Electronic device with attachment and switching between batteries therefor

I. Field of the Invention

0001The present invention relates generally to consumer electronic devices with battery-powered attachable options.

II: Background of the Invention

0002Many battery-powered consumer electronic devices ("host devices") can include attachable options ("attachments") that themselves can have batteries. An example might be a personal digital assistant (PDA) or camera/camcorder to which can be attached a wireless modem card, for transmitting data to and from the PDA/camera/camcorder. A separate battery on the attachment can be required under some circumstances because design limitations on the amount of current flow through the interface between host and attachment limit the amount of current that can be supplied to the attachment from the host battery.

0003The present invention understands that for size and cost purposes, it is desirable to minimize the size of the battery particularly on the attachment, with the electrical load of the combined system being shared between the battery in the attachment and the host battery. As an example, a code division multiple access (CDMA) wireless modem card attachment that is designed to meet the Compact Flash Interface specification can require more than 800 mA at peak transmit output power, but the compact flash interface allows the host battery to supply no more than 500 mA across the host-attachment interface. For this reason, a separate battery must be provided on the card, and it can share the power load with the host battery.

0004Documents which discuss the use of cards having associated power supplies are: <patcit id="pcit0001" dnum="US6011323A"><text>US-A-6 011 323</text></patcit> which discloses an apparatus and method for providing auxiliary battery conversion in adapters requiring auxiliary batteries; and <patcit id="pcit0002" dnum="US5928336A"><text>US-A-5 928 336</text></patcit> which discloses the use of a PC card which can be inserted into a host computer system and can be driven by a built-in battery so as to serve as a stand-alone apparatus.

0005The present invention critically observes, however, that it can be difficult to join battery power supplies by simply tying them together. Even though the batteries may be the same type, the voltages can be different based on their relative states of discharge and relative temperatures. Under circumstances of such environmental imbalance, charge from one battery can immediately begin to flow into the other battery, and may flow back across the interface, which might be forbidden by the design specification. On the other hand, if the batteries are separated from each other by, e.g., supplying separate parts of the card from each battery, it may be difficult to find a good division where the peak currents required of both batteries satisfies design limits.

0006Moreover, different circuits may have different and hard to predict voltage needs. With particular respect to a CDMA card attachment, for example, its power amplifier exhibits a very non-linear, roughly exponential, requirement for current versus output power. Consequently, due to this wide variation of current demand from the CDMA modem, mostly attributable to the power amplifier, it is not possible to predict the amount of current the power amplifier will require relative to the rest of the CDMA modem card at any one time. The result is that a larger than needed attachment battery might be required, with its capacity most of the time going to waste. As understood by the present invention, while it is desirable to minimize the size of the attachment battery, it is also desirable to achieve a balance whereby one battery does not always exhaust itself before the other battery.

0007The present invention has considered the above-noted problems and has provided the solutions below to one or more of them.

0008In a first aspect, there is provided an electronic system in accordance with Claim 1 appended hereto.

0009In a second aspect, there is provided a method in accordance with Claim 10 appended hereto.

0010The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which:

BRIEF DESCRIPTION OF THE DRAWINGS

0011<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Figure 1</figref> is a simplified block diagram of one embodiment of the present invention;</li><li><figref idref="f0001">Figure 2</figref> is a block diagram of the electrical circuits of the combined host/attachment; and</li><li><figref idref="f0001">Figure 3</figref> is a flow chart of the present logic.</li></ul>

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

0012Referring initially to <figref idref="f0001">Figure 1</figref>, a system is shown, generally designated 10, which includes a host device 12 such as but not limited to a personal digital assistant (PDA), or an imaging device such as camcorder, etc. The system 10 also includes an attachment 14 such as but not limited to a wireless modem card, e.g., a CDMA modem card. It is to be understood that a wide range of hosts 12/attachments 14 are contemplated herein, with the attachment 14 preferably being removably engaged by hand with a bay or other socket 16 of the host device 12 by means known in the art.

0013As shown in <figref idref="f0001">Figure 1</figref>, the host device 12 has at least one host battery 18 and a logic module 20 that can be accessed by the processor of the host device 12 to execute the logic discussed below. An interface 22 electrically connects the host device 12 to the attachment 14.

0014Like the host device 12, the attachment 14 may include a logic module 24 that may be accessed by a processor within the attachment 14 to execute the logic herein in lieu of or in consonance with the host device 12 executing its logic module 20. The logic modules 20, 24 may be embodied in hardware or software, and may be stored on computer readable media.

0015<figref idref="f0001">Figure 1</figref> shows that the attachment 14 includes at least one attachment battery 26. An exemplary non-limiting attachment battery 26 may be a Lithium-ion type battery rated for 250 milliamp-hours. A first circuit 28 in the attachment 14 is always powered by the attachment battery when the attachment 14 is operating. The first circuit can be, without limitation, a power amplifier in a CDMA modem or other circuit. A second circuit 30, also referred to herein as a shared-power circuit, is contained in the attachment 14 and it is selectively powered either by the host battery 18 (over the interface 22) or attachment battery 26 as more fully disclosed below.

0016Before explaining the logic by which it is determined whether to power the shared-power circuit 30 using the host battery 18 or attachment battery 26, reference is made to <figref idref="f0001">Figure 2</figref>, to gain an understanding of a non-limiting sharing circuitry. As shown, the host battery 18 is used to power host battery-only loads 32 within the host device 12. A current measurement device 34 such as but not limited to a mili-Ohm type series resistance that may sample current to the loads 32 at, e.g., 0.5 second intervals can be provided to generate a signal representative of the current to the host-only loads 32. The samples may be averaged if desired over the last twenty six (or some other appropriate number of) samples.

0017In contrast, the attachment battery 26 powers attachment battery-only loads such as the first circuit 28. A current measurement device 36 can be provided to generate a signal representative of the current to the attachment-only loads 28.

0018<figref idref="f0001">Figure 2</figref> also illustrates that shared loads such as the second circuit 30 shown in <figref idref="f0001">Figure 1</figref> can be powered by either battery 18, 26, depending on whether a host battery switch 38 or attachment battery switch 40 is closed. Which switch is closed is determined by the logic below. A current measuring device 42 can be provided to measure the current that is drawn by the loads 30. It is to be understood that while three current measuring devices are shown, other current measuring configurations may be used in accordance with present principles.

0019With the above understanding in mind, attention is drawn to the logic flow chart of <figref idref="f0001">Figure 3</figref>. While the logic is shown in flow format it is to be understood that in actual implementation software, state machines, and/or other logical mechanisms may be used.

0020Commencing at decision diamond 44, in one preferred non-limiting embodiment it is determined whether a predetermined circuit load is less than a threshold. As one example, it can be determined whether the total current being supplied from the attachment battery 26 is less than twice the capacity of the battery. As another example, if the attachment is a CDMA modem, at decision diamond 44 it may be determined whether the receiver is operating above or below a particular power level, e.g., -94 dBm.

0021If the threshold is exceeded, the logic proceeds to block 46, wherein shared loads 30 are powered by the host battery 18 (by, e.g., causing the host battery switch 38 to close and the attachment battery switch 40 to open). In contrast, if the threshold is not exceeded, the logic may move to decision diamond 48 for another test.

0022At decision diamond 48, the preferred logic contemplates ascertaining the relationship between the remaining capacities of the batteries 18, 26. Specifically, at least one and preferably all three current signals from the current measuring devices 34, 36, 42 shown in <figref idref="f0001">Figure 2</figref> are used to determine which battery should power the shared loads 30. In one exemplary non-limiting embodiment, the determination at decision diamond 48 is undertaken using the following inequality: <maths id="math0001"><math display="block"><mi>Cc</mi><mo mathvariant="normal">></mo><mi>Hc</mi><mo>⁢</mo><mfenced><mi mathvariant="normal">A</mi><mo mathvariant="normal">+</mo><mi mathvariant="normal">C</mi><mo mathvariant="normal">/</mo><mn mathvariant="normal">2</mn></mfenced><mo mathvariant="normal">/</mo><mfenced><mi mathvariant="normal">B</mi><mo mathvariant="normal">+</mo><mi mathvariant="normal">C</mi><mo mathvariant="normal">/</mo><mn mathvariant="normal">2</mn></mfenced><mo mathvariant="normal">,</mo></math><img file="EP1537643B1_D0001.tif" /></maths> wherein Cc is the remaining charge capacity of the attachment battery, Hc is the remaining charge capacity of the host battery, A is the current sensed by the measuring device 36, B is the current sensed by the measuring device 34, and C is the current sensed by the measuring device 42.

0023If the inequality does not hold (meaning that the capacity of the attachment battery 26 is relatively lower), the logic moves to block 46 to allow the host battery 18 to power the shared loads 30. Otherwise, if the inequality holds, indicating that the capacity of the attachment battery 26 is relatively high, the logic moves to block 50. At block 50, the attachment battery 26 is used to power the shared loads 30 (by, e.g., causing the host battery switch 38 to open and the attachment battery switch 40 to close).

0024While the particular ELECTRONIC DEVICE WITH ATTACHMENT AND SWITCHING BETWEEN BATTERIES THEREFOR as herein shown and described in detail is fully capable of attaining the above-described objects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and is thus representative of the subject matter which is broadly contemplated by the present invention, that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more".