for an NFC device that does not drain the battery but can still detect any card which comes within its proximity. 
     SUMMARY 
     In accordance with exemplary embodiments of the present invention, a proximity sensing method using a loopback mechanism and a related wireless communications device are proposed to solve the above-mentioned problem. 
     According to a first aspect of the present invention, an exemplary proximity sensing method employed by a wireless communications device is disclosed. The exemplary proximity sensing method includes the steps of: performing a first predetermined operation to detect presence of transponder(s) in the proximity of the wireless communications device; when the presence of transponder (s) in the proximity of the wireless communications device is not detected by the first predetermined operation, performing a second predetermined operation to obtain a first characteristic value and after a period of time, performing the second predetermined operation to obtain a second characteristic value sequentially; checking if the first characteristic value and the second characteristic value satisfy a predetermined criteria; and when the predetermined criterion is satisfied, performing the first predetermined operation again to check the presence of the transponder in the proximity of the wireless communications device. 
     According to a second aspect of the present invention, a wireless communications device having proximity sensing capability is disclosed. The exemplary wireless communications device includes a first circuit and a second circuit. The first circuit is arranged for performing a first predetermined operation to detect the presence of transponder(s) in the proximity of the wireless communications device, and when the presence of transponder(s) in the proximity of the wireless communications device is not detected by the first predetermined operation, performing a second predetermined operation to obtain a first characteristic value and after a period of time, performing the second predetermined operation to obtain a second characteristic value sequentially. The second circuit is arranged for checking if the first characteristic value and the second characteristic value satisfy a predetermined criterion. When the predetermined criterion is satisfied, the first circuit performs the first predetermined operation again to check the presence of the transponder in the proximity of the wireless communications device. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a block diagram of a wireless communication device according to an embodiment of the present invention. 
         FIG. 1B  is a schematic diagram of one possible implementation of the wireless communication device  100  according to an embodiment of the present invention. 
         FIG. 1C  is a schematic diagram of a dual local oscillation scheme according to an embodiment of the present invention 
         FIG. 2  is a flowchart of a proximity sensing method employed by the wireless communications device. 
         FIG. 3  is another flowchart of a proximity sensing method employed by the wireless communications device. 
     
    
    
     DETAILED DESCRIPTION 
     Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is electrically connected to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
     Conventionally, a first wireless communications device (a near field communications (NFC) reader) and a second wireless communications device (an NFC tag) operate in a conventional polling mode to establish communication. The first wireless communications device provides a polling command to the second wireless communications device. The second wireless communications device provides a response to the polling command. Since the first wireless communications device has no knowledge of the geographical location of the second wireless communications device, the first wireless communications device has to constantly perform the polling operation, which may drain the battery of the first wireless communications device. 
     The concept of the present invention is for the wireless communications device to have low power consumption. Instead of constantly polling for potential connection establishment, the wireless communications device only polls for connection establishment when it detects the presence of a transponder. The present invention proposes a low power consumption proximity sensing scheme for the first wireless communications device, to detect presence of the second wireless communications device in an operating distance of the first wireless communications device before the first wireless communications device performs the polling operation. Therefore, the present invention may optimize power consumption in the first wireless communication device and overcome the shortcomings described above. Further aspects and advantages of the present invention will become apparent from the following detailed description. 
     Please refer to  FIG. 1A , which is a block diagram of a wireless communication device  100  according to an embodiment of the present invention. The wireless communication device  100  may be an NFC device, such as a radio frequency identification (RFID) card. The wireless communication device  100  includes a digital baseband  110 , a synthesizer  120 , a transmitter  130 , a receiver  140 , an antenna  160  and an antenna matching network  150 . The digital baseband  110  is arranged to issue a baseband transmission signal S_BT to the transmitter  130 , and receive a baseband reception signal S_BR from the receiver  140 . The synthesizer  120  includes a first local oscillator  130  and a second local oscillator  140 . The first local oscillator  130  is arranged to generate a first local oscillation (LO) frequency LO 1  to the receiver  140 , and the second local oscillator  140  is arranged to generate a second LO frequency LO 2  to the transmitter  130 . The transmitter is arranged to generate a transmission signal S_TX according to the baseband transmission signal S_BT and the second LO frequency LO 2 , and transmit the transmission signal S_TX to the antenna matching network  150 . The receiver  140  is arranged to receive a reception signal S_RX from the antenna matching network  150 , generate the baseband reception signal S_BR according to the reception signal S_RX and the first LO frequency LO 1 , and send the baseband reception signal S_BR to the digital baseband  110 . Please note that, in this embodiment, the reception signal S_RX uses the second LO frequency LO 2  as its center frequency and further mixes the reception signal S_RX with the first LO frequency LO 1  to obtain the baseband reception signal S_BR. 
     Please refer to  FIG. 1B , which is a schematic diagram of the wireless communication device  100  according to an embodiment of the present invention. In  FIG. 1B , the antenna  160  includes a resistor R 1 , an inductance L 1  and a capacitor C 1 . The inductance L 1  is connected with the resistor R 1  in series, and the capacitor C 1  is coupled to the R 1 -L 1  circuit in parallel. However, this is for illustrative purpose only, and not meant to be a limitation of the present invention. The value of each element of the antenna  160  may be changed according to different applications. As can be seen from  FIG. 1B , the matching network  150  may include a pair of matching circuits, and each of the matching circuits may include a first capacitor C 2   b,  a second capacitor C 2   a,  a third capacitor C 3 , and a resistor RQ. Please note that the design of the matching network  150  is only for illustrative purpose only, and it not meant to be a limitation of the present invention. The matching circuits are coupled between the antenna  160  and the transmitter  130  (not shown), wherein one matching circuit is arranged for transmitting an output signal TXP of the transmitter  130  while the other matching circuit is arranged for transmitting the other output signal TXN of the transmitter  130 . Here, TXN is differential transmit signal of TXP. In addition, the matching network  150  can be optionally coupled to a signal rectifier (not shown) via the pair of the first capacitors C 2   b.  In addition, the receiver  140  includes a mixer  142  and a frontend  144 . The mixer  142  mixes the first LO frequency LO 1  and the second LO frequency LO 2  in order to obtain the frequency of the baseband reception signal S_BR. In this embodiment, the first LO frequency LO 1  may be 12.05 MHz, the second LO frequency LO 2  is 13.26 MHz, and the frequency of the output of the mixer  142  is 15. MHz˜1.5 MHz. The frontend  144  process the output of the mixer  142  and then passes the processed signal to the digital baseband  110 . 
     Please refer to  FIG. 1C , which is a schematic diagram of a dual local oscillation scheme according to an embodiment of the present invention. As shown n  FIG. 1C , the synthesizer  120  includes a LO divider  122 . The LO divider  122  takes a frequency F_VCO as its input. In this embodiment, the frequency F_VCO is 162.72 MHz. The LO divider  122  divides the frequency F_VCO by 13.5 in order to obtain the first LO frequency LO 1 , and LO divider  122  divides the frequency F_VCO by  12  in order to obtain the second LO frequency LO 2 . As can be seen from  FIG. 1C , the factor 13.5 can be derived from a series simple division. 
     Please note that the receiver architecture mentioned above is only one embodiment to the present invention. The present invention is not limited to direct or low-IF receiver architectures. For different implementations, one may use other types of receiver architecture, such as direct-sampling receiver. For example, when using direct-sampling receiver, LO 1  is the ADC sampling clock which can be any value higher than 13.56 MHz (can be 27.12 MHz or 54.24 MHJz, etc.). 
     It should be understood that, if a transponder appears in proximity to the wireless communication device  100 , the antenna matching network  150  will detect the difference in electro-magnetic fields caused by the presence of the transponder. The transmission signal S_TX will also be affected by the presence of the transponder. The change in characteristics of the transmission signal S_TX may be regarded as an ambient factor which indicates “a change in antenna environment”. 
     In this embodiment, the transmitter  130  first sends a polling command signal S_POLL to inquire if there is a potential connection establishment. If there is no response, the wireless communication device  100  enters a sensing loop where the ambient factor is periodically measured to monitor the change of surroundings; otherwise, the receiver will receive a response signal S_RES of the polling command signal S_POLL from a transponder, and the wireless communications device  100  will establish connection with the transponder. The ambient factor is measured as follows: the transmitter sends the transmission signal S_TX as a probe signal to the antenna matching network  150 , and then the transmission signal S_TX loops back through the antenna matching network to the wireless communication device  100  where it is received by the receiver  140 . The receiver  140  generates the baseband reception signal S_BR as a first ambient factor AF 1 . The first ambient factor AF 1  is saved as a “no communication” level in the digital baseband  110 . After a short period of time T 1  (e.g. 0.5 second), the wireless communication device  100  measure the ambient factor again, and obtains a second ambient factor AF 2 . If the digital baseband  110  determines that the difference between the first ambient factor AF 1  and the second ambient factor AF 2  is smaller than a threshold TH, it indicates that no change occurs, and hence no transponder appears in the proximity to the wireless communication device  100 . In this case, the sensing loop continues, and the wireless communication device  100  enters into a sleep mode for a period of time T 2 , wherein the measuring operation will be performed again after exiting the sleep mode. The wireless communication device  100  will keep measuring the ambient factor until the difference between the first ambient factor AF 1  and the second ambient factor AF 2  exceeds the threshold TH. Please note that the time period T 1 , T 2  and the threshold TH are all programmable. 
     If the digital baseband  110  determines that the difference between the first ambient factor AF 1  and the second ambient factor AF 2  exceeds the threshold TH, this may suggest that some noticeable change occurs in the antenna environment, and hence there might be a transponder in proximity to the wireless communication device  100 . The transmitter  130  will send another polling command signal S_POLL to inquire if there a potential connection establishment. If there is no response, the digital baseband  110  updates the first ambient factor AF 1  with the second ambient factor AF 2 , and the sensing loop continues; otherwise, the receiver will receive a response signal S_RES of the polling command signal S_POLL from a transponder, and the wireless communications device  100  will establish connection with the transponder. That is, if there is no response, the wireless communication device  100  will enter into the sleep mode after updating the first ambient factor AF 1 , and perform the measuring operation after exiting the sleep mode. 
     Please note that, in this embodiment, the transmission signal S_TX can be a single-tone signal. For example, the transmission signal S_TX may be a single-tone signal whose frequency is 13.56 MHz if the wireless communication device  100  is a NFC device. Both the transmitter  130  and the receiver  140  have to be turned on for a short period of time in order to realize the signal loopback. Please note that the transmission signal S_TX is not necessary a single tone signal. For example, it can be a square wave signal with fundamental frequency of 13.56 MHz. In some cases, it can also be an arbitrary signal, a triangular signal or a white noise signal. 
     The operations of the above-mentioned wireless communications device can be summarized into a flowchart. Please refer to  FIG. 2 , which is a flowchart of a proximity sensing method employed by the wireless communications device  100 . The exemplary proximity sensing method may be briefly summarized by the following steps. 
     Step  200 : Start. 
     Step  201 : Poll for potential connection. The polling operation can be a full looping of transmitting A, B, F and any NFC protocol to see if there is any response. 
     Step  202 : Check if there is a response from a transponder. If yes, go to step  203 ; otherwise, go to step  204 . 
     Step  203 : Establish connection with the transponder. In a certain implementation, after establishing connection with transponder, the wireless communications device can enter into a sleep mode to save power, for example Step  208 . It will wait for a period of time and then wake up to re-perform the polling operation as stated in Step  201  for another potential connection. 
     Step  204 : Measure a first ambient factor. 
     Step  205 : Wait for a period of time. The waiting action can be implemented as entering a sleep mode. In other words, the wireless communications device will enter into a sleep mode after obtaining the first ambient factor to save power. It will then leave the sleep mode for Step  206  after the period of time. 
     Step  206 : Measure a second ambient factor. 
     Step  207 : Check if the difference between the first ambient factor and the second ambient factor exceeds a threshold. If yes, go to step  209 ; otherwise, go back to step  205 . 
     Step  208 : Wait for a period of time, go to step  201 . 
     Step  209 : Poll for potential connection. The polling operation can be a full looping of transmitting A, B, F and any NFC protocol to see if there is any response. 
     Step  210 : Check if there is a response from a transponder. If yes, go to step  211 ; otherwise, go to step  212 . 
     Step  212 : Update the first ambient factor. In a certain implementation, after the update, it can go back to step  205 , where it will wait for a period of time by entering into a sleep mode. 
     As a person skilled in the art can readily understand the operation of each step shown in  FIG. 2  after reading the above paragraphs, further description is omitted here for brevity. 
     Please note that, provided that the result is substantially the same, the steps are not required to be executed in the exact order shown in  FIG. 2 . For example, in another embodiment, the exemplary proximity sensing method may be summarized into another flowchart where the step of polling for potential connection is taking place after the step of measuring the first and/or second ambient factor. Please refer to  FIG. 3 , which is another flowchart of a proximity sensing method employed by the wireless communications device  100 . The exemplary proximity sensing method may be briefly summarized by the following steps. 
     Step  300 : Start. 
     Step  301 : Check if a first ambient factor is available. If yes, go to step  302 ; otherwise, go to step  304 . 
     Step  302 : Measure a second ambient factor. 
     Step  303 : Check if the difference between the first ambient factor and the second ambient factor exceeds a threshold. If yes, go to step  304 ; otherwise, go to step  308 . 
     Step  304 : Poll for potential connection. 
     Step  305 : Check if there is a response from a transponder. If yes, go to step  306 ; otherwise, go to step  307 . 
     Step  306 : Inform the wireless communications device that a card is detected. 
     Step  307 : Measure the first ambient factor. 
     Step  308 : End. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

Technology Classification (CPC): 8