Patent Publication Number: US-9893565-B2

Title: Power receiver control circuit, control method of wireless power receiver, and electronic apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-265336, filed on Dec. 26, 2014, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to wireless power supply technologies. 
     BACKGROUND 
     In recent years, wireless power supplies have become widespread as a method to supply electric power to electronic apparatuses. As a wireless power supply, there exist two types, i.e., an MI (Magnetic Induction) type and an MR (Magnetic Resonance) type. The MI type includes two standards, i.e., the standard “Qi” established by the WPC (Wireless Power Consortium) and a standard established by the PMA (Power Matters Alliance) (hereinafter referred to as the PMA standard), which are currently mainstream standards. 
       FIG. 1  is a diagram showing the configuration of a wireless power supply system  100 R in compliance with the PMA standard. The power supply system  100 R includes a power transmitter (TX)  200 R and a power receiver (RX)  300 R. The power receiver  300 R is equipped in an electronic apparatus such as a mobile phone, a smartphone, an audio player, a game machine, a tablet terminal or the like. 
     The power transmitter  200 R includes a transmission coil (primary coil)  202 , a driver  204 , a controller  206 , and a demodulator  208 . The driver  204  includes an H bridge circuit (full bridge circuit) or a half bridge circuit and applies a drive signal S 1 , specifically a pulse signal, to the transmission coil  202 . An electromagnetic power signal S 2  is generated in the transmission coil  202  by a drive current flowing through the transmission coil  202 . The controller  206  generally controls the overall operation of the power transmitter  200 R. Specifically, the controller  206  changes transmission power by controlling a switching frequency of the driver  204  or a duty cycle of switching. 
     The power receiver  300 R includes a reception coil  302 , a rectification circuit  304 , a smoothing capacitor  306 , a modulator  308 , a load  310 , a controller  312 , and a power supply circuit  314 . The reception coil  302  receives the power signal S 2  of the transmission coil  202  and transmits a control signal S 3  to the transmission coil  202 . The rectification circuit  304 /the smoothing capacitor  306  rectifies/smooths a current I RX  induced in the reception coil  302  in response to the power signal S 2  to convert the current I RX  to a DC voltage V RECT . 
     The power supply circuit  314  uses the power supplied from the power transmitter  200 R to charge a secondary battery (not shown) or steps up or down the DC voltage V RECT  to supply it to the controller  312  and the load  310 . 
     In the PMA standard or Qi standard, a communication protocol is established between the power transmitter  200 R and the power receiver  300 R. Therefore, information can be delivered by the control signal S 3  from the power receiver  300 R to the power transmitter  200 R. The control signal S 3  is transmitted from the reception coil  302  (secondary coil) to the transmission coil  202  in the form of an FSK (Frequency Shift Keying) or ASK (Amplitude Shift Keying) signal by using backscatter modulation. 
     The control signal S 3  contains power control data (also referred to as packets) indicating the amount of power supplied to the power receiver  300 R, data indicating specific information of the power receiver  300 R, and the like. The demodulator  208  demodulates the control signal S 3  contained in the current or voltage of the transmission coil  202 . The controller  206  controls the driver  204  based on the power control data contained in the demodulated control signal S 3 . 
     The PMA standard (parent standard) includes three children standards, i.e., PMA-1, PMA-3, and PMA-4. The inventors of the present application have examined the design of the power receiver  300 R supporting the PMA-1, PMA-3, and PMA-4 standards and the Qi standard. 
     Since frequencies used in the PMA-1, PMA-3, and PMA-4 standards and the Qi standard are different from each other, communication cannot be established between the power transmitter  200 R and the power receiver  300 R until the standards (protocols) are determined. Therefore, the power receiver  300 R requires the ability to automatically determine a standard which the power transmitter  200 R complies with, without relying on means such as communication or the like, immediately after being placed on a charging stand of the power transmitter  200 R. 
     SUMMARY 
     The present disclosure provides some embodiments of a power receiver which is capable of automatically determining a standard that a power transmitter complies with. 
     According to one embodiment of the present disclosure, there is provided a control circuit of a wireless power receiver. The wireless power receiver comprises a reception coil, a rectification circuit that rectifies a current of the reception coil, and a smoothing capacitor connected to an output of the rectification circuit. The control circuit comprises a frequency detecting part configured to determine a frequency of a signal received by the reception coil in a detection period after a lapse of predetermined first time from a predetermined start timing before a lapse of predetermined second time; a modulation detecting part configured to determine whether the signal received by the reception coil is subjected to FSK (Frequency Shift Keying); and a standard determining part configured to determine a standard that a wireless power transmitter complies with, depending on the frequency detected by the frequency detecting part and the presence or absence of FSK. 
     The wireless power supply system transitions from an analog ping phase, through a digital ping phase, to a power transfer phase to supply electric power from a power transmitter to a power receiver. Here, the frequency of a signal generated by the power transmitter after the start of the digital ping phase is changed to different frequencies or waveforms for different standards. Then, the wireless power receiver can automatically determine a standard that the power transmitter complies with, by determining a certain start timing, measuring a frequency in a predetermined period after the start timing, and detecting the presence or absence of FSK if necessary. 
     The standard determining part may (i) determine that the wireless power transmitter complies with the PMA (Power Matters Alliance)-1 standard if the detected frequency is higher than a first frequency that is set between 230 kHz and 250 kHz, and (ii) determine that the wireless power transmitter complies with the PMA-3 standard if the detected frequency is higher than a second frequency that is set between 190 kHz and 220 kHz and is lower than the first frequency and FSK is detected. In addition, the standard determining part may (iii) determine that the wireless power transmitter complies with the PMA-4 standard if the detected frequency is lower than the second frequency and FSK is detected, and (iv) determine that the wireless power transmitter complies with the Qi standard if the detected frequency is lower than the second frequency and no FSK is detected. 
     The standard determining part may (v) determine that the wireless power transmitter is an unknown wireless power transmitter if the detected frequency is higher than the second frequency and is lower than the first frequency and no FSK is detected. 
     The standard determining part may have at least two of the determination criteria (i) to (v). 
     The start timing may be a reset release. The reset release occurs in the power receiver. Therefore, when the frequency detection period is set on the basis of the timing of the reset release. It is possible to correctly detect different frequencies set for different standards. 
     The first frequency may be 240 kHz. The second frequency may be 200 kHz. By setting a threshold frequency substantially at the center of the frequency range of each standard, erroneous determination of standards may be prevented even if there exist a frequency measurement error or a frequency variation. 
     The standard determining part may (a) determine that the wireless power transmitter complies with the PMA (Power Matters Alliance)-1 standard if the detected frequency is higher than a third frequency that is set to be equal to or lower than 250 kHz, and (b) determine that the wireless power transmitter complies with the PMA-3 standard if the detected frequency is lower than a fourth frequency that is set to be equal to or higher than 230 kHz and is higher than a fifth frequency that is set to be equal to or lower than 220 kHz and FSK is detected. 
     The standard determining part may (c) determine that the wireless power transmitter complies with the PMA-4 standard if the detected frequency is lower than a sixth frequency that is set to be equal to or higher than 190 kHz, and (d) determine that the wireless power transmitter complies with the Qi standard if the detected frequency is lower than the sixth frequency and no FSK is detected. 
     The standard determining part may (e) determine that the wireless power transmitter is an unknown wireless power transmitter if the detected frequency is higher than the fifth frequency and is lower than the fourth frequency and no FSK is detected. 
     The standard determining part may have at least two of the determination criteria (a) to (e). 
     The standard determining part may include any combinations of the determination criteria (i) to (v) and (a) to (e). 
     The control circuit may be integrated on a single semiconductor substrate. As used herein, the term “integrated” is intended to include both of a case where all elements of a circuit are formed on a semiconductor substrate and a case where main elements of the circuit are integrated on the semiconductor substrate. In addition, some resistors, capacitors and the like for adjustment of a circuit constant may be provided outside the semiconductor substrate. By integrating the circuit as a single IC, it is possible to reduce a circuit area and allow circuit elements to have uniform characteristics. 
     According to another embodiment of the present disclosure, there is provided a wireless power receiver or an electronic apparatus including: a reception coil; a rectification circuit configured to rectify a current of the reception coil; a smoothing capacitor connected to an output of the rectification circuit; and the above-described control circuit. 
     Any combinations of the above-described elements or changes of the representations of the present disclosure between methods, apparatuses, and systems are effective as embodiments of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing the configuration of a wireless power supply system in compliance with the PMA standard. 
         FIG. 2  is a block diagram of an electronic apparatus including a power receiver according to an embodiment. 
         FIGS. 3A to 3D  are diagrams showing the transition of frequency of a digital ping phase in the PMA-1, PMA-3, PMA-4, and Qi standards, respectively. 
         FIG. 4  is a diagram showing the correspondence relation between the standards and a frequency and the presence or absence of FSK in a detection period T DET . 
         FIG. 5  is a flow chart of standard determination. 
         FIG. 6  is a diagram showing an electronic apparatus including the power receiver according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Preferred embodiments will now be described in detail with reference to the drawings. Throughout the drawings, the same or similar elements, members and processes are denoted by the same reference numerals and explanation of which will not be repeated. The disclosed embodiments are provided for the purpose of illustration, not limitation, of the present disclosure and all features and combinations thereof described in the embodiments cannot be necessarily construed to describe the spirit of the present disclosure. 
     In the specification, the phrase “a member A is connected to a member B” is intended to include direct physical connection of the member A and the member B as well as indirect connection thereof via another member as long as the other member has no substantial effect on the electrical connection thereof or does not damage the functions or effects of the electrical connection thereof. Similarly, the phrase “a member C is provided between a member A and a member B” is intended to include direct connection of the member A and the member C or direct connection of the member B and the member C as well as indirect connection thereof via another member as long as the other member has no substantial effect on the electrical connection thereof or does not damage the functions or effects of the electrical connection thereof. 
       FIG. 2  is a block diagram of an electronic apparatus  500  including a power receiver  300  according to an embodiment. The power receiver  300  receives a power signal S 2  from a power transmitter (not shown), stores its energy in a smoothing capacitor  306 , and supplies the stored energy to a load  502 . 
     The power receiver  300  includes a reception coil  302 , a rectification circuit  304 , a smoothing capacitor  306 , and a control circuit  400 . The power receiver  300  of  FIG. 2  is in compliance with the PMA standard and the Qi standard and can be used in the power supply system  100 R of  FIG. 1 . 
     The reception coil  302  receives the power signal S 2  from the transmission coil  202  (see  FIG. 1 ) and transmits the control signal S 3  to the transmission coil  202 . A current I RX  induced by the power signal S 2  is flown through the reception coil  302 . The input side of the rectification circuit  304  is connected to the reception coil  302  to full-wave or half-wave rectify the current I RX . The rectification circuit  304  may be a diode bridge circuit or an H bridge circuit. The smoothing capacitor  306  is connected to an output of the rectification circuit  304  and smooths an output voltage of the rectification circuit  304 . A DC voltage (also referred to as a rectification voltage) V RECT  generated in the smoothing capacitor  306  is supplied to the load  502  at the subsequent stage. 
     The load  502  includes a power supply circuit  504 , a secondary battery  506  and various processors  508 . The power supply circuit  504  is provided because it is difficult to directly drive electronic circuits such as the processor  508  and the like by using the rectification voltage V RECT . The power supply circuit  504  includes a linear regulator and/or a switching regulator (DC/DC converter) and regulates the rectification voltage V RECT  to an appropriate voltage level which is then supplied to the processor  508 . In addition, the power supply circuit  504  may include a charging circuit for charging the secondary battery  506  by using the power supplied from the power transmitter  200 . 
     Subsequently, the control circuit  400  according to the embodiment will be described. The control circuit  400  includes a voltage measuring part  402 , a power controller  406 , a modulator  408 , a frequency detecting part  420 , a modulation detecting part  422 , and a standard determining part  424  and is a functional IC (Integrated Circuit) integrated on a single semiconductor substrate. A portion of the rectification circuit  304  may be integrated in the control circuit  400 . All the configurations of the control circuit  400  are not necessarily shown in  FIG. 2  and blocks unrelated to the present disclosure are omitted for the sake of ease of understanding and simplicity of description. 
     The voltage measuring part  402  measures the rectification voltage V RECT  generated in the smoothing capacitor  306  or a corresponding voltage. The voltage measuring part  402  may be an A/D converter for generating a digital value D RECT  indicating the measured rectification voltage V RECT . 
     The power controller  406  generates power control data D PC , which indicates the power transmitted from the power transmitter, based on the rectification voltage V RECT . For example, for the Qi standard, the power controller  406  quantizes an error between the rectification voltage V RECT  and its desired point (DP) and generates the power control data D PC . 
     For the PMA standard, an upper limit voltage V H  and a lower limit voltage V L  are set near the target level of the rectification voltage V RECT . The power controller  406  compares the rectification voltage V RECT  with the upper limit voltage V H  and the lower limit voltage V L  and generates the power control data D PC  based on a result of the comparison. Specifically, the power controller  406  changes the power control data D PC  in a first direction if the rectification voltage V RECT  exceeds the upper limit voltage V H , and changes the power control data D PC  in a second direction if the rectification voltage V RECT  is lower than the lower limit voltage V L . In this embodiment, the first direction is a decreasing direction and the second direction is an increasing direction. The power controller  406  decreases the power control data D PC  by one step if the rectification voltage V RECT  exceeds the upper limit voltage V H , and increases the power control data D PC  by a plurality of steps if the rectification voltage V RECT  is lower than the lower limit voltage V L . 
     The modulator  408  generates a signal obtained by modulating the power control data D PC  (FSK or ASK) and transmits the control signal S 3  obtained by superimposing the modulated signal on the current I RX  flowing through the reception coil  302 . 
     The control circuit  400  has the ability to automatically determine whether or not the power transmitter  200  complies with one of the PMA-1, PMA-3, PMA-4, and Qi standards. To achieve this automatic determining ability, the control circuit  400  includes the frequency detecting part  420 , the modulation detecting part  422 , and the standard determining part  424 . 
     The frequency detecting part  420  detects a frequency of the power signal S 2  received by the reception coil  302  in a detection period T DET  after the lapse of predetermined first time τ 1  from a predetermined start timing before the lapse of predetermined second time τ 2 , and generates frequency data D 11  indicating the detected frequency f DET . A method of measuring the frequency is not particularly limited but may employ a technique known in the art, such as a frequency counter. 
     The modulation detecting part  422  determines whether or not the signal received by the reception coil  302  has been subjected to FSK (Frequency Shift Keying) in the detection period T DET , and generates FSK determination data D 12  indicating the presence or absence of FSK. The modulation detecting part  422  monitors a change with time in the frequency f (or the frequency data D 11 ) detected by the frequency detecting part  420 . If a frequency change is measured, it may be determined that the power signal has been subjected to FSK. Otherwise, if the frequency is consistent, it may be determined that the power signal has not been subjected to FSK. 
     The standard determining part  424  receives the frequency data D 11  and the FSK determination data D 12  and determines a standard which the wireless power transmitter  200  complies with, depending on the frequency f detected by the frequency detecting part  420  and the presence or absence of FSK determined by the frequency detecting part  420 . 
     Hereinafter, a determination process performed by the standard determining part  424  will be described. The inventors of the present application have paid attention to a temporal change in the frequency of the power signal S 2  generated by the power transmitter  200  immediately after a digital ping phase is started. 
       FIGS. 3A to 3D  are diagrams showing the transition of frequency of a digital ping phase in the PMA-1, PMA-3, PMA-4, and Qi standards, respectively. In the PMA-1 standard of  FIG. 3A , after the start of the digital ping phase, the frequency is gradually reduced from 480 kHz (frequency sweep). Thereafter, the frequency takes 250 kHz to 260 kHz over a period M_period. 
     In the PMA-3 standard of  FIG. 3B , after the start of the digital ping phase, the frequency is gradually reduced from 315 kHz. Thereafter, the frequency takes 220 kHz to 230 kHz over a period M_period. In the PMA-4 standard of  FIG. 3C , the frequency is reduced from the start of the digital ping phase. Thereafter, the frequency takes 150 kHz over a period M_period. In  FIG. 3D , the frequency can take 110 kHz to 190 kHz. 
     With attention paid to  FIGS. 3A to 3D , in any standards, when a common detection period T DET  (t 1  to t 2 ) is set to be included in the period M_period, the power signal S 2  has a frequency or a frequency range corresponding to the respective standard within its time window. That is, it is possible to determine the standard by appropriately setting the detection period T DET  and measuring the frequency in the detection period T DET . 
     In the PMA-3 and PMA-4 standards, the power signal S 2  is subjected to FSK in the period M_period. Therefore, it is possible to determine the standard by determining the presence or absence of FSK in the detection period T DET . 
     At time t=0, the digital ping phase is started. In the power receiver  300 , a reset is released when the digital ping phase is started. Therefore, when the start timing is taken to the reset release, the first time τ 1  may be set to t 1  and the second time τ 2  may be set to t 2 . Therefore, the frequency detecting part  420  starts time measurement in response to the reset release and sets a period between time t 1  after the lapse of the first time τ 1  and time t 2  after the lapse of the second time τ 2  as the detection period (window) T DET  of frequency and FSK. 
     As the detection period T DET , for example, t 1  and t 2  are suitably 4 ms and 7 ms, respectively. t 1  may be set to fall within a range from 3 to 5 ms and t 2  may be set to fall within a range from 6 to 8 ms. 
       FIG. 4  is a diagram showing the correspondence relation between the standards and the frequency and the presence or absence of FSK in the detection period T DET . 
     (i) If the frequency f DET  detected in the detection period T DET  is higher than a first frequency f 1  set between 230 kHz and 250 kHz, the standard determining part  424  determines that the wireless power transmitter complies with the PMA (Power Matters Alliance)-1 standard. For example, the first frequency f 1  is set at (or near) 240 kHz which corresponds to the center of the range from 230 kHz to 250 kHz. 
     (ii) If the detected frequency f DET  is higher than a second frequency f 2  set between 190 kHz and 220 kHz and is lower than the first frequency f 1  and FSK is detected, the standard determining part  424  determines that the wireless power transmitter complies with the PMA-3 standard. For example, the second frequency f 2  is set at 200 kHz (or 205 kHz) near the center of the range from 190 kHz to 220 kHz. 
     (iii) If the detected frequency f DET  is lower than the second frequency f 2  and FSK is detected, the standard determining part  424  determines that the wireless power transmitter complies with the PMA-4 standard. (iv) If the detected frequency f DET  is lower than the second frequency f 2  and no FSK is detected, the standard determining part  424  determines that the wireless power transmitter complies with the Qi standard. (v) If the detected frequency f DET  is higher than the second frequency f 2  and is lower than the first frequency f 1  and no FSK is detected, the standard determining part  424  determines that the wireless power transmitter is an unknown wireless power transmitter. 
       FIG. 5  is a flow chart of standard determination. When the reset release occurs (S 200 ), the time measurement is started, the period between time t 1  after the lapse of τ 1  and time t 2  after the lapse of τ 2  is set as the detection period T DET  (S 202 ), and the frequency f DET  is measured in the detection period T DET  (S 204 ). Then, a branching process based on the frequency f DET  is performed (S 206 ). If the frequency f DET  is higher than the first frequency f 1  (f DET =240 kHz to 300 kHz) (S 208 ), it is determined that the wireless power transmitter complies with the PMA-1 standard (S 210 ). 
     If the frequency f DET  is higher than the second frequency f 2  and is lower than the first frequency f 1  (f DET =200 kHz to 239 kHz) (S 212 ), it is determined whether FSK is present or absent (S 214 ). If FSK is detected (Y in S 214 ), it is determined that the wireless power transmitter complies with the PMA-3 standard (S 216 ). If no FSK is detected (N in S 214 ), it is determined that the wireless power transmitter complies with an unknown standard (S 218 ). 
     If the frequency f DET  is lower than the second frequency f 2  (f DET =100 kHz to 199 kHz) (S 220 ), it is determined whether FSK is present or absent (S 222 ). If FSK is detected (Y in S 222 ), it is determined that the wireless power transmitter complies with the PMA-4 standard (S 226 ). If no FSK is detected (N in S 222 ), it is determined that the wireless power transmitter complies with the Qi standard (S 228 ). 
     This control can automatically determine the PMA-1, PMA-3, PMA-4, and Qi standards. 
     (Use) 
     Finally, an example of an electronic apparatus using the wireless power receiver  300  according to the embodiment will be described.  FIG. 6  is a diagram showing an electronic apparatus  500  including the power receiver  300  according to the embodiment. Examples of the electronic apparatus  500  of  FIG. 6  may include a smartphone, a tablet PC, a portable game machine, a portable audio player, and the like. A housing  501  of the electronic apparatus  500  contains a power supply circuit  504 , a secondary battery  506 , a processor  508 , a display  510 , and the above-described power receiver  300 . The processor  508  may include an RF (Radio Frequency) part, a baseband processor, an application processor, an audio processor, and so on. 
     The present disclosure has been described above by way of embodiments. The above-described embodiments have been described for exemplary purposes only. It should be understood by those skilled in the art that various modifications to combinations of elements or processes may be made and such modifications fall within the scope of the present disclosure. Such modifications will be described below. 
     (Modification 1) 
     The determination algorithm by the standard determining part  424  is not limited to the combination of determination criteria (i) to (v) described in the embodiment. For example, two, three or four (i.e., at least two) of the determination criteria (i) to (v) may be employed and other criteria may be employed for the remaining standards. 
     (Modification 2) 
     Although it has been illustrated in the above embodiment that two frequencies f 1  and f 2 , which are threshold values, are set to determine the standards, the present disclosure is not limited thereto. In Modification 2, four threshold values of third frequency f 3  to sixth frequency f 6  are set as shown in the upper portion of  FIG. 4 . The third frequency f 3  is set to be equal to or lower than 250 kHz, the fourth frequency f 4  is set to be equal to or higher than 230 kHz, the fifth frequency f 5  is set to be equal to or lower than 220 kHz, and the sixth frequency f 6  is set to be equal to or higher than 190 kHz. 
     Then, (a) when f DET &gt;f 3 , it is determined that the wireless power transmitter complies with the PMA (Power Matters Alliance)-1 standard. When f 5 &lt;f DET &lt; 4 , (b) it is determined that the wireless power transmitter complies with the PMA-3 standard when FSK is detected and (e) it is determined that the wireless power transmitter complies with an unknown standard when no FSK is detected. When f DET &lt;f 6 , (C) it is determined that the wireless power transmitter complies with the PMA-4 standard when FSK is detected and (d) it is determined that the wireless power transmitter complies with the Qi standard when no FSK is detected. This modification can provide stricter determination on the standards than the above embodiment. 
     Alternatively, the standard determining part  424  may employ two, three or four (i.e., at least two) of the determination criteria (a) to (e) and employ other criteria for the remaining standards. 
     As another alternative, the standard determining part  424  may determine a plurality of standards by combining the determination criteria (i) to (v) and the determination criteria (a) to (e). 
     As described above, there are many variations in the standard determination method, which fall within the scope of the present disclosure. 
     (Modification 3) 
     Although it has been illustrated in the above embodiment that the start timing serving as a reference for setting of the detection period T DET  is reset-released, the present disclosure is not limited thereto. For example, the detection period T DET  may be set based on events other than the reset release. The detection period T DET  may be set to be included in the period M_period in which the frequency is stabilized, and the first time τ 1  and the second time τ 2  may be appropriately set in response to an event such as the start timing. 
     (Modification 4) 
     Although it has been illustrated in the above embodiment that the rectification voltage V RECT  is converted to the digital value D RECT  and the power controller  406  controls the power control data D PC  according to the digital signal processing, the present disclosure is not limited thereto. In other words, all or some of the control of the power control data D PC  may be performed according to analog signal processing. For example, a voltage comparator may be used for voltage comparison. 
     According to the present disclosure in some embodiments, it is possible to provide a power receiver which is capable of automatically determining a standard that a power transmitter complies with. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the novel methods and apparatuses described herein may be embodied in a variety of other forms, furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.