United States Patent
`US 7,170,308 Bl
`(10) Patent No.:
`(12)
`Rahim et al.
`(45) Date of Patent:
`Jan. 30, 2007
`
`
`US007170308B1
`
`(54) ON-CHIP VOLTAGE REGULATOR USING
`FEEDBACK ON PROCESS/PRODUCT
`PARAMETERS
`
`15
`
`(75)
`
`.
`
`7
`
`sy:
`
`Inventors: Tuite:MeastallGaoe
`
`.
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`1/1999 Bryson voces 323/268
`5,864,225 A *
`...
`6,140,831 A * 10/2000 Loughmiller
`
`7/2002 Hiraki et al. ww. 323/268
`6,424,128 BL*
`6,541,948 BL*
`4/2003 Wong ou... eeeeeeeeeeeee 323/284
`6,683,767 B2*
`1/2004 Ito et al. oe. 361/56
`
`6/2004 Giacomottoet al.
`
`....... 323/269
`
`6,744,242 BL*
`
`John Costello, Los Altos, CA (US)
`
`:
`ee
`cited by examiner
`
`(73) Assignee: Altera Corporation, San Jose, CA
`Primary Examiner—Vinh Nguyen
`(US)
`Assistant Examiner—Emily Y Chan
`Subject to any disclaimer, the term ofthis ee, Agent, op Fne—Morgan, Lewis & Backius
`
`(*) Notice:
`
`patent is extended or adjusted under 35
`US.C. 154(b) by 0 days.
`
`(57)
`
`ABSTRACT
`
`The present invention optimizes the performance of inte-
`(21) Appl. No.: 10/628,711
`grated circuits by adjusting the circuit operating voltage
`“yg,
`using feedback on process/product parameters. To determine
`(22)
`Filed:
`dul: 28; 2005
`a desired value for the operating voltage of an integrated
`(51)
`Int. Cl
`circuit, a preferred embodiment provides for on-wafer prob-
`(2006.01)
`GolR 31/00
`ing of one or morereference circuit structures to measure at
`(2006.01)
`GOIR 31/28
`least one electrical or operational parameter of the one or
`(2006.01)
`GOSF 1/00
`more reference circuit structures; determining an adjusted
`a
`:
`:
`(02) RSH NED researc eenissanae value for the operating voltage based on the measured
`,
`,
`,
`,
`>
`;
`parameter; and establishing the adjusted value as the desired
`(58) Field of Classification Search ay a730-765;
`value for the operating voltage. The reference circuit struc-
`Lo.
`323/266, 268, 285; 702/64: 714/733
`tures may comprise process control monitor structures or
`See application file for complete search history.
`structures in other integrated circuits fabricated in the same
`References Cited
`production run. In an alternative embodiment, the one or
`more parameters are directly measured from the integrated
`U.S. PATENT DOCUMENTS
`circuit whose operating voltage is being adjusted.
`
`(56)
`
`5,319,302 A *
`5,440,520 A *
`
`........ 323/273
`6/1994 Koshikawaet al.
`8/1995 Schutz et al... 365/226
`
`5 Claims, 2 Drawing Sheets
`
`10
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`14
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`INTEL 1007
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`INTEL 1007
`
`

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`U.S. Patent
`
`Jan. 30, 2007
`
`Sheet 1 of 2
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`US 7,170,308 B1
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`$1
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`Measure Parameter(s)
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`Met Ne
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`$2
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`Operating Voltage
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`Set Voltage Regulator
`to Deliver Adjusted
`Operating Voltage
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`$3
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`FIG. 2
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`

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`U.S. Patent
`
`Jan. 30, 2007
`
`Sheet 2 of 2
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`US 7,170,308 B1
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`
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`FIG. 3
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`

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`US 7,170,308 Bl
`
`1
`ON-CHIP VOLTAGE REGULATOR USING
`FEEDBACK ON PROCESS/PRODUCT
`PARAMETERS
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates generally to integrated cir-
`cuits and in particular to providing integrated circuits with
`optimized operating voltages.
`Although the manufacture of integrated circuits is care-
`fully controlled, inherent variations in the fabrication pro-
`cess cannot be avoided. These process-related variations
`translate into variations of functional and electrical param-
`eters of the manufactured devices and affect the device
`
`performance. One example of a parameter that may be
`subject to variations during the manufacturing process is
`temperature. Of course, there are numerous other process
`parameters that may vary, as well. The resulting device
`parametric variations occur from lot to lot and from wafer to
`water, but also within wafers and even within dice. They can
`cause variations in timing performance and operating mar-
`gin of the fabricated integrated circuits.
`Device parametric variations due to process variations can
`be considerable in magnitude and therefore havea critical
`impact on the yield of the fabrication process. Because of
`this, circuit designers have to accommodate these variations
`when designing the circuit. Specifically, they have to design
`the circuit so as to meetthe specification not only at optimal
`fabrication conditions but at process corners. However,
`performance requirements are difficult
`to achieve at the
`process corners. The designer thus has to weigh the goals of
`high performance and high yield, forcing him to make a
`trade-off between the two goals.
`
`SUMMARY OF THE INVENTION
`
`The present invention uses the adjustmentof the operating
`voltage of integrated circuits to optimize circuit performance
`and achieve higher yield per wafer. The adjustment is made
`based on one or more measured product parameters affected
`by process variations.
`the present invention provides a
`In one embodiment,
`method of determining a desired value for an operating
`voltage of an integrated circuit. The method comprises the
`steps of: on-wafer probing one or more reference circuit
`structures to measure at least one parameter of the one or
`more reference circuit structures; determining an adjusted
`value for the operating voltage based on the measured
`parameter; and establishing the adjusted value as the desired
`value for the operating voltage of the integrated circuit. In
`this embodiment, the reference circuit structures are struc-
`tures distinct from the integrated circuit whose operating
`voltage is being adjusted but fabricated in the same produc-
`tion run. Process control monitor structures or other inte-
`
`grated circuits fabricated on the same wafer or in the same
`lot as the integrated circuit whose operating voltage is being
`adjusted maybe suitably usedas reference circuit structures.
`In another embodiment, method comprises the steps of:
`measuring at least one parameter of one or more circuit
`structures of an integrated circuit; determining an adjusted
`value for the operating voltage based on the measured
`parameter; and establishing the adjusted value as the desired
`value for the operating voltage of that integrated circuit.
`The parameter to be measured is preferably an electrical
`or functional parameter of the integrated circuit or the
`probed referencecircuit structure, e.g., a leakage (stand-by)
`current or a circuit operating speed. Of course, more than
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`one parameter may be measured and used for adjusting the
`operating voltage. Advantageously, any parameter measure-
`ment is made while operating the examined circuit struc-
`tures, whether reference structures or structures of the inte-
`grated circuit itself, at a voltage having the nominal value.
`In still other embodiments, the present invention provides
`methods of providing an operating voltage to an integrated
`circuit using a voltage regulator. The voltage regulator
`comprises: a voltage down-converter arranged to convert a
`chip-external supply voltage to a converted voltage based on
`a signal
`indicative of a desired value of the converted
`voltage, and output the converted voltage as the operating
`voltage; and an adjustable signal generator for adjustably
`generating the signal indicative of the desired value of the
`converted voltage. In these embodiments, the signal genera-
`tor is adjusted dependenton at least one measuredelectrical
`or operational parameter of one or more reference circuit
`structures or at least one measured electrical or operational
`parameter of one or more circuit structures of the integrated
`circuit.
`In a preferred embodiment, the voltage regulator is an
`on-chip regulator.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In the following, the present invention is described in
`more detail by way of example only, and not by way of
`limitation, in conjunction with the accompanying drawings,
`wherein:
`
`FIG. 1 is a schematic diagram of an integrated circuit chip
`incorporating an on-chip voltage regulator, in accordance
`with preferred embodiments of the present invention;
`FIG. 2 is a flow diagram of methodsteps for optimizing
`an output voltage delivered by the voltage regulator of FIG.
`1; and
`FIG. 3 is a schematic view of a wafer having built thereon
`a number of integrated circuit chips and process control
`monitor structures.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`With the trend in integrated circuit fabrication technology
`to reduced characteristic lengths, the operating voltage for
`an integrated circuit also needs to be reduced. This is due
`primarily to the reduction in breakdown voltage as circuit
`structures are more densely packed and therefore distances
`betweencritical circuit structures are reduced. Voltage regu-
`lation becomes an important issue at reduced circuit oper-
`ating voltages. In order to provide operating voltages as low
`as, e.g., 3.3 V, 2.5 V, 1.8 V, 1.2 V orless, that are needed by
`modern integrated circuits fabricated in sub-micron or
`nanometer technology, a voltage regulator is required that
`performs down-conversion from a supply voltage of typi-
`cally 5 V or 12 V. To maintain tight regulation with low
`fluctuation of the regulated voltage,
`the trend is to use
`on-chip voltage regulators, i.e., regulators integrated on the
`same chip as the integrated circuit.
`FIG. 1 illustrates a semiconductor chip 10 having built
`thereon an integrated circuit 12 and an on-chip voltage
`regulator 14. A chip-external power supply 16, which may
`be arranged on the sameprinted circuit board (not shown) as
`the semiconductor chip 10, delivers a supply voltage Vextof,
`e.g., 5 V. The integrated circuit 12 requires an operating
`voltage VCC lower than the supply voltage Vext. For
`example, it may be specified as requiring a nominal oper-
`ating voltage of 3.3 V, 2.5 V or 1.8 V. The voltage regulator
`
`

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`US 7,170,308 Bl
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`3
`14 receives the supply voltage Vext and outputs the voltage
`VCC, which is fed to the integrated circuit 12. Specifically,
`the voltage regulator 14 includes a down-converter section
`18 and a signal generator section 20. The signal generator
`section 20 generates a signal representative of a target value
`of the output voltage VCC and supplies it to the down-
`converter section 18. The down-converter section 18 per-
`forms down-conversion of Vext and regulates the converted
`voltage to the target value as given by the signal from the
`signal generator section 20. The signal generator section 20
`is adjustable or trimmable, so that the target value of VCC
`may be varied. Hence, by suitably adjusting the signal
`generator section 20, a desired value of VCC can be
`obtained.
`
`While only oneintegrated circuit 12 is illustrated in FIG.
`1 for the sake of simplicity, a person versed in the art will
`easily appreciate that two or more integrated circuits 12 may
`be fabricated on chip 10, which may all receive their
`operating voltage from voltage regulator 14. Each integrated
`circuit 12 can be anytype of circuit, digital or analogue.Its
`circuit technology (e.g., CMOS, bipolar or hybrid), fabrica-
`tion technology and function are notcritical to the invention.
`Possible realizations of the integrated circuit 12 comprise,
`but are not limited to, a processor, a programmable logic
`device (PLD), an application-specific integrated circuit
`(ASIC),ete.
`Due to variations in the manufacturing process, perfor-
`mance parameters of integrated circuits,
`such as,
`for
`example, operating speed, output leakage current, and power
`consumption, may vary from chip to chip. These variations
`can be so large that some ofthe integrated circuits may, and
`typically do, fail to meet the specification, with the result
`that they have to be discarded. For example, higher leakage
`current loff of an integrated circuit generally implies higher
`circuit supply current ICC. In deep sub-micron chip fabri-
`cation technology, the leakage current off may become very
`large, especially at process corners whenall process-related
`variations are taken into account,
`leading to too high a
`supply current ICC.
`Performance-characterizing parameters of an integrated
`circuit usually depend on the operating voltage ofthecircuit.
`Thus, varying the circuit operating voltage is typically
`accompanied by concomitant variations in one or more of
`these parameters. For example, lowering the operating volt-
`age typically lowers the leakage current of an integrated
`circuit. On the other hand, increasing the operating voltage
`may increase the circuit operating speed.
`The production yield in chip fabrication can be enhanced
`by adjusting the operating voltage of integrated circuits
`based on measurements made of electrical or operational
`parameters of (1) select reference circuit structures fabri-
`cated in the same production run as the integrated circuits or
`(2) the integrated circuits themselves. Specifically, the cir-
`cuit operating voltage is adjusted from a pre-set nominal
`value by an adjustment amount determined from the mea-
`sured data. Suitably adjusting the operating voltage can
`make integrated circuits acceptable whose performance
`parameters would otherwise have been outside the specifi-
`cation. In this way, a significantly higher yield can be
`achieved. As an example, rough calculations have shown
`that on 90 nm technology up to about 10% ofthe total die
`area on a wafer can be recovered.
`FIG. 2 illustrates steps to be taken in order to optimize the
`operating voltage for the integrated circuit 12 shown in FIG.
`1. In step S1, data are acquired by measuring one or more
`performance-characterizing parameters of one or morecir-
`cuit structures. As indicated above, these circuit structures
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`can be reference circuit structures fabricated preferably in
`the samelot or on the same waferas the integrated circuit 12.
`It is equally possible to obtain performance-characterizing
`data from direct measurements of the integrated circuit 12.
`Advantageously, the one or more parameters are measured
`under nominal operating conditions of the probed circuit
`structures. Specifically, the parameters are measured while
`the nominal operating voltage as specified by the designeris
`applied to the probed circuit structures.
`Following step S1, an adjusted target value for the oper-
`ating voltage of the integrated circuit 12 is determined in
`step S2 based on the acquired measurement data. For
`example,
`in a case where the integrated circuit 12 is
`designed for a nominal operating voltage of 1.8 V, an
`optimized value for the operating voltage may be, e.g., 1.7
`V if the measured data indicate that the leakage current loff
`of the integrated circuit 12 1s, or is likely to be, too high at
`the nominal operating voltage. On the other hand, increasing
`the operating voltage to, e.g., 1.9 V may compensate for
`unacceptable slowness of the circuit operating speed at the
`nominal operating voltage. Evaluation of the measurement
`data and determination of the adjusted target value for the
`operating voltage may be made based on empiric informa-
`tion or using mathematical algorithms or formulas. Of
`course,if the evaluation of the measured data reveals that the
`examined parameters are in fact within acceptable limits, no
`adjusted target value for the operating voltage is determined.
`Rather, the nominal value as given in the device specifica-
`tion is established as the target value for the operating
`voltage.
`Finally, in step S3, the voltage regulator 14 is set so as to
`deliver the adjusted operating voltage. Specifically,
`the
`signal generator 20 is set so that the signal delivered by the
`signal generator section 20 to the down-converter section 18
`is indicative of the adjusted target value for the output
`voltage VCC as determined in step 82.
`So-called process control monitor (PCM)structures are
`one advantageous example of reference circuit structures
`suitable for being probed for performance-characterizing
`parameters. Conventionally, when fabricating a wafer, a set
`oftest structures, e.g., individual transistors, diodes or other
`circuit elements, is fabricated on the wafer in addition to the
`integrated circuits proper. Thesetest structures are known as
`the PCMstructures. They may be implemented as separate
`cells on extra wafer area or integrated side by side with the
`integrated circuits on the same die area. The PCM structures
`are strategically distributed across the wafer so as to deliver
`representative data for all areas of the wafer. After fabrica-
`tion of the wafer, tests for operational and electrical param-
`eters (also referred to as Process Control Monitor or E-Test)
`are carried out on the PCM structures using suitable test
`equipment. Measurement data originating from this para-
`metric testing can be used to refine the manufacturing
`process. For the purpose of illustration only, FIG. 3 sche-
`matically depicts a wafer 110 having built thereon a number
`of integrated circuits 120. PCM structures 130 are formed on
`the wafer 110 outside the die area of the integrated circuits
`120. After the wafer 110 is diced into chips,
`the PCM
`structures 130 are disposed of as waste.
`Rather than relying on data obtained from testing PCM
`structures,
`the adjustment of the operating voltage of a
`particular integrated circuit may be based on data gained
`from parametric measurements of one or more selected other
`integrated circuits fabricated in the same production run or
`on the same wafer as the integrated circuit whose operating
`voltage is being adjusted. Preferably, several
`integrated
`circuits are selected on the same wafer. By strategically
`
`

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`US 7,170,308 Bl
`
`5
`choosing several integrated circuits out of the totality of
`integrated circuits 120, representative performance-charac-
`terizing data can be gained for all wafer areas. Thus, the
`selected integrated circuits function as reference circuits in
`substantially the same way as the PCM structures. The
`parameter measurements can be carried out before or after
`cutting the wafer 110 into chips.
`Alternatively, measurements for performance-character-
`izing parameters may be made ona portion ofthe integrated
`circuit whose operating voltage is being adjusted. In this
`case, adjustment of the operating voltage of a specific
`integrated circuit may be based solely on the data measured
`for that integrated circuit.
`Measurement step S1, determination step S2 and setting
`step S3 of FIG. 2 may all be carried out by the chip
`manufacturer as part of the various functional and other test
`procedures typically performed on chips before shipping
`them. In particular, adjustments to the operating voltage of
`individual integrated circuits may be madeprior to shipping
`based on measured parameters of reference circuit structures
`in PCMstructure or other integrated circuits or on measured
`parameters of the individual integrated circuit.
`Alternatively, integrated circuit chips may have integrated
`thereon a suitable on-chip device that performs steps S1-S3
`without
`the use of additional external equipment. This
`permits parameter measurements and operating voltage
`adjustments even during use of the chips. For a better
`understanding of such on-chip measurement and adjustment
`facility, refer again to FIG. 1 where a detection section 22
`and an evaluation section 24 are shownas part of chip 10.
`Asthe detection section 22 and the evaluation section 24 are
`
`optional features, they are depicted in broken lines in FIG.
`1. The detection section 22 is arranged to measure one or
`more electrical or operational parameters of the integrated
`circuit 12. I'or example, detection section 22 may measure
`a voltage drop across a specific structure or it may measure
`a leakage current or a circuit operating speed. Detection
`section 22 delivers its measured signals to the evaluation
`section 24. Evaluation section 24 is arranged to determine,
`based on the measured signals, a desired value for the
`operating voltage VCC of the integrated circuit 12 and to
`adjust, if necessary, the signal generator section 20 so that
`the latter supplies to the down-converter section 18 a signal
`indicative of the desired value as determined by the evalu-
`ation section 24. Advantageously, the detection section 22
`may be arranged to take parameter measurements repeatedly
`during operation of the integrated circuit 12, e.g., continu-
`ously or in regular intervals.
`The evaluation section 24 may be implementedusing, for
`example, programmable logic or a processor. A program-
`mable logic device can be easily programmedto perform the
`functions of the evaluation section 24. Similarly, a program-
`mable logic device may also be used to form the signal
`generator section 20. Programmable or trimmable elements,
`e.g., fuses, in the signal generator section 20 enable easy
`adjustmentof the target value of the operating voltage VCC.
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`In an alternative embodiment, detection section 22 and
`evaluation section 24 may be arranged separately from chip
`10, yet on the sameprinted circuit board.
`In summary, the present invention permits the perfor-
`manceofintegrated circuits to be optimized andthe yield to
`be increased by adjusting the circuit operating voltage using
`feedback on process/product parameters. While preferred
`embodiments have been described above, it will be apparent
`to those skilled in the art that modifications can be made
`
`without departing fromthe spirit and scope of the invention.
`Whatis claimed is:
`1. A voltage regulator for providing an operating voltage
`to an integrated circuit formed on a samechipas said voltage
`regulator, said voltage regulator comprising:
`a voltage down-converter arranged to convert a chip-
`external supply voltage to the operating voltage based
`on a signalindicative of a desired value of the operating
`voltage and output the operating voltage;
`an adjustable signal generator for adjustably generating
`the signal indicative of the desired value of the oper-
`ating voltage;
`a detector for measuring at least one electrical or opera-
`tional parameter of the integrated circuit when the
`integrated circuit is operated at a nominal voltage; and
`an evaluator to determine the desired value of the oper-
`ating voltage based on the parameter(s) measured by
`the detector when the integrated circuit is operated at
`the nominal voltage and to supply a signal to the signal
`generator indicative of the desired value.
`2. The voltage regulator of claim 1, wherein the adjustable
`signal generator is implemented in a programmable logic
`device.
`3. The voltage regulator of claim 1, wherein the evaluator
`is implemented in a programmable logic device.
`4. A voltage regulator for providing an operating voltage
`to an integrated circuit formed on a samechipas said voltage
`regulator, said voltage regulator comprising:
`a voltage down-converter arranged to convert a chip-
`external supply voltage to a converted voltage based on
`a signal indicative of a desired value of the converted
`voltage and output the converted voltage as the oper-
`ating voltage;
`an adjustable signal generator for adjustably generating
`the signal indicative of the desired value of the con-
`verted voltage; and
`a detector for measuring at least one electrical or opera-
`tional parameter of a circuit of the integrated circuit
`when the integrated circuit is operated at a nominal
`voltage and producing a measurement signal that is
`used to control
`the signal generated by the signal
`generator.
`5. The voltage regulator of claim 4, wherein the adjustable
`signal generator is implemented in a programmable logic
`device.
`
`