USOO736000432
`
`(12) United States Patent
`(10) Patent No.:
`US 7,360,004 32
`(45) Date of Patent:
`Daugherty et a1.
`*Apr. 15, 2003
`
`(54) POWERIN‘G A NU’I'EBOOK ACROSS A USB
`INTERE-ufli
`
`(7'5)
`
`inventors: Michael J. Dougherty. Houston. TX
`(US): Kenneth W. Stufllebeam.
`Houston. TX (US); Rahul V.
`Lakdawala. Cypress. TX (US):
`Thomas 1". Sawyers. Hempstead. TX
`(US)
`
`(T3) Assignee: Hewlett-Packard lkvelepment
`Company, LP.. Houston. TX (US)
`
`( * ) Notice:
`
`Subject to any disclaimer. the term ol'thjs
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 470 days.
`
`This patent is subject to a terminal dis-
`clziinter.
`
`(2]) App]. No: 101674.923
`
`(22)
`
`Filed:
`
`Sep. 30, 2003
`
`(65}
`
`Prior Puhlleatinn Data
`
`US 20041006462] Al
`
`Apr. 1. 2004
`
`Related U.S. Application Data
`
`(63) Continuation of application No. 091603.082. filed on
`Jun. 30. 2000. now Pat. No. 6.668296.
`
`(51')
`
`Int. (Tl.
`(2006.01)
`GOtiF LVI'JO
`(2006.01)
`0061’ 13.44
`(2006.01)
`(Fflfif' 1226
`7101303: 710305: 213800
`(52) US. Cl.
`(58) Field of (Siassificatian Search
`7110803.
`710116: 7131300. 340
`See application file for complete search history.
`
`(56)
`
`References Cited
`1.1.3. i’ATl-EN'I' lmTlJMHN'l'E-i
`
`5.263.238 A
`
`[1'1993 Canova etal.
`
`5.625.813 A
`5.34l .424 A
`5.884.049 A *
`5.834.086 A "‘
`(1.009.363 A “
`6.0“.486 A ‘
`(1.044.422 A
`(1.0405711 A
`6.094.700 A
`6.l05.097 A
`fi.| I923? A "
`6.128.514 Bl *
`(1.134.652 Bl "‘
`6.211.649 BI
`6.28l.784 Bl“
`6.283.?89 BI
`6.308.215 BI
`
`1051997 l-Iolmtiahl
`111993 Kikinis
`3-1999 Alkinson .................... 2105303
`.. 7133300
`3-”[999 Amoni at al.
`..
`
`............... 201.533
`[2-1999 Beckett et al.
`l"2000 Casey
`34037.29
`3"2000 Tran
`4"2000 Bovio et al.
`7"2000 Desehepper et a1.
`8"2000 Lark)? et a].
`9"2000 f'ho ........................... 2135300
`.. 2135300
`|-'200|
`
`2"200l Yang
`3203110
`4-"200I Malsutta
`8-"200I Redgzttc ct al.
`9-"200I Tsai
`[ti-"200i Kolbet et a].
`
`340.'3l0.01
`
`(Continued)
`0TH [ER PU BI JCA'I‘IONS
`
`Universal Serial Bus Specification. Revision 2.0- Apr. 2?. 2000-
`Section Ill.“
`
`Primary Ermuim'r Reliant] l’ct'vectl
`Assistant Exmm'ncr— Jeren‘ty S. Cerullo
`
`(57)
`
`manner
`
`A laptop computer and mating docking station where the
`docking station provides power to the laptop computer over
`power rails of the Universal Serial Bus (USB) interface. The
`laptop computer has laptop docking logic that both provides
`power in accordance with standard USB protocol. and also
`receiving power acmss the power rails of the USB interface.
`LikeWisc.
`the docking station has a docking station dock
`logic that establishes communication with the laptop dock-
`ing logic across the U SB power rails. Once positive coni-
`munication is established. the dock station provides voltages
`on the USB power mils sufficient
`to power the laptop
`computer as well as charge the laptop‘s battery.
`
`15 Claims. 3 Drawing Sheets
`
`12
`
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`
`ZTE/SAMSUNG 1005-0001
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`US 7,360,004 32
`Page 2
`
`U.S. PATENT DOCUMENTS
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`U.S. Patent
`
`Apr. 15, 2008
`
`Sheet 2 of 3
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`US 7,360,004 B2
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`U.S. Patent
`
`Apr. 15, 2008
`
`Sheet 3 of 3
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`US 7,360,004 B2
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`US 7,360,004 82
`
`l
`POWERING A NO’I‘EMH)K ACROSS A USB
`INTERFACE
`
`CROSS-REFERENCE TO RELA'I‘ED
`APPLICATIONS
`
`This application is a continuation of U S application Ser.
`No. DWGOSflBZ. filed Jun. 30. 2000 now U.S. Pat. No.
`6.658.296. and entitled “Powering A Notebtxik Across A
`USB Interface."
`
`ltl
`
`STATEMENT REGARDING FEDERALLY
`SPONSORED RESEARCH OR DEVELOPMENT
`
`Not applicable.
`
`BACKGROUND OF 'I‘l—lh' INVENTION
`
`1. Field of the Invention
`
`invention relates generally to docking a
`The present
`laptop computer to a docking station. More particularly. the
`invention relates to powering the laptop through the docking
`station when the laptop is in the (locked position. More
`particularly still. the invention relates to powering the laptop
`across a USB interface when in the docked position.
`2. Background of the Invention
`Computer systems cotnc in many shapes. sizes and com-
`putational ability. For persons who work in designated
`locations. a standard desktop computer may be sullicient to
`fulfill that person‘s needs. However. for a ttser who travels
`frequently and needs computing power in those travels. a
`portable or laptop computer is desirable.
`the entire
`Laptop computers are characterized in that
`computing functionality is incorporated into a single pack-
`age. That is. the motherboard. hard drive. disk drives. CD
`ROM drives. keyboard and display are all packaged in a
`compact device typically weighing less than ten pounds.
`laptop computers are Fully functional
`in that
`tltey may
`execute the very saute programs. for example word proces—
`sors and spreadslteet progrants. as full sized or desktop
`computers. Laptop computers have a battery that allows for
`remote operation of the laptop even itt
`locations where
`alternating current (AC) wall socket power is not available.
`While laptop computers may address portable computing
`needs. they are not without their limitations. For exzunple.
`the keyboards ol~ most laptop computers are a non—standard
`size. That is. the keys may be slightly closer together and not
`as ergonomically placed as a standard keyboard. Further.
`standard keyboards typically have function keys. cursor
`control keys and a full numerical keypad. ln laptop com-
`puters these keys are incorporated onto the standard keys by
`means of shill and function control. A further limitation of
`laptops. given the relatively small size. is they only have a
`limited number of communication ports available. That is_. a
`laptop may support only a single parallel port. a single serial
`port and a single Universal Serial Bus (USB) port. Also. the
`display devices for laptop computers are typically small. as
`compared to desktop monitors. to keep the overall sire of the
`laptop computer small.
`Many laptop users address litnitatiotts of laptops by some
`form of docking station. When the user returns to the home
`or ollice. the laptop is “docked“ with a non—portable tutit.
`Docking in this mamter may expand the capabilities of the
`laptop computer to include a lull size keyboard. a full size
`monitor. more serial ports. and other functionality typically
`associated only with desktop computing devices.
`
`2
`The docking station can take many forms. For example.
`the docking station may extend one of the expansion bttscs
`within the laptop computer. e.g. a peripheral components
`interconnect (PCI} bus. to the docking station such that full
`compttting functionality may be housed within the docking
`station. Expanding the PCI bus gives the docking station the
`ability to include a hard drive, expansion cards and the like.
`For laptop computers that dock to this type of docking
`station. the docking station typically provides power to the
`laptop within the docking connector between the laptop and
`the docking station.
`A second type of docking station. while extending the
`laptop's capabilities. it is not as extensive as the dock station
`that extends one of the expansion buses of the laptop. This
`second type docking station is commonly referred to as a
`port replication docking station. By port replication it
`is
`meant that by plugging the laptop into the docking station.
`more serial and parallel ports are available for connection to
`printers. scanners. full sire display devices. serial or parallel
`pointing devices and the like. As with the full docking
`station explained above. these port replication docks typi-
`cally also include power connections in the docking con-
`nector.
`
`2H
`
`30
`
`3S
`
`4ft
`
`Another method of expanding the capabilities ol'a laptop
`I.) .tt
`_ may be a form of port replication across a USB port. A user
`connects a laptop. via a USE! connection. to a port replica—
`tion device which generates plurality ol~ communication
`ports for use as described above. However.
`in situations
`where port replication is accomplished across the USB
`connector.
`tlte laptop user also plugs the laptop into a
`separate sottrcc of power. or operates the laptop on battery
`power. Given that the user most likely intends to use the
`laptop for an extended period of litne in the location where
`port replication is desirable. a user 01‘ the such a system plugs
`the ACfl'XI power converter (also known as a power
`“brick"J into a standard AC wall socket on its input and its
`output into the laptop computer. Thus. in this situation the
`user is required to plug in at
`least
`the USE expansion
`connection as well as a power cable. Also. there are prior art
`devices that have the appearance of a full docking station.
`that is the laptop may physically couple to a non-portable
`docking station where the act of docking cottplcs the USB
`ports: however, these devices still require the user to sepa-
`rately apply power to the laptop.
`Thus. it would be desirable to have a USB based docking
`station that has the capability of both operating the laptop
`computer and charging the batteries in the laptop computer
`while docked without the need to plug in a separate power
`connection. thus reducing the time and complexity to couple
`the laptop to the docking ttnit. Despite the desirability of
`such systems. none are available in the prior art.
`
`4S
`
`Stt
`
`BRIEF SUMMARY OF THE [NVENTION
`
`55
`
`oil
`
`The problems noted above are solved in large part by a
`laptop computer and related docking station adapted to
`supply power from the docking station to the laptop com—
`puter across the USB connection. To accomplish this. the
`laptop computer is modified to [rave circuitry which is
`capable of being detected across USB power rails by the
`docking station and also capable ol‘tunting 011' the five volts
`typical supplied by the laptop onto the USB port. and
`instead. receiving power at 18.5 volts. from the docking
`statiott across the USB cotmcctions. The laptop computer
`may be operated by the dock uttit supplied power and. if
`necessary. the laptop‘s battery may be charged. Likewise.
`the docking station contains circuitry coupled to the power
`
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`US 7,360,004 82
`
`3
`rails of the USB port which allows the docking station to
`detect wltether the laptop computer coupled to the docking
`station is capable of receiving power.
`Thus. a laptop ttser need ottly plug tlte laptop into the
`docking station via the USB port. even iflhe battery for the
`laptop computer is drained. Once physically coupled to the
`docking station. the docking station detects whether or not
`the attached laptop is capable of receiving power across the
`USB port. If so. the docking station ramps power to the
`laptop cotnpttter to facilitate its operation.
`
`BRIEF l')l:lSCRll"I'ION OF THE DRAWINGS
`
`For a detailed description of the preferred embodiments of
`the invention. reference will now be made to the accompa-
`nying drawings in which:
`FIG. 1 shows an exemplary computer systent of the
`preferred embodiment;
`FIG. 2 shows a partial block diagram elechieal schematic
`of a docked laptop and docking station; and
`FIG. 3 shows a more detailed electrical schematic of the
`reactive signaling circuit of the preferred embodiment.
`
`NOTATION AND NOMENCLATURE
`
`Certain terms are used throughout the following descrip-
`tiott and claitns to refer to particular system components. As
`one skilled in the art will appreciate. computer companies
`may refer to a component by different names. This document
`does not
`intend to distinguish between cotnponents that
`differ in name but not function. In the following discussion
`and in the claims. the terms “including" and “comprising“
`are used in an open-ended fashion. and thus should be
`interpreted to mean "including, bttt not limited to .
`. .“. Also.
`the term “couple“ or “couples" is intended to ntean either an
`indirect or direct electrical connection. Thus. ifa lirst device
`couples to a second device. that connection may be through
`a direct electrical connection. or through an indirect elec—
`trical comtection via other devices and connections.
`
`I.)ETAII.I~II) [DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`The preferred embodiment o l'tltis invention. as illustrated
`in FIGS. 1—3. comprises a laptop eotnptlter 100 and an
`associated docking station 200. The computer system 100
`may be coupled to the docking station 200 and thus be in a
`“docked" configuration. Likewise. the computer system 100
`may be de-coupled from a docking station 200 rutd therefore
`be in an “undocked” configuration.
`FIG. 1 illustrates a laptop computer 100 in accordance
`with a preferred embodiment of the invention. Laptop cont-
`pttter 100 generally includes a processor or CPU 102
`coupled to a ntain memory array 104 and a variety of other
`peripheral computer system components through an inte-
`grated Host bridge logic device 106. The CPU 102 prefer—
`ably couples to bridge logic 106 via a (“PU bus 108, or the
`bridge logic 106 tnay be integrated into the CPU 102. The
`(“PU 102 may comprise.
`tor example, a PentiumLR'J
`Ill
`microprocessor.
`It should be understood. however.
`that
`compttter system 100 could include other alternative types
`of microprocessors. Further. an embodiment of computer
`system 100 may include multiple processors. with each
`processor coupled through the CPU bus 108 to the bridge
`logic unit 106.
`The main memory array 104 preferably couples to the
`bridge logic unit 106 through a memory bus 110. and the
`
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`
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`
`30
`
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`bridge logic 106 preferably includes a memory control unit
`(not shown) that controls transactions to the maitt memory
`104 by asserting the necessary control signals during
`memory accesses. The main memory 104 functions as the
`working memory for the CPU 102 and generally includes a
`cottventional memory device or array of memory devices itt
`which program instructions and data are stored. The main
`memory array may comprise any suitable type ol'memory
`such as dynamic random access memory (DRAM) or any of
`the various types of DRAM devices such as synchronous
`DRAM (SDRAM). extended data output DRAM (H130
`DRAM), or Rambus'm DRAM (RDRAM).
`The laptop computer 100 also preferably includes a
`graphics controller 112 that couples to the bridge logic 106
`via an expansion bus .114. As shown in FIG. 1. the expansiott
`bus 114 preferably comprises an Advanced Graphics Port
`(AGI‘) bus. Alternatively, the graphics controller 112 may
`couple to bridge logic 106 through a Peripheral Component
`Interconnect (I’CI) bus 116. As one skilled in the art under-
`stands. the graphics controller 112 controls the rendering of
`text and images on a display device 118. The graphics
`controller 112 may embody a typical graphics accelerator
`generally known in the art to render three-dimensional data
`structures oit display 118. These data structures can be
`I.) .n
`_ eflectively shifted into and out of main memory 104 via
`bridge logic itlfi. The graphics controller 112 therefore may
`be a master of the expansion bus {either PCI or AGI’ bus)
`enabling the graphics controller 112 to request and receive
`access to a target interface within the bridge logic unit 106.
`including the memory control uttit. This ntastersltip capa-
`bility permits the graphics controller 112 to access ntaitt
`memory 104 without
`the assistance of the CPU 102. A
`dedicated graphics bus accommodates rapid retrieval of data
`from maitt memory 104. As will be apparent to one skilled
`in the art. the bridge logic 106 includes an AGP interface
`(not specifically shown) to permit master cycles to be
`transmitted and received by bridge logic 106. The display
`118 contprises any suitable electronic display device upon
`which an image or text can be represented. A suitable display
`device may include. for example. a liquid crystal display
`(LCD). a thin film transistor ('l‘lt'l‘). a virtual retinal display
`(V'RD). or any other type of suitable display device for a
`laptop computer system.
`The laptop computer system 100 preferably comprises
`another bridge logic device 120 that bridges the primary
`expansion bus 122 to various secondary buses including a
`low pin count (“[.l’(.‘"} bus 124 and the PC] bus 116.
`[n
`aceordrutce with the preferred embodiment.
`the bridge
`device 120 is an lnputhutput Controller [-1th (“Hill”). The
`lCI-l 120 supports the [.l’(‘ bus 124. the PU bus 116. the
`USB bus 126 as well as various other secondary buses.
`either directly or by way of further bus bridges.
`lit
`the preferred embodiment of FIG. 1.
`the primary
`expansion bus l22 comprises a Hub-link bus which is a
`proprietary bus of the Intel® Corporation. Ilowever. laptop
`computer system 101] is not limited to any particular type of
`primary expansion bus 122. and thus other suitable buses
`may he used.
`The preferred embodiment of laptop computer 100 also
`has docking logic 134. Docking logic 134 is a set of circuitry
`coupled to tlte USB port 136 power litres 138. More spe-
`cifically. the standard USB cotmnunication cable has four
`conductors. Two of these conductors are serial communica—
`tiott conductors 126 which allow communication between
`devices using USB protocol. The other two conductors carry
`power between USB devices. Under 1158 protocol.
`the
`power conductors 138 carry live volts. Referring to FIG. 1.
`
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`US 7,360,004 82
`
`the laptop computer ll]. of tlte preferred embodiment does
`not modify operation of the serial communication conduc-
`tors 126 of the USB protocol. Preferably. all conununica-
`tions to establish whether laptop computer 100 is capable of
`receiving power front the docking station 200 take place
`over the power conductors or power rails [38 of the USB
`cable connector.
`
`FIG. 2 shows in more detail the docking logic 134 of the
`laptop computer 100 coupled to docking logic 234 of the
`docking station 200. Docking of these two logic circuits is
`preferably through USB connector 136 of the laptop cont—
`puter 100 and a mating USB connector 236 of the docking
`station 200.
`
`Under standard USB protocol. the laptop computer [00
`provides power to USB devices downstream of the laptop
`computer It"). Thus. in normal operation. the USB protocol
`voltage control tutit 140 receives a live volt input signal 142
`which it couples to the positive power rail 144 ofthe power
`conductors 138. Downstream USB devices may draw cur-
`rent through the positive power rail 144. lfa user of the
`laptop computer 100 plugs in. for example. a USB mouse
`into tlte USB connector 136. that mouse Lutder USB protocol
`may draw power across tlte power conductors 138 for its
`operational use.
`Assume for pttrposcs of explanation that laptop computer
`100 Itas a charged battery and is in an operational state. In
`stlch a condition. the laptop computer 100 preferably pro—
`vides live volt power across the power conductors 138.
`Further asstune that the user docks the laptop 100 with a
`docking station 200 of the preferred embodiment. In so
`doing. the user either physically plugs in a USB cable to the
`cotuiector 136 or slides the laptop cotnputer 100 into a
`docking station 200. In this instance. with the laptop com-
`puter 100 on and fully functional. the laptop computer 100
`attempts to provide power across the USB cable to the
`docking station 200.
`Under normal USB protocol, coupling of USB devices
`requires a series of USB ltandshaking protocols to identify
`both the ltost or master device. which would be the laptop
`computer 100. rutd any downstream device. which in this
`exemplary case is the docking station 200. [n the preferred
`embodiment of this invention.
`this handshaking protocol
`between the laptop comptttcr 100 and the docking station
`200 reveals to soliware running in the laptop computer lflfl
`that the docking station 200 is capable of providing power
`across the power rails 138 of the USB interface. It will be
`understood that this handshaking protocol between the lap-
`top computer 100 and the docking station 200 oceurs over
`the serial communication littes 126. and these lilies are not
`shown in FIG. 2.
`
`Based on the haudshaking between the two devices.
`operating system software loads a driver specifically used
`with the docking station 200. Though this driver may
`provide trinity Functions. the function of concern is that the
`driver prettirably turns of? the laptop computer‘s ability to
`provide live volts to the power rails 138. More specifically.
`the driver loaded by the operating system of the laptop
`computer 100 preferably commands the Super 1K) controller
`130 to issue a live volt shut-oll‘ command signal 148.
`preferably through one of its digital outputs. This five volt
`shut—oll' command couples to the USB protocol voltage
`control unit 140 of the docking logic 134. Upon receiving
`this live volt shttt-ofl‘oonunand signal 148. the USB protocol
`voltage control unit 140 preferably de‘couples the five volt
`input line [42 from the positive power rail 144. Thus, the
`
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`laptop computer 100 breaks with standard USB protocol and
`the power rails 138 are no longer capable ofproviding power
`to downstream devices.
`
`As far as docking logic 234 of the docking station 200 is
`concemed. the situation where laptop computer 10!! turns off
`the live volt supply presents itself in the same manner as
`coupling a laptop computer 100 that either does not have a
`battery. and therefore is not operational. or whose battery is
`completely discharged. Titus.
`the following description is
`equally applicable to both situations.
`It
`is possible that
`laptop computers that do not have the capability of receiving
`power across the USB port may be docked with docking
`station 200. Therefore. docking station dock logic 234 mttst
`establish that the laptop computer to which it is docked is
`capable of receiving power. Preferably this is dotte by
`attempting to establish communications across the power
`mils 138 of the USB connector.
`
`Initially voltage ramp logic 210 (FIG. 2) provides no
`voltage whatsoeVer to the positive power rail 244 on the
`docking station 200 side of the connection. Upon detecting
`no voltage on the USB power rails. communication and
`control logic 250 commands the voltage ramp logic 210 to
`ramp-up a small voltage. preferably 3.] volts. onto power
`rail 244. Positive power rail 244 couples to the power rail
`144 on the laptop side of the connection and therefore also
`couples to the reactive signaling circuit 150. Communica-
`tion and control circuit 250 couples to reactive signaling
`circuit 150 across these power rails. In broad terms, the
`communication and control circuit 250 of the docking logic
`234 attempts to establish communication with the reactive
`signaling circuit 150 of the laptop docking logic 134.
`11‘
`communication and control circuit 250 establishes prisitive
`conununication with reactive signaling circuit 150.
`the
`docking station 200 has made a positive identification that
`the laptop to which it
`is docked is capable of receiving
`power across the USB cotutection.
`More specilically, communication and control circuit 250
`preferably communicates with reactive signaling circuit 150
`by serially communicating across the positive power rail
`144. While there may be many protocols and devices
`capable of this conuntulication. the preferred embodiment of
`the reactive signaling circuit 150 comprises a Dallas Semi-
`conductor devicc part number D82401. as shown in FIG. 3.
`This DSZ401 has the characteristic that
`it stores charge
`drawn from its signaling line. and then,
`in response to a
`specilic pattent of high and low voltages on its signaling
`Iiue. transmits a series of high and low pulses across the
`signaling line to uniquely identify the device. Preferably. the
`communication and control logic 250 performs the noses—
`sary steps to initiate conuuunication withthe [)52401 device
`and receives any return communication issued thereby.
`Upon receiving the commtuiication from the DS2401 of
`the reactive signaling circuit 150. the communication and
`control circuit 250 preferably performs checks on the infor-
`mation received to verify whether the laptop to which it is
`docked is capable of receiving power across the USB
`connection. Dallas Semiconductor makes another device. a
`DSZ480. which is specifically made to communicate with
`the [)52401. However. in the preferred embodiment this
`device is not used and instead a Programmable Array Logic
`(“PAL“) is used. A PAL has the characteristic that it may be
`lield programmed to execute certain steps or states and is
`therefore considered a lield programmable state machine.
`The PAL of the prelcrrcd embodiment performs all steps
`necessary to conuntuticate with the reactive signaling circuit
`150 to establish positive identification that the laptop to
`
`ZTE/SAMSUNG 1005-0008
`ZTE/SAMSUNG 1005-0008
`IPR2018-00110
`|PR2018-00110
`
`

`

`US 7,360,004 82
`
`7
`which the docking station 200 is docked is capable of
`receiving power across its USB connector.
`The conununication and control logic 250. after positively
`identifying the laptop as capable ofreceiving power. informs
`the voltage ramp logic 210 across the ramp signal line 213
`to ramp the voltage on the positive USB power rail 244. 144
`up to approximately 18 volts. Voltage ramp logic 210
`couples to an 18 volt supply 212 which preferably comes
`from a power supply {not specifically shown).
`Voltage ramp logic 210, tipon receiving the ramp indica-
`tion front the comnun'rication and control logic 250. prefer-
`ably ramps the voltage to 18 volts over a period of 20 50
`milli-seconds. Thus. the voltage on positive power rail 144
`with respect to the negative pewer rail 146 in tile laptop
`computer begins to rise toward 18 volts. Laptop computer
`100 preferably operates using the 18 volt power supplied by
`the docking station 200 across the USB interface. Also. the
`laptop computer may charge its battery. if needed. with this
`same supply.
`It is possible that laptop computers that are not capable of
`receiving power across their USB interfaces ntay be cotiplcd
`to the docking station 200. Indeed. it may be possible that a
`user quickly changes or swaps the USB connection from a
`laptop capable of receiving power to a laptop not capable of
`receiving power. The docking station 200 preferably detects
`that a computer user has decoupled the USB port. Detection
`must be fast enough to insure that the dock station docking
`logic 234 removes the 18 volt power supply before the user
`couples it to another computer. This capability is preferably
`accomplished by a combination of ftmctionality in the laptop
`docking logic 134. specifically the reactive signaling circuit
`150. and the dock station docking logic 234. specifically
`current sense logic 220.
`Reactive signaling circuit 150 in the laptop computer 100
`in combination with current sense logic 220 in the docking
`station 200 operate to detect that a user has unplugged or
`decoupled the laptop computer 100 and the docking station
`200. More specifically. after voltage ramp circuit 210 of the
`docking logic 234 ramps voltage on the positive power rail
`244. 144 above a predetermined value. preferably 6 volts.
`the reactive signaling circtiit 150 preferably draws a small
`amount of current from the docking station 200. This small
`amount ofcurrent. a coupling current. is detected by current
`sense logic 220 of the dock station docking logic 234. This
`small Coupling current
`is monitored by the dock station
`docking logic 234 as an indication that
`two compatible
`devices remain coupled together. When the dock station 2130
`provides power for full operation of the laptop compttter
`100. as many as 2.5 amps of ctirrcnt may flow from the dock
`station 200 to the laptop computer 100 across the USB
`connectors 136. 236. The coupling current is pan of Lhat 2.5
`amp power flow. That is to say. when the laptop computer
`100 is operating frorn power supplied by the dock station
`200. the coupling current may be undistinguisliable from the
`power drawn by the laptop.
`As long as current sense logic 220 detects at least art
`amount of current equal
`to the coupling current. the dock
`station docking logic 234 is assured that the laptop computer
`100 is capable of receiving power across the USB port. If the
`laptop computer system user unplugs the U SB connection.
`or de-couples the laptop from the docking station. current
`sense logic 220 detects the loss of current flow and imme-
`diately notifies the communication control logic 250 across
`logic line 252. Communicaliou and control
`logic 250
`instructs voltage ramp logic 210 to cease providing power to
`the power rails 138 of the USB interface. Thus. the current
`sense logic 220. in combination with reactive signal circuit
`
`ltl
`
`30
`
`4ft
`
`‘Jtl
`
`8
`150. assures a system user cannot dock a laptop that is not
`capable of receiving power to a powered USB port.
`Current sense logic 220 is preferably implemented with a
`Schottky diode in parallel with a resistor of small resistance.
`The voltage across this parallel combination is preferably
`detected by a comparator or operational amplifier whose
`output quickly saturates as current flow exceeds the coupling
`current minimum. One of ordinary skill
`in the art. new
`understanding the functionality of the current sense logic
`220. could implement many circuits to perform this function
`including the use of precision current sense resistors. Like-
`wise. current logic 156. as indicated in FIG. 3. preferably
`comprises 1 k9 resistor coupled across the power rails.
`l'Iowever. this 1 k9 resistance couples across the power rails
`only as the voltage on those rails reaches and exceeds the
`threshold voltage of 6 volts. Below the threshold voltage.
`which includes the voltage that
`the laptop supplies in
`conliirmance With standard USB protocol. the | RS? resis—
`tance does not draw current front the positive power rail.
`Because powering the laptop computer across the USB
`interface power rails requires voltages that may exceed
`breakdown voltages ofthe signaling device 152. the reactive
`signaling circuit 150 prelicrably also comprises a selfvpro-
`tection logic 154 coupled across the positive and negative
`r.) .n
`_ USB power rails. The self protection circuit 154 electrically
`floats the signaling device 152 when the supply voltage
`exceeds the threshold voltage preferably set at 6 volts. but in
`any case set below the breakdown voltage of device 152.
`In operation. a user takes a laptop computer 100 that
`either does not have battery. or has a discharged battery. and
`docks it to docking station 200. Dock station docking logic
`234 places a small voltage across the power rails 138.
`preferably 3.] volts. Communication and control logic 250
`attempts to cormnunicatc with the reactive signaling circuit
`150 serially over the positive U SB power rail 144, 244. It
`will be understood that in the preferred implementation of
`the reactive signaling circuit 150. the device 152, though
`being part of a laptop computer that
`is without power. is
`capable of serial communication powered by current drawn
`and stored frorn the 3.1 volts applied to the power rails by
`dock logic 234. Once the communication and control logic
`250 establishes positive communication with the reactive
`signaling circuit 150. the voltage ramp logic 210 ramps the
`voltage on the positive power rails 144. 244 to 18 volts. As
`the voltage exceeds 6 volts. coupling current
`logic 156
`couples a resistance across the power rails ofapproximately
`1 k9. and self protection logic 154 electrically floats sig-
`nally device 152. Coupling resistance across the power rails
`results in a current flow to the laptop eomptlter 100 of
`approximately six milliamps. Current sense logic 220 senses
`this six rnilliamp current as a continuing indication that the
`laptop computer 100 is capable of receiving power across
`the USB interface. As the voltage approaches 18 volts. the
`laptop computer preferably draws sullici