US007049865B2
`
`a2) United States Patent
`US 7,049,865 B2
`(10) Patent No.:
`May23, 2006
`(45) Date of Patent:
`Parkeret al.
`
`
`(54) POWER-ON DETECT CIRCUIT FOR USE
`WITH MULTIPLE VOLTAGE DOMAINS
`
`(75)
`
`Inventors: Rachael J. Parker, Forest Grove, OR
`(US); Mark L. Neidengard, Hillsboro,
`OR (US); Patrick J. Ott, Hillsboro, OR
`
`(58) Field of Classification Search ................ 327/142,
`327/143, 198, 63, 65, 69, 71, 74, 75, 76,
`327/77, 80, 81, 82
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`(73) Assignee:
`
`.
`(*) Notice:
`
`Intel Corporation, Santa Clara, CA
`(US)
`.
`.
`.
`.
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 10/794,497
`(22)
`Filed:
`Mar. 5, 2004
`
`(65)
`
`Prior Publication Data
`US 2005/0195000 Al
`Sep. 8, 2005
`
`(51)
`
`Int. Cl.
`(2006.01)
`HO3L 7/00
`(62) U.S: Cl. san wmennenncnnnmeen 327/143
`
`244
`
`oN
`
`V1
`
`V2
`
`v1
`
`V2
`
`5,446,404 A *
`
`8/1995 Badyal et al... 327/143
`
`
`ont ‘ : 0soe Gioly sesneeneey 8
`;
`-
`TOUY
` sscmesvesvievesvese
`6,236,250 Bl
`§/2001 Salmon et al.
`6,281,724 BL*
`8/2001 Ellis wee 327/143
`ao
`x
`.
`6,448,824 Bl
`9/2002 Rodriguez et al... 327/74
`* cited by examiner
`
`amde Examiner”JelireyZweizig
`ttorney,
`Wyatt, P.C.
`
`Agent, or
`
`Firm—schwabe, Wilhamson
`
`ne. Will
`
`&
`
`ABSTRACT
`(57)
`Embodiments of the present invention include a circuit, a
`yi
`P
`ry
`method, and a system for power-on detect circuitry
`for use
`with multiple voltage domains.
`
`33 Claims, 5 Drawing Sheets
`
`100
`
`( v1v2good = V2 good in V1 domain )
`
`yt
`
`tL
`
`
`
`248 >) 252 >) 248 ) 252 >)
`
`
`256 — I. WY
`|<
`
`
`
`
`
`
`
`KK
`
`4
`|
`
`We
`
`LJ
`2 gee
`
`vigood
`
`viv2good
`
`v2good
`
`v2v1good
`
`APPLE 1014
`
`APPLE 1014
`
`1
`
`

`

`U.S. Patent
`
`May23, 2006
`
`Sheet 1 of 5
`
`US 7,049,865 B2
`
`
`
`nn ST
`
`V2 GoodnessDetection|yyyocoog
`
`for V1 Domain
`
`Voltage Divider V2 V2 GoodnessDetection|yocood
`
`Domain
`for V2 Domain
`
`SS
`
`(A)
`
`104a
`
`V1 Goodness Detection
`For V1 Domain
`
`
`104b
`
`
`V1 Goodness Detection
`
`for V2 Domain
`J
`
`106b
`
`Fig. 1a
`
`
`
`102a or 102b
`
`i=1or2
`
`V1Good
`
`VANIGO0d »
`
`
`
`102a ~)
`
`
`
`Voltage Divider V1
`Domain
`
`102b
`
`(A)
`
`114a
`
`2
`
`

`

`U.S. Patent
`
`May23, 2006
`
`Sheet 2 of 5
`
`US 7,049,865 B2
`
`ViL
`
`ViH
`
`VL
`
`VH
`
`V;
`
`104a or 104b
`i=1or2
`
`122
`
`124
`
`V,Good
`
`106a or 106b
`
`i=1or2
`j=2or1
`
`222
`
`224
`
`V,Good
`
`226
`
`ViV|Good
`
`FIG. 1c
`
`FIG.
`
`3
`
`

`

`U.S. Patent
`
`May23, 2006
`
`Sheet 3 of 5
`
`US 7,049,865 B2
`
`244 ~\
`
`V1
`
`V2
`
`v1
`
`V2
`
`400
`
`Oo
`
`( v1v2good = V2 good in V1 domain )
`
`=
`
`1
`
`V2H
`
`[Cs
`H Po
`
`
`
`252 Y
`248
`248 > 252
`256 |
`
`
`
`; V2L =FTTT|
`|
`eeeee Vi 7|
`wy
`oiley
`
` (a)
`
`KE
`
`(1H>VIL
`
`fT
`
`
`
`N ono
`
`vigood
`
`vi1v2good
`
`v2good
`
` v2vigood
`
`FIG. 2
`
`v1igood
`
`v2good
`
`viv2good
`
`v2v1good
`
`(b)
`
`FIG. 3
`
`4
`
`

`

`U.S. Patent
`
`May23, 2006
`
`Sheet 4 of 5
`
`US 7,049,865 B2
`
`Vec1
`Vec2
`
`in2
`/
`
`204
`
`operational
`circuit
`(V2 domain)
`
`
`
`
`
`302
`
`208
`
`306
`
`v2v1good »
`
`
`
`
`operational
`circuit
`(Vidomain)
`
`304
`
`FIG. 4
`
`Vece1 down: OK
`
`Vec2 down: OK
`
`Supplies
`Nominal
`
`5
`
`

`

`U.S. Patent
`
`May23, 2006
`
`Sheet 5 of 5
`
`US 7,049,865 B2
`
`280
`
`
`
`if282
`
`~
`
`CE oe -
`
`Fig. 6
`
`6
`
`

`

`US 7,049,865 B2
`
`1
`POWER-ON DETECT CIRCUIT FOR USE
`WITH MULTIPLE VOLTAGE DOMAINS
`
`FIELD OF THE INVENTION
`
`Disclosed embodiments of the present invention relate to
`the field of integrated circuits (IC), and moreparticularly to
`providing signal integrity across multiple voltage domains
`of the IC.
`
`BACKGROUND OF THE INVENTION
`
`Manytypes of modern electronic devices may incorporate
`multiple voltage domains. For example, a modern micro-
`processor chip may include core logic that operates in one
`voltage domain while interacting with input/output (I/O)
`circuitry operating in another.
`During the initial power up sequencing the different
`voltage domains may reach a nominal power level at dif-
`ferent times. If logic in a first voltage domain is required to
`function only when the voltages of both domainsare at their
`nominal levels, the logic in the first voltage domain may
`need an indication that the signal(s) outputted by the second
`domain logic is(are) valid. Prior art methods have attempted
`to accomplish this by sending a signal througha level shifter
`from the second voltage domainto the first voltage domain.
`Unfortunately, the level shifter output may be an undefined
`signal if the voltage in the second voltage domain has not
`reached the nominal voltage level. The propagation of this
`undefined signal into the first voltage domain could falsely
`indicate that the signal(s) outputted from the second voltage
`domain is(are) valid.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Embodiments of the invention are illustrated by way of
`example and not by way oflimitation in the figures of the
`accompanying drawings, in which the like references indi-
`cate similar elements and in which:
`
`FIGS. 1a—1d illustrate a power-on detect circuit for use to
`assure proper voltage levels of multiple voltage supplies for
`multiple voltage domains, in accordance with an embodi-
`ment of the present invention;
`FIG.2 illustrates an example of a power-on detect circuit
`described in FIGS.
`la—1d, in accordance with an embodi-
`ment of the present invention;
`FIGS. 3a—36 illustrate various voltage levels and voltage
`goodness signals as a function of time, for an example
`sequential ramp up of two voltage supplies;
`FIG. 4 illustrates an integrated circuit with multiple
`voltage supplies, multiple operational circuits operating in
`multiple voltage domains, a level shifter circuit, and a
`power-on detect circuit, in accordance with an embodiment
`of the present invention;
`FIG. 5 represents a truth table correspondingto the level
`shifter circuit diagram in FIG. 4, in accordance with one
`embodiment of the present invention; and
`FIG.6 illustrates a system using a power-on detectcircuit,
`in accordance with one embodiment of the present inven-
`tion.
`
`DETAILED DESCRIPTION OF EMBODIMENTS
`OF THE INVENTION
`
`In the following detailed description, reference is made to
`the accompanying drawingsthat form a part hereof, wherein
`like numerals designate like parts throughout, and in which
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`is shown by wayofillustration of specific embodiments in
`which the invention maybepracticed.It is to be understood
`that other embodiments may be utilized and structural or
`logical changes may be made without departing from the
`scope of the embodiments of the present invention. There-
`fore, the following detailed description is not to be taken in
`a limiting sense and the scope of the embodiments of the
`present invention is defined by the appended claims and
`their equivalents.
`FIGS. 1a—1d illustrate a power-on detect (POD) circuit
`100 that may be used to assure voltage levels of multiple
`voltages for multiple voltage domains, in accordance with
`one embodiment of this invention. In particular, for this
`embodiment, POD circuit 100 may be used to assure the
`voltage levels of first (V1) and second (V2) voltage supplies
`for two voltage domains.
`For the embodiment, as illustrated in FIG. 1a, POD circuit
`100 includes voltage dividers 102a—102b, V1 goodness
`detectors 104@ and 1064 and V2 goodness detectors 106a
`and 1044 coupled to each other as shown. The goodness
`detectors 104a, 1045, 106a, and 106 mayalso be referred
`to as analyzers. Voltage divider 102a, V1 goodness detector
`104a and V2 goodness detector 106a serve the V1 domain,
`while voltage divider 1026, V2 goodness detector 1046 and
`V1 goodness detector 1065 serve the V2 domain. Accord-
`ingly, V1 or V2 domain may also be referred to as the
`“client” domain of the circuit elements that serve them.
`Each of the voltage dividers 102a/1025 is employed to
`generate two proxy signals V1L and V1H (or V2L and V2H)
`to reflect the voltage level of voltage V1/V2 in different
`manners. For the embodiment V1L/V2L rises rapidly as
`V1/V2rises and then plateaus out, whereas, V1H/V2Hrises
`more slowly initially as V1/V2 rises, but then very rapidly
`thereafter (see also FIG. 3). Each of proxy signal pairs, VIL
`and V1H or V2L and V2H,is designed, such that the two
`proxy signals VIL/V2L and V1H/V2H equal each other
`whenthe voltage of interest V1/V2 reachesa threshold level
`of “goodness.” The threshold level that defines goodness is
`application dependent, and may vary from application to
`application.
`Each of V1/V2 voltage goodness detectors 1044/1046 is
`employed to indicate whether the voltage level of the
`voltage of its client domain V1/V2 has reached the corre-
`sponding desired threshold level. In other words, V1 voltage
`goodness detector 104a is employed to indicate for the V1
`voltage domain, whetherthe voltage level of the V1 voltage
`is good, and V2 voltage goodness detector 1045 is employed
`to indicate for the V2 voltage domain, whether the voltage
`level of the V2 voltage is good. Accordingly, V1/V2 voltage
`goodness detector 104a/104b may also be referred to as
`local voltage goodness detector. As illustrated, each of
`V1/V2 voltage goodness detectors 104a and 104generates
`its indicator based on the corresponding proxy signals, VIL
`and V1H or V2L and V2H.
`
`Each of V2/V1 voltage goodness detectors 106a and
`1064, on the other hand, is employed to indicate whether the
`voltage level of the voltage of the other voltage domain
`V1/V2 has reached the corresponding desired threshold
`level. In other words, V2 voltage goodness detector 106a is
`employedto indicate for the V1 voltage domain, whether the
`voltage level of the V2 voltage is good, and V1 voltage
`goodness detector 1065 is employed to indicate for the V2
`voltage domain, whetherthe voltage level of the V1 voltage
`is good. Accordingly, V2/V1 voltage goodness detectors
`106a and 1065 mayalso be referred to as neighbor voltage
`goodness detector. As illustrated, for the embodiment, each
`of V2/V1 voltage goodness detectors 106a and 1066 gen-
`
`7
`
`

`

`US 7,049,865 B2
`
`3
`erates its indicator based on two complementary proxy
`signals of the two domains (e.g. V2H and V1L for indicating
`voltage level of V2 for the V1 domain, and V1H and V2L
`for indicating voltage level of V1 for the V2 domain), and
`the voltage goodness signal of the client domain V1good/
`V2good.
`FIG. 18 illustrates a voltage divider in further detail, in
`accordance with one embodiment. Asillustrated, for the
`embodiment, each of voltage dividers 102a and 1025
`includes two branches. The first branch of the voltage
`divider 102a/1025 mayinclude a linear device 112a coupled
`to Vi (where Vi may be V1 or V2). In one embodiment, the
`linear device may be any type of resistive device (e.g., a
`resistor). The linear device 112a may load a saturating
`device 114a, which may be coupled to a ground. Examples
`of the saturating device may include, but are not limited to,
`a diode and a diode-connectedtransistor. It should be noted
`
`that although in this embodiment groundis used as the base
`voltage,
`it
`is not essential and may not be so in other
`embodiments. As illustrated, ViL (e.g., VIL or V2L)is taken
`at node 118 which is disposed in between the two devices
`112a and 114a. The second branch of the voltage divider
`may besimilar to the first, except that the saturating device
`1145 and the linear device 1125 may have an opposite
`orientation. ViH (e.g. V1H or V2H) is taken at node 130
`disposed in between devices 1144 and 1124.
`With the two branches of the voltage dividers having the
`linear and the saturation devices in opposite positions, as the
`voltage supply V1/V2 is ramped from zero to its nominal
`level, the intermediate voltages V1H/V2H and V1L/V2L
`characterize V1/V2 differently as earlier described. Further,
`for an embodiment using grounded voltage dividers,
`the
`linear and the saturation devices are designed such that
`V1H/V2H and V1L/V2L may be identical at exactly one
`non-ground voltage, when the voltage supply V1/V2 reaches
`the threshold level.
`
`FIG. 1c illustrates the local voltage goodness detector
`104a/1046 in further detail, in accordance with one embodi-
`ment. Substantively, each of the local voltage goodness
`detectors 104a and 1046is a differential logic arrangement
`for detecting a condition indicating that ViH is approxi-
`mately greater than ViL (e.g., V1H and V1L, or V2H and
`V2L). In one embodiment, the differential logical arrange-
`ment could include a voltage comparator 122 and an inverter
`124, coupled to each other and to terminals manifesting
`voltages ViL/ViH. The terminals may correspond to nodes
`118 and 130 of FIG. 15. The terminal manifesting voltage
`V1L/V2L, may be coupledto, e.g., the (+) input terminal of
`the voltage comparator 122, whereas terminal 130, mani-
`festing voltage V1H/V2H maybe coupledto, e.g., the (-)
`input terminal of the voltage comparator 122. The voltage
`comparator 122 may be an operational amplifier. Thus,
`before the condition of V1H/V2H being greater than V1L/
`V2L,the output of comparator 122 is positive, but after the
`condition of V1H/V2H being greater than V1L/V2L, the
`output of comparator 122 is negative. Thus inverter 124 will
`output a positive signal indicating V1/V2 is good in the
`V1/V2 domain (also referred to as the Vigood or V2good
`signal).
`In an alternate embodiment,
`the inputs on the
`comparator 122 may be switched and the inverter 124
`removed without changing the function of the goodness
`detector.
`FIG.1d illustrates the neighbor voltage goodness detector
`106a/1066 in further detail, in accordance with one embodi-
`ment. Similar to local voltage goodness detector 1044/1046,
`neighbor voltage goodness detector 106a/1065, substan-
`tively,
`is also a differential
`logic arrangement.
`In one
`
`20
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`30
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`35
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`40
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`45
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`4
`embodiment, the differential logic arrangement may include
`comparator 222 and inverter 224 coupled to each other as
`shown. Comparator 222 mayalso be a differential amplifier.
`The (+) and (-) terminals of comparator 222 are coupled to
`two terminals manifesting two complementary proxy signals
`of two voltage domains (e.g., VIL and V2H or V2L and
`V1H) instead. Furthermore, a logic gate such as an AND
`gate 226 maybe usedto gate the output of the inverter 224
`with the local voltage good indication (V1good or V2good)
`for the client domain. Depending on the power-up sequence
`of a particular embodiment,
`the AND gate may not be
`needed to gate the control signal with the local voltage good
`signal.
`In summary, FIG. 2 illustrates one example of a power-on
`detect circuit 100 including the elements discussed with
`reference to FIGS. la—1d. This power-on detect circuit 100
`may include a pair of voltage dividers 244, a pair of local
`voltage goodness detectors 248, and a pair of neighbor
`voltage goodness detectors 252 including a pair of logic
`gates 256. This power-on detect circuit 100 may be capable
`of outputting four signals including Vigood, V2good,
`V1V2good, and V2V1 good, locally assuring the V1 and V2
`voltage domains that V1 and V2 havereachedtheir respec-
`tive desired threshold levels, as well as neighborly assuring
`the V2 and V1 voltage domains of the same.
`In one
`application, selected ones of these signals may then be used
`to qualify all signals transmitted across the voltage domains,
`to be discussed further with reference to FIG. 4.
`
`As is commonin the art, the power-on detect circuit 100
`may also be described as a power detect, power-on reset,
`powerenable, and/or voltage detect circuit. Embodiments of
`the present invention relate to all of the above as they are
`generally understood in the field.
`Although the above embodimentis illustrated depicting
`two power-supply domains, embodiments of this invention
`are not limited in use to only two domains.
`As illustrated in FIG. 2,
`the power-on detect circuit
`includes semiconductor devices such as saturation and linear
`
`devices. Although these semiconductor devices are illus-
`trated schematically as single transistors/resistors,
`this is
`doneto facilitate the discussion ofthe circuit characteristics.
`When implemented or manufactured these may comprise
`multiple devices, depending, for example, upon the appli-
`cation or the particular integrated circuit chip. For example,
`as it is well known, some form of digital and/or analog
`circuit compensation may be includedto address the poten-
`tial variation in circuit parameters knownto occur as a result
`of the fabrication process. Therefore, the simplified circuit
`diagram in FIG. 2 is provided primarily for purposes of
`illustration and, as one of ordinary skill
`in the art will
`appreciate, when actually implementing a particular power-
`on detect circuit, more complex circuitry to provide a
`desired operation, such as operations described herein, may
`be employed. For example, a plurality of transistors having
`sizes that are binary weighted may be coupled so that each
`of the transistors may be switched on and off independently
`to “tune” the overall collection of binary weighted transis-
`tors to achieve a particular impedanceoreffective transistor
`width.
`
`Also, certain logical functions schematically represented
`by a logic component should not be limited to that specific
`component. For example, the AND gate 226 represents the
`logical function of producing a certain output once two
`conditions have been satisfied. However, there are logical
`components other than an AND gate, which may be com-
`bined to produce the same function (e.g., a NAND gate
`followed by an inverter).
`
`8
`
`

`

`US 7,049,865 B2
`
`5
`Devices that operate with multiple voltage domains may
`require a power-up sequence for properinitialization. In one
`embodiment, for example, an input/output domain may be
`sequenced to power-up before the core logic domain. How-
`ever, this is not always the case, and other embodiments may
`use alternative power-up sequencing procedures. Embodi-
`ments of the present invention may be readily adapted to any
`number of power-up supply sequences with multiple voltage
`domains.
`
`FIGS. 3a—36 further explain the timing of the signals
`output from the power-on detect circuit 100 in correlation to
`a particular power-up sequence,
`in accordance with one
`example application. FIG. 3a may depict a set of waveforms
`where the two voltages V1 and V2 are ramped sequentially.
`The different characterizations of V1 and V2 by the proxy
`signals VIL, V1H, V2L and V2H are as shown. FIG. 3b
`depicts the binary signals that may be emitted from the
`differential logic arrangements to denote the goodness ofthe
`local or neighbor voltage. The V1lgood signal may be turned
`on after V1H is greater than V1L. Similarly, the V2good
`signal may be turned on after V2H is greater than V2L. Both
`of these signals indicate that,
`in their respective voltage
`domains, the voltage has reached the desired nominallevel.
`In this embodiment, the V1V2good signal may not be
`turned on until V2H becomesgreater than V1L. This may
`give an indication in the first voltage domain that
`the
`neighbor voltage V2 has reached the desired nominal level.
`The V1V2good signal may also need the Vigoodsignal;
`however, because of the power-up sequence of this embodi-
`ment, this signal may have already been generated earlier
`and therefore V2H>V1L is the final condition for the
`
`V1V2good signal. The V2V1good signal may work in the
`opposite way. That is, the V1H signal being greater than the
`V2L happens early in the sequence; however, the V2good
`signal has not been issued yet. Therefore, the V2good signal
`is the final event prior to the V2V1goodsignal.
`FIG. 4 depicts an integrated circuit incorporated with an
`implementation of the power-on detect circuit 100, in accor-
`dance with one embodiment. Asillustrated, integrated cir-
`cuit 300 includes an operational circuit 302 designed to
`operate with voltage V2, defining the V2 voltage domain,
`and another operational circuit 304 designed to operate with
`voltage V1, defining the V1 voltage domain. For the
`embodiment, in addition to operational circuits 302 and 304
`and POD 100, integrated circuit 300 also includes level shift
`arrangement 306 to facilitate transmission of signals from
`the V2 voltage domain to the V1 voltage domain.
`In particular, POD 100 is used to qualify any signal
`transitioning between the two voltage domains. For the
`embodiment,
`level shift arrangement 306 includes level
`shifter 208 and AND gate 212 coupled to each other and the
`other elements as shown.In this embodiment, a logic signal,
`in2 204, may be input from the V2 voltage domain. In2 204
`may enter a level shifter 208 to be shifted from the V2
`voltage domain into the V1 voltage domain. The output may
`be gated after the level shifter 208 by a control signal
`indicating that
`the V2 voltage has reached the desired
`nominal level, e.g. VI1V2good, using AND gate 212. When
`the AND gate 212 receives the control signal it may provide
`a level shifted logic signal, out1 210, to operational circuit
`304 of the V1 voltage domain. The arrangement may help to
`reduce the propagation of an X (unknown signal) by the
`level shifter 208 for the case where the destination voltage
`supply (e.g., V1) is valid but the driving supply (e.g., V2) is
`not. In various embodiments,
`integrated circuit 300 is a
`general purpose microprocessor, operational circuit 304 may
`
`6
`be the core logic of the microprocessor, while operational
`circuit 302 may be the I/O section of the microprocessor.
`FIG. 5 illustrates a truth table depicting the state of the
`logical outputs (outl) of FIG. 4 under various conditions, in
`accordance with one embodiment. If the voltage in the V1
`voltage domain is indeed V1 and the voltage in the V2
`voltage domain is also indeed V2, then by virtue of the
`power-on detect circuit outputting a V1V2goodsignal, out-
`put outl will be valid accordingly. That is, under these
`conditions, if in2 is V2, then out1 will be V1. Conversely,if
`in2 is 0, then outl will also be 0. However,if either voltage
`(V1 or V2) is 0, then by virtue of the fact that VIV2good
`will also be 0, regardless of what in2 is, outl will be 0.
`Therefore, the occurrence of an undefined X propagated as
`outl may be reduced.
`there is illustrated one of many
`Referring to FIG. 6,
`possible systems in which embodiments of the present
`invention may be used. Asillustrated, system 270 includes
`integrated circuit 280, and a number of other components
`and/or input/output devices. The integrated circuit 280 may
`be coupled to the other components and the input/output
`devices by means of a bus 282. A power-on detect circuit,
`similar to the earlier discussed embodiments, may be incor-
`porated with integrated circuit 280 to validate signals trans-
`ferring between different domains of the integrated circuit
`280.
`
`The other components may include memory 284, a graph-
`ics processor 286, a mass storage device 288, and the
`input/output devices may include, e.g., a network interface
`290. Examples of the memory 284 include but are not
`limited to static random access memory (SRAM) and
`dynamic random access memory (DRAM). Examples of the
`massstorage device 288 include butare not limited to a hard
`disk drive, a compact disk drive (CD), a digital versatile disk
`drive (DVD), and so forth. Examples of other input/output
`modules 290 include but are not limited to a keyboard,
`cursor control devices, a display, a network interface, and so
`forth. Examples of the bus 282 include but are not limited to
`a peripheral control interface (PCI) bus, and Industry Stan-
`dard Architecture (ISA) bus, and so forth.
`In various
`embodiments, the system 270 may be a wireless mobile
`phone, a personaldigital assistant, a pocket PC, a tablet PC,
`a notebook PC, a desktop computer, a set-top box, an
`audio/video controller, a DVD player, and a server.
`Although specitic embodiments have been illustrated and
`described herein for purposes of description of the preferred
`embodiment, it will be appreciated by those of ordinary skill
`in the art that a wide variety of alternate and/or equivalent
`implementations calculated to achieve the same purposes
`may be substituted for the specific embodiment shown and
`described without departing from the scope of the present
`invention. Those with skill in the art will readily appreciate
`that the present invention may be implemented in a very
`wide variety of embodiments. This application is intended to
`cover any adaptations or variations of the embodiments
`discussed herein. Therefore, it is manifestly intended that
`this invention be limited only by the claims and the equiva-
`lents thereof.
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`Whatis claimedis:
`
`1. A circuit comprising:
`a first terminal adapted to manifest a first proxy signal that
`reflects a first level of a first voltage source ofa first
`voltage domain;
`a second terminal adapted to manifest a second proxy
`signal at a second level of a second voltage source of
`a second voltage domain; and
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`US 7,049,865 B2
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`the first and third proxy signals are equal at only one,
`a first analyzer, coupledto the first and second terminals,
`non-ground, voltage; and
`adapted to receive the first and second proxy signals
`and to generate,
`in response, a first control signal
`the second and fourth proxy signals are equal at only one,
`indicative for said first voltage domain, whether the
`non-ground, voltage.
`second voltage source has reached a first threshold
`12. The circuit of claim 10, wherein the first voltage
`level in said second voltage domain.
`divider comprises:
`2. The circuit of claim 1 wherein a goodness of informa-
`a first branch including a first linear device andafirst
`tion sent from the second domain to the first domain is
`saturation device coupled in series with the first linear
`conveyed to the first domain based at least in part on the
`device, with the first proxy signal being taken atafirst
`node located in betweenthe first linear device and the
`control signal.
`3. The circuit of claim 1, wherein the first proxy signalis
`at the first level of the first voltage.
`4. The circuit of claim 1, wherein the first analyzer is
`equipped to detect for a condition indicating that the second
`proxy signal is approximately greater than the first proxy
`signal, and to generate the first control signal upon detection
`of the condition.
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`14. Thecircuit of claim 13, wherein at least a selected one
`of the first and secondlinear devices of the first and second
`
`first saturation device, the first node being coupled to
`the first terminal; and
`a second branch including a second saturation device and
`a secondlinear device coupled in series with the second
`saturation device, with the third proxy signal being
`taken at a second node located in between the second
`saturation device and the second linear device,
`the
`5. The circuit of claim 1, wherein the first analyzer
`second node being coupled to the third terminal.
`comprises:
`13. The circuit of claim 12, wherein the second voltage
`a comparator adaptedto receivethe first and second proxy
`divider comprises:
`signals and to generate, in response, a difference signal;
`a first branch includinga first saturation device andafirst
`and
`linear device coupled in series with the first saturation
`device, with the second proxy signal being taken at a
`first node located in betweenthe first saturation device
`andthe first linear device, said first node of the second
`voltage divider coupled to the second terminal; and
`a second branch including a second linear device and a
`second saturation device coupled in series with the
`second linear device, with the fourth proxy signal being
`taken at a second node located in between the second
`linear device and the second saturation device.
`
`an inverter, coupled to the comparator, adapted to receive
`the difference signal and to generate, in response, the
`first control signal.
`6. The circuit of claim 1, further comprising:
`a third terminal adapted to manifest a third proxy signal
`that reflects a second levelof the first voltage source of
`the first voltage domain;
`a second analyzer, coupled to the first and third terminals,
`adapted to receive the first and third proxy signal and
`to generate, in response, a second control signal indica-
`tive of whether the first voltage source has reached a
`second threshold level in said first voltage domain; and
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`voltage dividers comprise a resistor.
`the first analyzer includingafirst logic gale, coupled to
`15. Thecircuit of claim 13, wherein at least a selected one
`the second analyzer, adapted to receive the second
`of the first and second saturating devices of the first and
`control signal and to generate, in response, the first
`second voltage dividers comprise a diode connected tran-
`control signal.
`sistor.
`7. The circuit of claim 6, wherein the second analyzeris
`equipped to detect for a condition indicating that the third
`proxy signal is approximately greater than the first proxy
`signal and to generate the second control signal upon
`detection of the condition.
`
`16. The circuit of claim 13, wherein the circuit further
`comprises:
`a fourth terminal coupled to the second nodeof the second
`voltage divider, adapted to manifest the fourth proxy
`signal, whichreflects a first level of the second voltage
`source of the second voltage domain; and
`a third analyzer, coupled to the third and fourth terminals,
`adapted to receive the third and a fourth proxy signal
`and to generate,
`in response, a third control signal
`indicative for said second voltage domain, whether the
`an inverter, coupled to the comparator, adapted to receive
`first voltage source has reached the second threshold
`the difference signal and to generate, in response, the
`level in said first voltage domain.
`second control signal.
`17. The circuit of claim 16, further comprising:
`9. The circuit of claim 8, wherein the first logic gate
`a fourth analyzer, coupled to the second and fourth
`comprises:
`terminals, adapted to receive the second and fourth
`an AND gate, coupled to the inverter, adapted to receive
`proxy signals and to generate, in response, a fourth
`the first and second control signals and to generate, in
`control signal indicative of whether the second voltage
`response, the first control signal.
`source has reached the first threshold level
`in said
`10. The circuit of claim 6, further comprising:
`second voltage domain; and
`a first voltage divider adapted to be applied with thefirst
`the third analyzer including a second logic gate, coupled
`voltage source and to generate, in response, the first and
`to the fourth analyzer, adapted to receive the fourth
`third proxy signals; and
`control signal and to generate, in response, the third
`a second voltage divider adapted to be applied with the
`control signal.
`second voltage source and to generate, in response, the
`18. An integrated circuit comprising:
`second proxy signal and a fourth proxy signal.
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`11. The circuit of claim 10, wherein
`a first operational circuit, coupledtoafirst voltage source,
`the first and second voltage dividers are coupled to a
`adapted to receive a first voltage from the first voltage
`ground;
`source, defining a first voltage domain;
`
`8. The circuit of claim 6, wherein the second analyzer
`comprises:
`a comparator adapted to receive the first and third proxy
`signals and to generate, in response, a difference signal;
`and
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`a second operational circuit, coupled to a second voltage
`source, adapted to receive a second voltage from the
`device of the first branch of the first voltage divider;
`second voltage source, defining a second voltage
`domain; and
`applying the second voltage toafirst branch of a second
`a power-on detect circuit, coupled to the first and second
`voltage divider including a saturation device coupled in
`voltage sources, adapted to outputa first control signal
`series to a first linear device; and
`for the first voltage domain indicating whether the
`measuring the secondlevel of the second voltage at a node
`second voltage has reacheda first threshold level in the
`between the first saturation device and the first linear
`second voltage domain.
`19. The integrated circuit of claim 18, wherein the power-
`on detect circuit is further adapted to output a second control
`signal indicating for the first voltage domain whether the
`first voltage has reached a secondthreshold level.
`20. The integrated circuit of claim 18, wherein the power-
`on detect circuit is further adapted to output a second control
`signal indicating for the second voltage domain whether the
`first voltage has reached a second threshold level in the first
`voltage domain.
`21. The integrated circuit of claim 18, wherein the power-
`on detect circuit is further adapted to output a third and a
`fourth control signal
`indicating for the first and second
`voltage domains whether the first and the second voltages
`have reached the second andfirst threshold levels in the first
`
`device ofthe first branch of the second voltage divider.
`27. The method of claim 26, further comprising:
`qualifying the first logic signal with a second control
`signal indicating that the first voltage has reached a
`second threshold level in the first voltage domain; and
`generating the second control signal at some point w