Patent Publication Number: US-8971971-B2

Title: Mobile wireless communications device including a self-contained rechargeable battery pack with filter and related methods

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of electronic devices, and, more particularly, to mobile wireless communications devices and related methods. 
     BACKGROUND OF THE INVENTION 
     Cellular communications systems continue to grow in popularity and have become an integral part of both personal and business communications. Cellular telephones allow users to place and receive voice calls most anywhere they travel. Moreover, as cellular telephone technology has increased, so too has the functionality of cellular devices. For example, many cellular devices now incorporate personal digital assistant (PDA) features such as calendars, address books, task lists, etc. Moreover, such multi-function devices may also allow users to wirelessly send and receive electronic mail (email) messages and access the Internet via a cellular network and/or a wireless local area network (WLAN), for example. 
     Even so, as the functionality of cellular communications devices continues to increase, so too does the demand for smaller devices which are easier and more convenient for users to carry. Such size constraints may pose challenges for providing suitable rechargeable battery packs, which can not only provide adequate power but also desired battery life. Further developments in mobile electronic device battery packs may therefore be desirable to provide adequate power and performance in certain applications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a mobile wireless communications device including a self-contained rechargeable battery pack in accordance with one aspect. 
         FIG. 2  is a schematic block diagram illustrating the battery pack and wireless communications components of the device of  FIG. 1 . 
         FIG. 3  is a schematic diagram of a battery pack in accordance with the prior art. 
         FIG. 4  is a schematic diagram of a battery pack for use in the device of  FIG. 1  in accordance with one exemplary embodiment. 
         FIG. 5  is a schematic block diagram illustrating exemplary components of a mobile wireless communications device for use with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present description is made with reference to the accompanying drawings, in which exemplary embodiments are shown. However, many different embodiments may be used, and thus the description should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. Like numbers refer to like elements throughout. 
     Generally speaking, a mobile wireless communications device is disclosed herein which may include a portable device housing, wireless communications circuitry carried by the portable device housing, and a self-contained rechargeable battery pack carried by the portable housing for powering the wireless communications circuitry. More particularly, the self-contained rechargeable battery pack may include a battery casing, at least one internal battery cell carried within the battery casing, internal battery circuitry carried within the battery casing, and at least one internal filter element carried within the battery casing and coupled to the internal battery circuitry. 
     The self-contained rechargeable battery pack may further include a battery connection interface carried by the battery casing and coupled to the internal battery circuitry. By way of example, the at least one internal filter element may include at least one of a capacitor and an inductor. Also, the at least one filter element may include at least one pair of series-connected filter elements defining a tap therebetween. Moreover, each series-connected filter element may include an inductor, and the battery pack may further include a capacitor connected between the tap and a voltage reference. By way of example, the at least one filter element may include at least one ferrite bead. 
     More particularly, the battery pack may include a power supply line and a ground line, and the at least one filter element may include respective filter elements coupled to each of the power supply line and the ground line. The battery pack may also include a battery temperature signal line, and the at least one filter element may include respective filter elements coupled to each of the battery temperature signal line and the ground line. Similarly, the battery pack may further include a battery identification signal line, and the at least one filter element may include respective filter elements coupled to each of the battery identification signal line and the ground line. By way of example, the at least one internal battery cell may include at least one lithium-ion battery cell. 
     A self-contained rechargeable battery pack for a mobile electronic device, such as the one described briefly above, and a related method for making a self-contained rechargeable battery pack are also provided. The method may include positioning at least one internal battery cell within a battery casing, positioning internal battery circuitry within the battery casing, and positioning at least one internal filter element within the battery casing and coupled to the internal battery circuitry. 
     Referring initially to  FIGS. 1 and 2 , a mobile wireless communications device  30  illustratively includes a portable housing  31 , an antenna  32  carried by the housing, wireless communications circuitry  33  carried by the housing, and a self-contained rechargeable battery pack  34  also carried by the housing. In the illustrated example, the antenna  32  is an embedded or internal antenna carried within the portable housing  31 , and it is connected to the battery pack  34  by positive and negative contacts V_BAT+ and V_BAT−. It will be appreciated that multiple antennas as well as different types of antennas, such as external antennas, may be used as well in different embodiments. Moreover, in the illustrated example the wireless communications circuitry  33  includes a mobile radio transceiver  40  and antenna matching circuitry  41 , as will also be appreciated by those skilled in the art, although other configurations (e.g., without matching circuitry, etc.) may be used in different embodiments. Also, one or more clock reference circuits  42  (e.g., crystal oscillator) may also be included to provide a reference clock signal to the transceiver  40 . 
     By way of example, the device  30  may operate in accordance with various wireless communications formats, such as cellular, wireless LAN (e.g., 802.11x, Bluetooth, etc.), WiMAX, satellite, etc., as will be appreciated by those skilled in the art. In some embodiments, more than one such wireless communications format may be used in the same device (e.g., cellular, wireless LAN, and Bluetooth). Also, various types of mobile wireless communications devices  30  may be used, such as mobile phones, PDAs, laptop computers, wireless-enabled cameras, wireless-enabled media players, etc., for example, although in the present example a cellular device is illustrated, and the discussion provided herein will be with reference to a cellular device. 
     One difficulty with battery packs in wireless devices is that in some instances they may cause interference with the device antenna  32 . More specifically, radio frequency (RF) energy from the wireless communications circuitry  33  is coupled to the battery housing or casing  35  of the battery pack  34 , as illustrated in  FIG. 2 . This coupling may in turn cause various problems ranging from an audible buzzing noise to interference with data signal reception or transmission. Coupling may be particularly problematic with lithium ion battery packs, for example, which are commonly used for cellular phones and other mobile devices because of their relatively high electrochemical potential and relatively large energy density per weight. 
     By way of background, reference is now made to a prior art lithium ion battery pack  340  shown in  FIG. 3 , which illustratively includes a lithium ion cell  370  with positive and negative electrodes  360 ,  380 , respectively, a battery connection interface  440  providing electrical connection or contact points between the battery and external components, and internal battery circuitry  430 . As will be appreciated by those skilled in the art, it is generally desirable to include protection circuitry in lithium ion battery packs to provide for safe operation. By way of example, the circuitry  430  may perform such functions as regulating peak voltage of the cell  370  during charging, and preventing the cell voltage from dropping too low when discharging. Additionally, maximum charge and discharge current may be regulated, and the cell  370  temperature may be monitored to avoid temperature extremes. Moreover, the circuitry  430  may also advantageously store identification information of the battery pack  340 , such as battery type, operational characteristics/ratings, serial numbers, etc. The circuitry  430  may communicate the operating/identification information to the device microprocessor by way of battery temperature and identification signal lines BAT_TEMP, BAT_ID, for example, although other signal lines could also be used. 
     In a typical lithium ion battery pack the casing  35  is metal, and a positive electrode  36  of the battery cell  37  is located outside of the casing. However, the negative electrode is located on the inside of the casing  35 , and this configuration makes it difficult to adequately ground the battery casing, such as to the ground plane of a device printed circuit board (PCB) upon which the wireless communications circuitry and other components are mounted, as will be appreciated by those skilled in the art. While the embodiments described herein are made with reference to a lithium ion battery for illustrational purposes, it should be noted that the techniques described herein may also advantageously be used with other types of batteries as well (e.g., NiCd, NiMH, etc.). 
     Referring additionally to  FIG. 4 , the battery pack configuration and methods described herein advantageously address the above-noted technical problem by providing enhanced filtering and grounding from within the battery casing  35 . One or more internal filter elements  39  ( FIG. 2 ) are carried within the battery casing  35  and coupled to the internal battery circuitry. In the illustrated example, both capacitor and inductor filter elements are used. More particularly, connected between the V-BAT+ power supply line connection point of the battery connection interface  44  and the positive electrode  36  is a pair of series-connected inductors (e.g., ferrite beads) F_vcc defining a tap therebetween. In addition, an RF decoupling capacitor C_vcc is connected between the tap and a voltage reference, namely the V_BAT− line, which is in turn connected to a device ground (e.g., the PCB ground plane). 
     The inductors F_vcc and capacitor C_vcc therefore define a “T” shaped filter that provides filtering in two ways, namely (1) providing direct filtering of RF energy in the V_BAT+ line, and (2) forcing received RF energy to ground, as will be discussed further below. Accordingly, the amount of RF energy received by the metal in the battery pack  34  that would otherwise proceed through the interface  44  to the wireless communications circuitry  33  and other electronic components of the device  30  is significantly reduced. 
     Ferrite beads provide a relatively low equivalent series resistance (ESR) to allow desired transient current to flow through the battery. For cellular device applications, for example, such currents may be relatively high, namely about 2.5-3.0 Amps. One exemplary ferrite bead which may be used is the chip ferrite bead BLM185 series from Murata Electronics N.A. Inc., although other suitable beads or inductors may also be used. The RF decoupling capacitor C_vcc may advantageously be selected to provide the low impedance, which advantageously helps to shunt the residual RF energy passing through the ferrite bead to ground. By way of example, for a GSM/GPRS/EDGE cellular device implementations, the RF decoupling capacitor may be selected with as low an ESR as possible and so that its series self-resonance is close to the middle of all the bands, as will be appreciated by those skilled in the art, although other selection values/criteria may also be used. 
     Similar T-shaped filter configurations are also illustratively used for the BAT_TEMP and BAT_ID signal lines. More particularly, the BAT_TEMP signal line filter includes series-connected inductors (e.g., ferrite beads) F_temp defining a tap therebetween, and a capacitor C_temp connected between the tap and the V_BAT− reference voltage line. Similarly, the BAT_ID signal line filter includes series-connected inductors (e.g., ferrite beads) F_id defining a tap therebetween, and a capacitor C_id connected between the tap and the V_BAT− reference voltage line. Moreover, the V_BAT− line also illustratively includes a pair of series-connected inductors (e.g., ferrite beads) F_gnd defining a tap therebetween to advantageously filter the RF energy that is passed to the device  30  signal ground, and the C_id, C_temp, and C_vcc capacitors are illustratively connected to the V_BAT− line at this tap, as shown. Exemplary part numbers and values of ferrite beads and capacitors used in a GSM cellular phone implementation are BLM15HG102SN1 (0402 size of 1000 Ohm @ 1 GHz) and GRM1555C1H330JZ01 (0402 size of 33 pF), respectively, although other values may be used in different embodiments. 
     It will be appreciated that in some embodiments all of the above-described exemplary filter elements need not be used, and that filters need not be provided on each of these power/signal lines. That is, more or less filter elements may be used depending upon the particular application, frequencies used, the amount of coupling experienced, the battery type, etc., as will be appreciated by those skilled in the art. 
     The above-described filter arrangement thereby addresses such technical problems as (1) audible buzz (e.g., in Global System for Mobile communications (GSM) implementations) due to the coupling of transmitter RF energy from the embedded antenna  32  inside the device  30  to the battery metal casing  35 ; (2) RF receiver de-sense due to digital noise and RF spurious energy radiated by the battery via the battery supply lines V_BAT+, V_BAT− and pickup by the antenna  32  in receive mode; and (3) degradation of the antenna performance due to RF coupling with the battery which represents low impedance to the antenna. 
     More particularly, by positioning (i.e., embedding) the electromagnetic compatibility (EMC)/electromagnetic interference (EMI) filter array in the battery casing  35  as illustrated in  FIG. 4  (i.e., similar to the internal battery circuitry  43 ), this advantageously helps to block the RF energy picked up by the battery from the antenna  32  during the transmit mode and prevent this energy from coupling onto the power supply lines, and also reduce the emitted digital noise and RF spurious energy from the various sources on the PCB (e.g., LCD, camera circuitry, harmonics from clock circuitry  42 , etc.) to prevent the noise/spurious coupling onto the battery. This is significant because the battery pack  34  could thereby behave like an antenna and radiate such noise, which could be picked up by the RF antenna in the receiver mode and thus cause receiver de-sense. The filter arrangement may also advantageously improve antenna performance in comparison with the conventional mobile battery as shown in  FIG. 3  (e.g., by 10 to 30 dB) by providing higher RF impedance on the battery interface lines, as will be appreciated by those skilled in the art. Such performance gains are likely not possible by filtering components positioned outside of the battery housing, as excessive spurious noise may still get into the power supply lines. 
     Further exemplary components that may be used in the device  30  are now further described with reference to a mobile wireless communications device  1000  shown in  FIG. 5 . The device  1000  illustratively includes a housing  1200 , a keypad  1400  and an output device  1600 . The output device shown is a display  1600 , which is preferably a full graphic LCD. Other types of output devices may alternatively be utilized. A processing device  1800  is contained within the housing  1200  and is coupled between the keypad  1400  and the display  1600 . The processing device  1800  controls the operation of the display  1600 , as well as the overall operation of the mobile device  1000 , in response to actuation of keys on the keypad  1400  by the user. 
     The housing  1200  may be elongated vertically, or may take on other sizes and shapes (including clamshell housing structures). The keypad may include a mode selection key, or other hardware or software for switching between text entry and telephony entry. 
     In addition to the processing device  1800 , other parts of the mobile device  1000  are shown schematically in  FIG. 5 . These include a communications subsystem  1001 ; a short-range communications subsystem  1020 ; the keypad  1400  and the display  1600 , along with other input/output devices  1060 ,  1080 ,  1100  and  1120 ; as well as memory devices  1160 ,  1180  and various other device subsystems  1201 . The mobile device  1000  is preferably a two-way RF communications device having voice and data communications capabilities. In addition, the mobile device  1000  preferably has the capability to communicate with other computer systems via the Internet. 
     Operating system software executed by the processing device  1800  is preferably stored in a persistent store, such as the flash memory  1160 , but may be stored in other types of memory devices, such as a read only memory (ROM) or similar storage element. In addition, system software, specific device applications, or parts thereof, may be temporarily loaded into a volatile store, such as the random access memory (RAM)  1180 . Communications signals received by the mobile device may also be stored in the RAM  1180 . 
     The processing device  1800 , in addition to its operating system functions, enables execution of software applications  1300 A- 1300 N on the device  1000 . A predetermined set of applications that control basic device operations, such as data and voice communications  1300 A and  1300 B, may be installed on the device  1000  during manufacture. In addition, a personal information manager (PIM) application may be installed during manufacture. The PIM is preferably capable of organizing and managing data items, such as e-mail, calendar events, voice mails, appointments, and task items. The PIM application is also preferably capable of sending and receiving data items via a wireless network  1401 . Preferably, the PIM data items are seamlessly integrated, synchronized and updated via the wireless network  1401  with the device user&#39;s corresponding data items stored or associated with a host computer system. 
     Communication functions, including data and voice communications, are performed through the communications subsystem  1001 , and possibly through the short-range communications subsystem. The communications subsystem  1001  includes a receiver  1500 , a transmitter  1520 , and one or more antennas  1540  and  1560 . In addition, the communications subsystem  1001  also includes a processing module, such as a digital signal processor (DSP)  1580 , and local oscillators (LOs)  1601 . The specific design and implementation of the communications subsystem  1001  is dependent upon the communications network in which the mobile device  1000  is intended to operate. For example, a mobile device  1000  may include a communications subsystem  1001  designed to operate with the Mobitex™, Data TAC™ or General Packet Radio Service (GPRS) mobile data communications networks, and also designed to operate with any of a variety of voice communications networks, such as AMPS, TDMA, CDMA, WCDMA, PCS, GSM, EDGE, etc. Other types of data and voice networks, both separate and integrated, may also be utilized with the mobile device  1000 . The mobile device  1000  may also be compliant with other communications standards such as 3GSM, 3GPP, UMTS, etc. 
     Network access requirements vary depending upon the type of communication system. For example, in the Mobitex and DataTAC networks, mobile devices are registered on the network using a unique personal identification number or PIN associated with each device. In GPRS networks, however, network access is associated with a subscriber or user of a device. A GPRS device therefore requires a subscriber identity module, commonly referred to as a SIM card, in order to operate on a GPRS network. 
     When required network registration or activation procedures have been completed, the mobile device  1000  may send and receive communications signals over the communication network  1401 . Signals received from the communications network  1401  by the antenna  1540  are routed to the receiver  1500 , which provides for signal amplification, frequency down conversion, filtering, channel selection, etc., and may also provide analog to digital conversion. Analog-to-digital conversion of the received signal allows the DSP  1580  to perform more complex communications functions, such as demodulation and decoding. In a similar manner, signals to be transmitted to the network  1401  are processed (e.g. modulated and encoded) by the DSP  1580  and are then provided to the transmitter  1520  for digital to analog conversion, frequency up conversion, filtering, amplification and transmission to the communication network  1401  (or networks) via the antenna  1560 . 
     In addition to processing communications signals, the DSP  1580  provides for control of the receiver  1500  and the transmitter  1520 . For example, gains applied to communications signals in the receiver  1500  and transmitter  1520  may be adaptively controlled through automatic gain control algorithms implemented in the DSP  1580 . 
     In a data communications mode, a received signal, such as a text message or web page download, is processed by the communications subsystem  1001  and is input to the processing device  1800 . The received signal is then further processed by the processing device  1800  for an output to the display  1600 , or alternatively to some other auxiliary I/O device  1060 . A device user may also compose data items, such as e-mail messages, using the keypad  1400  and/or some other auxiliary I/O device  1060 , such as a touchpad, a rocker switch, a thumb-wheel, or some other type of input device. The composed data items may then be transmitted over the communications network  1401  via the communications subsystem  1001 . 
     In a voice communications mode, overall operation of the device is substantially similar to the data communications mode, except that received signals are output to a speaker  1100 , and signals for transmission are generated by a microphone  1120 . Alternative voice or audio I/O subsystems, such as a voice message recording subsystem, may also be implemented on the device  1000 . In addition, the display  1600  may also be utilized in voice communications mode, for example to display the identity of a calling party, the duration of a voice call, or other voice call related information. 
     The short-range communications subsystem enables communication between the mobile device  1000  and other proximate systems or devices, which need not necessarily be similar devices. For example, the short-range communications subsystem may include an infrared device and associated circuits and components, or a Bluetooth™ communications module to provide for communication with similarly-enabled systems and devices. 
     Many modifications and other embodiments will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that various modifications and embodiments are intended to be included within the scope of the appended claims.