Patent Publication Number: US-2016226293-A1

Title: Demodulation circuit and wireless charging device having the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The instant disclosure relates to a demodulation circuit; in particular, to a demodulation circuit that can demodulate signals fast and a wireless charging device using the same. 
     2. Description of Related Art 
     With the development of technology, many kinds of personal mobile devices and wearable devices, which connect with the Internet, provide people a mobile life, and thus increase our daily lives&#39; convenience. However, the requirement of electric power for using these electric products has also gradually increased. For solving this problem, a wireless charging device has been developed currently. The wireless charging devices can be generally categorized as two kinds, wherein one is the wireless charging device using the Electromagnetic Induction Technology and the other is the wireless charging device using the Electromagnetic Resonance Technology. Particularly, the wireless charging device using the Electromagnetic Induction Technology is more common. The advantage of the wireless charging device is that the electric device and the wireless charging device do not need wires to have a connection. 
     When the wireless charging device (such as a first wireless charging device) receives a signal sent by another wireless charging device (such as a second wireless charging device), the first wireless charging device needs to demodulate the received signal to obtain the signal content. In the prior art, after the demodulation circuit in the wireless charging device receives a signal, the signal would be filtered via a low-pass filter and a high-pass filter and then be processed via an amplifier, so as to distinguish the signal from noise. After that, the demodulation circuit filters out the high-frequency noise of the amplified signal via another filter. The demodulation circuit compares the processed signal and a reference signal via a comparator, and then outputs a signal at a high logic level or a low logic level. Finally, the output signal at a high logic level or a low logic level can be converted to a digital signal via the analog digital converting circuit of the demodulation circuit for a subsequent process via the back end circuit. 
     From the above, the traditional demodulation circuit has to use a low-pass filter, a high-pass filter, an operational amplifier and a comparator to demodulate a signal, which increases the manufacturing cost and circuit area of the demodulation circuit and also increases the time and power consumption for demodulating signals with an increasing amount of filters and amplifiers. 
     SUMMARY OF THE INVENTION 
     The instant disclosure provides a demodulation circuit, used in a wireless charging device. The demodulation circuit comprises a detection unit, a delay unit and a demodulation unit. The detection unit is electrically connected to a coil and a power stage circuit for detecting a pulse width modulation signal received by a coil and outputting a modulation signal. The delay unit is electrically connected to the detection unit for delaying the modulation signal and generating a delay signal. The demodulation unit is electrically connected to the detection unit and the delay unit for comparing the modulation signal and the delay signal so as to generate a demodulation signal. The demodulation signal is a binary data signal. When a voltage level of the modulation signal is higher than or equal to a voltage level of the delay signal, the demodulation unit outputs a high logic level demodulation signal. When the voltage level of the modulation signal is lower than the voltage level of the delay signal, the demodulation unit outputs a low logic level demodulation signal. 
     The instant disclosure further provides a wireless charging device. The wireless charging device comprises a coil, a power stage circuit, a control unit and a demodulation circuit. The coil is configured to receive a pulse width modulation signal. The power stage circuit is electrically connected to the coil, and configured to output a voltage or an electromagnetic energy to the coil. The control unit is electrically connected to the power stage circuit, and configured to control the power stage circuit. The demodulation circuit is electrically connected to the coil, the power stage circuit and the control unit, and comprises a detection unit, a delay unit and a demodulation unit. The detection unit is electrically connected to a coil and a power stage circuit, and configured to detect a pulse width modulation signal received by a coil and to output a modulation signal. The delay unit is electrically connected to the detection unit, and configured to delay the modulation signal and to generate a delay signal. The demodulation unit is electrically connected to the detection unit and the delay unit, and configured to compare the modulation signal and the delay signal so as to generate a demodulation signal. The demodulation signal is a binary data signal. When a voltage level of the modulation signal is higher than or equal to a voltage level of the delay signal, the demodulation unit outputs a high logic level demodulation signal. When the voltage level of the modulation signal is lower than the voltage level of the delay signal, the demodulation unit outputs a low logic level demodulation signal. After receiving the demodulation signal, the control unit correspondingly controls the power stage circuit according to the demodulation signal. 
     To sum up, the demodulation circuit and the wireless charging device using the same provided by the embodiments in the instant disclosure can demodulate a modulation signal via comparing the modulation signal and its delay signal and then obtain a demodulation signal. Compared with the traditional demodulation circuit, the demodulation circuit provided by the embodiments in the instant disclosure can demodulate the modulation signal without a low-pass filter, a high-pass filter, an analog to digital converter or other operational amplifiers, which decreases the manufacturing cost and the circuit area. Moreover, in the demodulation circuit provided by the embodiments in the instant disclosure, it is unnecessary to use many filters or operational amplifiers, so the overall power of circuit would be effectively reduced. 
     For further understanding of the instant disclosure, reference is made to the following detailed description illustrating the embodiments and examples of the instant disclosure. The description is only for illustrating the instant disclosure, not for limiting the scope of the claim. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which: 
         FIG. 1  shows a block diagram of a wireless charging device of one embodiment of the instant disclosure; 
         FIG. 2  shows a block diagram of a demodulation circuit of one embodiment of the instant disclosure; 
         FIG. 3  shows a schematic diagram of a demodulation circuit of one embodiment of the instant disclosure; 
         FIG. 4  shows a schematic diagram of a demodulation circuit of another embodiment of the instant disclosure; 
         FIG. 5  shows a waveform timing diagram for an operation of a demodulation circuit of an embodiment of the instant disclosure; and 
         FIG. 6  shows a flow chart for an operation of a wireless charging device of an embodiment of the instant disclosure. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The aforementioned illustrations and following detailed descriptions are exemplary for the purpose of further explaining the scope of the instant disclosure. Other objectives and advantages related to the instant disclosure will be illustrated in the subsequent descriptions and appended drawings. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. 
     It will be understood that, although the terms first, second, third, and the like, may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only to distinguish one element, component, region, layer or section from another region, layer or section discussed below which could be termed a second element, component, region, layer or section without departing from the teachings of the instant disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Please refer to  FIG. 1 ,  FIG. 1  shows a block diagram of a wireless charging device of one embodiment of the instant disclosure. The wireless charging device  1  comprises a control unit  10 , a power stage circuit  11 , a coil  12 , a demodulation circuit  13 , a power processing unit  14  and a power storage unit  15 . The control unit  10  is electrically connected to the power stage circuit  11 . The power stage circuit  11  is electrically connected to the coil  12 . The demodulation circuit  13  is electrically connected to the control unit  10 , the power stage circuit  11  and the coil  12 . The power processing unit  14  is electrically connected to the power storage unit  15 . The power storage unit  15  is electrically connected to the power stage circuit  11 . 
     The wireless charging device  1  is a unidirectional wireless charging device or a bidirectional wireless charging device. If the wireless charging device  1  is a unidirectional wireless charging device, the wireless charging device  1  is used as a transmitter. Under this circumstance, the wireless charging device  1  does not include any elements necessary for a receiver. For example, the wireless charging device  1  does not include a modulation unit, a rectification unit or a voltage-regulating unit that are necessary for a receiver. The wireless charging device  1 , such as a wireless charger, can charge other wireless charging devices, such as a mobile phone, a tablet computer, a laptop, a smart watch, a set top box or the like. 
     If the wireless charging device  1  is a bidirectional wireless charging device, the wireless charging device  1  can be used as a transmitter or a receiver. In this case, in addition to the control unit  10 , the power stage circuit  11 , the coil  12 , the demodulation circuit  13 , the power processing unit  14  and the power storage unit  15 , the wireless charging device  1  further comprises a modulation unit, a rectification unit, a voltage-regulating unit, another control unit and another power stage circuit (not shown in  FIG. 1 ), so that the wireless charging device  1  can work as a transmitter or a receiver via corresponding elements. The wireless charging device  1  can be a bidirectional wireless charging device mentioned above. If the wireless charging device  1  is used as a transmitter, it can provide electromagnetic energy to other wireless charging devices. If the wireless charging device  1  is used as a receiver, it can receive electromagnetic energy provided by other wireless charging devices. The detailed structure and operation mechanism of the wireless charging device are well known by the skilled in the art, and the information is not repeated. 
     It will be understood that, the above description about the elements in the wireless charging device  1  is merely for instruction, and thus the instant disclosure should not be limited by these elements. The wireless charging device  1  can be a traditional unidirectional wireless charging device or a traditional bidirectional wireless charging device. For easy instruction and understanding of the instant disclosure, the wireless charging device  1  is, for example, a wireless charging device such as a transmitter, and the following description is a further teaching of the elements of the wireless charging device  1 . 
     The control unit  10 , such as a Microcontroller Unit (MCU) is configured to control a voltage or electromagnetic energy output by the power stage circuit  11 . 
     The power stage circuit  11  comprises a power switch, a Pulse Width Modulation (PWM) circuit, a high-frequency isolation transformer and an output filter (not shown in  FIG. 1 ), for outputting a voltage to the coil  12 . 
     The coil  12  can be a cable coil or other inductors that can generate an induced voltage correspondingly according to a variable electromagnetic field. The coil  12  can convert a voltage into a pulse width modulation (PWM) signal and send out the PWM signal. The PWM signal includes electromagnetic energy. Also, the coil  12  can receive a signal PWM&#39; sent by other wireless charging devices, such as a receiver, and the signal PWM&#39; includes electric quantity information of the receiver (for example, how much electric quantity is currently stored by the receiver). 
     The power processing unit  14  is configured to manage the electric energy stored by the wireless charging device  1 . For example, the power processing unit  14  controls the power storage unit  15  to provide the electric energy to the power stage circuit  11 . 
     The power storage unit  15 , such as a battery of the wireless charging device  1  or other power storage device (such as a capacitor), is configured to store the electric energy. The power storage unit  15  is also configured to provide the electric energy to the power stage circuit  11 , so that the power stage circuit  11  can provide a voltage to the coil  12 . 
     Please refer to  FIG. 2 .  FIG. 2  shows a block diagram of a demodulation circuit of one embodiment of the instant disclosure. The demodulation circuit  13  is configured to detect the signal PWM&#39; received by the coil  12  or the power stage circuit  11 , and to demodulate the signal PWM&#39;. The demodulation circuit  13  further comprises a detection unit  130 , a delay unit  131  and a demodulation unit  132 . The detection unit  130  is electrically connected to the coil  12  or the power stage circuit  11 , which depends on the type of the detection unit  130 . The delay unit  131  is electrically connected to the detection unit  130 . The demodulation unit  132  is electrically connected to the detection unit  130 , the delay unit  131  and the control unit  10 . 
     The detection unit  130  is, for example, a current detection unit or a voltage detection unit. If the detection unit  130  is a current detection unit, the detection unit  130  detects a current amplitude change when the power stage circuit  11  receives the signal PWM&#39;, so as to obtain a modulation signal MS. The modulation signal MS includes the electric quantity information of the receiver, for example, how much electric quantity is currently stored in the receiver. If the detection unit  130  is a voltage detection unit, the detection unit  130  detects a voltage amplitude change when the coil  12  receives the signal PWM&#39;, so as to obtain a modulation signal MS. 
     The delay unit  131  is configured to delay the modulation signal MS and to generate a delay signal DS of the modulation signal MS. The demodulation unit  132  receives and compares the modulation signal MS and the delay signal DS, so as to generate a demodulation signal DMS. In addition, the demodulation signal DMS is a binary data signal. The demodulation signal DMS includes an energy storage status of the receiver, for example, how much energy is currently stored. After that, the demodulation unit  132  outputs the demodulation signal DMS to the control unit  10 . The control unit  10  correspondingly adjusts the voltage or the electromagnetic energy output by the power stage circuit  11  according to the energy storage status of the receiver indicated by the demodulation signal DMS, so as to adjust the electromagnetic energy of the pulse width modulation signal PWM. 
     For example, when the demodulation signal DMS indicates that the energy stored in the receiver reaches a predetermined value (such as 90% of the maximum stored energy of the receiver), the control unit  10  would make the power stage circuit  11  stop outputting the voltage or the electromagnetic energy to the coil  12 . In another case, when the demodulation signal DMS indicates that the energy stored in the receiver is within a predetermined range (such as 70%-90% of the maximum stored energy of the receiver), the control unit  10  would control the voltage or the electromagnetic energy output by the power stage circuit  11  to the coil  12 . 
     Please refer to  FIG. 3 .  FIG. 3  shows a schematic diagram of a demodulation circuit of one embodiment of the instant disclosure. As described above, the demodulation circuit  13  comprises a detection unit  130 , a delay unit  131  and a demodulation unit  132 . Regarding the relevant connecting relationships between the detection unit  130 , the delay unit  131  and the demodulation unit  132  in the instant disclosure, it is identical to the previous embodiment, and it is not repeated. 
     In this embodiment, the detection unit  130  is a current detection unit of which the circuit consists of resistors, amplifiers, diodes and capacitors. The amplifier receives an input voltage Vin. The resistors include a first resistor R 1 . One end of the first resistor R 1  is electrically connected to the power stage circuit  11  (such as the power stage circuit  11  shown in  FIG. 1  and  FIG. 2 ), and the other end of the first resistor R 1  receives a working voltage VCC. It should be noted that, the composition and structure of the detection unit  130  shown in  FIG. 3  is merely for instruction, and thus the instant disclosure should not be limited thereto. The structure of the detection unit  130  in other embodiments can be different, as long as the detection unit  130  has a current detecting function. 
     After the coil receives the signal PWM&#39;, based on the electromagnetic induction principle, the coil  12  would correspondingly induce the power stage circuit  11  according to the signal PWM&#39;, so that the power stage circuit  11  would generate a current. The current generated by the power stage circuit  11  would affect a current ICC flowing through the first resistor R 1 , so that the amplitude of the current ICC would change. The current ICC is related to the working voltage VCC. The detection unit  130  detects an amplitude change of the current ICC to obtain a modulation signal MS. 
     The delay unit  131  is a resistor-capacitor network consisting of at least one capacitor and one resistor. Via the resistor-capacitor network, the modulation signal MS would result in a RC delay and generate a delay signal DS. In short, the modulation signal MS plus a period of delay time equals to the delay signal DS, resulting in a signal delay via a resistor-capacitor network well known by those skilled in the art and thus the information is not repeated. In addition, the composition and structure of the delay unit  131  shown in  FIG. 3  is merely for instruction, and thus the instant disclosure should not be limited thereto. Those skilled in the art can design the structure of the delay unit  131  based on need. 
     In conjunction with  FIG. 3 ,  FIG. 5  shows a waveform timing diagram for an operation of a demodulation circuit of an embodiment of the instant disclosure. The two waveforms shown at the upper side of  FIG. 5  respectively represent the modulation signal MS and the delay signal DS. The modulation signal MS and the delay signal DS are analogue signals of which the voltage levels are related to a voltage change resulting from a signal PWM&#39;. From  FIG. 5 , the modulation signal MS plus a period of delay time tl equals to a delay signal DS. In addition, the structure of the resistor-capacitor network can be designed by those skilled in the art to adjust the delay time t 1 , and how long the delay time t 1  would be is not limited herein. 
     The demodulation unit  132  comprises a comparator  1320  and a logic controller  1321 . The non-inverting input end of the comparator  1320  is electrically connected to the detection unit  130 , and the inverting input end of the comparator  1320  is electrically connected to the delay unit  131 . The output end of the comparator  1320  is electrically connected to the logic controller  1321 . The logic controller  1321  is electrically connected to the control unit (such as the control unit  10  in  FIG. 2 , but not shown in  FIG. 3 ). 
     The non-inverting input end of the comparator  1320  receives the modulation signal MS and the inverting input end of the comparator  1320  receives the delay signal DS. After that, the comparator  1320  compares the voltage levels of the modulation signal MS and the delay signal DS and outputs a comparison signal CS. Referring to  FIG. 5  based on  FIG. 3 , the three waveforms shown at the upper side of  FIG. 5  respectively represent the modulation signal MS, the delay signal DS and the comparison signal CS. If the voltage level of the modulation signal MS is higher than or equal to the voltage level of the delay signal DS, the comparator  1320  outputs a comparison signal CS having a high logic level. On the other hand, if the voltage level of the modulation signal MS is lower than the voltage level of the delay signal DS, the comparator  1320  outputs a comparison signal CS having a low logic level. Thereby, the comparator  1320  will obtain a comparison signal CS having a high logic level or a low logic level. 
     The logic controller  1321  is further electrically connected to a timing generator (not shown in  FIG. 3 ). The logic controller  1321  receives the comparison signal CS and a clock signal CLK output by the timing generator, and compares the comparison signal CS and the clock signal CLK. In a further instruction, the modulation signal MS and the delay signal DS would be affected by noise, so the voltage levels of the modulation signal MS and the delay signal DS would not be constant. In addition, the logic level of the comparison signal CS is related to voltage levels of the modulation signal MS and the delay signal DS. In other words, the logic level of the comparison signal CS would also be affected by noise and thus change. In order to avoid an error demodulation caused by noise, the demodulation unit  132  comprises a logic controller  1321 . The logic controller calculates a time duration when the comparison signal CS maintains at the same logic level via the clock signal CLK. 
     Please again refer to  FIG. 5 . The three waveforms shown at the lower side of  FIG. 5  respectively represent the comparison signal CS, the demodulation signal DMS and the clock signal CLK. If the time duration when the comparison signal CS maintains at the same logic level is over a predetermined time duration t 2 , the logic controller outputs the demodulation signal DMS according to the logic level of the comparison signal CS. In other words, the demodulation signal DMS is generated according to the comparison signal CS. If the time duration when the comparison signal CS maintains at the same logic level is not over a predetermined time duration t 2 , the logic level of the demodulation signal DMS output by the logic controller  1321  would not change but maintain at its original logic level. 
     For example, if the logic controller  1321  determines that the time duration when the comparison signal CS maintains at a high logic level is over a predetermined time duration t 2 , the logic controller  1321  outputs a demodulation signal DMS at a high logic level (such as the “1” in a binary system). If the logic controller  1321  determines that the time duration when the comparison signal CS maintains at a high logic level is not over a predetermined time duration t 2 , the logic controller  1321  maintains the demodulation signal DMS at its original logic level. On the other hand, the logic controller  1321  determines that the time duration when the comparison signal CS maintains at a low logic level is over a predetermined time duration t 2 , the logic controller  1321  outputs a demodulation signal DMS at a low logic level (such as the “0” in a binary system). If the logic controller  1321  determines that the time duration when the comparison signal CS maintains at a low logic level is not over a predetermined time duration t 2 , the logic controller  1321  maintains the demodulation signal DMS at its original logic level. 
     In addition, the predetermined time duration t 2  is, for example, an interval between one of the rising edges of the clock signal CLK and the next two rising edge of the clock signal CLK (that is, the predetermined time duration t 2  equals to two periods of the clock signal CLK). In this embodiment, the predetermined time duration t 2  is 10 μs, but it is not limited herein. Those skilled in the art can design the length of the predetermined time duration t 2  based on need. 
     After the control unit  10  receives the demodulation signal DMS, the control unit  10  will control the power stage circuit (such as the power stage circuit  11 , but not shown in  FIG. 3 ) according to the demodulation signal DMS, so that the power stage circuit  11  will change the output voltage or the electromagnetic energy and further adjust the electromagnetic energy included in the PWM signal PWM output by the wireless charging device  1 . 
     From the above, the logic controller  1321  calculates the time duration when the comparison signal CS maintains at the same logic level via the clock signal CLK, so as to generate a demodulation signal DMS. In other embodiments, the demodulation unit  132  does not include the logic controller  1321 . The demodulation unit  132  uses the comparison signal CS output by the comparator  1320  to calculate the demodulation signal DMS, and outputs it to the control unit  10  so that the control unit  10  correspondingly controls the power stage circuit  11  according to the demodulation signal DMS. 
     Please refer to  FIG. 4 .  FIG. 4  shows a schematic diagram of a demodulation circuit of another embodiment of the instant disclosure. The demodulation circuit  13 ′ shown in  FIG. 4  comprises a detection unit  130 ′, a delay unit  131 ′ and a demodulation unit  132 ′. Regarding the relevant connecting relationship between the detection unit  130 ′, the delay unit  131 ′ and the demodulation unit  132 ′ in the instant disclosure, it is identical to the previous embodiment, and it is not repeated. 
     Different from the demodulation circuit  13  shown in  FIG. 3 , the detection unit  130 ′ shown in  FIG. 4  is a voltage detection unit consisting of resistors, diodes and capacitors. 
     After the coil  12  receives the signal PWM&#39; output by the receiver, based on the electromagnetic induction principle, the coil  12  will correspondingly generate a voltage according to the signal PWM&#39;. In other words, the amplitude of voltage generated by the coil  12  will change because of the signal PWM&#39;. After that, the coil  12  charges the first capacitor C 1  by the generated voltage. The detection unit  130 ′ obtains the modulation signal MS via detecting the change of amplitude of the charging voltage of the first capacitor C 1 . It should be noted that the composition and structure of the detection unit  130 ′ shown in  FIG. 4  is merely for instruction, and thus the instant disclosure should not be limited thereto. The structure of the detection unit  130 ′ in other embodiments can be different, as long as the detection unit  130 ′ has a voltage detecting function. On the other hand, the operation mechanism of the delay unit  131 ′ and the demodulation unit  132 ′ are identical to the delay unit  131  and the demodulation unit  132  shown in  FIG. 3 , and thus the redundant information is not repeated. 
     Please refer to  FIG. 6 .  FIG. 6  shows a flow chart for an operation of a wireless charging device of an embodiment of the instant disclosure. The operation shown in  FIG. 6  is applied to the above wireless charging device  1 . In Step S 601 , the coil receives a PWM&#39; signal. The detection unit obtains a modulation signal via detecting an amplitude change of voltage generated by the coil because of the PWM&#39; signal or via detecting an amplitude change of current generated by the power stage circuit because of the PWM&#39; signal. In Step S 602 , the delay unit receives and delays the modulation signal output by the detection unit, so as to generate a delay signal. In Step S 603 , the comparator of the demodulation unit compares the voltage levels of the modulation signal and the delay signal. If the voltage level of the modulation signal is higher than or equal to the voltage level of the delay signal, it goes to Step S 604 . If the voltage level of the modulation signal is lower than the voltage level of the delay signal, it goes to Step S 605 . In Step S 604 , the comparator outputs a comparison signal at a high logic level. In Step S 605 , the comparator outputs a comparison signal at a low logic level. 
     In Step S 606 , the logic controller receives the comparison signal at a high logic level, and calculates whether the time duration when the comparison signal maintains at the high logic level is over a predetermined time duration via clock signals. If the time duration when the comparison signal maintains at a high logic level is over the predetermined time duration, it goes to Step S 607 . If the time duration when the comparison signal maintains at a high logic level is not over the predetermined time duration, it goes to Step S 608 . In Step S 607 , the logic controller outputs a demodulation signal at a high logic level. In Step S 608 , the logic controller outputs a demodulation signal remaining at its original logic level. 
     In Step S 609 , the logic controller receives a comparison signal at a low logic level, and calculates whether the time duration when the comparison signal maintains at the low logic level is over a predetermined time duration via clock signals. If the time duration when the comparison signal maintains at the low logic level is over the predetermined time duration, it goes to Step S 610 . If the time duration when the comparison signal maintains at the low logic level is not over the predetermined time duration, it goes to Step S 611 . In Step S 610 , the logic controller outputs a demodulation signal at a low logic level. In Step S 611 , the logic controller outputs a demodulation signal remaining at its original logic level. In Step S 612 , the control unit receives the demodulation signal and correspondingly controls the power stage circuit according to the demodulation signal. 
     To sum up, the demodulation circuit and the wireless charging device using the same provided by the embodiments in the instant disclosure can demodulate a modulation signal via comparing the modulation signal and its delay signal and then obtain a demodulation signal. Compared with the traditional demodulation circuit, the demodulation circuit provided by the embodiments in the instant disclosure can demodulate the modulation signal without a low-pass filter, a high-pass filter, an analog to digital converter or other operational amplifiers, decreasing the manufacturing cost and the circuit area. Moreover, in the demodulation circuit provided by the embodiments in the instant disclosure, it is unnecessary to use many filters or operational amplifiers, so the overall power of circuit would be effectively reduced. 
     The demodulation circuit provided by embodiments of the instant disclosure does not include analog to digital converters. In other words, the modulation signal does not need to go through any digital process during the demodulating process. The demodulation circuit can demodulate the PWM&#39; signal received by the coil via the detection unit, the delay unit and the demodulation unit. Compared to the traditional demodulation circuit, the demodulation circuit provided by embodiments of the instant disclosure can obtain a demodulation signal faster. 
     The descriptions illustrated supra set forth simply the preferred embodiments of the instant disclosure; however, the characteristics of the instant disclosure are by no means restricted thereto. All changes, alterations, or modifications conveniently considered by those skilled in the art are deemed to be encompassed within the scope of the instant disclosure delineated by the following claims.