`(12)
`(10) Patent No.:
`US 7,360,004 B2
`Dougherty etal.
`(45) Date of Patent:
`*Apr. 15, 2008
`
`
`US007360004B2
`
`(54) POWERING A NOTEBOOK ACROSSA USB
`INTERFACE
`
`(75)
`
`Inventors: Michael J. Dougherty, Houston, TX
`(US); Kenneth W. Stufflebeam,
`Houston, TX (US); Rahul V.
`Lakdawala, Cypress, TX (US):
`Thomas P. Sawyers, Hempstead, TX
`(US)
`
`;
`(*) Notice:
`
`(73) Assignee: Hewlett-Packard Development
`Company, LP., Houston, TX (US)
`.
`;
`.
`Subject to any disclaimer, the termof this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 470 days.
`—
`.
`[his patent is subject to a terminal dis-
`claimer.
`
`(21) Appl. No.: 10/674,923
`
`G2);
`(65)
`
`Filed:
`
`SAB: 20, ZOOS
`Prior Publication Data
`US 2004/0064621 Al
`Apr. 1, 2004
`
`Related U.S. Application Data
`
`(63) Continuation ofapplication No. 09/608,082, filed on
`Jun. 30, 2000, now Pat. No. 6,668,296,
`
`(51)
`
`Int. Cl.
`(2006.01)
`GO6F 13/00
`(2006.01)
`GO6F 13/14
`(2006.01)
`G06F 1/26
`(52) US. Che cecccccccscees 710/303; 710/305; 713/300
`(58) Field of Classification Search ................ 710/303,
`710/16: 713/300, 340
`:
`«att
`ae
`ana
`ee application fle tur <pmplets searBiskary:
`References Cited
`U.S. PATENT DOCUMENTS
`
`(56)
`
`10/1997 Holmdahl
`5,675,813 A
`11/1998 Kikinis
`5,841,424 A
`5,884,049 A 3/1999 AtKINSON .....cccecerseeneees 710/303
`.. 713/300
`5,884,086 A *
`3/1999 Amoni et al.
`..
`
`12/1999 Beckert et alo cc 701/33
`6,009,363 A ™
`6.011486 A *
`1/2000 Casey ....cceccceeeeene, 340/729
`6,044,422 A
`3/2000 Tran
`6,046,571 A
`4/2000 Bovio etal.
`6,094,700 A
`7/2000 Deschepperet al.
`6,105,097 A
`8/2000 Larky et al.
`6,119,237 A *
`9/2000 CHO siccessessescesessesssenees 713/300
`1/2001 Wood..
`.. 713/300
`6,178,514 BI*
`
`2/2001 Yang -.seeesesecesseseeeeee 320/110
`6,184,652 BL*
`6.211.649 BL
`4/2001 Matsuda
`6,281,784 BL*
`8/2001 Redgate etal. ......... 340/310.01
`6,283,789 BL
`9/2001 Tsai
`6,308,215 BL
`10/2001 Kolbet et al.
`
`(Continued)
`OTHER PUBLICATIONS
`Universal Serial Bus Specification, Revision 2.0- Apr. 27, 2000-
`EI Es
`Primary Examiner—Rehana Perveen
`Assistant Examiner—Jeremy 8. Cerullo
`
`(57)
`
`ABSTRACT
`
`.
`.
`.
`A laptop computer and mating docking station where the
`dockingstation provides powerto the laptop computer over
`powerrails ofthe Universal Serial Bus (USB) interface. ‘The
`laptop computer has laptop docking logic that both provides
`powerin accordance with standard USB protocol, and also
`receiving poweracross the powerrails ofthe USBinterface.
`Likewise,
`the docking station has a docking station dock
`Eee thatOres ba the laptop dock-
`ing
`logic across the
`USB
`powerrails.
`Once
`positive com-
`caret is established, fhe dock station Novice voltages
`on the USB power rails sufficient
`to power the laptop
`computer as well as charge the laptop’s battery.
`
`§,265,238 A
`
`11/1993 Canova etal.
`
`15 Claims, 3 Drawing Sheets
`
`
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`
`
`U.S. PATENT DOCUMENTS
`.
`SeSeeEh Be Set Silber
`6,362,610 BL
`3/2002 Yang
`6,530,026 BI*
`3/2003 Bard .......:cceeceseeees F13/320
`6,633,932 B1* 10/2003 Bork et al.
`..cscecseeseee TLO/72
`
`6,668,296 BI" 12/2003 Dougherty et al.
`......... 710/303
`
`6,886,104 BI*
`4/2005 McClurg et al.
`............ 713/300
`2001/0034250 Al
`10/2001 Chadha
`
`* cited by examiner
`
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`U.S. Patent
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`Apr. 15, 2008
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`Sheet 1 of 3
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`US 7,360,004 B2
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`Apr. 15, 2008
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`Sheet 2 of 3
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`US 7,360,004 B2
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`Sheet 3 of 3
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`US 7,360,004 B2
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`US 7,360,004 B2
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`1
`POWERING A NOTEBOOK ACROSS A USB
`INTERFACE
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation of U.S. application Ser.
`No. 09/608,082, filed Jun. 30, 2000 now U.S. Pat. No.
`6,668,296, and entitled “Powering A Notebook Across A
`USB Interface.”
`
`if
`
`STATEMENT REGARDING FEDERALLY
`SPONSORED RESEARCH OR DEVELOPMENT
`
`2
`The docking station can take many forms. For example,
`the docking station may extend one of the expansion buses
`within the laptop computer, e.g. a peripheral components
`interconnect (PCI) bus, to the docking station such that full
`computing 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 andthelike.
`For laptop computers that dock to this type of docking
`station, the docking station typically provides power to the
`laptop within the docking connector betweenthe 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 size 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.
`
`Notapplicable.
`
`BACKGROUND OF THE 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 docked position. More
`particularly still, the inventionrelates to powering the laptop
`across a USB interface when in the docked position.
`2. Background ofthe Invention
`Computer systems come in many shapes, sizes and com-
`putational ability. For persons who work in designated
`locations, a standard desktop computer may be sufficient to
`fulfill that person’s needs. However, for a user who travels
`frequently and needs computing powerin those travels, a
`portable or laptop computeris 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
`they may
`execute the very same programs, for example word proces-
`sors and spreadsheet programs, as full sized or desktop
`computers. Laptop computers have a battery that allows for
`remote operation of the laptop even in locations where
`alternating current (AC) wall socket poweris not available.
`While laptop computers may address portable computing
`needs, they are not without their limitations. For example,
`the keyboards of most laptop computers are a non-standard
`size. Thatis, the keys may beslightly 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. In laptop com-
`puters these keys are incorporated onto the standard keys by
`means of shift 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 size of the
`laptop computer small.
`Manylaptop users address limitations of laptops by some
`form of docking station. When the user returns to the home
`or office, the laptop is “docked” with a non-portable unit.
`Docking in this manner may expand the capabilities of the
`laptop computer to include a full size keyboard, a full size
`monitor, moreserial ports, and other functionality typically
`associated only with desktop computing devices.
`
`30
`
`35
`
`40
`
`Another method of expanding the capabilities ofa laptop
`5 may be a form of port replication across a USB port. A user
`connects a laptop, via a USB connection, to a port replica-
`tion device which generates plurality of communication
`ports for use as described above. However,
`in situations
`where port replication is accomplished across the USB
`connector,
`the laptop user also plugs the laptop into a
`separate source 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 time in the location where
`port replicationis desirable, a user of the such a systemplugs
`the AC/DC power converter (also known as a power
`“brick”) 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 USB expansion
`connection as well as a power cable. Also, there are priorart
`devices that have the appearance ofa full docking station,
`that is the laptop may physically couple to a non-portable
`docking station where the act of docking couples the USB
`ports; however, these devicesstill require the user to sepa-
`rately apply powerto the laptop.
`Thus, it would be desirable to have a USB based docking
`station that has the capability ofboth 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 unit. Despite the desirability of
`such systems, none are available in the priorart.
`
`45
`
`SC
`
`BRIEF SUMMARY OF THE INVENTION
`
`55
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`cr
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`ana
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`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 have circuitry which is
`capable of being detected across USB powerrails by the
`docking station and also capable ofturing off the five volts
`typical supplied by the laptop onto the USB port, and
`instead, receiving power at 18.5 volts, from the docking
`station across the USB connections. The laptop computer
`may be operated by the dock unit 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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`3
`rails of the USB port which allows the docking station to
`detect whether the laptop computer coupled to the docking
`station is capable of receiving power.
`Thus, a laptop user need only plug the laptop into the
`docking station via the USB port, even ifthe batteryfor the
`laptop computeris 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 computer to facilitate its operation.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`if
`
`20
`
`NOTATION AND NOMENCLATURE
`
`Certain terms are used throughout the following descrip-
`tion and claims to refer to particular system components. As
`one skilled in the art will appreciate, computer companies
`may refer toa componentby different names. This document
`does not
`intend to distinguish between components 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, but not limited to... *. Also,
`ed wn
`the term “couple” or “couples” is intended to mean either an 3:
`indirect or direct electrical connection. Thus,ifa first device
`couples to a second device, that connection may be through
`a direct electrical connection, or through an indirect elec-
`trical connection via other devices and connections.
`
`30
`
`4
`bridge logic 106 preferably includes a memory control unit
`(not shown) that controls transactions to the main memory
`104 by asserting the necessary control signals during
`memory accesses. The main memory 104 functions as the
`working memoryfor the CPU 102 and generally includes a
`conventional memory device or array of memorydevices in
`which programinstructions and data are stored. The main
`memory array may comprise any suitable type of 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 (EDO
`DRAM), or Rambus™ DRAM (RDRAM).
`The laptop computer 100 also preferably includes a
`Foradetailed description ofthe preferred embodiments of
`graphics controller 112 that couplesto the bridge logic 106
`wa
`the invention, reference will now be made to the accompa-
`via an expansion bus 114, As shownin FIG, 1, the expansion
`nying drawings in which:
`bus 114 preferably comprises an Advanced Graphics Port
`FIG. 1 shows an exemplary computer system of the
`(AGP) bus. Alternatively, the graphics controller 112 may
`preferred embodiment:
`couple to bridge logic 106 through a Peripheral Component
`FIG. 2 shows a partial block diagramelectrical schematic
`Interconnect (PCI) bus 116. As one skilled in the art under-
`of a docked laptop and docking station; and
`stands, the graphics controller 112 controls the rendering of
`FIG. 3 shows a more detailed electrical schematic of the
`text and images on a display device 118. The graphics
`reactive signaling circuit of the preferred embodiment.
`controller 112 may embody a typical graphics accelerator
`generally knownin the art to render three-dimensional data
`structures on display 118. These data structures can be
`ho A
`5 effectively shifted into and out of main memory 104 via
`bridge logic 106. The graphics controller 112 therefore may
`be a master of the expansion bus (either PCI or AGP 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 unit. This mastership capa-
`bility permits the graphics controller 112 to access main
`memory 104 without
`the assistance of the CPU 102. A
`dedicated graphics bus accommodates rapidretrieval of data
`from main 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 comprises any suitable electronic display device upon
`whichan image ortext can be represented. A suitable display
`device may include, for example, a liquid crystal display
`(LCD), a thin film transistor (TFT), a virtual retinal display
`(VRD), 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 (“LPC”) bus 124 and the PCI bus 116.
`In
`accordance with the preferred embodiment,
`the bridge
`device 120 is an Input/Output Controller Hub (“ICH”). The
`ICH 120 supports the LPC bus 124, the PCI bus 116, the
`USBbus 126 as well as various other secondary buses,
`either directly or by way offurther bus bridges.
`In the preferred embodiment of FIG. 1,
`the primary
`expansion bus 122 comprises a Hub-link bus which is a
`proprietary bus ofthe Intel® Corporation. However, laptop
`computer system 100is not limited to any particular type of
`primary expansion bus 122, and thus other suitable buses
`may be used.
`The preferred embodiment of laptop computer 100 also
`has docking logic 134. Docking logic 134 is a set of circuitry
`coupled to the USB port 136 power lines 138. More spe-
`cifically, the standard USB communication cable has four
`conductors. Twoofthese conductors are serial communica-
`tion conductors 126 which allow communication between
`devices using USB protocol. The other two conductors carry
`power between USB devices. Under USB protocol,
`the
`power conductors 138 carry five volts. Referring to FIG. 1,
`
`The preferred embodiment ofthis invention, as illustrated
`in FIGS, 1-3, comprises a laptop computer 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 and therefore
`be in an “undocked” configuration.
`FIG. 1 illustrates a laptop computer 100 in accordance
`with a preferred embodimentofthe invention. Laptop com-
`puter 100 generally includes a processor or CPU 102
`coupled to a main memory array 104 and a variety of other
`peripheral computer system components through an inte-
`grated Host bridge logic device 106, The CPU 102 preter-
`ably couples to bridge logic 106 via a CPUbus 108, orthe
`bridge logic 106 may be integrated into the CPU 102. The
`CPU 102 may comprise,
`for example, a Pentium® II]
`microprocessor.
`It should be understood, however,
`that
`computer 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
`
`40
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
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`5
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`the laptop computer 100 of the preferred embodiment does
`not modify operation ofthe serial communication conduc-
`tors 126 of the USB protocol. Preferably, all communica-
`tions to establish whether laptop computer 100 is capable of
`receiving power from the docking station 200 take place
`over the power conductors or powerrails 138 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 ofthese twologic circuits is
`preferably through USB connector 136 of the laptop com-
`puter 100 and a mating USB connector 236 of the docking
`station 200.
`
`Under standard USB protocol, the laptop computer 100
`provides power to USB devices downstream ofthe laptop
`computer 100. Thus, in normal operation, the USB protocol
`voltage control unit 140 receives a five volt input signal 142
`whichit couples to the positive powerrail 144 ofthe power
`conductors 138. Downstream USB devices may draw cur-
`rent through the positive power rail 144. If a user ofthe
`laptop computer 100 plugs in, for example, a USB mouse
`into the USB connector 136, that mouse under USB protocol
`may draw power across the power conductors 138 for its
`operational use.
`Assume for purposes of explanationthat laptop computer
`100 has a charged battery and is in an operational state. In
`such a condition, the laptop computer 100 preferably pro-
`vides five volt power across the power conductors 138.
`Further assume that the user docks the laptop 100 with a
`docking station 200 of the preferred embodiment. In so
`doing, the usereither physically plugs ina USBcable to the
`connector 136 or slides the laptop computer 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 handshaking protocols to identify
`both the host or master device, which would be the laptop
`computer 100, and any downstream device, which in this
`exemplary case is the docking station 200. In the preferred
`embodiment of this invention,
`this handshaking protocol
`between the laptop computer 100 and the docking station
`200 reveals to software running inthe laptop computer 100
`that the docking station 200 is capable of providing power
`across the powerrails 138 of the USB interface. It will be
`understood that this handshaking protocol betweenthe lap-
`top computer 100 and the docking station 200 occurs over
`the serial communicationlines 126, and these lines are not
`shownin FIG. 2.
`
`Based on the handshaking between the two devices,
`operating system software loads a driver specifically used
`with the docking station 200. Though this driver may
`provide many functions, the function of concernis that the
`driver preferably turns off the laptop computer's ability to
`provide five volts to the powerrails 138. More specifically,
`the driver loaded by the operating system of the laptop
`computer 100 preferably commandsthe Super I/O controller
`130 to issue a five volt shut-off command signal 148,
`preferably through one ofits digital outputs. This five volt
`shut-off command couples to the USB protocol voltage
`control unit 140 of the docking logic 134, Upon receiving
`this five volt shut-off commandsignal 148, the USB protocol
`voltage control unit 140 preferably de-couples the five volt
`input line 142 from the positive powerrail 144. Thus, the
`
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`laptop computer 100 breaks with standard USBprotocol and
`the powerrails 138 are no longer capable of providing power
`to downstream devices.
`
`As far as docking logic 234 of the dockingstation 200 is
`concerned,the situation where laptop computer 100 turns off
`the five 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. Thus,
`the following description is
`equally applicable to both situations.
`It
`is possible that
`laptop computers that do not have the capability ofreceiving,
`power across the USB port may be docked with docking
`station 200. Therefore, docking station dock logic 234 must
`establish that the laptop computer to which it is docked is
`capable of receiving power. Preferably this is done by
`attempting to establish communications across the power
`rails 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 ofthe 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 3.1 volts, onto power
`rail 244. Positive power rail 244 couples to the powerrail
`144 onthe 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 powerrails. 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. If
`communication and control circuit 250 establishes positive
`communication with reactive signaling circuit 150,
`the
`docking station 200 has made a positive identification that
`the laptop to which it
`is docked is capable ofreceiving
`poweracross the USB connection.
`Morespecifically, 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 communication,the preferred embodiment of
`the reactive signaling circuit 150 comprises a Dallas Semi-
`conductor device part number DS2401, as shown in FIG,3.
`This DS2401 has the characteristic that
`it stores charge
`drawn from its signaling line, and then,
`in response to a
`specific pattern of high and low voltages on its signaling
`line, 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 neces-
`sary steps to initiate communication with the DS2401 device
`and receives any return communication issued thereby.
`Upon receiving the communication 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 whichit is
`docked is capable of receiving power across the USB
`connection. Dallas Semiconductor makes another device, a
`DS2480, which is specifically made to communicate with
`the DS2401. 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
`field programmed to execute certain steps or states and is
`therefore considered a field programmable state machine.
`The PALofthe preferred embodiment performs all steps
`necessary to communicate with the reactive signaling circuit
`150 to establish positive identification that the laptop to
`
`ZTE/SAMSUNG 1005-0008
`ZTE/SAMSUNG 1005-0008
`IPR2018-00110
`IPR2018-00110
`
`
`
`US 7,360,004 B2
`
`{
`
`wa
`
`20
`
`aSo
`
`7
`which the docking station 200 is docked is capable of
`receiving poweracross its USB connector.
`‘The communicationand 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 powerrail 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, upon receiving the ramp indica-
`tion from the communication and contro! logic 250, prefer-
`ably ramps the voltage to 18 volts over a period of 20-50
`milli-seconds. Thus, the voltage on positive powerrail 144
`with respect to the negative power rail 146 in the 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 maycharge its battery, if needed, with this
`same supply.
`It is possible that laptop computers that are not capable of
`receiving poweracross their USB interfaces may be coupled
`to the docking station 200. Indeed, it may be possible that a
`user quickly changes or swaps the USB connection from a
`laptop capable ofreceiving powerto a laptop not capable of
`receiving power. The docking station 200 preferably detects
`that a computeruser has de-coupled the USB port. Detection
`must be fast enoughto insure that the dock station docking
`logic 234 removes the 18 volt power supply before the user
`couplesit to another computer. This capability is preferably
`accomplished by a combination offunctionality 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 3:
`station 200 operate to detect that a user has unplugged or
`de-coupled 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 powerrail
`244, 144 above a predetermined value, preferably 6 volts,
`the reactive signaling circuit 150 preferably draws a small
`amount ofcurrent from the docking station 200, This small
`amount of current, a coupling current, is detected by current
`sense logic 220 ofthe 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. Whenthe dock station 200
`provides power for full operation of the laptop computer
`100, as many as 2.5 amps ofcurrent may low fromthe dock
`4
`station 200 to the laptop computer 100 across the USB
`connectors 136, 236. The coupling currentis part ofthat 2.5
`amp power flow. That is to say, when the laptop computer
`100 is operating from power supplied by the dock station
`200. the coupling current may be undistinguishable from the
`power drawnby the laptop.
`As long as current sense logic 220 detects at least an
`amount of current equal
`to the coupling current, the dock
`station docking logic 234is assured that the laptop computer
`100 is capable of receiving power across the USBport. If the
`laptop computer system user unplugs the USB 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. Communication and control
`logic 250
`instructs voltage ramp logic 210 to cease providing power to
`the powerrails 138 of the USB interface. Thus, the current
`sense logic 220, in combination with reactive signal circuit
`
`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 flowexceedsthe coupling
`current minimum. One of ordinary skill
`in the art, now
`understanding the functionality of the current sense logic
`220, could implement manycircuits to performthis function
`including the use ofprecision current sense resistors. Like-
`wise, current logic 156, as indicated in FIG. 3, preferably
`comprises | k@ resistor coupled across the powerrails.
`However,this 1 kQ resistance couples across the powerrails
`only as the voltage on those rails reaches and exceeds the
`threshold voltage of 6 volts. Belowthe threshold voltage,
`which includes the voltage that
`the laptop supplies in
`conformance with standard USB protocol, the 1 kQ resis-
`tance does not draw current from the positive powerrail.
`Because powering the laptop computer across the USB
`interface power rails requires voltages that may exceed
`breakdownvoltagesofthe signaling device 152, the reactive
`signaling circuit 150 preferably also comprises a sell-pro-
`tection logic 154 coupled across the positive and negative
`ho A
`5 USB powerrails. 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 breakdownvoltage of device 152.
`In operation, a user takes a laptop computer 100 that
`either does not have battery, or has a discharged battery, and
`docksit to docking station 200. Dock station docking logic
`234 places a small voltage across the power rails 138,
`preferably 3.1 volts. Communication and control logic 250
`attempts to communicate with the reactive signaling circuit
`150 serially over the positive USB powerrail 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 from 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 powerrails 144, 244 to 18 volts. As
`the voltage exceeds 6 volts, coupling current
`logic 156
`couples a resistance across the powerrails of approximately
`1 kQ, and self protection logic 154 electrically floats sig-
`nally device 152. Coupling resistance across the powerrails
`results in a current flow to the laptop computer 100 of
`approximately six milliamps. Current sense logic 220 senses
`this six milliamp 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 sufficient current through
`the USB connector 136, 236, and through the diode 158, or
`an equivalent circuit thereof, to operate the laptop computer.
`The term “operate” includes not only running the power
`supply, but also, if necessary, charging the system battery
`132.
`It is also possible that an operating laptop, providing five
`volts on the power rails 138 of the USB inter