fig2 shows a driver calibration circuit arrangement 30 according to a first exemplary embodiment of the invention , together with a driver circuit arrangement 20 , illustrated schematically . the illustration shows a driver calibration circuit arrangement 30 , which has a monitoring device 31 , a variable impedance 32 , a reference voltage divider 33 , a comparator 34 , and control lines 36 . the driver calibration circuit arrangement 30 is connected to a reference impedance z ref and to the driver circuit arrangement 20 . the latter connection is made via a control line 24 which , for example , has four conductors . the variable impedance 32 comprises two or more switchable impedances 35 a - d , which can be switched on and off via the control lines 36 . the driver circuit arrangement 20 has a pull - up branch 21 and a pull - down branch 22 , whose respective impedance can be influenced via the control line 24 . together with the reference impedance z ref , the variable impedance 32 forms a voltage divider between two predetermined potentials . a point which is located between the variable impedance 32 and the reference impedance z ref is connected to one input of the comparator 34 . the other input of the comparator 34 is connected to one output of the reference voltage divider 33 , which is likewise connected between the two predetermined potentials . the output of the comparator 34 is fed back to the monitoring device 31 . during a calibration process for calibration of the driver circuit arrangement 20 , the monitoring device 31 varies the impedance value of the variable impedance 32 in accordance with a predetermined search algorithm , with the switchable impedances 35 a - d being addressed individually and switched on and off specifically via the signal lines 36 . the progress through the search algorithm is determined dynamically as a function of the output signal from the comparator 34 . the search algorithm ends when the two input signals applied to the comparator 34 are matched to one another as well as possible . the reference voltage divider 33 thus to a considerable extent determines the calibration result . if the reference voltage divider 33 is between the supply potentials of the driver circuit arrangement 20 and between the potentials which supply the series circuit formed by the variable impedance 32 and the reference impedance z ref , then , according to the invention , the reference voltage divider 33 will have a division ratio other than 50 : 50 . in the illustrated situation , the variable impedance 32 simulates the impedance of the pull - up branch 21 of the driver circuit arrangement 20 . in a corresponding way , the monitoring device 31 calibrates the impedance value of the pull - up branch 21 in the driver circuit arrangement 20 by signals via the control line 24 as a function of the impedance value of the variable impedance 32 at the end of the search algorithm . if the variable impedance 32 is relatively a 1 : 1 simulation of the impedance of the pull - up branch 21 of the driver circuit arrangement 20 , there is , for example , a 1 : 1 relationship between the calibrated configuration of the variable impedance and the configuration , to be calibrated , of the pull - up branch 21 of the driver circuit arrangement 20 . other relationships are , of course , also possible within the scope of the invention . the pull - down branch is calibrated in an analogous manner , using an appropriately different reference voltage divider . fig3 shows a schematic illustration of various current / voltage characteristics of a driver circuit arrangement over its entire operating range , with the voltage ranges annotated by p fet and n fet denoting the operating range of a pull - up and pull - down branch of the driver circuit arrangement , respectively . the line c shown in the bold form represents the iv characteristic of an ideal resistance . in contrast , the dashed line a represents the iv characteristic of a conventional driver circuit arrangement , whose pull - up and pull - down branches have been calibrated at v dd / 2 . in the operating range of the pull - up branch of a driver circuit arrangement which has been calibrated in this way , the characteristic a does not differ significantly from the ideal behavior , owing to the linearity of the driver circuit arrangement in this operating range . in the operating range of the pull - down branch , the driver circuit arrangement which has been calibrated in this way differs considerably from the ideal behavior . the thin line b represents the iv characteristic for a driver circuit arrangement according to the invention whose pull - up branch has been calibrated at the operating point v 1 and whose pull - down branch has been calibrated at the operating point v 2 . this characteristic has a relatively ideal behavior over the entire operating range of the driver circuit arrangement . this illustrates one advantage of the invention . in summary , the invention may have some or all of the following features . a driver system can include a first driver part and a first monitoring system . the first driver part has at least one variable impedance by which an operating point is determined for the first driver part with respect to a first potential and a second potential which supply the first driver part . the first monitoring device adjusts an impedance value of the variable impedance such that the operating point differs from a mid - point between the first and the second potential . the driver system may have a second driver part , which is supplied by the first and the second potential , and a second monitoring device . the second driver part can have at least one variable an impedance by which an operating point is determined for the second driver part with respect to a first potential and a second potential . the second monitoring device adjusts an impedance value of the variable impedance of the second driver part such that the operating point of the second driver part differs from a mid - point between the first and the second potential . alternatively , the driver system may have a second driver part , which is supplied by the first and the second potential . the second driver part has at least one variable impedance by which an operating point is determined for the second driver part with respect to a first potential and a second potential . the first monitoring device adjusts an impedance value of the variable impedance of the second driver part such that the operating point of the second driver part differs from a mid - point between the first and the second potential . the driver system may also have the operating point of the first and / or of the second driver part differ from the mid - point by more than 15 % of the difference between the first and the second potential . alternately , the driver system may have the operating point of the first and / or of the second driver part differ from the mid - point by less than 35 % of the difference between the first and the second potential . the driver system may have the magnitude of the difference between the mid - point and the operating point of the first driver part may be the same , but in the opposite direction of the difference between the mid - point and the operating point of the second driver part . the driver system may have the first and / or the second driver part form the pull - up and pull - down branch , respectively , of an off - chip driver . the driver system may have the operating point of the first driver part as the mid - point in a predetermined operating range of a transistor of a first conductance type in the first driver part , and / or the operating point of the second driver part as the mid - point in a predetermined operating range of a transistor of a second conductance type in the second driver part . the driver system may further include a first voltage divider and / or a second voltage divider . the first voltage divider has two series - connected impedances between the first and the second potential . the two impedances are chosen such that the potential at a junction point between the two impedances is the mid - point in a predetermined operating range of a transistor of a first conductance type in the first driver part . the second voltage divider has two series - connected impedances between the first and the second potential . the two impedances in the second voltage divider are chosen such that the potential at a junction point between the two impedances in the second voltage divider is the mid - point in a predetermined operating range of a transistor of a second conductance type in the second driver part . a memory system , in particular , a gddr3 / ddr3 memory chip , can include a driver system as described above . a driver calibration circuit arrangement for calibration of an impedance of a driver circuit arrangement , which is fed by a first and a second potential and has a predetermined operating range with respect to the first and the second potential , can include a circuit arrangement and a monitoring device . the circuit arrangement has a variable impedance and accommodates a reference impedance . the monitoring device is arranged and designed for sequential variation of the impedance of the circuit arrangement with a variable impedance , until the potential at a junction point between the reference impedance and the circuit arrangement with a variable impedance is equal to a mid - point in the predetermined operating range , within + 10 %, for example , within + 3 %, of the difference between the first and the second potential . the mid - point in the predetermined operating range differs from the mid - point between the first and the second potential . the driver calibration circuit arrangement can have the mid - point of the predetermined operating range differ from the mid - point between the first and the second potential by more than 15 % of the difference between the first and the second potential . alternatively , the driver calibration circuit arrangement can have the mid - point of the predetermined operating range differ from the mid - point between the first and the second potential by less than 35 % of the difference between the first and the second potential . in another alternative , the driver calibration circuit arrangement can have the mid - point of the predetermined operating range differing from the mid - point between the first and the second potential by 20 % of the difference between the first and the second potential . the driver calibration circuit arrangement may have the circuit arrangement with the variable impedance form an impedance for the driver circuit arrangement . a memory system , in particular , a gddr3 / ddr3 memory chip , can have a driver calibration circuit arrangement as described above . a method for calibration of an impedance of a driver circuit arrangement , which is fed by a first and a second potential and has a predetermined operating range with respect to the first and the second potential , can include sequentially varying the impedance of a circuit arrangement with a variable impedance . the circuit arrangement accommodates a reference impedance , until the potential at a junction point between the reference impedance and the circuit arrangement with the variable impedance equals a mid - point of the predetermined operating range within ± 10 %, for example , within ± 3 %, of the difference between the first and the second potential . the mid - point of the predetermined operating range differs from the mid - point between the first and the second potential . in this method , the mid - point of the predetermined operating range differs from the mid - point between the first and the second potential by more than 15 % of the difference between the first and the second potential . alternately , in this method , the mid - point of the predetermined operating range differs from the mid - point between the first and the second potential by less than 35 % of the difference between the first and the second potential . in another alternative , in this method , the mid - point of the predetermined operating range differs from the mid - point between the first and the second potential by 20 % of the difference between the first and the second potential . in this method , the circuit arrangement with the variable impedance forms an impedance for the driver circuit arrangement . in this method , the driver circuit arrangement is part of a memory system , in particular , a gddr3 / ddr3 memory chip . a driver calibration circuit arrangement for calibration of an impedance of a driver circuit arrangement can include a circuit arrangement with a variable impedance , and a monitoring device . the monitoring device sequentially varies the impedance of the circuit arrangement with the variable impedance , until its impedance is equal to a predetermined percentage of the impedance of a reference impedance within 10 %, for example , within ± 3 %, of the impedance of the reference impedance , with the percentage not being 100 %. the driver calibration circuit arrangement can have the predetermined percentage differ by more than 15 % from 100 %. alternately , the driver calibration circuit arrangement can have the predetermined percentage differ by less than 35 % from 100 %. in another alternative , the driver calibration circuit arrangement can have the predetermined percentage differing by 20 % from 100 %. the driver calibration circuit arrangement can have the circuit arrangement with the variable impedance form an impedance of the driver circuit arrangement . the driver calibration circuit arrangement can connect an external reference impedance as the reference impedance . a memory system , in particular , a gddr3 / ddr3 memory chip , can have a driver calibration circuit arrangement as described above . a method for calibration of an impedance of a driver circuit arrangement can include sequentially varying the impedance of a circuit arrangement with a variable impedance , until its impedance is equal to a predetermined percentage of the impedance of a reference impedance within + 10 %, for example , within ± 3 %, with the percentage not being 100 %. in this method , the predetermined percentage differs by more than 15 % from 100 %. alternately , in this method , the predetermined percentage differs by less than 35 % from 100 %. in another alternative , in this method , the predetermined percentage differs by 20 % from 100 %. in this method , the circuit arrangement with the variable impedance forms an impedance of the driver circuit arrangement . in this method , the circuit arrangement with the variable impedance connects an external reference impedance as the reference impedance . in this method , the driver circuit arrangement is part of a memory chip , in particular , a gddr3 / ddr3 memory chip . in the driver calibration circuit arrangement or method for calibration of an impedance of a driver circuit arrangement , as described above , the circuit arrangement with a variable impedance is formed by a single integrated circuit arrangement . in the driver system , the memory system , the driver calibration circuit arrangement , or the method for calibration of an impedance of a driver circuit arrangement , as described above , the driver system or the driver circuit arrangement is an off - chip driver . a driver system can include a first driver part and a first monitoring device . the first driver part has at least one variable impedance by which an operating point is determined for the first driver part with respect to a first potential and a second potential , which supply the first driver part . the first driver part has a predetermined operating range with respect to the first and the second potential with a mid - point that differs from the mid - point of the first and of the second potentials . the first monitoring device adjusts an impedance value of the variable impedance such that the operating point corresponds to a predetermined point , for instance , the mid - point , of the predetermined operating range within ± 10 %, for example , within ± 3 %, of the difference between the first and the second potential . a driver calibration circuit arrangement for calibration of an impedance of a driver circuit arrangement , which is fed by a first and a second potential , has a predetermined operating range with respect to the first and the second potential , and has a mid - point that differs from the mid - point of the first and of the second potentials , can include a circuit arrangement with a variable impedence and a monitoring device . the circuit arrangement accommodates a reference impedance . the monitoring device sequentially varies the impedance of the circuit arrangement with the variable impedance , until the potential at a junction point between the reference impedance and the circuit arrangement with the variable impedance equals a predetermined point , for instance , the mid - point , of the predetermined operating range within ± 10 %, for example , within ± 3 %, of the difference between the first and the second potential . a method for calibration of an impedance of a driver circuit arrangement , which has a predetermined operating range with respect to a first and a second potential and a mid - point that differs from the mid - point of the first and of the second potentials , can include sequentially varying the impedance of a circuit arrangement with the variable impedance , until an operating point , which is governed by the impedance , of the driver circuit arrangement coincides with a predetermined point , for instance , with the mid - point , of the predetermined operating range within ± 10 %, for example , within ± 3 %, of the difference between the first and the second potential . although the embodiments of the invention have been disclosed and described in detail in this description , it is obvious to a person skilled in the art that various changes can be made with respect to the configuration , the method of operation and the form of the invention without departing from the inventive idea or the area of protection . in particular , it should be noted that the respective features of the invention , including those which are disclosed only in conjunction with other features of the invention , may be combined in any desired configuration , apart from those which the person skilled in the art identifies as being obviously pointless . furthermore , the use of the singular or of the plural indicates only a preference , and should therefore not be regarded as being restrictive . except where the opposite is explicitly mentioned , the plural may be replaced by the singular , and vice versa . while the invention has been described in detail and with reference to specific embodiments thereof , it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof . accordingly , it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents .