Abstract:
A short-distance contactless communication apparatus includes a chip. The chip includes: a signal receiving port capable of receiving a modulation signal from the outside of the chip; a first receiver capable of operating under a proximity coupling device mode and/or a proximity inductively coupled card mode; and an adjusting device separate from the first receiver for tracking an envelope of the modulation signal on the signal receiving port of the chip and scaling the modulation signal on the signal receiving port of the chip proportionally during data communication phase of the short-distance contactless communication apparatus. The scaled modulation signal on the signal receiving port of the chip is received by the first receiver, and a peak voltage level of the scaled modulation signal on the signal receiving port of the chip falls within a predetermined voltage range.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 14/476,749, filed on Sep. 4, 2014, which claims the benefit of U.S. Provisional Application No. 61/873,442, which was filed on Sep. 4, 2013. The entire contents of the related applications are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to a short-distance contactless communication apparatus and method thereof, and more particularly to a short-distance contactless communication apparatus capable of adjusting the envelope of a receiving modulation signal, and method thereof. 
         [0003]    Short-range, standards-based contactless connectivity technology such as Near field communication (NFC) uses magnetic field induction to enable communication between electronic devices in close proximity. Based on RFID technology, NFC provides a medium for the identification protocols that validates secure data transfer. Conventionally, a NFC device encompasses a PCD (Proximity Coupling Device) transceiver and a PICC (Proximity Inductively Coupled Card) receiver. When the NFC device is configured as an initiator (i.e. the PCD mode), the transmitter in the PCD transceiver is used to emit a modulation signal to another NFC device, i.e. the target NFC device. Meanwhile, the receiver in the PCD transceiver receives the emitted modulation signal as an in-band blocking signal or an in-band blocker. Upon detecting the modulation signal transmitted from the transmitter of the PCD transceiver, the target NFC device responds with a load modulation (LM) signal to the receiver of the PCD transceiver. On the other hand, when the NFC device is configured as a PICC target (i.e. the PICC mode), the PICC receiver receives a modulation signal transmitted from another PCD device (i.e. the initiator). Therefore, no matter the NFC device is configured as PCD mode or PICC mode, the NFC device always needs to receive a modulation signal. However, the voltage swing or the power of the modulation signal is depended on the relative position between the two NFC devices, and the matching network and the antenna coils of the two NFC devices. If the voltage swing or the power of the modulation signal is too large, it may exceed the dynamic range of the receiver of the NFC device. If the voltage swing or the power of the modulation signal is too small, the modulation signal may not be accurately demodulated by the NFC device. Therefore, providing an NFC device capable of accurately receiving the modulation signal during the PCD mode and the PICC mode is an urgent problem in the NFC field. 
       SUMMARY 
       [0004]    One of the objectives of the present invention is to provide a short-distance contactless communication apparatus capable of adjusting the envelope of a receiving modulation signal, and method thereof. 
         [0005]    According to a first embodiment of the present invention, a short-distance contactless communication apparatus is disclosed. The short-distance contactless communication apparatus comprises a receiver configured to operate under at least a first receiving mode and a second receiving mode, wherein the receiver receives a modulation signal with a first modulation scheme when the receiver is configured to operate under the first receiving mode, and the receiver receives a modulation signal with a second modulation scheme when the receiver is configured to operate under the second receiving mode. The receiver utilizes an oscillation signal to receive the modulation signal, and the oscillation signal utilized by the receiver is derived from the modulation signal or derived from a reference clock of a local source based on the receiving mode of the receiver. 
         [0006]    According to a second embodiment of the present invention, a short-distance contactless communication apparatus is disclosed. The short-distance contactless communication apparatus comprises a receiver capable of operating under a proximity coupling mode and/or a proximity inductively coupled card mode and an adjusting device. The receiver is coupled to a signal receiving port of the short-distance contactless communication apparatus. The adjusting device is coupled to the signal receiving port for adjusting a peak voltage level of a modulation signal on the signal receiving port to fall within a predetermined voltage range. 
         [0007]    According to a third embodiment of the present invention, a short-distance contactless communication method is disclosed. The short-distance contactless communication method comprises the steps of: using a receiver capable of operating under a proximity coupling device (PCD) mode and/or a proximity inductively coupled card (PICC) mode to couple to a signal receiving port; and adjusting a peak voltage level of a modulation signal on the signal receiving port to fall within a predetermined voltage range. 
         [0008]    According to a fourth embodiment of the present invention, a NFC device comprising an NFC integrated circuit (IC) capable of supporting PCD and PICC reception is disclosed. The NFC device comprises PCD and PICC receivers have a common input port, a fixed resistor coupled to the common input port, an envelope detector coupled to the common input port, a programmable resistor circuit having a first node coupled to the common input port and a second node coupled to ground. The resistance of the programmable resistor circuit is adjusted according to the peak voltage level at the input of the envelope detector, and the adjustment of the programmable resistor circuit continues until the peak voltage at the input of the envelope detector is within a predetermined voltage range. 
         [0009]    According to a fifth embodiment of the present invention, a short-distance contactless communication apparatus comprising a chip is disclosed. The chip comprises: a signal receiving port; a first receiver and an adjusting device separate from the first receiver. The signal receiving port is capable of receiving a modulation signal from the outside of the chip. The first receiver is coupled to the signal receiving port of the chip and capable of operating under a proximity coupling device (PCD) mode and/or a proximity inductively coupled card (PICC) mode. The adjusting device separate from the first receiver is coupled to the signal receiving port of the chip, and for tracking an envelope of the modulation signal on the signal receiving port of the chip and scaling the modulation signal on the signal receiving port of the chip proportionally during data communication phase of the short-distance contactless communication apparatus. Further, the scaled modulation signal on the signal receiving port of the chip is received by the first receiver, and a peak voltage level of the scaled modulation signal on the signal receiving port of the chip falls within a predetermined voltage range. 
         [0010]    According to a sixth embodiment of the present invention, a short-distance contactless communication method is disclosed. The short-distance contactless communication method comprises: using a first receiver capable of operating under a proximity coupling device (PCD) mode and/or a proximity inductively coupled card (PICC) mode to couple to a signal receiving port of a chip; and tracking an envelope of a modulation signal on the signal receiving port of the chip and scaling the modulation signal on the signal receiving port of the chip proportionally during data communication phase, wherein a peak voltage level of the scaled modulation signal falls with a predetermined voltage range; and receiving at the signal receiving port of the chip, by the first receiver, the scaled modulation signal, wherein the first receiver is located in the chip. 
         [0011]    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 
         [0012]      FIG. 1  is a diagram illustrating a short-distance contactless communication apparatus according to an embodiment of the present invention. 
           [0013]      FIG. 2  is a diagram illustrating a short-distance contactless communication apparatus operated under a first mode according to an embodiment of the present invention. 
           [0014]      FIG. 3  is a diagram illustrating a short-distance contactless communication apparatus operated under a second mode according to an embodiment of the present invention. 
           [0015]      FIG. 4  is a diagram illustrating the voltage level of a modulation signal on a signal receiving port before and after the adjustment of an adjusting device according to an embodiment of the present invention. 
           [0016]      FIG. 5  is a diagram illustrating a predetermined voltage range that is considered to be the optimum to a peak voltage level of a modulation signal according to an embodiment of the present invention. 
           [0017]      FIG. 6  is a diagram illustrating an embodiment of a programmable resistor according to an embodiment of the present invention. 
           [0018]      FIG. 7  is a diagram illustrating an embodiment of an envelope detector according to an embodiment of the present invention. 
           [0019]      FIG. 8  is a diagram illustrating a PICC receiver according to an embodiment of the present invention. 
           [0020]      FIG. 9  is a diagram illustrating a PCD receiver according to an embodiment of the present invention. 
           [0021]      FIG. 10  is a diagram illustrating a short-distance contactless communication integrated circuit according to another embodiment of the present invention. 
           [0022]      FIG. 11  is a diagram illustrating a receiver according to an embodiment of the present invention. 
           [0023]      FIG. 12  is a flowchart illustrating a short-distance contactless communication method according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, electronic equipment 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 coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
         [0025]    Please refer to  FIG. 1 , which is a diagram illustrating a short-distance contactless communication apparatus (e.g. a near-field communication (NFC) apparatus  100 ) according to an embodiment of the present invention. It is noted that NFC is just an example of the short-distance contactless communication, and this is not a limitation of the present invention. The NFC apparatus  100  comprises an NFC integrated circuit  102 , an EMI (Electromagnetic interference) low-pass filter  104 , a matching network  106 , a phase shifting network  108 , and an antenna  110 . The NFC integrated circuit  102  is arranged to transmit a NFC signal and/or to receive a NFC signal. The NFC integrated circuit  102  comprises a baseband processor  1022 , a first mode receiver, such as a proximity coupling device (PCD) receiver  1024 , a second mode receiver, such as a proximity inductively coupled card (PICC) receiver  1026 , an adjusting device  1028 , a first mode transmitter, such as a PCD transmitter  1030 , and a switching circuit  1032 . The NFC integrated circuit  102  in this embodiment has at least five signal ports (i.e. IC pad) ANTP, RX, TXP TXN, ANTN. The signal ports ANTP and ANTN are differential ports coupled to the switching circuit  1032 . The signal transmitting ports TXP and TXN are differential ports coupled to the PCD transmitter  1030 . The signal receiving port RX is the common port coupled to the PCD receiver  1024 , the PICC receiver  1026 , and the adjusting circuit  1028 . On the other side, the matching network  106  is coupled to the signal ports ANTP and ANTN. The EMI low-pass filter  104  is coupled to the signal transmitting ports TXP and TXN. The phase shifting network  108  is coupled to the signal receiving port RX. Note that the configuration of the signal ports is for illustrative purpose rather than limitations for the present invention. In other embodiment, the antenna port and the transmitting ports can be single-ended, the receiving port can be differential, and the phase shifting network  108  can be duplicated to provide inputs to the differential receiving ports. 
         [0026]    In this embodiment, the NFC integrated circuit  102  is a single-chip. The EMI low-pass filter  104 , the matching network  106 , the phase shifting network  108 , and the antenna  110  are external to the NFC integrated circuit  102 . 
         [0027]    The EMI low-pass filter  104  comprises a first inductor  104   a , a second inductor  104   b , a first capacitor  104   c , and a second capacitor  104   d . The matching network  106  comprises a first capacitor  106   a , a second capacitor  106   b , a third capacitor  106   c , a fourth capacitor  106   d , a fifth capacitor  106   e , and a sixth capacitor  106   f . The phase shifting network  108  comprises a resistor R 130  and a capacitor C 130 . The connectivity of the above circuit elements is shown in  FIG. 1 , and the detailed description is omitted here for brevity. However, the connectivity shown in  FIG. 1  is for illustrative purpose, rather than a limitation of the present invention. In  FIG. 1 , the resistor R 130  connects to the capacitor C 130  in series, and the resistor and the capacitor C 130  are connected between the signal receiving port RX and the terminal N 1 . 
         [0028]    More specifically, the EMI low-pass filter  104  is arranged to filter out the EMI signal of the transmitting NFC signal generated by the PCD transmitter  1030 . The matching network  106  is arranged to perform impedance matching between the antenna  110  and the EMI low-pass filter  104  and the impedance matching between the antenna  110  and the switching circuit  1032 . The phase shifting network  108  provides a path to receive the NFC signal from the antenna  110  to the PCD receiver  1024  and the PICC receiver  1026  or to receive the transmitting NFC signal from the EMI low-pass filter  104  to the PCD receiver  1024 . 
         [0029]    In the NFC integrated circuit  102 , the baseband processor  1022  is coupled to the PCD receiver  1024 , the PICC receiver  1026 , the adjusting device  1028 , the PCD transmitter  1030 , and the switching circuit  1032 . The switching circuit  1032  comprises a first switch  1032   a  and a second switch  1032   b . The adjusting device  1028  is arranged for presently adjusting a peak voltage level of a modulation signal Sm on the signal receiving port RX to fall within a predetermined voltage range when the modulation signal Sm appears on the signal receiving port RX. In other words, the adjusting device  1028  adjusts the modulation signal Sm in real time. The adjusting device  1028  comprises a programmable impedance component, such as a programmable resistor  1028   a , and an envelope detector  1028   b . The programmable resistor  1028   a  has a first terminal coupled to the signal receiving port RX and a second terminal coupled to a reference voltage, e.g. the ground voltage Vgnd, for providing impedance between the signal receiving port RX and the ground voltage Vgnd according to an adjusting signal Sad. The envelope detector  1028   b  is coupled to the signal receiving port RX and the baseband processor  1022  for detecting an envelope of the modulation signal Sm to generate a detecting signal Sd. The baseband processor  1022  receives the detecting signal Sd and accordingly generates the adjusting signal Sad to adjust the impedance of the programmable resistor  1028   a  such that the peak voltage level of the modulation signal Sm on the signal receiving port RX falls within the predetermined voltage range. 
         [0030]    It should be noted that the adjusting device  1028  is not limited to adjust the peak voltage level of the modulation signal Sm on the signal receiving port RX to fall within the predetermined voltage range, the adjusting device  1028  may be arranged to adjust the peak voltage level of the modulation signal Sm on the signal receiving port RX to be a predetermined voltage level or to adjust the peak voltage level of the modulation signal Sm on the signal receiving port RX to be a predetermined voltage level in the predetermined voltage range. 
         [0031]    According to the embodiment, the NFC apparatus  100  (or the NFC integrated circuit  102 ) can be configured to operate under a PCD mode or a PICC mode. During the PCD mode, the NFC apparatus  100  functions as an initiator, i.e. the reader. During the PICC mode, the NFC apparatus  100  functions as a card. 
         [0032]    When the NFC apparatus  100  is configured as the initiator during the PCD mode, the differential PCD transmitter  1030  emits an ASK modulation signal to the antenna  110  through the EMI low-pass filter  104 , which is an optional device, and the matching network  106 . The first switch  1032   a  and the second switch  1032   b  are closed to connect the capacitor  106   c  and  106   e  to the ground voltage Vgnd respectively. Before the PCD receiver  1024  receives a load modulation (LM) signal from the target NFC apparatus (not shown), which is configured as a card (i.e. PICC mode), the NFC apparatus  100  is re-configured. When the NFC apparatus  100  is re-configured, the PCD transmitter  1030  emits a transmitting modulation signal St to the target NFC apparatus. The transmitting modulation signal St is a continuous wave (CW) signal having an oscillating frequency substantially equal to 13.56 MHz as shown in  FIG. 2 .  FIG. 2  is a diagram illustrating the NFC apparatus  100  operated under the PCD mode according to an embodiment of the present invention. As the phase shifting network  108  is directly connected to the EMI low-pass filter  104  via the terminal N 1 , the large transmitting modulation signal St will appear at the input (i.e. the signal receiving port RX) of the PCD receiver  1024  as an in-band blocker. Upon detecting the transmitting modulation signal St from the NFC apparatus  100 , the target NFC apparatus will respond with a load modulation (LM) signal to the NFC apparatus  100 . The LM signal will pass through the matching network  106  and the phase shifting network  108  before it is demodulated and decoded by the to the PCD receiver  1024 . 
         [0033]    On the other hand, when the NFC apparatus  100  is configured as the card during the PICC mode, the NFC apparatus  100  receives a receiving modulation signal Sr from the other NFC apparatus which is configured as an initiator. The receiving modulation signal Sr is an ASK modulation signal. The receiving modulation signal Sr is received through the antenna  110 , the matching network  106 , and the phase shifting network  108  before it is demodulated and decoded by the PICC receiver  1026  as shown  FIG. 3 .  FIG. 3  is a diagram illustrating the NFC apparatus  100  operated under the PICC mode according to an embodiment of the present invention. When the NFC apparatus  100  is configured as the PICC mode, the PICC receiver  1026  responds to the PCD transmitter (i.e. the other NFC apparatus) by modulating the antenna load, which is known as load modulation, using the first switch  1032   a  and the second switch  1032   b . It is noted that there are many ways to modulate the antenna load without change the essence of the present invention. 
         [0034]    Accordingly, no matter the NFC apparatus  100  is configured to operate under the PCD mode or the PICC mode, the voltage level of the modulation signal Sm on the signal receiving port RX should be fall within an appropriate range such that the PCD receiver  1024  or the PICC receiver  1026  can receive the modulation signal Sm (e.g. the load modulation signal or the receiving modulation signal Sr) correctly. 
         [0035]    According to the embodiment, the fixed resistor R 130  in the phase shifting network  108  forms a voltage divider with the input impedance ZRX at the signal receiving port RX of the NFC integrated circuit  102 . After the values of the resistor R 130  and the capacitor C 130  are determined, the voltage level of the modulation signal Sm on the signal receiving port RX may only be adjusted by the programmable resistor  1028   a  in the adjusting device  1028  such that the voltage level of the modulation signal Sm on the signal receiving port RX is adjusted into the usable input dynamic range of the PCD receiver  1024  or the PICC receiver  1026 . Please refer to  FIG. 4 , which is a diagram illustrating the voltage level of the modulation signal Sm on the signal receiving port RX before and after the adjustment of the adjusting device  1028  according to an embodiment of the present invention.  FIG. 4  also shows the corresponding programmable resistor  1028   a  and the resistor R 130  in the form of circuit divider. 
         [0036]    In the left side of  FIG. 4 , the impedance of the programmable resistor  1028   a  is set to the default maximum value Rmax before the adjustment of the adjusting device  1028 . The threshold voltage level corresponding to the maximum dynamic range of the PCD receiver  1024  (or the PICC receiver  1026 ) is VTH 0 . When the modulation signal Sm appears on the common terminal VB (i.e. the signal receiving port RX) during the PCD mode or the PICC mode, the envelope detector  1028   b  starts to detect the envelope of the modulation signal Sm. When the baseband processor  1022  determines that the peak voltage value of the modulation signal Sm on the common terminal VB is V 1 , which is larger than the predetermined threshold voltage level VTH 0 , this means that the voltage level of the modulation signal Sm is larger than the dynamic range of the NFC integrated circuit  102 , and this may saturate the PCD receiver  1024  (or the PICC receiver  1026 ). Then, the baseband processor  1022  starts to adjust (e.g. decrease) the resistance of the programmable resistor  1028   a  by using the adjusting signal Sad until the peak voltage level of the modulation signal Sm reaches the voltage level VTH 0  as shown in the right side of  FIG. 4 . Accordingly, the envelope of the modulation signal Sm falls within the dynamic range of NFC integrated circuit  102  when the resistance of the programmable resistor  1028   a  is reduced to Ra from the maximum value Rmax. 
         [0037]    In addition, the resistance of the programmable resistor  1028   a  is set to be the maximum value as default, and is gradually reduced by the adjusting device  1028  in real time. This ensures that the envelope of the modulation signal Sm on the common terminal VB always has the maximized carrier-to-noise (CNR) ratio after the adjustment of the adjusting device  1028 . Nevertheless, other methods of adjusting the resistor R 130  are also possible. Moreover, the resistor R 130  is placed externally in this embodiment, and this will provide the flexibility of one-time adjustment with respect to different antenna designs. Obviously, the resistor R 130  can also be integrated into the NFC integrated circuit  102 . 
         [0038]    According to the present method, when the signal level of the receiving signal (i.e. the modulation signal Sm) is too high and beyond the receiver dynamic range, the adjusting device  1028  reduces the resistance of the programmable resistor  1028   a  to make the signal level of the receiving signal to fall within the dynamic range. When the signal level of the receiving signal is too small and fails to be detected by the PCD receiver  1024  (or the PICC receiver  1026 ), the adjusting device  1028  increases the resistance of the programmable resistor  1028   a  to increase the signal level of the receiving signal. 
         [0039]    It is noted that the adjusting device is not limited to adjust the peak voltage level of the modulation signal Sm to equal a predetermined voltage level, the adjusting device  1028  may also be designed to adjust the peak voltage level of the modulation signal Sm to fall within a predetermined voltage range as long as the envelope of the modulation signal Sm falls within the dynamic range of NFC integrated circuit  102 , which also belongs the scope of the present invention.  FIG. 5  is a diagram illustrating a predetermined voltage range that is considered to be the optimum to the peak voltage level of the modulation signal Sm according to an embodiment of the present invention. The predetermined voltage range varies from a minimum threshold voltage VTHmin to a maximum threshold voltage VTHmax. In other words, the above embodiment having a fixed target voltage level is a special case of this embodiment where the minimum threshold voltage VTHmin is the same as the maximum threshold voltage VTHmax. 
         [0040]    According to the embodiment, the adjustment of the adjusting device  1028  will stop when the peak voltage level of the envelope of the modulation signal Sm at the common terminal VB falls within the dynamic voltage range of the NFC integrated circuit  102 . If the peak voltage level of the envelope of the modulation signal Sm is still below the minimum threshold voltage VTHmin while the resistance of the programmable resistor  1028   a  is already in the maximum resistance, then the adjusting device  1028  will terminate the adjustment. Similarly, if the peak voltage level of the envelope of the modulation signal Sm still exceeds the maximum threshold voltage VTHmin while the resistance of the programmable resistor  1028   a  is already in the minimum resistance, then the adjusting device  1028  will also terminate the adjustment. 
         [0041]    By using the present adjusting device  1028 , the value of the resistor R 130  needs not to be very accurately determined during the design phase because the programmable resistor  1028   a  will automatically compensate the measurement error or the component variation of the resistor R 130  during the PCD mode or the PICC mode. In fact, if the dynamic range of the programmable resistor  1028   a  is sufficiently large, the adjustment of the resistor R 130  during the design phase can be eliminated, thus allowing the resistor R 130  to be integrated into the NFC integrated circuit  102 . 
         [0042]    Please refer to  FIG. 6 , which is a diagram illustrating an embodiment of the programmable resistor  1028   a  according to an embodiment of the present invention. The programmable resistor  1028   a  comprises a plurality of switches S 1 -SN and a plurality of resistors R 1 -RN. One switch is connected to a corresponding resistor in series. The adjusting signal Sad is a digital signal, and is arranged to selectively control the on/off of the plurality of switches S 1 -SN to control the effective resistance between the common terminal VB and the ground. It is noted that there are many embodiments to realize the programmable resistor  1028   a  without changing the essence of the present method. 
         [0043]    Please refer to  FIG. 7 , which is a diagram illustrating an embodiment of the envelope detector  1028   b  according to an embodiment of the present invention. The envelope detector  1028   b  comprises an operational amplifier AMP, a P-type field-effect transistor (PMOS) M 1 , a capacitor C 1 , and an analog-to-digital converter ADC. The negative terminal (−) of the operational amplifier AMP is coupled to the common terminal VB for receiving the modulation signal Sm. When the envelope of the modulation signal Sm falls below a predetermined threshold Vp, the P-type field-effect transistor M 1  is turned on to charge the capacitor C 1  by voltage Vg. The voltage across the capacitor C 1  will continue to increase until the voltage Vp equals the envelope of the modulation signal Sm. Then, the P-type field-effect transistor M 1  is turned off by voltage Vg. This mechanism allows the circuit to track the envelope of the modulation signal Sm. The analog-to-digital converter ADC is used to feedback the voltage Vp to the baseband processor  1022  for determining the peak voltage level of the envelope of the modulation signal Sm. 
         [0044]    It is noted that, in another embodiment of the present invention, when the NFC apparatus  100  is configured to be the PCD mode, the adjustment scheme is activated only when NFC apparatus  100  is transmitting a continuous wave signal. When the NFC apparatus  100  is configured to be the PICC mode, the adjustment scheme is activated to detect the magnetic field (i.e. the receiving modulation signal Sr) from the other PCD. 
         [0045]    In another embodiment of the present invention, the adjustment scheme is activated periodically when the PCD transmitter  1030  is transmitting the modulation signal St. In this embodiment, the adjustment scheme is always activated during the PICC mode. 
         [0046]    Please refer to  FIG. 8 , which is a diagram illustrating the PICC receiver  1026  according to an embodiment of the present invention. The PICC receiver  1026  comprises a comparator  1026   a , a diode  1026   b , a first resistor  1026   c , a second resistor  1026   d , and a capacitor  1026   e . The first resistor  1026   c  is coupled between the negative input terminal (−) of the comparator  1026   a , and the negative input terminal (−) of the comparator  1026   a  is coupled to the common terminal VB (i.e. the signal receiving port RX) of the NFC apparatus  100 . The positive input terminal (+) of the comparator  1026   a  is coupled to a reference DC voltage Vdc. The anode of the diode  1026   b  is coupled to the output of the comparator  1026   a  and the cathode of the diode  1026   b  is coupled to a low pass filer, in which the low-pass filter is comprised of the second resistor  1026   d  and the capacitor  1026   e . The element connectivity of the PICC receiver  1026  has been shown in  FIG. 8 , thus the detailed description is omitted here for brevity. For illustrative purposes, the resistor R 130  and the capacitor C 130  are also shown in  FIG. 8 . The ASK modulation signal is inputted to the capacitor C 130 . The incoming ASK modulation signal has two distinct amplitude levels, i.e. V 1  (indicating no ASK modulation) and V 2  (indicating some level of ASK modulation). When the voltage V 1  is higher than the reference DC voltage Vdc, the capacitor  1026   e  is charged, and the voltage level at node V 0  increases. When the reference DC voltage Vdc is higher than the voltage V 2 , the capacitor  1026   e  is discharged through the second resistor  1026   d  and the voltage level at the node V 0  decreases. The resulting waveform at the node V 0  is the demodulated ASK signal as shown in  FIG. 8 . 
         [0047]    Please refer to  FIG. 9 , which is a diagram illustrating the PCD receiver  1024  according to an embodiment of the present invention. The PCD receiver  1024  comprises a first mixer  1024   a , a first high-pass filter  1024   b , a first programmable-gain amplifier  1024   c , a first low-pass filter  1024   d , a first ADC  1024   e , a second mixer  1024   f , a second high-pass filter  1024   g , a second programmable-gain amplifier  1024   h , a second low-pass filter  1024   i , a second ADC  1024   j , a baseband processor  1024   k , an oscillator  1024   l , and a phase shifter  1024   m . The first mixer  1024   a  and the second mixer  1024   f  are coupled to the common terminal VB (i.e. the signal receiving port RX) of the NFC apparatus  100 . The phase shifter  1024   m  is arranged to provide two oscillation signals having 90° phase difference, one is provided to the first mixer  1024   a , and the other is provided to the second mixer  1024   f . The gains of the first programmable-gain amplifier  1024   c  and the second programmable-gain amplifier  1024   h  are controlled by the baseband processor  1024   k . The element connectivity of the PCD receiver  1024  has been shown in  FIG. 9 , thus the detailed description is omitted here for brevity. The load modulation signal is inputted to the terminal VB. The PCD receiver  1024  is a quadrature down-conversion receiver. Therefore, the demodulation of the amplitude and phase information of the load modulation signal can be realized by the PCD receiver  1024 . Direct conversion receiver (DCR) with a band-pass filter is used for PCD receiver as it rejects the large transmitter leakage from the PCD transmitter meanwhile retains the load modulation signal at the subcarrier frequency as shown in  FIG. 9 . In the PCD mode, an automatic gain control (AGC) scheme can be used to adjust the gains of the first programmable-gain amplifier  1024   c  and the second programmable-gain amplifier  1024   h  according to the levels of the sub-carriers, thus helping to maintain a relatively constant sub-carrier level at the ADC input. It is noted that the most important circuits in the PCD receiver  1024  are the direct conversion mixer (i.e.  1024   a  and  1024   f ) and the high-pass filter (i.e.  1024   b  and  1024   g ). The addition of any circuits before the mixer, the removal of the low-pass filter (i.e.  1024   d  and  1024   i ), or moving the low-pass filter to place before the high-pass filter will not change the benefits of the PCD receiver  1024 . 
         [0048]    Moreover, the proposed adjustment scheme can be implemented for all types of PCD and PICC receivers with different demodulator architectures. The separate PCD and PICC receivers  1024 ,  1026  can also be merged into a single receiver without affecting the operation of the proposed adjustment scheme as shown in  FIG. 10 . In other words, the single receiver may comprise the functions of the PCD and PICC receivers  1024 ,  1026 , which also belongs to the scope of the present invention. 
         [0049]    In another embodiment, the proposed adjustment scheme can also be implemented in a NFC integrated circuit  102  having the PCD receiver  1024  and the PCD transmitter  1030 , i.e. without the PICC receiver  1026 . 
         [0050]      FIG. 10  is a diagram illustrating the NFC integrated circuit  1002  according to another embodiment of the present invention. For illustrative purpose, the EMI low-pass filter  104 , the matching network  106 , the phase shifting network  108 , and the antenna  110  are also shown in  FIG. 10 . The NFC integrated circuit  1002  comprises a baseband processor  10022 , a receiver  10026 , an adjusting device  10028 , a PCD transmitter  10030 , and a switching circuit  10032 . It is noted that the baseband processor  10022 , the adjusting device  10028 , the PCD transmitter  10030 , and the switching circuit  10032  are similar to the baseband processor  1022 , the adjusting device  1028 , the PCD transmitter  1030 , and the switching circuit  1032  respectively, thus the detailed description is omitted. In this embodiment, the receiver  10026  is a combined circuit that comprises the functions of the PCD and PICC receivers  1024 ,  1026 . 
         [0051]    Please refer to  FIG. 11 , which is a diagram illustrating the receiver  10026  according to an embodiment of the present invention. The receiver  10026  comprises a first mixer  10026   a , a first low-pass filter  10026   b , a first programmable-gain amplifier  10026   c , a first high-pass filter  10026   d , a first ADC  10026   e , a second mixer  10026   f , a second low-pass filter  10026   g , a second programmable-gain amplifier  10026   h , a second high-pass filter  10026   i , a second ADC  10026   j , a limiter  10026   k , a phase-locked loop  100261 , a multiplexer  10026   m , and a phase shifter  10026   n . The receiver  10026  is a single direct conversion receiver for both the PCD and PICC operation. The first mixer  10026   a  and the second mixer  10026   f  are coupled to the common terminal VB (i.e. the signal receiving port RX) of the NFC apparatus  100 . The modulation signal is inputted to the terminal VB. The multiplexer  10026   m  is controlled by the operation mode of the receiver  10026 . When the receiver  10026  operates under the PICC mode, the multiplexer  10026   m  passes the output of the limiter  10026   k  to the phase shifter  10026   n . When the receiver  10026  operates under the PCD mode, the multiplexer  10026   m  passes the output of the phase-locked loop  100261  to the phase shifter  10026   n . The phase shifter  10026   n  is arranged to provide two oscillation signals having 90° phase difference, one is provided to the first mixer  10026   a , and the other is provided to the second mixer  10026   f . The phase-locked loop  100261  can be an integer-N PLL, or a fractional-N PLL. A control signal will be triggered so that the multiplexer  10026   m  will select its input from the phase-locked loop  100261 . The element connectivity of the receiver  10026  has been shown in  FIG. 11 , thus the detailed description is omitted here for brevity. 
         [0052]    More specifically, when the receiver  10026  operates under the PICC mode, the limiter  10026   k  is arranged to use the modulation signal at the terminal VB to generate the oscillation signal with 13.56 MHz, but not a limitation, to the phase shifter  10026   n . More specifically, in the PICC mode, the oscillation signal is obtained from the carrier of the incoming ASK signal at the terminal VB. This can be done by simply passing the ASK signal through an amplitude limiter (i.e. the limiter  10026   k ). In the PICC mode, the control signal of the multiplexer  10026   m  is toggled so that the multiplexer  10026   m  obtains its input from the output of the limiter  10026   k.    
         [0053]    When the receiver  10026  operates under the PCD mode, the phase-locked loop  10026   l  is arranged to use the external reference clock of a local source to generate the oscillation signal with 13.56 MHz, but not a limitation, to the phase shifter  10026   n . The oscillation signals generated by the phase shifter  10026   n  are provided to the ADCs  10026   e  and  10026   j.    
         [0054]    In summary, the operation of the proposed adjustment scheme in  FIG. 1  (or  FIG. 10 ) can be summarized into the following steps in  FIG. 12 .  FIG. 12  is a flowchart illustrating an NFC method  1200  according to an embodiment of the present invention. Provided that substantially the same result is achieved, the steps of the flowchart shown in  FIG. 12  need not be in the exact order shown and need not be contiguous; that is, other steps can be intermediate. The power amplifying method  1200  comprises the steps: 
         [0000]    Step  1202 : Use the PCD receiver  1024  to couple to the signal receiving port RX;
 
Step  1204 : Use the PICC receiver  1026  to couple to the signal receiving port RX;
 
Step  1206 : Use the programmable resistor  1028   a  to provide an impedance between the signal receiving port RX and the ground voltage Vgnd according to an adjusting signal Sad;
 
Step  1208 : Detect the envelope of the modulation signal Sm to generate the detecting signal Sd; and
 
Step  1210 : Receive the detecting signal Sd and accordingly generate the adjusting signal Sad to adjust the impedance of the programmable resistor  1028   a  such that the peak voltage level of the modulation signal Sm on the signal receiving port RX falls within the predetermined voltage range.
 
         [0055]    Briefly, the present invention is to instantly detect the peak voltage level of the modulation signal Sm on the signal receiving port RX of the NFC integrated circuit  102 , and accordingly adjust the peak voltage level of the modulation signal Sm to fall within the dynamic range of the NFC integrated circuit  102  by adjusting the programmable resistor  1028   a . The adjustment scheme can be activated when transmitting a continuous wave signal, and/or in the PCD mode and/or the PICC mode. By using the proposed adjustment scheme, the value of the resistor R 130  needs not to be very accurate during the design phase because the programmable resistor  1028   a  can be used to adjust the peak voltage level of the modulation signal Sm to fall within the dynamic range of the NFC integrated circuit  102 , and the resistor R 130  can also be integrated into the NFC integrated circuit  102 . 
         [0056]    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.