as is evident in fig1 , a liquid crystal display lcd having additional functionality is provided as a touch - sensitive input device , and such a liquid crystal display may be used as a bottom area 12 of a mobile communications device 7 . however , it may also be advantageously implemented in other fields of application where a combination of liquid crystal display and touch - sensitive input device is desired . in essence , it is possible to apply the basic principles of designing a usual liquid crystal display lcd , which are known per se , and the wiring thereof as well as the basic principles of wiring a touch - sensitive input devices on the basis of ito layers . the mobile communications device 7 illustrated has a first housing part 8 and a second housing part 10 which may be adjusted relative to each other by means of an adjustment mechanism 11 . this adjustment mechanism 11 is in particular an articulated connection that allows the first housing part 8 having a display device 9 integrated therein to be folded against the wall of the second housing part 10 . however , as an alternative other mechanisms for pivoting or sliding the corresponding housing parts may be realised . in the illustrated communications device 7 , an input device 14 for inputting characters and / or other control instructions may , for example , be provided as a rotationally operable assembly in the area of a pivot axis x for pivoting the two housing parts 8 , 10 relative to one another . however , additionally or alternatively also other types of input devices in the form of , for example , keypad elements may be disposed on one or both of the housing parts 8 , 10 . for speech communication , the two housing parts 8 , 10 include a microphone 15 or a speaker 16 , as this is known per se from mobile phones . in a likewise usual manner , the communications device 7 is provided with a circuit 13 , in particular with a circuit in the form of an integrated processor . the circuit 13 is used for operating the various functions offered to the user by the communications device 7 . this circuit 13 or , if any , a further stand - alone circuit is additionally used to operate the liquid crystal display lcd which is formed as a bottom area in the second housing part 10 . fig1 shows the communications device 7 in a first position in which the second housing part 10 including the display device 9 is located at a distance from the first housing part 8 . fig2 shows the communications device 7 of fig1 in a second , folded - together position , in which the display device 9 of the first housing part 8 adjoins the liquid crystal display lcd of the second housing part 10 . in this connection , fig2 shows a bottom view with a liquid crystal display lcd which in this view is located at the top . as is evident in particular from fig1 , the second housing part 10 preferably has a recess 17 , the opening circumference of which corresponds to the first housing part 8 and extends through to the liquid crystal display lcd 12 . in the folded - together state , it is then possible to view the display device 9 with the images , symbols etc . shown thereon through the liquid crystal display lcd , which is now wholly or mainly in the transparent state . as a result , the actual display device 9 remains visible even in the folded - together state . in order to switch the liquid crystal device ldc into the transparent state , no transparency voltage vt will have to be applied to the liquid crystal display lcd or the electrodes thereof . in the folded - together state , characters , grids and / or symbols 18 may be displayed , if desired , by a corresponding triggering of electrodes of the liquid crystal display lcd and / or the display device 9 . such symbols may advantageously refer to touch - sensitive areas , which may be touched in order to activate functions etc . such touch - sensitive functionality as an input device is provided by the liquid crystal display lcd having an additional function as a touch - sensitive input device . in the first position shown in fig1 , a user will hold the communications device usually in such a way that the second housing part 10 lies on the user &# 39 ; s hand . the upper surface of the bottom area 12 , which is exposed once the first housing part 9 has been opened up , will accordingly be facing the user and his / her view . in this position , the liquid crystal display lcd forming the bottom area 12 is preferably connected as a touch - sensitive input device that may be operated from the top . to this end , expediently no longer the bottom electrode layer , but now the top electrode layer of the liquid crystal device will be connected as a touch - sensitive electrode layer . in this folded - open position , a voltage will preferably be applied across all or nearly all of the liquid crystal display lcd in such a way that it will switch into the non - transparent state . individual symbols 18 , grid lines or other characters may be displayed by means of the liquid crystal device lcd , and the display will be carried out particularly preferably by switching the corresponding symbols and characters to be displayed into the transparent state . in this way , the bottom area 12 of the second housing part 10 may be used as an additional input device with touch - sensitive functionality and at the same time as a display of control elements . fig1 shows a section of an example of an lcd on an enlarged scale . what is shown is , in a usual manner , two substrates 19 , 20 made of a transparent material such as glass , acrylic or plastics . on the surfaces facing each other , a first or a second electrode layer 5 , 6 is provided , which are divided into individual electrodes 1 , 2 in order to form pixels 3 . usually , further layers such as a hard layer and / or a polyimide layer 21 or 22 are applied onto the surfaces of the two electrode layers 5 , 6 , which face one another . between these , a space is defined by individual spacers 23 , into which a liquid crystal layer 4 has been inserted . on the outside of the two substrate materials , polarizers have been applied in the form of , for example , films 27 , 28 . the voltage diagram schematically shown above the section of the liquid crystal display lcd shows an example of a voltage diagram of a voltage v , which is applied to at least one electrode pair made up of a first electrode 1 and a second electrode 2 , which are used for depicting a pixel 3 . moreover , the first electrode 1 or the second electrode 2 additionally serves as a sensor element for touch - sensitive input . the circuit - related evaluations are preferably carried out in relation to capacity in a manner known per se for touch - sensitive input devices , for example according to a principle schematically shown in fig8 . two different voltage threshold values for the functionalities as a liquid crystal display or as a touch - sensitive input device are provided . the base voltage 0 is , for example , a ground or zero voltage of the circuitry 13 , but in principle may also have a different voltage level . on the basis of the base voltage 0 , an optional first sensor voltage threshold vss * will be closest to the base voltage 0 . above this first sensor voltage threshold vss *, there is a threshold voltage vd for the functionality as a liquid crystal display lcd , and above this threshold voltage vd there is a further sensor threshold voltage vss for the sensor functionality . the voltage diagram shows a first state of the liquid crystal displays lcd or the corresponding pixel 3 with a transparent state over two first periods t . the curve of the voltage v applied to the two electrodes 1 , 2 remains below the threshold value vd . in two subsequent periods t , the second state of the liquid crystal display lcd or of the pixel 3 triggered by the voltage v is schematically shown . in this state , the voltage increases starting from the base voltage 0 during an initial time period as a feedback duration tr , which is shorter than or equal to a feedback period customary for liquid crystal displays , up to the threshold voltage vd or up to the voltage ranges above the threshold voltage vd , and will for the remaining time tr * of this period t remain in the voltage range which is equal to or higher than the threshold voltage vd . by this means , the corresponding pixel 3 will be switched into the non - transparent state for the duration of the third and the fourth periods t . triggering of the transparent or the non - transparent state is carried out by means of a threshold voltage vt , which , for example during the first two periods t , will preferably be equal to the base voltage 0 and will , for example during the two next periods t , increase respectively for at least the second time period tr * up to the threshold voltage vd and will stay there . in order to prevent burn - in , a transparency voltage vt alternately switched to the positive or the negative range is applied to the electrodes , so that as shown the curve of the voltage v for each second period t will not be switched to the positive , but to the negative voltage range . accordingly , further threshold values vss * − , vd − and vss − are provided in the negative voltage range , and an evaluation may be carried out on the basis of the nominal voltage values . it is an essential feature of this embodiment that , for the sensor functionality , a sensor voltage vs is superimposed on or added to the transparency voltage vt . the voltage v applied to the electrodes 1 , 2 will thus be made up of the transparency voltage vt and additionally the sensor voltage vs . the sensor voltage vs has a periodic curve over the respective periods t ; in principle , any continuously changing voltage function may be used . however , voltage curves of the saw tooth type , which at the start of each period t begin with the base voltage 0 and the nominal value of which increases continuously depending on the respective period in the positive or the negative direction in a manner known per se , are particularly preferred . once the first threshold voltage vss * has been reached , the period t will end and the sensor voltage vs will be returned to the base voltage 0 . across this period t , a number clkt of clocks clk will be counted within the period t . if an object 5 approaches the electrodes 1 , 2 of the pixel 3 , the capacity value will increase so that a higher number of clocks is needed for the sensor threshold voltage vss * or vss * − to be reached and thus the period t ends . thus , the number clkt of clocks clk is a direct measurement for an object 5 approaching the electrodes 1 , 2 . in addition to a customary circuit for triggering the pixels 3 or for triggering their electrodes 1 , 2 for switching into a transparent or non - transparent state , therefore , a capacity present on the electrodes 1 , 2 or on at least one of the electrodes 1 , 2 is taken into account . due to the superimposition of the transparency voltage vt and the sensor voltage vs , the respective first sensor voltage vss *, vss * − will necessarily be exceeded in the depicted third and fourth periods , without giving , in doing so , a relevant criterion for the sensor property . accordingly , the second sensor threshold vss , vss − is used as a criterion for an approaching object 5 , if the pixel 3 assigned to the electrodes 1 , 2 is to be switched into the non - transparent state . instead of making the period duration t dependent on reaching the first or the second sensor threshold voltage vss *, vss , which requires an adaptation of the switching periods for the transparency voltage vt or might , if applicable , require a complicated variable fixing of the sensor voltage thresholds , a possible alternative could also be an embodiment having a fixed period t . in this case it is checked whether or not the voltage v applied to the electrodes exceeds a correspondingly selected sensor threshold voltage vss * or vss within the period t . instead of a binary signal value for indicating an approaching object 5 or no approaching object 5 it is also possible to output a variable value as a sensor signal . in the case of the first embodiment with a variable period duration , the value of the number clkt of the clocks during the period t could be used as a direct measurement for the state of an approaching object 5 . in the case of the second embodiment having a fixed period t , the maximum voltage v reached during the period t would represent such a variable value . in addition to the voltage diagram schematically shown in fig1 , fig3 shows a schematic view of a sensor device circuitry per se known . in this case , the sensor voltage vs is supplied by a suitable voltage source or current source 25 having a current limiter for generating the increasing voltage . for example , such a current source 25 may be formed by a transistor including a zener diode . the voltage will be applied to one of the two electrodes 1 or to both electrodes 1 , 2 , with the two electrodes 1 , 2 having a capacity value cp between them . this capacity value cp will increase during the approach of an object 5 , so that the slope of the voltage curve will be less steep . by means of the operational amplifier 26 as well as further downstream components , the approach of an object 5 will be determined in a usual manner . the circuit 25 will preferably apply a voltage v having various levels depending on whether a transparent or a non - transparent state is to be triggered . fig3 shows that , in particular in the case of the circuit of the non - transparent state , the curve within one period is not linear , but rather increasing in a varying manner , since in practice in particular the transparency voltage vt will not be present as a pure square - wave voltage due to , amongst others , relaxation effects . fig4 shows an alternative voltage curve for the case where the transparency voltage vt is applied as a pure square - wave voltage and the purely saw tooth - shaped sensor voltage vs is superimposed on this for the case of four periods with alternating signs and pixel 3 is switched into the non - transparent state . fig5 a and 5b show a further embodiment of connecting the first and second electrodes 1 , 2 forming the pixel 3 , with pixel 3 at the same time serving as a sensor element . the top voltage curve shows the voltage v 1 of the first electrode 1 . the bottom voltage curve shows the voltage v 2 of the second electrode 2 . v 12 symbolises the voltage differential between the electrodes 1 and 2 . also shown is the circuit of fig1 and 3 complemented , however , by a switch as a switching device 29 . the switching device 29 is used for connecting or particularly short - circuiting the two electrodes 1 and 2 for triggering the transparent state ( fig5 b ). as a result , the voltages applied to both electrodes 1 , 2 will be on the same level as the sensor voltage vs and they will have the same value as one another , i . e . v 1 = v 2 . the voltage differential v 12 will accordingly be equal to zero . in the other switching state , the switching device 29 is used to disconnect the two electrodes 1 and 2 from each other for triggering the non - transparent state and to pull a second electrode to the base voltage 0 or ground ( fig5 a ). here , the first electrode 1 will be on the sensor voltage vs which is high enough above the value of the voltage differential v 12 or the threshold value vd in order to blacken pixel 3 . fig6 shows the principle of the voltages v 1 , v 2 according to fig5 a . this shows a schematic view of an alternative circuit having a voltage source 25 which will generate , instead of an alternating voltage v , a voltage v having a saw tooth - like curve increasing in just one direction . not only combinations of the individually described components and functions are possible , but also modified embodiments based on the same basic concepts may be advantageously implemented . for example , in the opened condition of the mobile device , the entire then bottom area of the second electrode layer 6 may advantageously be connected to ground , in order to prevent any interfering influences by the hand of a user holding the device .