Abstract:
A supply voltage distribution system for distributing a supply voltage through a semiconductor device, the supply voltage distribution system comprising: a first supply voltage distribution line arrangement and a second supply voltage distribution line arrangement, said first supply voltage distribution line arrangement and said second supply voltage distribution line arrangement being adapted to receive from outside the semiconductor device a semiconductor device supply voltage and to distribute a supply voltage to respective first and second portions of the semiconductor device; a voltage-to-voltage conversion circuit connected to the first supply voltage distribution line arrangement, wherein the voltage-to-voltage conversion circuit is adapted to either transfer onto the first supply voltage distribution line arrangement the semiconductor device supply voltage received from outside the semiconductor device, or to put on the first supply voltage distribution line a converted supply voltage having a value different from the semiconductor device supply voltage, wherein the voltage-to-voltage conversion circuit further comprises means selectively activatable for causing the first supply voltage distribution line arrangement to be electrically coupled to said second supply voltage distribution line arrangement.

Description:
PRIORITY CLAIM  
       [0001]     This application claims priority from European patent application No. EP06117949.5, filed Jul. 27, 2006, which is incorporated herein by reference.  
       TECHNICAL FIELD  
       [0002]     An embodiment of the present invention relates to the field of semiconductor devices and Integrated Circuits (ICs). More specifically, an embodiment of the present invention relates to semiconductor devices and ICs supporting different supply voltages.  
       BACKGROUND  
       [0003]     Semiconductor devices, such as semiconductor memory devices, can be designed so as to be capable of supporting different supply voltages, depending on the intended application. For example, dual-power-supply semiconductor devices (such as, for example, flash memory ICs) can operate with either a first, higher supply voltage (e.g., 3V) or a second, lower supply voltage (e.g., 1.8V).  
         [0004]     Operation at a lower supply voltage is for example typical of battery-powered systems, and allows reducing the power consumption.  
         [0005]     In both cases, the (lower or higher) supply voltage is fed to the internal circuitry of the semiconductor device, through supply-voltage distribution lines, which are adapted to distribute the supply voltage through the device.  
         [0006]     In particular, a known design rule provides for having supply-voltage distribution lines for distributing the supply voltage to the device&#39;s core circuitry, comprising key circuital structures adapted for performing the desired tasks (like, in the case of memory devices, memory cells row and column selectors, sense amplifiers, control logic controlling the memory device operation), which are distinct from supply-voltage distribution lines for distributing the supply voltage to input/output circuits, like input/output buffers. By this measure, it is possible to reduce the risk that the operation of the core circuitry is affected by noise on the supply voltage produced by the switching of the input/output circuits. In other words, dedicated supply-voltage distribution lines are used for the core circuitry and the input/output circuits, for decoupling the disturbs occurring during the input/output buffers operation from the remaining circuitry of the semiconductor device.  
         [0007]     In order to reduce power consumption, the internal circuitry, particularly the core circuitry of dual-power-supply devices is typically designed to operate with a supply voltage that is lower than the first, higher supply voltage (for example, the internal circuitry of the semiconductor device voltage may be designed to operate with an internal supply voltage of 2.3V, which is intermediate between the first, higher supply voltage and the second, lower supply voltage). For down-converting the external, higher supply voltage into the (lower) internal voltage, a Voltage Down-Converter “VDC” is provided for, which is able to lower the voltage (e.g., starting from the external voltage of 3V, the VDC generates the internal voltage of 2.3V). The VDC has also the function of stabilizing the internal supply voltage of the semiconductor device.  
         [0008]     On the other hand, those parts of the circuitry of the semiconductor device that, like input/output buffers, are used for interfacing the semiconductor device with the external environment (typically a system bus), need to be supplied at either the first, higher supply voltage, or to the second, lower supply voltage, depending on the environment in which the semiconductor device is inserted. Voltage-level adapters (shifters) are provided for interfacing the core circuitry with the input/output circuits.  
         [0009]     When the semiconductor device is employed in low-supply voltage applications, the internal circuitry of the semiconductor device should be supplied by a supply voltage equal to the external supply voltage. A voltage switch is provided for the electrical connection between the supply-voltage distribution line that receives (from the semiconductor device terminals) the externally supplied supply voltage and the supply-voltage distribution line that distributes the supply voltage to the core circuitry; the VDC is in this case kept off, and bypassed by the voltage switch.  
         [0010]     The dual-power-supply semiconductor device is typically configured for either a lower-voltage application or a higher-voltage application during the testing, for example by burning a fuse in a control structure that controls the activation of the VDC or, in alternative, of the voltage switch.  
         [0011]     Typically, the voltage switch is implemented by a MOS transistor, particularly of p-type conductivity (i.e., a PMOS), which is connected between the semiconductor device terminals that, in operation, are connected to the supply-voltage distribution line that receives the externally supplied supply voltage and the supply-voltage distribution line distributing the supply voltage to the core circuitry, and has a control (i.e. a gate) terminal receiving the control signal. When, as a consequence of the semiconductor device configuration during the testing, the PMOS transistor is turned on, the low supply voltage received from the supply-voltage distribution line is fed to the core circuitry.  
         [0012]     The voltage switch has a resistance (the PMOS transistor on resistance) that inevitably causes a voltage drop across it. Thus, the actual internal supply voltage, which is fed to the core circuitry, is often lower than the external low supply voltage.  
       SUMMARY  
       [0013]     A drawback of the above-described solution is that in order to reduce the voltage drop across the voltage switch, the resistance of the MOS transistor should be kept as low as possible. This however has a detrimental impact on the size of the semiconductor device, and thus on the IC chip size, since the on-resistance of a MOS transistor typically decreases with the increase in size of the MOS transistor.  
         [0014]     Moreover, when the size of the MOS transistor is increased, the size of the supply-voltage distribution lines which are connected thereto may be increased as well. This may result in a further increase in the IC chip area and at the same time may have a detrimental impact on the resistance of the supply-voltage distribution lines (since the resistance thereof increases as they become longer).  
         [0015]     A further problem of the above-described solution is that in order to reduce the overall resistance due to both the voltage switch and the supply-voltage distribution lines, the complexity of the floor plan (i.e., the design of the IC layout) may be increased.  
         [0016]     In general, an embodiment of the present invention is based on the idea that, in low-supply-voltage applications, the supply voltage for the core circuitry of the semiconductor device can be derived also from the supply-voltage distribution line(s) dedicated to supplying the input/output circuits of the semiconductor device.  
         [0017]     In detail, an embodiment of the present invention proposes a supply-voltage distribution system for distributing a supply voltage through a semiconductor device. The supply-voltage distribution system comprises: a first supply-voltage distribution line arrangement and a second supply-voltage distribution line arrangement, said first supply-voltage distribution line arrangement and said second supply-voltage distribution line arrangement being adapted to receive from outside of the semiconductor device a semiconductor-device supply voltage and to distribute a supply voltage to respective first and second portions of the semiconductor device; a voltage-to-voltage conversion circuit connected to the first supply-voltage distribution-line arrangement, wherein the voltage-to-voltage conversion circuit is adapted to either transfer onto the first supply-voltage distribution-line arrangement the semiconductor-device supply voltage received from outside the semiconductor device, or to put on the first supply-voltage distribution line a converted supply voltage having a value different from the semiconductor device supply voltage. The voltage-to-voltage conversion circuit further comprises means selectively activatable for causing the first supply-voltage distribution-line arrangement to be electrically coupled to said second supply-voltage distribution line arrangement. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  schematically shows a semiconductor device according to an embodiment of the present invention;  
         [0019]      FIG. 2  schematically shows a layout of power-supply distribution lines for the semiconductor device of  FIG. 1 , according to an embodiment of the present invention; and  
         [0020]      FIG. 3  shows an exemplificative electronic system wherein the semiconductor device according to an embodiment of the present invention is employed. 
     
    
     DETAILED DESCRIPTION  
       [0021]     Referring to  FIG. 1 , a semiconductor device  100  according to an embodiment of the present invention is shown. The semiconductor device  100  is integrated in a semiconductor material, typically silicon, chip. For example, but not limitatively, the semiconductor device  100  may be a semiconductor memory, like a non-volatile memory, e.g. a Flash memory.  
         [0022]     The semiconductor device  100  is a dual-power-supply device, i.e. it is designed so as to be capable of operating with different supply voltages, depending on the intended application. For example, the semiconductor device  100  may operate with a first, higher-supply voltage, e.g. of 3V nominally, or with a second, lower supply voltage, e.g. of 1.8V nominally. It is pointed out that, more generally, the semiconductor device  100  might be designed so as to be able of operating with more then two different voltage supplies.  
         [0023]     The semiconductor device  100  has first terminals  105   a  and second terminals  105   b  (typically, metal pads of the IC), intended for the connection to an external power-supply voltage-distribution line  110  of the electronic system where the semiconductor device  100  has to be inserted.  
         [0024]     The first terminals  105   a  are connected to a first supply-voltage-distribution-line arrangement  115   a,  and the second terminals  105   b  are connected to a second supply-voltage-distribution-line arrangement  115   b , which are provided internally to the semiconductor device IC for distributing the supply voltage that, in use, is received from the outside through the external power-supply-voltage distribution line  110 .  
         [0025]     In particular, the first supply-voltage-distribution-line arrangement  115   a  is provided for distributing the supply voltage to a first portion of the semiconductor device  100 , like for example a core circuitry  120  of the semiconductor device  100 . For example, in the case of a memory device, the core circuitry  120  may include address decoders, memory cell matrix rows and columns selectors, sensing circuits, programming circuits, control circuits. The second supply-voltage-distribution-line arrangement  115   b  is instead provided for distributing the supply voltage to a second portion of the semiconductor device  100  comprising for example interface circuits of the semiconductor device  100 , particularly input/output buffers  125 , for example, input buffers for receiving from the outside addresses of memory locations, and input/output buffers for outputting data read from the memory locations, or for inputting data to be written into the memory locations of the semiconductor device  100 .  
         [0026]     The external power-supply-voltage distribution line  110  supplies a voltage VDD_ext, which, as described above, depending on the intended application, may take the first, higher value of, e.g., 3V, or the second, lower value of, e.g., 1.8V. The voltage VDD_ext is distributed internally to the semiconductor device  100  by the first and second supply-voltage-distribution-line arrangements  115   a  and  115   b . In the following, the voltage received by the first supply-voltage-distribution-line arrangement  115   a  from the terminals  105   a  will be referred to as VDDE_CORE, whereas the voltage received (and distributed) by the second supply-voltage-distribution-line arrangement  115   b  from the terminals  105   b  will be referred to as VDDE_ 10 .  
         [0027]     The core circuitry  120  of the semiconductor device is assumed to be designed so as to be capable of operating with a maximum supply voltage that is lower than the first, higher supply voltage, but higher than the second, lower supply voltage. For example, the internal circuitry of the semiconductor device voltage may be designed to operate with an internal supply voltage of 2.3V, which is intermediate between the exemplary values of 3V for the first, higher supply voltage, and of 1.8V for the second, lower supply voltage. This is a known measure that IC designers take so as to trade off operating speed for power consumption (operating at a higher supply voltage increases the speed, but also the power consumption).  
         [0028]     For this purpose, a voltage-to-voltage conversion circuit  130  is provided in the semiconductor device  100 , for supplying the core circuitry  120  with the most appropriate supply voltage, depending on the intended application. The voltage-to-voltage conversion circuit  130  is provided along the first supply-voltage-distribution-line arrangement  115   a , and is adapted to generate a supply voltage VDDI that is distributed to the core circuitry  120 . In greater detail, the first supply-voltage-distribution-line arrangement  115   a  comprises a first section  115   a - 1  and a second section  115   a - 2 ; the first section  115   a - 1  extends from the first terminals  105   a  to the voltage-to-voltage conversion circuit  130 , whereas the second section  115   a - 2  extends from the voltage-to-voltage conversion circuit  130  to the core circuitry  120 . The second section  115   a - 2  of the first supply-voltage-distribution-line arrangement  115   a  is used to distribute the supply voltage VDDI internally to the semiconductor device IC. Depending on the intended application, the supply voltage VDDI may either take the value (e.g., 1.8V) of the external voltage VDD_ext (this occurs in low-supply-voltage applications), or a value (e.g., 2.3V) lower (more generally, different) than the external voltage VDD_ext (this occurs in applications where the external supply voltage is for example equal to 3V).  
         [0029]     A voltage-level adapter (shifter)  132  is also provided in the semiconductor device  100 , for interfacing the core circuitry  120  with the input/output buffer  125 . In particular, the level shifter  132  receives both the supply voltage VDDI and the voltage VDDE_ 10 , through respectively the first and the second supply-voltage-distribution-line arrangements  115   a  and  115   b .  
         [0030]     The input/output buffers  125  are used for interfacing the semiconductor device  100  with the external environment, in particular for receiving input signals DATA_IN (for example in case of the memory Flash, comprising addresses of memory locations, and data to be written into the memory locations of the semiconductor device  100 ) and outputting output signals DATA_OUT (for example in case of the memory Flash, data read from the memory locations). The voltage levels of the input signals DATA_IN and the output signals DATA_OUT have to be compliant to the value of the external supply voltage VDD_ext, so they depend on the intended application; for example, in case the external supply voltage VDD_ext is equal to  3 V, the input signals DATA_IN and the output signals DATA_OUT have to take voltage levels varying between ground and 3V, whereas in case the external supply voltage VDD_ext is equal to 1.8V, the input signals DATA_IN and of the output signals DATA_OUT have to take voltage levels varying between ground and 1.8V.  
         [0031]     Since as mentioned above the core circuitry  120  operates at the supply voltage VDDI that, when the external voltage VDDE_ext is equal to e.g. 3V, is lower than 3V, being for example of 2.3V, the shifter  132  is adapted to shift (lower) the voltage of the input signals DATA_IN′ from the input/output buffers  125 , to make them compliant with the supply voltage of the core circuitry  120 , and to shift (increase) the voltage of the output signals DATA_OUT′ from the core circuitry  120  so as to make them compliant with the value of the external supply voltage VDD_ext.  
         [0032]     In applications where the external supply voltage VDD_ext takes the second, lower value of, e.g., 1.8V, the core circuitry  120  operates with a supply voltage VDDI of value equal to the voltage VDDE_ext, thus the shifter  132  leaves the signals&#39; voltage levels untouched.  
         [0033]     In greater detail, the voltage-to-voltage conversion circuit  130  has an input terminal  135  which is connected to the first section  115   a - 1  of the first supply-voltage-distribution-line arrangement  115   a  thus receiving the voltage VDDE_CORE, and an output terminal  140  which is connected to the second section  115   a - 2  of the first supply-voltage-distribution-line arrangement  115   a.    
         [0034]     As mentioned above, in applications where the external voltage VDD_ext takes the first, higher voltage value of, e.g., 3V, the voltage-to-voltage conversion circuit  130  is adapted to lower the voltage VDDE_CORE; for example, starting from the external voltage of 3V, the voltage-to-voltage conversion circuit  130  is adapted to lower the external supply voltage value to a value sustained by the core circuitry  120 , for example 2.3V; on the contrary, in applications where the external voltage VDD_ext takes the second, lower voltage, the voltage-to-voltage conversion circuit  130  transfers the voltage VDDE_CORE present on the first section  115   a - 1  of the first supply-voltage-distribution-line arrangement  115   a  to the second section  115   a - 2 , so that the supply voltage VDDI is equal to the voltage VDD_ext.  
         [0035]     The voltage-to-voltage conversion circuit  130  comprises a VDC  150  which is connected between the input terminal  135  and the output terminal  140  of the voltage-to-voltage conversion circuit  130 ; the activation of the VDC  150  is controlled by a first control signal VCON, which, according to assertion state thereof, causes the VDC  150  to generate the proper voltage value for the supply voltage VDDI to be fed to the core circuitry  120 .  
         [0036]     The voltage-to-voltage conversion circuit  130  further comprises a first voltage switch  155  (for example implemented by one or more MOS transistors, e.g., PMOS transistors) which is connected in parallel to the VDC  150 . The first voltage switch  155  receives and is controlled by the first control signal VCON and, according to assertion state of this signal, the first switch  155  connects the input terminal  135  to the output terminal  140  of the voltage-to-voltage conversion circuit  130 . More in particular, when the assertion state of the first control signal VCON is such that the VDC  150  is activated, the first voltage switch  155  is off (open-circuit); vice versa, when the assertion state of the first control signal VCON is such that the VDC  150  is de-activated, the first voltage switch  155  is on, thus providing an electrical connection between the input terminal  135  and the output terminal  140  (so by-passing the VDC  150 ). In other words, the VDC  150  and the first voltage switch  155  operate in mutually exclusive manner.  
         [0037]     The voltage-to-voltage conversion circuit  130  further includes a second voltage switch  160  (for example implemented by one or more further MOS transistors, e.g., PMOS transistors) having a first terminal  170  which is connected to the second supply-voltage-distribution-line arrangement  115   b  thus receiving the voltage VDDE_IO, and a second terminal  165  which is connected to the output terminal  140 , and thus to the second section  115   a - 2  of the first supply-voltage-distribution-line arrangement  115   a . The second voltage switch  160  receives and is controlled by a second control signal VCON′ and, according to assertion state thereof, electrically connects the first terminal  170  to the second terminal  165 , thereby transferring the voltage VDDE_IO present on the second supply-voltage-distribution-line arrangement  115   b  to the second section  115   a - 2  of the first supply-voltage-distribution-line arrangement  115   a.    
         [0038]     A voltage-to-voltage conversion control circuit  175  is provided, adapted to generate the first control signal VCON and the second control signal VCON′. The control circuit  175  is responsive to an operating mode signal(s) OP_MODE received from the core circuitry  120  and on a semiconductor-device configuration signal(s) CONF received from a configuration structure  180 , comprising for example fuses. In particular, the operating mode signal(s) OP_MODE is adapted to indicate an operating mode of the semiconductor device  100 : for example, the operating mode signal OP_MODE is de-asserted to indicate that the core circuitry  120  is operating simultaneously to the input/output buffers  125  (i.e., the input/output buffers  125  are active, because a transfer of data received from outside to the core circuitry, and/or a transfer of data received from the core circuitry and to be outputted is taking place); vice versa the operating mode signal OP_MODE is asserted to indicate that the input/output buffers  125  and the core circuitry  120  are not operating simultaneously (i.e., the input/output buffers  125  are inactive, since no transfer of data received from outside to the core circuitry, nor transfer of data received from the core circuitry and to be outputted is taking place). During the configuration of the semiconductor device  100 , for example during the post-manufacturing testing of the IC, the configuration structure  180  is set so that, in operation the configuration signal CONF takes the state corresponding to the intended application; for example, this may involve burning one or more fuses. For example, the configuration signal CONF may take an asserted state when the semiconductor device  100  is configured for applications in which the external supply voltage takes the first, higher value, whereas the configuration signal CONF may take a de-asserted state when the semiconductor device is configured for applications in which the external supply voltage takes the second, lower value.  
         [0039]     In particular, the first control signal VCON depends on the configuration signal CONF, i.e. on the device configuration stored in the configuration structure  180 ; the second control signal VCON′ depends as well on the configuration signal CONF, but also on the operating mode signal OP_MODE, and thus on the operating mode of the semiconductor device  100 .  
         [0040]     In operation, when the configuration signal CONF is asserted (meaning that the semiconductor device  100  is configured for applications in which the external supply voltage VDD_ext takes the first, higher value), the first control signal VCON is asserted; vice versa, when the configuration signal CONF is de-asserted (meaning that the semiconductor device  100  is configured for applications in which the external supply voltage VDD_ext takes the second, lower value) the first control signal VCON is de-asserted. The second control signal VCON′ is asserted when the configuration signal CONF is de-asserted (meaning that the semiconductor device  100  is configured for applications in which the external supply voltage VDD_ext takes the second, lower value) and the operating mode signal OP_MODE is asserted (meaning that the input/output buffers  125  and the core circuitry  120  are not operating simultaneously); in all the other cases, the second control signal VCON′ is de-asserted.  
         [0041]     As described above, the semiconductor device  100  may operate with a first, higher supply voltage, e.g. of 3V, or with a second, lower supply voltage, e.g. of 1.8V.  
         [0042]     When the semiconductor device  100  has been configured for applications in which the external voltage VDD_ext takes the first, higher supply voltage, e.g. of 3V, the configuration signal CONF is asserted. In this condition, the voltage-to-voltage conversion control circuit  175  asserts the first control signal VCON and de-asserts the second control signal VCON′. The first and second voltage switches  155  and  160  are both off, and the VDC  150  is activated; the VDC  150  converts the voltage VDDE_CORE, e.g. of 3V, received on the first section  115   a - 1  of the first supply voltage distribution line arrangement  115   a , into the supply voltage VDDI, e.g. 2.3V, and this voltage is distributed to the core circuitry  120  on the second section  115   a - 2 . For example, during the operation, the core circuitry  120  is able to perform the intended tasks operating with the voltage of 2.3V; for example, the core circuitry  120  may receive address signals of memory locations to be read/written, access the addressed locations, read/write data therefrom/thereinto, and sending to the shifter  132  the output signals DATA_OUT (such as data stored in memory locations of the Flash memory). The level shifter  132  properly shifts the voltage levels of the signals, so that, at the output of the shifter  132 , the output signals DATA_OUT are compliant with the external supply voltage.  
         [0043]     Since the second control signal VCON′ is de-asserted, the second voltage switch  160  is off, and no electrical connection results between the second supply voltage distribution line arrangement  115   b  carrying the voltage VDDE_IO and the second section  115   a - 2  of the first supply-voltage-distribution-line arrangement  115   a  carrying the voltage VDDI.  
         [0044]     When the semiconductor device  100  has been configured for applications in which the external voltage VDD_ext takes the second, lower supply voltage, e.g. of 1.8V, the configuration signal CONF is de-asserted. In this condition, the voltage-to-voltage conversion control circuit  175  de-asserts the first control signal VCON so that the first voltage switch  155  is kept on, whereas the VDC  150  is de-activated and by-passed.  
         [0045]     In particular, the first voltage switch  155  electrically connects the input terminal  135  of the voltage-to-voltage conversion circuit  130  to the output terminal  140  thereof so that the internal supply voltage VDDI is equal to the second, lower supply voltage.  
         [0046]     When the operation mode signal OP_MODE is asserted (to indicate that the input/output buffers  125  and the core circuitry  120  are not operating simultaneously), the voltage-to-voltage conversion control circuit  175  asserts the second control signal VCON′, and thus the second voltage switch  160  is kept on. In such a way, the second supply-voltage-distribution-line arrangement  115   b , distributing the voltage VDDE_IO to the input/output circuits  125 , is coupled to the second section  115   a - 2  of the first supply-voltage-distribution-line arrangement  115   a , carrying the supply voltage VDDI to the core circuitry  120 . It is observed that since in this operating condition the core circuitry  120  and the input/output buffers  125  are not operating simultaneously, the latter do not induce disturbs on the voltage VDDE_IO, and thus no disturbs are induced on the supply voltage VDDI that supplies the core circuitry  120 ; thus, the correct operation of the core circuitry  120  is not impaired by the connection of the second section  115   a - 2  of the first supply-voltage-distribution-line arrangement  115   a  to the second supply-voltage-distribution-line arrangement  115   b.    
         [0047]     When instead the operation-mode signal OP_MODE is de-asserted (to indicate that the input/output buffers  125  and the core circuitry  120  are operating simultaneously), the voltage-to-voltage conversion control circuit  175  de-asserts the second control signal VCON′ so that the second voltage switch  160  is kept off (open circuit). In such a way, there is no electrical connection between the second supply-voltage-distribution-line arrangement  115   b  distributing the voltage VDDE_IO to the input/output buffers  125  and the second section  115   a - 2  of the first supply-voltage-distribution-line arrangement  115   a  distributing the voltage VDDI to the core circuitry  120 . As a result, the core circuitry  120  and the input/output buffers  125  can operate simultaneously without the disturbs on the voltage VDDE_IO produced by the switching of the input/output buffers propagating on the supply voltage VDDI that supplies the core circuitry  120  (these disturbs might impair the correct operation of the core circuitry  120 ).  
         [0048]     Moving now to  FIG. 2 , a layout of power-supply distribution lines for the semiconductor device of  FIG. 1 , according to an embodiment of the present invention is shown. Elements identical or similar to those shown in  FIG. 1  are denoted by the same reference numerals.  
         [0049]     The second supply-voltage-distribution-line arrangement  115   b  has a generic ring shape (in the shown example, the ring has a generic rectangular shape, and it is closed, however this is not to be intended as a limitation of the invention), and surrounds a region of the IC chip wherein the core circuitry  120 , the level shifter  132 , the input/output buffers  125  and the configuration structure  180  are integrated; in particular, the second supply-voltage-distribution-line arrangement  115   b  may run along a periphery of the IC.  
         [0050]     The second section  115   a - 2  of the first supply-voltage-distribution-line arrangement  115   a  has, similarly to the second supply-voltage-distribution-line arrangement  115   b , a generic ring shape (in the shown example, the ring formed by the second section  115   a - 2  has as well a generic rectangular shape, and it is closed, however this is not to be intended as a limitation of the invention), and extends internally to the second supply voltage distribution line arrangement  115   b.    
         [0051]     The core circuitry  120  is integrated in a region of the IC chip surrounded by the second section  115   a - 2  of the first supply-voltage-distribution-line arrangement  115   a . The voltage-to-voltage conversion control circuit  175  is as well integrated in this region of the IC chip.  
         [0052]     The input/output buffers  125  are instead integrated along the periphery of the IC chip.  
         [0053]     The first section  115   a - 1  of the supply voltage distribution line arrangement  115   a  occupies a narrow region of the IC chip, sufficient for connecting the IC first terminals  105   a  to the first input terminal  135  of the voltage-to-voltage conversion circuit  130 .  
         [0054]     According to an embodiment of the present invention, the voltage-to-voltage conversion circuit  130  includes a distributed arrangement of a plurality (in the shown example, four) of voltage switches  160 , distributed along and connected to the second supply voltage distribution line arrangement  115   b  and the second section  115   a - 2  of the first supply voltage distribution line arrangement  115   a  (in the schematic drawing, the voltage switches  160  are provided along three of the four sides of the rectangular rings forming the second supply voltage distribution line arrangement  115   b  and the second section  115   a - 2  of the first supply voltage distribution line arrangement  115   a , however it is underlined that this arrangement of voltage switches is merely exemplary). Each second voltage switch  160  receives the second control signal VCON′ from the voltage-to-voltage conversion control circuit  175 .  
         [0055]     As can be noted, the first voltage switch  155  is connected between the first section  115   a - 1  of the supply voltage distribution line arrangement  115   a  carrying the voltage VDD_ext and the second section  115   a - 2  of the supply voltage distribution line arrangement  115   a  distributing the internal supply voltage VDDI, whereas each second voltage switch  160  is connected between the second supply voltage distribution line arrangement  115   b  carrying the voltage VDD_ext and the second section  115   a - 2  of the supply voltage distribution line arrangement  115   a . In particular, the voltage switches  160  are parallel-connected each other and are also parallel-connected to the first voltage switch  155 . In such a way, the overall resistance of the circuital pathways connecting the second supply voltage distribution line arrangement  115   b  to the second section  115   a - 2  of the supply voltage distribution line arrangement  115   a  is reduced so that the voltage drop across the switches  155  and  160  is reduced. Such reduction of the resistance is obtained without any increment of the size of the PMOS transistor which is used for implementing each one of the switches  155  and  160 .  
         [0056]     Thus, in operation, when the external voltage VDD_ext takes the second, lower supply voltage, e.g. of 1.8V, the actual supply voltage VDDI, which is fed to the core circuitry, is substantially equal to the external low supply voltage, thanks to the contribution of the second supply voltage distribution line arrangement  115   b  and to the distribution of the supply voltage VDDI to the core circuitry  120 .  
         [0057]     The feature of having one or more second switches  160  within the voltage-to-voltage conversion circuit  130  has a beneficial impact on the size of each supply voltage distribution line arrangements supplying the switches  155  and  160 . In particular, by using the proposed solution it is possible to reduce the length of each supply voltage distribution line arrangement, thus reducing the corresponding resistance.  
         [0058]     Moreover, in an embodiment of the invention, the selective activation of the second voltage switch  160  conditioned on the fact that the input/output buffers  125  are not switching reduces or eliminates propagation of the disturbs caused by the input/output buffers switching to the core circuitry  120  of semiconductor device  100 .  
         [0059]     Naturally, in order to satisfy local and specific requirements, a person skilled in the art may apply to the solution described above many modifications and alterations. Particularly, although the present invention has been described with a certain degree of particularity with reference to one or more embodiments thereof, it should be understood that various omissions, substitutions and changes in the form and details as well as other embodiments are possible; moreover, it is expressly intended that specific elements and/or method steps described in connection with any disclosed embodiment of the invention may be incorporated in any other embodiment as a general matter of design choice.  
         [0060]     For example, although in the preceding preferred description reference has been made to the selective activation of the second switch  160  based on an indication of the operating mode of the semiconductor device, it is not to be construed as a limitation of the present invention.  
         [0061]     In any case, one or more embodiments of the invention are suitable to be implemented by using other types of transistors for implementing the first and the second switches.  
         [0062]     Alternatively, it is possible to use different exemplificative values for the supply voltage during the operation of the semiconductor device.  
         [0063]     As mentioned in the foregoing, although applicable in general to any kind of semiconductor device, one or more embodiments of the present invention are in particular applicable to semiconductor devices like semiconductor memories, particularly albeit not limitatively non-volatile memories, e.g. electrically-alterable memories like NAND memories. These kind of devices are nowadays widely used in electronic systems like storage devices like memory cards and USB hard drives, as schematically shown in  FIG. 3 , schematically illustrating a USB pen  300  with a USB connector  305  adapted to be inserted into a USB port of, e.g., a personal computer, and including a semiconductor device, particularly a semiconductor memory  100  of the type previously described. Alternatively, an integrated circuit incorporating an embodiment of the invention may be coupled to a controller to form part of a system.