Abstract:
A charging system for a portable electronic device is disclosed. The system comprises a charging station providing a magnetic field for power distribution by an alternating current source connected to a power transmission coil for providing the magnetic field, and the portable electronic device. The portable electronic device comprises a radio receiver; a charging mechanism for charging a battery of the portable electronic device; and an antenna arrangement for the radio receiver, wherein the charging mechanism comprises a first coil arranged to interact with the power transmission coil of the charging station upon charging; a rectifier connected to the first coil to receive an alternating current therefrom and to a power supply output to provide a direct current, and the antenna arrangement comprises an antenna element comprising the first coil; a resonator tuned for a frequency band in which the radio receiver is intended to receive radio transmissions; a series resonance circuit comprising a capacitor and a second coil connected in series between one terminal of the first coil and a reference voltage of the portable apparatus.

Description:
TECHNICAL FIELD  
       [0001]    The present invention relates to a portable electronic apparatus and a charging system for the portable apparatus. The present invention particularly relates to utilizing components used for charging also as an antenna for a radio receiver of the portable electronic apparatus. 
       BACKGROUND  
       [0002]    Portable electronic devices room more and more features, while remaining small and portable. Processing means can gain more processing power and memory space in the same physical size as the technology evolves. However, some components are restricted in size due to their need to have a certain size to work. An example on this is antennas, where a certain wavelength requires a certain size of the antenna. It is therefore a desire to cope with constraints in size, both with regard to demands of function, and with regard to demands of portability. 
       SUMMARY  
       [0003]    The present invention is based on the understanding that a radio receiver for Medium Frequency (MF) radio band requires a physically large, in terms of portable apparatuses, antenna for proper reception, and also on the understanding that charging using induction chargers, which use an induction coil to create an alternating magnetic field from a charging station, and then a second induction coil in the portable device takes power from the magnetic field and converts it back into electrical current to charge the battery, implies the need for a coil with non-negligible size in the portable electronic apparatus. The inventor has found that, by proper circuitry according to the invention, the same component, the coil, can be used as antenna as well as for the inductive charging. 
         [0004]    According to a first aspect, there is provided a portable electronic device, comprising a radio receiver; a charging mechanism for charging a battery of the portable electronic device; and an antenna arrangement for the radio receiver. The charging mechanism comprises a first coil arranged to interact with a charging station providing a magnetic field for power distribution to the portable electronic device upon charging; and a rectifier connected to the first coil to receive an alternating current therefrom and to a power supply output to provide a direct current. The antenna arrangement comprises an antenna element comprising the first coil; a resonator tuned for a frequency band in which the receiver is intended to receive radio transmissions; and a first series resonance circuit comprising a capacitor and a second coil connected in series between one terminal of the first coil and a reference voltage of the portable apparatus. 
         [0005]    The resonator may comprise the first coil and a capacitor connected in parallel therewith. The portable electronic device may further comprise a capacitor connected between another terminal of the first coil and the radio receiver. 
         [0006]    The resonator may alternatively comprise a second series resonance circuit connected between the another terminal of the first coil and the radio receiver. 
         [0007]    The portable electronic device may further comprise a third resonance circuit arranged between the another terminal of the first coil and the rectifier to provide a high impedance at frequencies for radio reception and a low impedance for a frequency of the magnetic field for power distribution to the portable electronic device. The third resonance circuit may comprise a capacitor and a coil connected in parallel and having a resonance frequency at frequencies for radio reception. The third resonance circuit may alternatively comprise a capacitor and a coil connected in series and having a resonance frequency at a frequency of the magnetic field for power distribution to the portable electronic device. 
         [0008]    The power supply output may comprise a capacitor electrically connected across output terminals of the power supply output. 
         [0009]    The radio receiver may be arranged to receive radio transmissions within the AM band, and the magnetic field for power distribution is provided in a frequency band different from the AM band. The magnetic field for power distribution may be provided in a frequency between 100 kHz and 400 kHz, preferably between 175 kHz and 300 kHz, preferably about 200 kHz. The magnetic field for power distribution may alternatively be provided in a frequency between 1800 kHz and 2400 kHz, preferably between 1900 kHz and 2200 kHz, preferably about 2000 kHz. 
         [0010]    The first series resonance circuit may be tuned to provide a short circuit for a frequency band in which the receiver is intended to receive radio transmissions. 
         [0011]    The reference voltage may be a ground reference of the portable electronic device. 
         [0012]    According to a second aspect, there is provided a charging system for a portable electronic device. The system comprises a charging station providing a magnetic field for power distribution by an alternating current source connected to a power transmission coil for providing the magnetic field; and a portable electronic device. The portable electronic device comprises a radio receiver; a charging mechanism for charging a battery of the portable electronic device; and an antenna arrangement for the radio receiver. The charging mechanism comprises a first coil arranged to interact with the power transmission coil of the charging station upon charging; a rectifier connected to the first coil to receive an alternating current therefrom and to a power supply output to provide a direct current. The antenna arrangement comprises an antenna element comprising the first coil; a resonator tuned for a frequency band in which the receiver is intended to receive radio transmissions; and a first series resonance circuit comprising a capacitor and a second coil connected in series between one terminal of the first coil and a reference voltage of the portable apparatus. 
         [0013]    The resonator may comprise the first coil and a capacitor connected in parallel therewith. The charging system may further comprise a capacitor connected between another terminal of the first coil and the radio receiver. 
         [0014]    The resonator alternatively comprises a second series resonance circuit connected between the another terminal of the first coil and the radio receiver. 
         [0015]    The charging system may further comprise a third resonance circuit arranged between the another terminal of the first coil and the rectifier to provide a high impedance at frequencies for radio reception and a low impedance for a frequency of the magnetic field for power distribution to the portable electronic device. 
         [0016]    The third resonance circuit may comprise a capacitor and a coil connected in parallel and having a resonance frequency at frequencies for radio reception. 
         [0017]    The third resonance circuit may comprises a capacitor and a coil connected in series and having a resonance frequency at a frequency of the magnetic field for power distribution to the portable electronic device. 
         [0018]    The power supply output may comprise a capacitor electrically connected across output terminals of the power supply output. 
         [0019]    The radio receiver may be arranged to receive radio transmissions within the AM band, and the magnetic field for power distribution may be provided by the charging station in a frequency band different from the AM band. 
         [0020]    The magnetic field for power distribution may be provided by the charging station in a frequency between 100 kHz and 400 kHz, preferably between 175 kHz and 300 kHz, preferably about 200 kHz. The magnetic field for power distribution may alternatively be provided by the charging station in a frequency between 1800 kHz and 2400 kHz, preferably between 1900 kHz and 2200 kHz, preferably about 2000 kHz. 
         [0021]    The first series resonance circuit may be tuned to provide a short circuit for a frequency band in which the receiver is intended to receive radio transmissions. 
         [0022]    The reference voltage may be a ground reference of the portable electronic device. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS  
         [0023]      FIG. 1  schematically illustrates a portable electronic device and a charging station. 
           [0024]      FIG. 2  is a schematic circuit diagram illustrating circuitry of a portable device and a charging station according to an embodiment. 
           [0025]      FIG. 3  is a schematic circuit diagram illustrating circuitry of a portable device and a charging station according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION  
       [0026]    Medium frequency (MF) radio band normally refers to radio frequencies (RF) in the range of 300 kHz to 3000 kHz. Medium Wave (MW) is a part of the MF radio band used mainly for amplitude modulated (AM) broadcasting, and is therefore here referred to at the “AM band”. For most of the world the frequencies used for broadcasting in the AM band ranges from 515 kHz to 1629 kHz, and in North America an extended AM band ranges from 515 kHz to 1715 kHz. MW signals have the property of following the curvature of the earth at all times, and also refracting off the ionosphere at night. This makes this frequency band suitable for both local and continent-wide service. Provision of an antenna for these long wavelength signals in a portable device can be made by arranging a coil, preferably with a ferrite core, which arrangement works as a compact antenna. 
         [0027]    Inductive charging charges electrical batteries using magnetic induction. The principle is that a charging station sends energy through inductive coupling to an electrical device, which stores the energy in its battery. The major advantage of the inductive approach over conductive charging is that there is no need for terminals for connection between the charger and the device, and further that exposure for electric discharge is reduced as there are no exposed conductors. This is particularly beneficial for devices arranged to be waterproof or suitable for use in harsh environments. Induction chargers use an induction coil to create an alternating magnetic field from the charging station, and then a second induction coil in the portable device takes power from the magnetic field and converts it back into electrical current to charge the battery. The two induction coils in proximity thus combine to form an electrical transformer. 
         [0028]    Coils, in particular when they comprise a large number of windings and are suitable for higher currents, become both large and costly. The re-use of such a coil for dual purposes according to the present invention, as will be demonstrated for a number of embodiments with reference to the drawings, therefore provides advantages accordingly. 
         [0029]      FIG. 1  schematically illustrates a portable electronic device  100  and a charging station  102 . The charging station  102  is arranged to provide a magnetic field for power distribution by an alternating current source  104  connected to a power transmission coil  106  for providing the magnetic field. Thus, an alternating magnetic flux is generated by the coil. The current source  104  can for example get its power from a power distribution network via a wired connection  108 . 
         [0030]    The portable electronic device  100  comprises a first coil  110  which, when the portable electronic device  100  is put at the charging station  102 , interacts inductively with the power transmission coil  106  such that the alternating magnetic flux induces an electrical field, and thus a voltage and current, in the first coil  110  according to the principles of a transformer. The harvested power in the first coil  110  is provided to a charging mechanism  112 , which thus is able to charge a battery  114 . 
         [0031]    The portable electronic device  100  further comprises a radio receiver  116 , which preferably is powered by the battery  114 . The radio receiver  116  is connected to an antenna, which is formed by the first coil  110 . The radio receiver can be arranged to receive radio transmissions on the AM band. The charging station preferably provides the alternating magnetic flux in a different frequency band than the AM band. This both provides for ability to use the radio receiver during charging, and for the ability to provide filters for avoiding the relatively high power of the “transformer” to reach the radio receiver circuitry. As elucidated above, the AM band reaches from about 500 to 1700 kHz, while the alternating flux can be selected to be either below or above the AM band in frequency. For example, when considering the range below the AM band, the alternating flux can be in the range between 100 kHz and 400 kHz. The efficiency of the transformer depend on ability to physically arrange the power transmission coil  106  and the first coil  110 , but for straightforward consumer adapted products, it has been found that frequencies between 175 and 300 kHz give a fair efficiency. In a particular test setup, the efficiency proved to be excellent in a range between 175 and 200 kHz, where a frequency of about 200 kHz was found to be preferred. When considering the range above the AM band, frequencies between 1800 and 2400 kHz were found feasible, while frequencies around 2000 kHz worked well without any unwanted effects down in the AM band. With a fair tuning of filters, believed suitable for production of consumer products, frequencies between 1900 and 2200 kHz were found to work properly. 
         [0032]      FIG. 2   a  is a schematic circuit diagram illustrating circuitry of a portable device  200  and a charging station  202 , and  FIGS. 2   b  and  2   c  illustrate relevant parts for variants with an optional resonance circuit  236 . The charging station  202  is arranged to provide a magnetic field for power distribution by an alternating current source  204  connected to a power transmission coil  206  for providing the magnetic field. Thus, an alternating magnetic flux is generated by the coil. 
         [0033]    The portable electronic device  200  comprises a first coil  210  which, when the portable electronic device  200  is arranged with the charging station  202  for charging, interacts inductively with the power transmission coil  206  such that the alternating magnetic flux induces an electrical field, and thus a voltage and current, in the first coil  210  according to the principles of a transformer. The harvested power in the first coil  210  is provided to a rectifier  212  which provides a rectified, and thus direct current (DC), voltage to output terminals  213 ,  214 . The power provided on the output terminals  213 ,  214  is used for charging a battery  216 , e.g. via a charging regulator  218 . Optionally, a smoothening capacitor  219  is provided across the output terminals  213 ,  214  to provide a smoother DC level. 
         [0034]    The portable electronic device  200  further comprises a radio receiver  220  and an antenna for the radio receiver  220 . The antenna is formed by the first coil  210 , which is connected in parallel with a first capacitor  222  such that the first coil  210  and the first capacitor form a parallel resonator for the radio band to be received. A series resonance circuit  224  comprising a second coil  226  and a second capacitor  228  is connected between one terminal of the first coil and a reference voltage, e.g. ground, of the portable electronic device  200 . The series resonance circuit  224  is preferably arranged to form a short circuit to the reference voltage for frequencies for the radio band to be received. The other terminal of the first coil  210  is connected to the radio receiver  220  via a third capacitor  230 . To provide a proper impedance in radio frequency for the antenna, a resonance circuit  236  can be arranged between the rectifier  212  and the connection to the radio receiver  220  and first coil  210 , through which the frequency of the charging experiences a low impedance, while the radio frequencies intended for the radio receiver  220  experience a high impedance. Thereby, a proper Q-value for the resonator  210 ,  222  is maintained. The resonator  236  can comprise a capacitor  238  and a coil  240  connected in parallel, and be arranged to resonate at frequencies of the radio band to be received, as illustrated in  FIG. 2   b.  Alternatively, the resonator  236  can comprise a capacitor  239  and a coil  241  connected in series, as illustrated in  FIG. 2   c,  and be arranged to resonate at a frequency of the alternating magnetic flux. The radio receiver  220  preferably comprises an amplifier  232  arranged to amplify the signal from the antenna  210 . Preferably, the radio receiver  220 , i.e. the amplifier, has high impedance not to load the resonant circuit  210 ,  222 . The amplified signal is provided to a demodulator  234  arranged to demodulate the received radio signal to provide the received information, e.g. to a speaker or to further signal processing. 
         [0035]      FIG. 3  is a schematic circuit diagram illustrating circuitry of a portable device  300  and a charging station  302 . The charging station  302  is arranged similar to what has been demonstrated with reference to  FIG. 2 . 
         [0036]    The portable electronic device  300  comprises a first coil  310  which, when the portable electronic device  300  is arranged with the charging station  302  for charging, interacts inductively with the power transmission coil  306  similar to what has been demonstrated with reference to  FIG. 2 . The harvested power in the first coil  310  is provided to a rectifier  312  which provides a rectified, and thus direct current (DC), voltage to output terminals  313 ,  314 . The power provided on the output terminals  313 ,  314  is used for charging a battery  316 , e.g. via a charging regulator  318 . Optionally, a smoothening capacitor  319  is provided across the output terminals  313 ,  314  to provide a smoother DC level. 
         [0037]    The portable electronic device  300  further comprises a radio receiver  320  and an antenna for the radio receiver  320 . The antenna is formed by the first coil  310 , which is connected in to the radio receiver  320  via a first series resonator  322  arranged to provide the frequencies for radio reception to the receiver  320 . The first series resonator  322  can comprise a capacitor  330  and a coil  331  connected in series. Further, a second series resonance circuit  324  is connected between one terminal of the first coil and a reference voltage, e.g. ground, of the portable electronic device  300 . The series resonance circuit  324  can comprise a coil  326  and a capacitor  328  connected in series, and is preferably arranged to form a short circuit to the reference voltage for frequencies for the radio band to be received. To provide a proper impedance in radio frequency for the antenna, a resonator  336  can be arranged between the rectifier  312  and the connection to the first series resonator  322  and first coil  310 , through which the frequency of the charging experiences a low impedance, while the radio frequencies intended for the radio receiver  320  experience a high impedance. Thereby, a proper Q-value for the resonator  322  is maintained. The resonator  336  can comprise a capacitor  338  and a coil  340  connected in parallel, and be arranged to resonate at frequencies of the radio band to be received, as illustrated in  FIG. 3   b.  Alternatively, the resonator  336  can comprise a capacitor  339  and a coil  341  connected in series, as illustrated in  FIG. 3   c,  and be arranged to resonate at a frequency of the alternating magnetic flux. The radio receiver  320  preferably comprises an amplifier  332  arranged to amplify the signal from the antenna  310 . Preferably, the radio receiver  320 , i.e. the amplifier, has high impedance not to load the resonant circuit  322 . The amplified signal is provided to a demodulator  334  arranged to demodulate the received radio signal to provide the received information, e.g. to a speaker or to further signal processing. 
         [0038]    The portable electronic device according to any of the demonstrated embodiments can for example be a mobile phone, a media player, a portable game console, a personal digital assistant, a digital camera, etc. In any of these, the feature of receiving MW band broadcasting can be a desired feature, as well as inductive charging. For any of these applications, the cost and space saving solution according to the invention is particularly advantageous.