I lllll llllllll Ill lllll lllll lllll lllll lllll 111111111111111111111111111111111
`US007124325B2
`
`c12) United States Patent
`Hartmann et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,124,325 B2
`Oct. 17, 2006
`
`(54) METHOD AND APPARATUS FOR
`INTERNALLY TRIMMING OUTPUT
`DRIVERS AND TERMINATIONS IN
`SEMICONDUCTOR DEVICES
`
`6,184,720 Bl*
`.................... 327/37
`2/2001 Kim et al.
`6,307,801 Bl* 10/2001 Ogawa et al.
`.............. 365/226
`7,000,160 Bl*
`212006 Tanaka et al . .............. 714/724
`1/2003 Yamaki et al. ......... 365/189.09
`2003/0016566 Al*
`
`(75)
`
`Inventors: Udo Hartmann, Neuried (DE); Sascha
`Nerger, Mlinchen (DE)
`
`(73) Assignee: Infineon Technologies AG, Munich
`(DE)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 544 days.
`
`(21) Appl. No.: 10/680,782
`
`(22) Filed:
`
`Oct. 7, 2003
`
`(65)
`
`Prior Publication Data
`
`US 2004/0066683 Al
`
`Apr. 8, 2004
`
`(30)
`
`Foreign Application Priority Data
`
`Oct. 7, 2002
`
`(DE)
`
`................................ 102 46 741
`
`(51)
`
`Int. Cl.
`G06F 11100
`(2006.01)
`GllC 5100
`(2006.01)
`(52) U.S. Cl. .................................... 714/30; 365/189.09
`( 58) Field of Classification Search ... ... ... ... .. ... . 714/30,
`714/32, 721; 365/189.09
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`5,426,616 A * 6/1995 Kajigaya et al. ............ 365/226
`
`FOREIGN PATENT DOCUMENTS
`
`DE
`DE
`EP
`EP
`
`37 83 963 T2
`690 19 621 T2
`0 254 011 Bl
`0 410 402 Bl
`
`1/1988
`1/1991
`1/1988
`1/1991
`
`* cited by examiner
`Primary Examiner-Nadeem Iqbal
`(74) Attorney, Agent, or Firm-Laurence A. Greenberg;
`Werner H. Sterner; Ralph E. Locher
`
`(57)
`
`ABSTRACT
`
`To trim interface devices on semiconductor devices, such as
`trimmable output drivers and terminations, a measurement
`current produced in the test apparatus is impressed onto the
`interface device, and a measurement voltage produced by
`the measurement current in the interface device is detected
`by a trimming unit provided within the semiconductor
`device and is trimmed using control elements and trimming
`registers controlled by the trimming unit. To this end, the
`trimming unit ascertains trimming information which is
`stored in nonvolatile fashion in a memory unit in the
`semiconductor device and is loaded into the trimming reg(cid:173)
`isters in the semiconductor device whenever the semicon(cid:173)
`ductor device is started up.
`
`20 Claims, 3 Drawing Sheets
`
`Vddq
`
`Control
`Element
`
`10b
`Interface
`Device
`Vssq
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`2
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`22
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`: 16b Control '
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`51
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`i
`
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`Unit
`
`24
`
`5
`
`1
`
`NVIDIA 1001
`
`

`

`U.S. Patent
`
`Oct. 17, 2006
`
`Sheet 1 of 3
`
`US 7,124,325 B2
`
`FIG 1
`PRIOR ART
`Vddq
`
`1
`Control Element
`Interface
`"
`~ Device
`
`Supply
`Connection
`
`2
`(
`
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`20
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`IM
`
`~
`
`22
`
`Device
`15b
`1 Od
`
`21
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`
`34
`------- _t ___ l _____
`24
`
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`Connection
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`10b
`
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`I
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`l
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`12b: I
`
`I
`I
`I
`
`11 b:
`
`I
`I
`
`13b~
`
`14
`
`Trimming
`Registers
`
`FIG 2
`PRIOR ART 1
`
`Interface
`Connection 1
`I
`I
`
`32
`
`2
`IM ~ ~
`
`Contact
`Resistance
`LiMt ~
`20
`
`21
`
`10b
`
`Vs sq
`
`12b
`
`Interface
`Device
`
`Supply Connection
`
`33
`
`2
`
`

`

`U.S. Patent
`
`Oct. 17, 2006
`
`Sheet 2 of 3
`
`US 7,124,325 B2
`
`11nterface
`\Device
`
`16a
`\
`:
`
`I
`I
`
`12a
`
`'
`
`~13a:
`
`I
`
`I
`I
`I
`
`12b:
`
`FIG 3
`
`Vddq
`Interface
`Device
`
`1 Oa
`
`Control
`Element
`
`1 Ob
`Interface
`Device
`Vssq
`
`2
`
`\
`
`22
`
`21
`
`Supply
`Connection
`
`I
`I
`
`:.-...._ 16b Control :
`13b -.,
`:
`Element 1
`,
`.-----"-....L.----1........, 14
`:
`34
`---------t----------___ }_ ____ ~
`~~~~~r;
`
`52a
`
`I
`I
`I
`I
`I
`
`35
`---------~ ____ ( __
`-----------L------
`
`I
`
`1
`I
`I
`I
`
`5
`
`Memory
`Unit
`
`Test Control
`Unit
`
`24
`
`3
`
`

`

`U.S. Patent
`
`Oct. 17, 2006
`
`Sheet 3 of 3
`
`US 7,124,325 B2
`
`FIG 4
`
`r------------------------------------------
`
`Trimming
`Registers
`
`14
`
`1
`I
`I
`I
`I
`I
`
`13b~
`
`Reference
`Voltage Unit
`
`Control
`Element
`
`UM
`
`12b
`
`54
`
`11b
`
`---t
`Vs sq
`
`55a
`
`55b
`
`52a
`
`52b
`
`Logic
`Unit
`
`59
`
`51
`--------------- .t!.~
`57
`
`Voltage
`Divider
`
`Counter
`Unit
`
`58
`
`5
`
`Trimming
`Unit
`
`4
`
`

`

`US 7, 124,325 B2
`
`1
`METHOD AND APPARATUS FOR
`INTERNALLY TRIMMING OUTPUT
`DRIVERS AND TERMINATIONS IN
`SEMICONDUCTOR DEVICES
`
`BACKGROUND OF THE INVENTION
`
`Field of the Invention
`
`The invention relates to a method for trimming interface
`devices on semiconductor devices using a test apparatus
`having at least one current source. Each of the interface
`devices has a settable control element.
`In data bus systems, data signals are transmitted between
`a plurality of semiconductor devices on data lines combined
`to form a common data bus. The power of the data bus
`system is characterized, inter alia, by a data transmission
`rate at which data are interchanged between the semicon(cid:173)
`ductor devices within the data bus system.
`An example of a data bus system with a high data 20
`transmission rate is the DDR (double data rate) II memory
`system for computer systems, such as PCs, workstations and
`servers. In this case, a system board for the DDR memory
`system is provided with slots for memory modules in the
`form of plug sockets, and these slots are fitted with a variable 25
`number of memory modules on the basis of the desired size
`of the main memory. The memory modules are normally in
`the form of DIMMs (dual inline memory modules) whose
`mechanical and electrical interfaces for the system board are
`subject to industrial standards. The memory modules hold 30
`DD RII-D RAMs (double data rate II-dynamic random access
`memories) as semiconductor memory devices. For DDRII
`memory systems, typical data transmission rates that are
`obtained to and from the DDRII-DRAMs are 333 Mbits per
`second and per data signal (Mbit/s/pin).
`As data transmission rates increase on the data bus, the
`semiconductor devices effecting access for the purpose of
`writing to the data bus or reading from the data bus demand
`narrower tolerances for the interface parameters in order to
`maintain the integrity of the data signals transmitted to the 40
`data bus.
`A first such interface parameter is the impedance of the
`output drivers (OCD-off chip driver), which a semiconduc(cid:173)
`tor device uses to effect a write access to the data bus, or to
`output data signals to the data bus. The impedance of an
`output driver influences the rise and fall times when there is
`a signal level change in the data signal driven by the output
`driver, and hence influences a signal delay in the data signal.
`A maximum skew in the signal delays of all of the output
`drivers in a semiconductor device or in all of the semicon(cid:173)
`ductor devices in a data bus system limits a maximum data
`transmission rate. The smaller the maximum skew in this
`case, the higher the data transmission rates that can be
`implemented.
`Another interface parameter is formed by terminations,
`which terminate the data bus locally in the semiconductor
`device in order to prevent reflections (ODT-on die termina(cid:173)
`tion). As the precision of the termination increases, inter(cid:173)
`ference signals arising at the location of the termination are
`attenuated to an increasing extent and a higher maximum
`data transmission rate is made possible in the data bus
`system.
`The interface parameters of semiconductor devices are
`subject to production variations and vary both from semi(cid:173)
`conductor device to semiconductor device and within a 65
`semiconductor device, for example, from output driver to
`output driver. The interface parameters are also subject to
`
`10
`
`2
`variations over time during the operation of the semicon(cid:173)
`ductor device. In this case, the variations over time result, by
`way of example, from any temperature dependency of the
`interface parameters or the latter's dependency on an oper(cid:173)
`ating voltage for the semiconductor device.
`For operation in data bus systems with a high data
`transmission rate, provision is therefore made for the semi(cid:173)
`conductor device's interface parameters to be trimmed at
`least once before or during the initial startup of the semi(cid:173)
`conductor device or repeatedly during the operation of the
`semiconductor device. The trimming is performed by con(cid:173)
`trol elements in the respective interface devices. The control
`elements are in the form of switchable impedances whose
`15 respective value can be progranimed on the basis of a
`register value in a trimming register (EMRS-extended mode
`register set).
`For ordinary DDRII memory systems, it is normally not
`possible to trim the interface parameters ofDDRII-DRAMs
`in a target system, since the DDRII-DRAMs cannot be
`addressed individually within the data bus system. However,
`selective addressing of individual DDRII-DRAMs is a nec(cid:173)
`essary prerequisite for trimming the interface parameters.
`For DDRII-DRAMs, it is therefore necessary to perform
`trimming in the course of testing the DDRII-DRAMs out(cid:173)
`side a target system on test apparatuses that are normally
`designed for conventional, untrimmable DRAMs or DDRII(cid:173)
`DRAMs.
`A DDRII-DRAM, which has interface devices to be
`trimmed, is trimmed on a conventional test apparatus by
`connecting a test output on the test apparatus to an interface
`connection on the semiconductor device. The test output is
`connected within the test apparatus to a first DC unit,
`35 operated as a current source, and to a further, second DC
`unit, operated as a voltmeter. As their control element, the
`interface devices have respective programmable resistors
`that each have the lowest possible value at the start of the
`trimming. The current source is used to impress a measure-
`ment current onto the interface device. A measurement
`voltage produced by the measurement current is compared
`in the test apparatus with a nominal voltage. While the
`measurement voltage is below the nominal voltage, the
`register value in the test piece's trimming register is incre-
`45 mented in stages, and the resultant newly obtained measure(cid:173)
`ment voltage is respectively compared with the nominal
`voltage again. If the measurement voltage is above the
`nominal voltage, then the register value corresponding
`thereto is detected and is stored in a suitable manner for
`further use.
`A drawback of this method is, in particular, the relatively
`low throughput of test pieces, which results from the limited
`number of DC units suitable for precise output and/or
`measurement of currents and voltages within test appara-
`55 tuses designed for conventional DRAMs. Since equipping
`the test apparatuses with a large number of precise DC units,
`if at all possible, results in high costs, and testing conven(cid:173)
`tional, untrimmable DRAMs does not require a large num(cid:173)
`ber of DC units, the number of the DC units is normally
`60 limited in relation to other system resources in the test
`apparatus.
`Another drawback is the time required for evaluating
`measurement and trimming data, since the test apparatuses
`designed for digitally operating semiconductor devices nor(cid:173)
`mally have only limited resources available for determining,
`evaluating and calculating analog measured variables. This
`is because such resources are expensive.
`
`50
`
`5
`
`

`

`US 7, 124,325 B2
`
`3
`In addition, test programs on the test apparatuses need to
`be prepared, implemented and continually aligned with the
`product lines.
`Since, normally, contact needles are used to make contact
`with the semiconductor devices that are to be trimmed, a
`contact resistance between the contact needle and a contact
`area on the semiconductor device is also included in the
`measurement of the measurement voltage and may signifi(cid:173)
`cantly corrupt the trimming.
`
`SUMMARY OF THE INVENTION
`
`It is accordingly an object of the invention to provide a
`semiconductor device and a method for trimming interface
`devices of the semiconductor device, which overcome the 15
`above-mentioned disadvantages of the prior art apparatus
`and methods of this general type.
`In particular, it is an object of the invention to provide a
`method for trimming interface devices such as output drivers
`and terminations in semiconductor devices of a novel, 20
`trimmable type. Test apparatus designed for testing func(cid:173)
`tionally comparable semiconductor devices of a conven(cid:173)
`tional, untrimmable type, can be used to test the semicon(cid:173)
`ductor devices of the trimmable type with high precision
`while achieving a throughput that is the same as that when 25
`testing semiconductor devices of the conventional type. It is
`also an object of the invention to provide a semiconductor
`device that supports the inventive method.
`With the foregoing and other objects in view there is
`provided, in accordance with the invention, a method for 30
`trimming interface devices. The method includes the fol(cid:173)
`lowing steps: A semiconductor device having a plurality of
`interface devices is provided and each one of the plurality of
`interface devices is provided with a settable control element.
`A test apparatus having a current source is provided. The 35
`current source in the test apparatus is connected to an
`interface connection on the semiconductor device. The inter(cid:173)
`face connection is connected to one of the plurality of
`interface devices. A measurement current produced by the
`current source is controlled and the control element of the 40
`one of the plurality of interface devices is set to an initial
`value. A trimming unit is provided in the semiconductor
`device. The trimming unit is used to acquire a measurement
`voltage produced by the measurement current in the one of
`the plurality of interface devices. The trimming unit is used 45
`to compare the measurement voltage with a nominal volt(cid:173)
`age. Based on a difference between the measurement voltage
`and the nominal voltage, the control element of the one of
`the plurality of interface devices is set to a trimming value
`at which the measurement voltage matches the nominal 50
`voltage. The trimming value for the control element of the
`one of the plurality of interface devices is acquired.
`In line with the invention, the trimming unit is in this case
`provided within the semiconductor device. As a result, it is
`not necessary to provide two DC voltage units within the test 55
`apparatus for each semiconductor device of novel type that
`is to be trimmed. Since the test parallelism, that is to say a
`number of semiconductor devices which can be tested and
`trimmed simultaneously using a test apparatus designed for
`testing semiconductor devices of a comparable conventional
`type that cannot be trimmed or can be trimmed in a different
`way, is limited by the number of available DC voltage units,
`the test parallelism is doubled by the inventive method. A
`further increase in a throughput on the test apparatus is
`obtained by evaluating analog measurement data in the test
`apparatus, and needing to trigger controls on the basis
`thereof, to a significantly reduced extent.
`
`4
`The inventive method also makes it urmecessary to con(cid:173)
`tinually implement and update test programs in the test
`apparatus in order to test product lines of semiconductor
`devices. Creating and maintaining test programs determine
`a fundamental part of the test laboratory costs.
`Finally, the inventive method makes it possible to provide
`measurement points for voltage measurement directly on the
`interface device, in a particularly advantageous manner. This
`prevents voltage drops, giving rise to measurement errors, in
`10 supply lines and on contact devices.
`The invention also provides for the trimming value for the
`control element to be stored in nonvolatile fashion in the
`semiconductor device. This makes it possible to trim the
`semiconductor device in a test laboratory before being used
`in a target system.
`Normally, trimmable semiconductor devices contain trim(cid:173)
`ming registers. In the case of DDRII-DRAMs, these are the
`EMRS (extended mode register set). The control elements in
`the interface devices are connected to the trimming register
`and can be programmed on the basis of the value stored in
`the trimming register. Whenever the DDRII-DRAM has
`been started up, the invention provides for the trimming
`register to be loaded with the trimming value that has been
`stored in nonvolatile fashion.
`Trimming is typically carried out by increasing a resis(cid:173)
`tance value for a semiconductor section in stages, starting
`from a low initial value, until the trimming unit records a
`change of arithmetic sign for a difference between the
`measurement voltage and the nominal voltage.
`In line with another advantageous exemplary embodiment
`of the inventive method, the trimming value is ascertained
`directly from the difference between the measurement volt(cid:173)
`age and the nominal voltage, as a result of which the time
`required for a trimming is reduced further.
`Preferably, the inventive method provides for the semi(cid:173)
`conductor devices to be tested at the wafer level. Besides the
`usual advantages of testing at the wafer level, which enables
`the early identification of faulty semiconductor devices
`before performing further cost-intensive production steps,
`for example, packaging, it is also possible to provide at least
`parts of the trimming unit in the wafer's cut region (kerf) in
`a space-saving marmer. The interface connections on the
`semiconductor devices are then arranged on a surface of the
`wafer and are produced in the form of contact areas.
`The test apparatus is normally connected to the semicon(cid:173)
`ductor device using contact needles that are provided in a
`needle board and are pressed onto the contact areas associ(cid:173)
`ated with the interface connections. Since conventional
`voltage measurement methods involve using a DC unit in
`the test apparatus, contact resistances resulting from press(cid:173)
`ing the contact needles onto the contact areas of the interface
`connections appear connected in series with the actual
`measurement voltage.
`The contact resistance for each contact needle/contact
`area transition fluctuates in a range between 0 and 10 ohms.
`The resistance through the interface device in the trimmed
`state reaches values of 18 ohms for output driver devices. A
`measurement error is thus up to 55%. In addition, the contact
`resistance fluctuates in the indicated range, so that it is also
`60 not a simple matter to remove the measurement error by
`calculation. This problem does not arise in the case of the
`inventive method, since the measurement points are pro(cid:173)
`vided in the immediate vicinity of the interface device in the
`semiconductor device itself, and the measurement is like-
`65 wise taken in the semiconductor device.
`In line with a first embodiment of the inventive method,
`the control element is set or programmed in the course of the
`
`6
`
`

`

`US 7, 124,325 B2
`
`6
`voltage. Since the voltage divider's ratio is set using dimen(cid:173)
`sions that are relatively easy to control using devices and
`processes which are customary in semiconductor process
`technology, no additional trimming is necessary for the
`internal reference voltage circuit.
`In addition, the trimming unit has: a comparator unit,
`which compares the nominal voltage with a measurement
`voltage produced in the interface device, and a logic unit
`which is suitable for writing to the trimming register on the
`basis of an output signal from the comparator unit.
`A nonvolatile memory unit that can be programmed on
`the basis of a trimming value can be used to control the
`trimming process completely from the trimming unit
`arranged on the semiconductor device and without any other
`control via the test apparatus.
`In this case, in line with a first embodiment of the
`inventive semiconductor device, the memory unit is suitable
`for directly controlling the control element.
`In line with an alternate embodiment of the inventive
`semiconductor device, the memory unit is suitable for load(cid:173)
`ing the trimming register. In this case, for every startup, the
`trimming register is loaded with the value stored in the
`memory unit and then controls the associated control ele(cid:173)
`ment in a conventional marmer.
`Other features which are considered as characteristic for
`the invention are set forth in the appended claims.
`Although the invention is illustrated and described herein
`as embodied in a method and apparatus for internally
`trimming output drivers and terminations in semiconductor
`devices, it is nevertheless not intended to be limited to the
`details shown, since various modifications and structural
`changes may be made therein without departing from the
`spirit of the invention and within the scope and range of
`equivalents of the claims.
`The construction and method of operation of the inven(cid:173)
`tion, however, together with additional objects and advan(cid:173)
`tages thereof will be best understood from the following
`description of specific embodiments when read in connec(cid:173)
`tion with the accompanying drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic diagram of a configuration for
`performing a prior art method for trimming interface devices
`in a semiconductor device;
`FIG. 2 is a schematic diagram of a detail from FIG. 1;
`FIG. 3 is a schematic diagram of a configuration for
`trimming interface devices in a semiconductor device; and
`FIG. 4 is a schematic diagram of a detail from FIG. 3.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`5
`trimming by virtue of the trimming unit setting the trimming
`register, which achieves further load reduction for the test
`apparatus.
`In line with another embodiment of the inventive method,
`the trimming register is set by the test apparatus in the course
`of the trimming, with the measurement result being trans(cid:173)
`mitted to the test apparatus in a first step and the test
`apparatus writing to the trimming register on the basis of the
`transmitted measurement result in a second step.
`Besides prescribing a loading value for the trimming 10
`register, the trimming value can be impressed onto the
`control element directly, for example, by laser-fuse ore-fuse
`devices. Thus, the trimming value for the control element is
`transmitted to the test apparatus preferably via a monitor
`output and is impressed in a nonvolatile fashion onto the 15
`control element by the test apparatus using laser or e-fuse
`devices.
`In line with another preferred embodiment of the inven(cid:173)
`tive method, the trimming value for the control element is
`impressed onto a loading register in the trimming register by 20
`the trimming unit in nonvolatile fashion. In this case, the
`loading register is a group of laser ore-fuse devices in the
`simplest case.
`If the semiconductor devices are DRAMs having a DDRII
`interface, then the latter's output driver devices and termi- 25
`nations are particularly suitable as trimmable interface
`devices within the context of the invention. The output
`drivers normally need to be provided at low impedance, that
`is to say in the region below 100 ohms, as do the termina(cid:173)
`tions. However, low-value resistances, in particular, can be 30
`provided only inaccurately in semiconductor devices using
`the means and processes that are customary in semiconduc-
`tor process technology. Since low-value contact resistances
`in the order of magnitude of the variable that is to be
`trimmed arise in conventional methods, however, the inven- 35
`tive method is particularly advantageous for this application.
`With particular preference, the current source, which is
`provided and operated in a current-limited fashion for the
`purpose of trimming, is an output driver in the test apparatus.
`This output driver is provided for the purpose of driving 40
`digital signals. The measurement current is then obtained
`from the value of the current limitation. Since, besides a
`voltage supply for the semiconductor devices, no other DC
`unit is then necessary in the test apparatus for the trimming.
`The number of DC units, as the factor which limits the test 45
`parallelism and hence the test throughput, is accordingly
`reduced. As compared with testing semiconductor devices of
`a conventional type, essentially the same throughput is also
`obtained for semiconductor devices of the novel, trimmable
`type when using the test apparatuses designed for testing 50
`semiconductor devices of the conventional type.
`A prerequisite of the inventive method is providing a
`semiconductor device including: at least one interface
`device having a settable control element, and a trimming
`register connected to the control element. In addition, the 55
`semiconductor device has a trimming unit connected to the
`interface device and to the trimming register and writes to
`the trimming register on the basis of a measured variable
`detected on the interface device.
`Preferably, the inventive semiconductor device has a
`monitor output. The monitor output is used to transmit a
`measured variable, for example, in digital form or via a data
`bus in the semiconductor device, and/or a trimming value,
`ascertained by the trimming unit, for the control element to
`a test apparatus.
`In addition, the trimming unit has a reference voltage
`device and a voltage divider for producing a nominal
`
`65
`
`Referring now to the figures of the drawing in detail and
`first, particularly, to FIG. 1 thereof, there is shown the
`components of a trimmable semiconductor device 1 and of
`a test apparatus 2 which are relevant for explaining a
`conventional method for trimming interface devices 10. The
`semiconductor device 1 has supply connections 31, 33 and
`60 interface connections 32, of which only the supply connec(cid:173)
`tions 31and33 for supplying potentials Vddq and Vssq and
`the interface connection 32 of a driver apparatus for a
`DDRII-DRAM are shown in order to simplify matters.
`The driver apparatus includes four interface devices
`lOa-lOd. Two of the interface devices are output driver
`lOb. The two other interface devices are
`devices lOa,
`termination devices lOc, 1 Od. The output driver devices lOa,
`
`7
`
`

`

`US 7, 124,325 B2
`
`7
`lOb are made up of an ideal MOS transistor lla, llb and a
`control element 12a, 12b for an output impedance in the
`output driver device lOa, lOb. The output driver devices
`lOa, lOb are simplified to enable a simplified consideration.
`The termination devices lOc, lOd respectively include an
`ideal controllable switching device 15a, 15b and a control
`element 17 a, 17 b formed as a trimmable termination resis(cid:173)
`tor. In addition, the semiconductor device 1 has a trimming
`register or a set of trimming registers 14 which are each
`connected, via control paths 13a, l3b, l6a, l6b, to the 10
`control elements 12a, 12b, 17a, 17b of the respectively
`corresponding interface devices lOa-1 Od.
`Besides a DC voltage source 22, the test apparatus 2 has
`a current source 21 and a voltmeter 23, which are each
`connected via a control path 25 and via a data path 26 to a 15
`test control unit 24 in the test apparatus 2.
`For the purpose of trimming the interface devices
`lOa-lOd, the DC voltage source 22, the current source 21
`and the voltmeter 23 are connected to the semiconductor
`device 1 via the supply connections 31, 33 and the interface
`connection 32.
`The control elements 12, 17 in the semiconductor device
`1 are set according to an initial value, and one of the
`interface devices 1 Oa-lOd is connected through. The current
`source 21 is used to impress a measurement current IM of
`known intensity onto the interface connection 32. A mea(cid:173)
`surement voltage UM obtained between the interface con(cid:173)
`nection 32 and one of the supply connections 31, 33 is
`measured using the voltmeter 23 and is transmitted to the
`test control unit 24.
`If the ascertained measurement voltage UM differs from a
`nominal value Us too greatly, then the test control unit 24
`uses a control path 34 to increment the value of a corre(cid:173)
`sponding trimming register 14 in stages. The value in the
`trimming register 14 is taken as a basis for altering the
`control elements 12, 17, for example, by increasing an
`impedance in stages. If an admissible value is recorded for
`the measurement voltage UM' then the current trimming
`value for the control elements 12, 17 which is stored in the
`corresponding trimming register 14 is detected. Using the
`trimming value, the test apparatus 2 subsequently programs
`a nonvolatile memory unit in the semiconductor device 1 in
`a known manner.
`FIG. 2 shows a detail from FIG. 1. The test apparatus 2 is
`normally connected to the semiconductor device 1 using
`contact needles 20, which are pressed onto supply and
`interface connections 31-33 on the semiconductor device 1.
`The supply and interface connections 31-33 are in the form
`of contact areas. Contact resistances 27 of up to several
`ohms act on the transitions between the contact needles 20 50
`and the supply and interface connections 31-33. In the case
`of a voltage measurement with the voltmeter 23, the voltage
`drop across the contact resistances is added to the voltage
`drop across the impedance that will be trimmed in the
`interface device 10, so that the impedance is incorrectly
`trimmed with an error of up to 55%. By contrast, present
`specifications for DDRII-DRAMs require trimming to
`approximately ±16%.
`FIG. 3 is a schematic diagram showing a configuration for
`performing an inventive method for trimming interface 60
`devices 10 in an inventive semiconductor device 1. In this
`case, the inventive semiconductor device 1 has a trimming
`unit 5, in contrast to the conventional semiconductor device
`1 shown in FIG. 1. The trimming unit 5 is switchably
`connected to each driver device which is to be trimmed in 65
`the semiconductor device 1. To preserve the clarity of the
`illustration, only the connection between the trimming unit
`
`8
`5 and one of the driver devices is shown. In line with an
`alternative solution, each driver device to be trimmed is
`assigned a trimming unit 5.
`The trimming unit 5 is connected within the semiconduc(cid:173)
`tor device 1 to the interface devices lOa-lOd in the driver
`device. Register paths 52a, 52b can be used by the trimming
`unit 5 to control a respective corresponding trimming reg(cid:173)
`ister 14. Optionally, the trimming unit 5 is connected to the
`test control unit 24 in the test apparatus 2 via a monitor
`output 51, and the test apparatus 2 is connected to the
`corresponding trimming register 14 via the control path 34.
`One of the interface devices lOa-lOd is now trimmed by
`taking the measurement voltage UM as a basis for increasing
`the value of the corresponding trimming register 14, starting
`from a low initial value, via the register path 52a until a
`tolerable discrepancy between the measurement voltage UM
`and a nominal voltage Us is detected. The register value,
`required for this measurement voltage UM' in the trimming
`register 14 is stored by the trimming unit 5 in a nonvolatile
`20 memory unit 59, for example using a soft-setting device in
`connection with electronic fuses or using EEPROM (elec(cid:173)
`trically erasable programmable read only memory) cells.
`The trimming of one of the interface devices 1 Oa-lOd is
`thus complete. Whenever the semiconductor device 1 is
`25 subsequently started up in a target system, the trimming
`value stored in the nonvolatile memory unit 59 is loaded into
`the respective corresponding trimming register 14, which
`accordingly sets the control elements 12, 17 in the associated
`interface devices lOa-lOd.
`Alternatively, it is also possible to transmit the trimming
`value to the test control unit 24 in the test apparatus 2 in a
`first step via the monitor output 51 or via a data bus system
`in the semiconductor device 1. In a second step, program(cid:173)
`ming of the nonvolatile memory unit 59, for example,
`35 programming e-fuses, is controlled using a progranmiing
`path 35. On the basis of a further alternative, laser fuses are
`set and erased by laser beam using an external programming
`apparatus.
`FIG. 4 shows fundam