Abstract:
A signal modulation device and a signal amplifier cooperative therewith. The signal modulation device includes a local oscillation signal source, a baseband signal source, a first NMOS transistor, and a second NMOS transistor, wherein the first and second NMOS transistors are coupled with the baseband signal source and form a circuit architecture of a Gilbert-cell based differential pair to be directly switched by a differential baseband signal, and a high-frequency signal from the local oscillation signal source is controlled by the baseband signal so as to generate an amplitude-modulation high-frequency signal at an output end. The single-stage signal power amplifier amplifies the amplitude-modulation signal from the preceding circuit so as to increase the magnitude of signals transmitted and simplify the preceding digital/analog signal conversion circuit in a conventional amplitude-modulation circuit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to signal modulation devices and signal amplifiers cooperative therewith, and more particularly, to a signal modulation device and a signal amplifier cooperative therewith for use in a wireless RFID tag reader. 
     2. Description of Related Art 
     Radio-frequency identification (RFID) system relates to an automatic identification technology that involves affixing a small electronic tag to a product which is to be checked and monitored by a device known as “reader” which in turn transmits the data stored in the electronic tag back to the system via a wireless RF means, thus achieving remote authentication, tracking, control, management and handling. 
     The electronic tags come in two general varieties, passive or active. In particular, passive RFID tags have no internal power supply. The minute electrical current induced in the antenna by the incoming radio-frequency (RF) signal provides just enough power for the CMOS integrated circuit in the tag to power up and transmit a response. 
     The amplitude shift keying (ASK) modulation is a form of modulation that represents digital data as variations in the amplitude of a carrier wave, which is adopted to modulate the above-mentioned RF signal. Hence, signal modulation circuit is often designed on RFID tag reader to convert the information to be transmitted to ASK signal, which is in turn transmitted to the RFID tag. 
     Referring to  FIG. 1 , a schematic of the ASK modulation circuit is illustrated, the modulation circuit includes a D/A converter, a frequency synthesizer, bandpass filters, mixers and a power amplifier. 
     However, due to characteristics of ASK modulation signal, an ASK modulation circuit design does not require a D/A converter to generate a precise ASK signal. Moreover, adding a D/A converter to the baseband I/O terminals will significantly increase the overall power consumption of the RF circuit as well as the chip area. 
     In summary, it has become an urgent issue to designers of the RF circuit design field to propose a circuit that decreases the design complexity of the conventional ASK modulation circuit having a D/A converter, so as to significantly reduce the overall power consumption of the RF circuit as well as the chip area. 
     SUMMARY OF THE INVENTION 
     In view of the disadvantages of conventional technique, a primary objective of the present invention is to provide a signal modulation device to reduce the design complexity of conventional ASK modulation circuit which includes a D/A converter, so as to reduce the overall power consumption of the RF circuit and the chip area significantly. Another objective of the present invention is to provide a signal amplifier to increase the efficiency of signal transmission. 
     In order to achieve the above and other objectives, the present invention provides a signal modulation device including a local oscillation signal source; a baseband signal source; a first NMOS transistor; a second NMOS transistor; a first NPN transistor having a base, an emitter and a collector; a second NPN transistor having a base, an emitter and a collector; and a third NPN transistor having a base, an emitter and a collector. 
     The source of the first NMOS transistor is connected to the source of the second NMOS transistor to form a first connection node, and the baseband signal source is connected in series between the gate of the first NMOS transistor and the gate of the second NMOS transistor. The base of the first NPN transistor is connected to the local oscillation signal source and the collector of the first NPN transistor is connected to the first connection node. The drain of the second NMOS transistor is connected to a signal amplifier. A signal output terminal then outputs the modulation signal. 
     Also, the signal modulation device of the present invention further includes a first resistor having a first resistor terminal and a second resistor terminal, a second resistor having a third resistor terminal and a fourth resistor terminal, a third resistor having a fifth resistor terminal and a sixth resistor terminal, a fourth resistor having a seventh resistor terminal and an eighth resistor terminal, a first inductor having a first inductor terminal and a second inductor terminal, and a second inductor having a third inductor terminal and a fourth inductor terminal. 
     In particular, the first resistor terminal is connected to a drain of the first NMOS transistor, the third resistor terminal is connected to a drain of the second NMOS transistor, the fifth resistor terminal is connected to the collector of the second NPN transistor, and the seventh resistor terminal is connected to the drain of the first NMOS transistor. 
     In addition, the first inductor terminal is connected to the base of the first NPN transistor, the second inductor terminal is connected to the collector of the second NPN transistor and the base of the second NPN transistor, the third inductor terminal is connected to the collector of the first NPN transistor, the fourth inductor terminal is connected to the base of the third NPN transistor and the collector of the third NPN transistor. 
     Finally, the signal modulation device of the present invention further includes a power source and a ground terminal. Also, the second resistor terminal, the fourth resistor terminal, and the sixth resistor terminal are connected to the power source. In addition, the local oscillation signal source, the emitter of the first NPN transistor, the emitter of the second NPN transistor, the emitter of the third NPN transistor, and the eighth resistor terminal are connected to the ground terminal. 
     It is noted that in order to provide the first NMOS transistor and the second NMOS transistor with an appropriate operating bias voltage, the signal modulation device of the present invention includes a first bias voltage unit and a second bias voltage unit, wherein the first bias voltage unit is connected to the gate of the first NMOS transistor so as to provide the first NMOS transistor with an appropriate bias voltage. Also, the second bias voltage unit is connected to the gate of the second NMOS transistor, thereby providing the second NMOS transistor with an appropriate bias voltage. 
     In addition, the first bias voltage unit further includes a first biased NPN transistor, a second biased NPN transistor, a third biased NPN transistor and a fifth resistor having a ninth resistor terminal and a tenth resistor terminal. 
     In particular, the collector and the base of the first biased NPN transistor are connected to the gate of the first NMOS transistor, the collector and the base of the second biased NPN transistor are connected to the emitter of the first biased NPN transistor, the collector and the base of the third biased NPN transistor are connected to the emitter of the second biased NPN transistor, the emitter of the third biased NPN transistor is connected to the ground terminal, the ninth resistor terminal is connected to the collector of the first biased NPN transistor, and the tenth resistor terminal is connected to the power source. 
     Also, the second bias unit further includes a fourth biased NPN transistor, a fifth biased NPN transistor, a sixth biased NPN transistor and a sixth resistor having an eleventh resistor terminal and a twelfth resistor terminal. 
     In particular, the collector and the base of the fourth biased NPN transistor are connected to the gate of the second NMOS transistor. The collector and the base of the fifth biased NPN transistor are connected to the emitter of the fourth biased NPN transistor. The collector and the base of the sixth biased NPN transistor are connected to the emitter of the fifth biased NPN transistor, the emitter of the sixth biased NPN transistor is connected to the ground terminal, the eleventh resistor terminal is connected to the collector of the fourth biased NPN transistor, and the twelfth resistor terminal is connected to the power source. 
     Moreover, the signal modulation device of the present invention further includes a first capacitor, a second capacitor, a third capacitor, a fourth capacitor and a fifth capacitor. 
     In particular, the first capacitor is connected in series between the gate of the first NMOS transistor and the baseband signal source. The second capacitor is connected in series between the gate of the second NMOS transistor and the baseband signal source. The third capacitor is connected in series between the local oscillation signal source and the base of the first NPN transistor. The fourth capacitor is connected in series between the seventh resistor terminal and the drain of the first NMOS transistor and the fifth capacitor is connected in series between the signal amplifier and the drain of the second NMOS transistor. 
     Based on the above configuration, the present invention discloses a signal modulation device requiring a circuit structure that directly switches between the Gilbert-cell based differential pair using a differential baseband signal formed by the first NMOS transistor and the second NMOS transistor. The baseband signal is used to switch between the ON and OFF states of the first NMOS transistor and the second NMOS transistor, thereby switching the transmission routes of the local oscillation signal and forming an ASK modulated high-frequency signal at the signal output terminal. 
     In order to achieve the aforementioned objective and other objectives, the present invention further provides a signal amplifier wherein the signal amplifier includes: an NPN transistor having a base, a collector and an emitter, a front-end impedance matching network, a back-end impedance matching network, and a first pn-diode and a second pn-diode each having an n-terminal and a p-terminal. 
     In particular, the base of the NPN transistor is connected to the front-end impedance matching network, the collector of the NPN transistor is connected to the back-end impedance matching network, the n-terminal of the first pn-diode is connected to the p-terminal of the second pn-diode, the p-terminal of the first pn-diode is connected to the collector of the NPN transistor, and the n-terminal of the second pn-diode is connected to the base of the NPN transistor. 
     Also, the front-end impedance matching network further comprises a signal input terminal. The back-end impedance matching network further comprises a signal output terminal. The front-end impedance matching network further includes a first transmission line, a second transmission line, and a front-end Snatching capacitor. The back-end impedance matching network further includes a third transmission line, a fourth transmission line and a back-end Snatching capacitor. 
     In particular, one end of the signal input terminal is formed by a connection of one end of the first transmission line and one end of the second transmission line. The front-end matching capacitor is connected in series between the other end of the first transmission line and the base of the NPN transistor, and the other end of the signal input terminal is connected to a fifth capacitor. Also, one end of the signal output terminal is formed by a connection of one end of the third transmission line and one end of the fourth transmission line. Furthermore, an antenna unit is connected to the signal output terminal to transmit wireless RF signal. In addition, the back-end matching capacitor is connected in series between the other end of the third transmission line and the collector of the NPN transistor. 
     Also, the signal amplifier further includes a power source and a ground terminal. The power source is connected to the p-terminal of the first pn-diode. The emitter of the NPN transistor, the other end of the second transmission line, and the other end of the fourth transmission line are all connected to the ground terminal. 
     Finally, the signal amplifier disclosed by the present invention further includes a first resistor and a second resistor. The first resistor is connected in series between the back-end matching capacitor and the third transmission line. One end of the second resistor is connected between the first resistor and the third transmission line, and the other end of the second resistor is connected to the ground terminal. 
     Based on the above arrangement, it has been known that the signal amplifier as disclosed by the present invention receives the signal on the signal input terminal. Next, the signal is transmitted to the NPN transistor for signal power amplification via the front-end impedance matching network. Lastly the signal is transmitted to the signal output terminal via the back-end impedance matching network. The first resistor and the second resistor are connected such that the NPN transistor amplifier operates in an unconditionally stable region in order to amplify the ASK modulated signal transmitted from the front-end circuit, thereby increasing the efficiency of signal transmission by the antenna. 
     In summary, the signal modulation device and the signal amplifier as disclosed by the present invention reduces the design complexity of conventional ASK modulation circuit that contains a D/A converter. The overall power consumption of the RF circuit as well as the chip area are significantly reduced. Moreover, the efficiency of signal transmission by the antenna is also increased. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing an ASK modulation process; 
         FIG. 2  illustrates a circuit schematic of a signal modulation device of the present invention; and 
         FIG. 3  is a diagram illustrating a signal amplifier of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following illustrative embodiments are provided to illustrate the disclosure of the present invention, these and other advantages and effects can be apparently understood by those in the art after reading the disclosure of this specification. 
     The present invention can also be performed or applied by other different embodiments. The details of the specification may be on the basis of different points and applications, and numerous modifications and variations can be devised without departing from the spirit of the present invention. The following embodiments further illustrate the points of the present invention in detail, however the scope of the invention is not limited to any points. 
       FIG. 2  illustrates a circuit schematic of a signal modulation device of the present invention. As shown in the diagram, the present invention provides a signal modulation device  10  including a local oscillation signal source  111 , a baseband signal source  112 , a first NMOS transistor  121 , a second NMOS transistor  122 , a first NPN transistor  131 , a second NPN transistor  132 , and a third NPN transistor  133 . 
     In particular, the first NMOS transistor  121  has a source  1211 , a drain  1212 , and a gate  1213 . The second NMOS transistor  122  has a source  1221 , a drain  1222 , and a gate  1223 . The first NPN transistor  131  has an emitter  1311 , a collector  1312 , and a base  1313 . The second NPN transistor  132  has an emitter  1321 , a collector  1322 , and a base  1323 . The third NPN transistor  133  has an emitter  1331 , a collector  1332  and a base  1333 . 
     Also the source  1211  of the first NMOS transistor  121  is connected to the source  1221  of the second NMOS transistor  122  to form a first connection node  101 , and the baseband signal source  112  is connected in series between the gate  1213  of the first NMOS transistor  121  and the gate  1223  of the second NMOS transistor  122 . The base  1313  of the first NPN transistor  131  is connected to a local oscillation signal source  111  and the collector  1312  of the first NPN transistor  131  is connected to the first connection node  101 . The drain  1222  of the second NMOS transistor  122  is connected to a signal output terminal  141 , which is then in turn connected to a back-end circuit  142  for outputting the modulation signal. 
     Besides, the signal modulation device of the present invention further includes a first resistor  151  having a first resistor terminal  1511  and a second resistor terminal  1512 , a second resistor  152  having a third resistor terminal  1521  and a fourth resistor terminal  1522 , a third resistor  153  having a fifth resistor terminal  1531  and a sixth resistor terminal  1532 , a fourth resistor  154  having a seventh resistor terminal  1541  and an eighth resistor terminal  1542 , a first inductor  161  having a first inductor terminal  1611  and a second inductor terminal  1612 , and a second inductor  162  having a third inductor terminal  1621  and a fourth inductor terminal  1622 . 
     In particular, the first resistor terminal  1511  is connected to the drain  1212  of the first NMOS transistor  121 . The third resistor terminal  1521  is connected to the drain  1222  of the second NMOS transistor  122 . The fifth resistor terminal  1531  is connected to the collector  1322  of the second NPN transistor  132 . The seventh resistor terminal  1541  is connected to the drain  1212  of the first NMOS transistor  121 . 
     The first inductor terminal  1611  is connected to the base  1313  of the first NPN transistor  131 . The second inductor terminal  1612  is connected to the collector  1322  of the second NPN transistor  132  and the base  1323  of the second NPN transistor  132 . The third inductor terminal  1621  is connected to the collector  1312  of the first NPN transistor  131 . The fourth inductor terminal  1622  is connected to the collector  1332  of the third NPN transistor  133  and the base  1333  of the third NPN transistor  133 . 
     Finally, the signal modulation device of the present invention further includes a power source  171  and a ground terminal  172 . In addition, the second resistor terminal  1512 , the fourth resistor terminal  1522  and the sixth resistor terminal  1532  are connected to the power source  171 . Also the local oscillation signal source  111 , the emitter  1311  of the first NPN transistor  131 , the emitter  1321  of the second NPN transistor  132 , the emitter  1331  of the third NPN transistor  133  and the eighth resistor  1542  are connected to the ground terminal  172 . 
     Based on the above configuration, the present invention discloses a signal modulation device requiring the utilization of the baseband signal source, the first NMOS transistor and the second NMOS transistor in order to form a circuit structure that directly switches between the Gilbert-cell based differential pair using a differential baseband signal. 
     The signal generated by the local oscillation signal source is injected into the base  1313  of the first NPN transistor  131 . The first NPN transistor  131  amplifies the signal and the first inductor  161  prevents high-frequency signals from being transmitted to the second NPN transistor  132 . The amplified signal is then sent to the source  1211  of the first NMOS transistor  121  of the differential pair and the source  1221  of the second NMOS transistor  122  of the differential pair. The baseband signal  112  serves to switch between the ON and OFF states of the first NMOS transistor  121  and the second NMOS transistor  122 , thereby achieving the switching of the transmission routes of the oscillating signal and forming the high-frequency oscillating modulation signal at the signal output terminal. Besides, the present invention further uses the second inductor  162  and the third NPN transistor  133  to generate the effect of an RF choke and maintain the operating bias voltage of the first NPN transistor  131  in the active region, so as to improve the quality of signal transmission. 
     On the other hand, in order to provide the first NMOS transistor  121  and the second NMOS transistor  122  with an appropriate operating bias voltage, the signal modulation device  10  of the present invention further includes a first bias voltage unit  181  and a second bias voltage unit  182 . In particular, the first bias voltage unit  181  is connected to the gate  1213  of the first NMOS transistor  121  so as to provide the first NMOS transistor  121  with an appropriate bias voltage. Also, the second bias voltage unit  182  is connected to the gate  1223  of the second NMOS transistor  122  so as to provide the second NMOS transistor  122  with an appropriate bias voltage. 
     The first bias voltage unit  181  further includes a first biased NPN transistor  1811 , a second biased NPN transistor  1812 , a third biased NPN transistor  1813  and a fifth resistor  1814  having a ninth resistor terminal  18141  and a tenth resistor terminal  18142 . Also, the first biased NPN transistor  1811  has an emitter  18111 , a collector  18112 , and a base  18113 . The second biased NPN transistor  1812  has an emitter  18121 , a collector  18122  and a base  18123 . The third biased NPN transistor  1813  has an emitter  18131 , a collector  18132  and a base  18133 . 
     In particular, the collector  18112  and the base  18113  of the first biased NPN transistor  1811  are connected to the gate  1213  of the first NMOS transistor  121 . The collector  18122  and the base  18123  of the second biased NPN transistor  1812  are connected to the emitter  18111  of the first biased NPN transistor  1811 . The collector  18132  and the base  18133  of the third biased NPN transistor  1813  are connected to the emitter  18121  of the second biased NPN transistor  1812 . The emitter  18131  of the third biased NPN transistor  1813  is connected to the ground terminal  172 . The ninth resistor terminal  18141  is connected to the collector  18112  of the first biased NPN transistor  1811 . The tenth resistor terminal  18142  is connected to the power source  171 . 
     The second bias voltage unit  182  further includes a fourth biased NPN transistor  1821 , a fifth biased NPN transistor  1822 , a sixth biased NPN transistor  1823  and a sixth resistor  1824  having a eleventh resistor terminal  18241  and a twelfth resistor terminal  18242 . Also, the fourth biased NPN transistor  1821  has an emitter  18211 , a collector  18212 , and a base  18213 . The fifth biased NPN transistor  1822  has an emitter  18221 , a collector  18222  and a base  18223 . The sixth biased NPN transistor  1823  has an emitter  18231 , a collector  18232  and a base  18233 . 
     In particular, the collector  18212  and the base  18213  of the fourth biased NPN transistor  1821  are connected to the gate  1223  of the second NMOS transistor  122 . The collector  18222  and the base  18223  of the fifth biased NPN transistor  1822  are connected to the emitter  18211  of the fourth biased NPN transistor  1821 . The collector  18232  and the base  18233  of the sixth biased NPN transistor  1823  are connected to the emitter  18221  of the fifth biased NPN transistor  1822 . The emitter  18231  of the sixth biased NPN transistor  1823  is connected to the ground terminal  172 . The eleventh resistor terminal  18241  is connected to the collector  18212  of the fourth biased NPN transistor  1821 . The twelfth resistor terminal  18242  is connected to the power source  171 . 
     Besides, the signal modulation device of the present invention further includes a first capacitor  191 , a second capacitor  192 , a third capacitor  193 , a fourth capacitor  194  and a fifth capacitor  195 . 
     In particular, the first capacitor  191  is connected in series between the gate  1213  of the first NMOS transistor  121  and the baseband signal source  112 . The second capacitor  192  is connected in series between the gate  1223  of the second NMOS transistor  122  and the baseband signal source  112 . The third capacitor  193  is connected in series between the local oscillation signal source  111  and the base  1313  of the first NPN transistor  131 . The fourth capacitor  194  is connected in series between the seventh resistor  1541  and the drain  1212  of the first NMOS transistor  121 . The fifth capacitor  195  is connected in series between the back-end circuit  142  and the drain  1222  of the second NMOS transistor  122 . 
     Hence, the aforementioned first bias voltage unit  181  and second bias voltage unit  182  designed into the signal modulation device  10  as disclosed by the present invention provide the first NMOS transistor  121  and the second NMOS transistor  122  with an appropriate operating bias voltage. Appropriate capacitors are placed on the signal transmission routes to allow the signal modulation device  10  to obtain a more stable operating state. 
     Next, referring to  FIG. 3 , the diagram illustrates a circuit schematic of a signal amplifier of the present invention. As shown in the diagram, a signal amplifier  20  disclosed by the present invention includes: an NPN transistor  21 , a front-end impedance matching network  22 , a back-end impedance matching network  23 , a first pn-diode  241  and a second pn-diode  242 . In particular, the NPN transistor  21  has an emitter  211 , a collector  212  and a base  213 . The first pn-diode  241  has a p-terminal  2411  and an n-terminal  2412 . The second pn-diode  242  has a p-terminal  2421  and an n-terminal  2422 . It is noted that a better invention places the signal amplifier  20  in the back-end circuit  142  of the previous embodiment. 
     In particular, the front-end impedance matching network  22  is connected to a base  213  of the NPN transistor  21 . The back-end impedance matching network  23  is connected to a collector  212  of the NPN transistor  21 . The n-terminal  2412  of the first pn-diode  241  is connected to the p-terminal  2421  of the second pn-diode  242 . The p-terminal  2411  of the first pn-diode  241  is connected to the collector  212  of the NPN transistor  21 . The n-terminal  2422  of the second pn-diode  242  is connected to the base  213  of the NPN transistor  21 . 
     Also the front-end impedance matching network  22  has a signal input terminal  221 . The back-end impedance matching network  23  has a signal output terminal  231 . The front-end impedance matching network  22  further includes a first transmission line  222 , a second transmission line  223  and a front-end matching capacitor  224 . The back-end impedance matching network  23  further includes a third transmission line  232 , a fourth transmission line  233  and a back-end matching capacitor  234 . 
     It is more appropriate in the present invention to form the signal input terminal  221  by connecting one end of the first transmission line  222  to one end of the second transmission line  223 , and connect the signal input terminal  221  to the fifth capacitor unit  195  of the previous embodiment to receive the modulation signal sent from the signal modulation device  10  of the present invention. Also, the front-end matching capacitor  224  is connected in series between the other end of the first transmission line  222  and the base  213  of the NPN transistor  21 . 
     The signal output terminal  231  is formed by connecting one end of the third transmission line  232  to one end of the fourth transmission line  233  and the signal output terminal  231  is connected to an antenna unit  27  for wireless RF signal transmission. Also, the back-end matching capacitor  234  is connected in series between the other end of the third transmission line  232  and the collector  212  of the NPN transistor  21 . 
     Also, the signal amplifier further includes a power source  251  and a ground terminal  252 . The power source  251  is connected to the p-terminal  2411  of the first pn-diode  241 . The emitter  211  of the NPN transistor  21 , the other end of the second transmission line  223 , and the other end of the fourth transmission line  233  are connected to the ground terminal  252 . 
     Finally, the signal amplifier  20  further includes a first resistor  261  and a second resistor  262 . In addition, the first resistor  261  is connected between the back-end matching capacitor  234  and the third transmission line  232 , and one end of the second resistor  262  is connected between the first resistor  261  and the third transmission line  232 . Also, the other end of the second resistor  262  is connected to the ground terminal  252 . 
     Based on the above arrangement, it has been known that the signal amplifier as disclosed by the present invention receives the signal at the signal input terminal  221 . Next, the signal is transmitted to the NPN transistor  21  for signal power amplification via the front-end impedance matching network  22 . Lastly the signal is transmitted to the signal output terminal  231  via the back-end impedance matching network  23 . The first resistor  261  and the second resistor  262  are connected such that the NPN transistor  21  amplifier operates in an unconditionally stable region to amplify the ASK modulated signal transmitted from the front-end circuit, thereby improving the performance of signal transmission. 
     While the invention has been particularly shown and described with reference to preferred embodiments for purposes of illustration, it will be understood that variations and modifications can be effected thereto by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.