Abstract:
The invention relates to reduced power cells. Some embodiments of the invention provide a memory circuit that has a storage cell. The storage cell contains several electronic components and an input. The electronic components receive a reduced voltage from the input to the cell. The reduced voltage reduces the current leakage of the electronic components within the cell. Some embodiments provide a memory circuit that has a level converter. The level converter receives a reduced voltage and converts the reduced voltage into values that can be used to store and retrieve data with stability in the cell. Some embodiments provide a method for storing data in a memory circuit that has a storage cell. The method applies a reduced voltage to the input of the cell. The method level converts the reduced voltage. The reduced voltage is converted to a value that can be used to store and retrieve data with stability in the cell. The reduced voltage reduces a current leakage of electronic components within the cell.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is related to U.S. patent application Ser. No. 11/081,870, filed Mar. 15, 2005. 
   FIELD OF THE INVENTION 
   The present invention relates to reduced power cells. 
   BACKGROUND OF THE INVENTION 
   Volatile memory circuits are quite common today. Such memory circuits can be contained in an individual integrated circuit (IC) chip or can be part of other IC&#39;s. These IC&#39;s include a configurable IC that uses a memory circuit to store configuration data. The configurable IC can be configured to perform a set of operations based on the stored configuration data. 
   The use of configurable IC&#39;s has dramatically increased in recent years. One example of a configurable IC is a field programmable gate array (FPGA). An FPGA is a field programmable IC that has an internal array of logic circuits (also called logic blocks) that are connected together through numerous interconnect circuits (also called interconnects) and that are surrounded by input/output blocks. Like some other configurable IC&#39;s, the logic circuits and the interconnect circuits of an FPGA are configurable. In other words, each of these circuits receives configuration data that configures the circuit to perform an operation in a set of operations that it can perform. One benefit of configurable IC&#39;s is that they can be uniformly mass produced and then subsequently configured to perform different operations. 
   As mentioned above, configurable IC&#39;s typically store their configuration data in memory cells.  FIG. 1  illustrates a memory circuit  100  of a configurable IC. As shown in this figure, the memory circuit  100  includes: (1) a storage cell  128  for storing a configuration data value; (2) a VDDcell line  106  for supplying power to the storage cell  128 ; (3) true and complement bit lines  110  and  115  for reading and/or writing the contents of the storage cell  128 ; (4) pass gates  120  and  125  for connecting the bit lines  110  and  115  to the storage cell  128 ; and (5) output lines  160  and  165  for outputting, through configuration buffers  140  and  145 , the contents of the storage cell  128  without the need for a read operation. 
   The typical storage cell  128  in the art requires that the voltage within the cell  128  and through the buffers  140  and  145  be driven to the rails in order for the cell  128  to retain stable values and output a useable configuration value (i.e., VDDcell  106  is typically VDD). If the voltage within the storage cell  128  is less than the voltage on a word line used to read the cell, then a read operation could cause instability in the value stored by the storage cell  128  by undesirably altering the value stored in the storage cell  128 . This condition is also known as “read upset.” 
   However, requiring the voltage within the cell  128  and through the buffers  140  and  145  to be driven to the rails exasperates current leakage from the cell, since current leakage from the memory cell is non linearly (e.g., exponentially) proportional to the voltages that are used to store data in the memory cell. Specifically, in the memory cell  100  there are two kinds of leakage that are problematic: sub threshold leakage and gate leakage. 
     FIG. 2  illustrates an example of sub threshold leakage through an NMOS transistor  200  that is commonly used in memory circuits. In  FIG. 2 , the gate and source leads of the NMOS transistor  200  are short circuited to represent that their voltage difference is zero (i.e., Vg−s=0). Even though the transistor is “off” in this sub threshold condition, there is still undesirable leakage current through the transistor  200 , as shown in  FIG. 2 . 
     FIG. 3  illustrates an example of gate leakage through an NMOS transistor  305 . Electron tunneling through the gate oxide of a transistor causes gate leakage current. For a 90 nm electronic component (e.g., a transistor), gate oxide can be about fourteen angstroms or approximately seven silicon dioxide atoms thick. This distance is sufficiently short to allow tunneling current to flow through the gate oxide even at voltage levels as low as one volt. Gate leakage in N-channel devices is significantly worse than in P-channel devices. 
   With the size of electronic components continually becoming smaller due to improvements in semiconductor technology, leakage current is a continually growing problem. Leakage current in a standard (six transistor) memory cell is exponentially proportionate to voltage. So if the voltage in the cell can be reduced, then the amount of leakage (i.e., both gate and sub threshold leakage) in the cell can be exponentially reduced. However, a typical memory cell has particular voltage requirements in order for the cell to function properly. Thus, if the voltage within the cell is reduced too much, then the cell becomes unstable and unable to store and output data reliably, as seen in the case of the read upset condition. Thus, there is a need in the art for a useable reduced power configuration storage cell, such that the leakage from electronic components within the cell is reduced, while retaining useable output configuration signals. 
   SUMMARY OF THE INVENTION 
   The invention relates to reduced power cells. Some embodiments of the invention provide a memory circuit that has a storage cell. The storage cell contains several electronic components and an input. The electronic components receive a reduced voltage from the input to the cell. The reduced voltage reduces the current leakage of the electronic components within the cell. Some embodiments provide a memory circuit that has a level converter. The level converter receives a reduced voltage and converts the reduced voltage into values that can be used to store and retrieve data with stability in the cell. Some embodiments provide a method for storing data in a memory circuit that has a storage cell. The method applies a reduced voltage to the input of the cell. The method level converts the reduced voltage. The reduced voltage is converted to a value that can be used to store and retrieve data with stability in the cell. The reduced voltage reduces a current leakage of electronic components within the cell. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects, features, and advantages of the invention will be apparent to one skilled in the art, in view of the following detailed description in which: 
       FIG. 1  illustrates a diagram of a typical memory circuit as is known in the art. 
       FIG. 2  illustrates sub threshold leakage through an NMOS transistor. 
       FIG. 3  illustrates gate leakage through an NMOS transistor and sub threshold leakage through a PMOS transistor. 
       FIG. 4  illustrates a diagram of a memory circuit comprising a reduced power storage cell according to some embodiments of the invention. 
       FIG. 5  illustrates a control circuit for a memory circuit comprising a reduced power storage cell according to some embodiments of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The invention is directed towards reduced power static random access memory (SRAM) cells. In the following description, numerous details are set forth for purpose of explanation. However, one of ordinary skill in the art will realize that the invention may be practiced without the use of these specific details. For instance, the invention has primarily been described with reference to the storage cells for volatile memory (e.g., SRAM) in a configurable IC. However, the same techniques can easily be applied for other types of memory and electronic circuits. In other instances, well-known structures and devices are shown in block diagram form in order not to obscure the description of the invention with unnecessary detail. 
   I. Reduced Power Memory Cell 
   To address the problems of current leakage present in memory cells, some embodiments provide a memory circuit  400  illustrated in  FIG. 4  that includes a reduced power storage cell  428 . During normal operation, the reduced power storage cell  428  is supplied with a lower voltage so that it will leak less current, and therefore consume less power than the storage cells known in the art. Moreover, the reduced power storage cell  428  outputs through an amplifier circuit  438 , which also leaks less current than the buffers in the art. 
   As shown in  FIG. 4 , the memory circuit  400  includes a word line  405 , a VDDcell line  406 , a bit line  410 , a complement bit line  415 , pass gates  420  and  425 , a reduced power storage cell  428 , and an amplifier stage  438 . In some embodiments, the pass gates  420  and  425  are NMOS transistors that connect the bit line  410  and the complement bit line  415  to the storage cell  428  when the signal on the word line  405  is high. 
   The pass gates  420  and  425  enable writes to, and reads from, the storage cell  428 . During a read operation, the value in the storage cell  428  is “read” out onto the bit line  410  and the complement bit line  415  (hereinafter also referred to as the bit lines). Specifically, for the read operation of some embodiments, the voltages stored at the nodes  426  and  427  pass through the pass gates  420  and  425  to affect the voltages on the bit lines  410  and  415 . In some embodiments, the bit lines  410  and  415  are precharged and then allowed to float high in anticipation of a read operation. Also during a read operation, a sense amplifier (not shown in  FIG. 4 ) monitors the bit lines  410  and  415  to sense or “read” the value stored in the storage cell  428  through the bit lines  410  and  415 . 
   During a write operation, the values on the bit lines  410  and  415  are “written” into the storage cell  428 . Specifically, for the write operation of some embodiments, voltages on the bit lines  410  and  415  pass through the pass gates  420  and  425  to alter the voltages stored at the nodes  426  and  427 . As shown in  FIG. 4 , some memory cells require a true configuration signal and its complement signal (provided by the bit lines  410  and  415 ) for the memory circuit  400  to execute reliable read and write operations. In these embodiments, the bit lines  410  and  415  are precharged, then one is pulled low to effect differential signals for the write operation. 
     FIG. 4  illustrates that the reduced power storage cell  428  of some embodiments is formed by cross coupling a pair of standard complementary metal oxide semiconductor (CMOS) inverters. These CMOS inverters are cross-coupled in that the output of the first inverter is coupled to the input of the second inverter and the output of the second inverter is coupled to the input of the first inverter. 
   The cut-out in  FIG. 4  illustrates the cross coupled transistors of two standard CMOS inverters. This cut-out includes PMOS transistors  431  and  436  and NMOS transistors  432  and  437 . To form a first inverter, the drains of the transistors  431  and  432  are connected, and the gates of these transistors are also connected. To form a second inverter, the drains of the transistors  436  and  437  are connected, and the gates of these transistors are also connected. Cross-coupling of the two inverters is achieved by connecting the drains of the first inverter&#39;s transistors to the gates of the second inverter&#39;s transistors, and by connecting the drains of the second inverter&#39;s transistors to the gates of the first inverter&#39;s transistors. The sources of the transistors  432  and  437  are connected to ground. 
   The source leads of the PMOS transistors  431  and  436  are connected to the VDDcell line  406 . When the VDDcell line  406  supplies power to the storage cell  428 , a value that represents a bit can be stored at the output (the transistor drains) of the first inverter (i.e., at node  426 ) and a value that represents the complement of the bit can be stored at the output (the transistor drains) of the second inverter (i.e., at node  427 ). In certain conditions (i.e., during the normal operation of the cell  428 ), the VDDcell line  406  supplies reduced power by using a reduced voltage. Thus, the storage cell  428  stores reduced voltages at the nodes  426  and  427  to represent the stored bit and its complement. 
   When operating based on a reduced voltage (e.g., VDDcell less than VDD), the storage cell  428  consumes less power, since the power consumed by a circuit is non linearly proportional to the voltage within the circuit. In some embodiments, the voltage supplied by the VDDcell line  406  is less than the voltage provided by the VDD line  407  by one NMOS threshold. In other embodiments, the voltage from the VDDcell line  406  is less than the voltage from the VDD line  407  by more than one NMOS threshold. At the reduced voltage, the current leakage from the electronic components of the storage cell  428  is exponentially lower at the lower voltage. 
   As mentioned above, the storage cell  428  normally provides continuous output of its stored value. While the storage cell  428  stores values at a voltage less than VDD, a typical useable configuration output has a voltage approximately equal to the full supply voltage VDD. Some embodiments compensate for the reduced voltage within the cell  428  by replacing the pair of configuration buffers  140  and  145  shown in  FIG. 1 , with the amplifier stage  438  of  FIG. 4 . In these embodiments, though reduced voltage is supplied to the storage cell  428 , the storage cell  428  outputs the value representing the stored bit through the amplifier stage  438  at the full supply voltage (VDD). Moreover, the amplifier stage  438  buffers the storage cell  428  from the configuration outputs  460  and  465 , to prevent an undesirable change in the stored data when these outputs  460  and  465  are accessed by external circuitry (not shown). 
   As shown in  FIG. 4 , the amplifier stage  438  can be implemented by using the PMOS transistors  441  and  446 , and the NMOS transistors  442  and  447 . In these embodiments, the sources of the PMOS transistors  441  and  446  are coupled to the VDD line  407  (VDD≧VDDcell). The PMOS transistors  441  and  446  are cross-coupled, meaning that the gate of the PMOS  441  is coupled to the drain of the PMOS  446 , and the gate of the PMOS  446  is coupled to the drain of the PMOS  441 . As further shown in  FIG. 4 , the drain of the PMOS  441  is coupled to the drain of the NMOS  442  and the drain of the PMOS  446  is coupled to the drain of the NMOS  447 . The sources of the NMOS transistors  442  and  447  are grounded. 
   Also shown in  FIG. 4 , the gate of the NMOS transistor  442  is coupled to the storage cell  428  and the pass gate  420  at the node  426 . Similarly, the gate of the NMOS transistor  447  is coupled to the storage cell  428  and the pass gate  425  at the node  427 . 
   In some embodiments, the four transistors  441 ,  442 ,  446  and  447  described above form the amplifier stage  438  by implementing a static level converter. In these embodiments, the level converter does not directly drive the PMOS transistors  441  and  446 . Rather, the cross-coupled PMOS transistors  441  and  446  provide differential level conversion. Thus, the voltage VDD supplied by the VDD line  407  from the level converter (the four transistors) of the amplifier stage  438  drives the configuration outputs  460  and  465 , instead of the reduced voltage from the VDDcell line  406 . 
   The advantage of the level converter is that the voltage swing on the NMOS transistors  442  and  447  from the storage cell  428  is not required to go all the way to the rails (all the way to the full supply voltage VDD) for the value in the storage cell  428  to be correctly outputted. This allows the storage cell  428  to operate at reduced voltages. The reduced operating voltage reduces both the sub threshold leakage and the gate leakage of the cell  428 . The storage cell  428  in the memory circuit  400  consumes less power at the reduced voltage (supplied by the VDDcell line  406 ). Despite operating at the reduced voltage, the cell  428  properly outputs its configuration value. 
   Moreover, since the supply voltage VDD (from VDD line  407 ) passes only through the PMOS transistors  441  and  446  before reaching the outputs  460  and  465 , the amplifier stage  438  leaks significantly less current than the configuration buffers  140  and  145  of the prior art memory cell  100  illustrated in  FIG. 1 . This is partly because the configuration buffers  140  and  145  are typically implemented with a greater number of transistors, each of which leaks current, and partly because these transistors include NMOS transistors, each of which leaks more current than PMOS transistors. 
   II. Operation and Control of the Reduced Power Cell 
   The operation of the reduced power storage cell  428  will now be described in relation to  FIGS. 4 and 5 . As previously described,  FIG. 4  illustrates a memory circuit  400  that includes the reduced power cell  428 .  FIG. 5  illustrates a control circuit  501  that provides control signals for the memory circuit  400 . The memory circuit  400  is represented in  FIG. 5  as the simplified memory circuit  500 . 
   More specifically,  FIG. 5  illustrates the control circuit  501  having two control inputs, Not_Enable (EN-bar  520 ) and Word_Line_Enable (WL_EN  530 ), that provide three states: 1) Disabled; 2) Read/Write; and 3) Normal states for the memory circuit  500 . The input Not_Enable  520  is coupled to the input of the inverter  525 . The output of the inverter  525  is coupled to the NMOS transistor  540 . The NMOS transistor  540  connects the VDD line  507  to the VDDcell line  506 . The input Word_Line_Enable  530  is coupled to the input of the inverter  535 . An output of the inverter  535  is coupled to the transistors  545 ,  550 , and  555 . 
   As further shown in  FIG. 5 , the PMOS transistor  545  connects the VDD line  507  to the VDDcell line  506 . The PMOS transistor  555  connects the VDDcell line  506  to the word line  505 . The PMOS transistor  545  is “stacked” above the PMOS transistor  555  such that the voltage on the word line  505  may never exceed the voltage on the VDDcell line  506 . Likewise, the voltage on the VDDcell line  506  may never exceed the voltage on the VDD line  507 . Since these voltages are tiered or “stacked” above and below the PMOS transistors  545  and  555  (i.e., the voltage on the VDD line  507 ≧VDDcell line  506 ≧word line  505 ), a read operation will not upset a value stored in the storage cell  528 . In other words, because the voltage on the word line  505  may equal, but may never exceed, the voltage on the VDDcell line  506 , a “read upset” condition is avoided by the control circuit  501 . 
   The three states for the memory circuit  500  will now be described by reference to the control circuit  501 . As previously discussed, the three states for the memory circuit  500  include a Disabled State, a Read/Write State, and a Normal State. 
   1. Disabled State (EN-bar=1, WL_EN=0) 
   When the input signal at the input Not_Enable  520  has a logical “1” and the signal at the input Word_Line_Enable  530  has a logical “0,” both the NMOS  540  and the PMOS  545  transistors are turned off and no power is supplied to the VDDcell line  506 . Thus, no power is supplied to the storage cell  528  that is coupled to the VDDcell line  506 . In this Disabled State, the memory circuit  500  that is controlled by the control circuit  501  is not used at all in the current arrangement. 
   As is more specifically shown by reference to  FIG. 4 , during the Disabled State, the word line  405  and the VDDcell line  406  have a logical “0.” When the VDDcell line  406  has a logical “0,” no power is provided to the storage cell  428 . Further, since the storage cell  428  outputs no value to the NMOS transistors  442  and  447 , the output of the amplifier stage  438  floats (e.g., at one P-channel threshold below the rail). Thus, the memory circuit  400  stores and outputs no value in the Disabled State. 
   The Disabled State is useful, for example, in the case of a configurable circuit where it is desirable to power off parts of the circuit (e.g., an array or parts of an array of memory cells). Powering off cells in this manner can additionally conserve power. 
   2. Read/Write State (EN-bar=0, WL_EN=1) 
   For the Read/Write State, the control circuit  501 : (1) provides the full supply voltage VDD to the storage cell  528 , so that it can store and output a value, and so that the memory circuit  500  can access the cell  528  through a read/write operation; (2) enables the word line  505  to select the cell  528  for the read/write operation; and (3) prevents the voltage on the word line  505  from exceeding the voltage on the VDDcell line  506 , such that a read upset condition is avoided. 
   More specifically, when an input signal at the input Not_Enable  520  has a logical “0” and the input Word_Line_Enable  530  has a logical “1,” then current flows from the VDD line  507  through the VDDcell line  506  (via the PMOS transistor  545 ), and from the VDDcell line  506  through the word line  505  (via the PMOS transistor  555 ). In other words, the PMOS transistors  545  and  555  switch to low impedance which pulls the voltages on these lines (VDD cell line  506  and word line  505 ) up to the level of approximately VDD. In this state, the memory circuit  500  performs a read and/or write operation by using the full supply voltage VDD, in the manner of a typical memory cell in the art. 
   As more specifically shown in  FIG. 4 , during a read or a write operation, both the VDDcell line  406  and the word line  405  are activated (have a logical “1”). As previously described, the VDDcell line  406  provides a voltage at approximately VDD to the storage cell  428  to allow for a typical read or write operation by using the full supply voltage VDD. Since the word line  405  is activated, the pass gates  420  and  425  are turned on, and voltage signals are allowed to pass between the bit lines  410  and  415 , and the storage cell  428 . During a write operation, the voltage signals on the bit lines  410  and  415  modify the voltages (which represent the stored value) at the nodes  426  and  427 . For instance, the value on the bit line  410  passes through the pass gate  420  and is stored in the storage cell  428  at node  426  during a write operation. Conversely, the value stored in the storage cell  428  at node  426  passes through the pass gate  420  to modify the voltage on the bit line  410 , during a read operation. Write and read operations occur in the same manner through the pass gate  425  between the node  427  and the complement bit line  415  in the Read/Write State. Moreover, the nodes  426  and  427  (representing the stored bit and its complement) each may have a value approximately equal to VDD that is applied to the amplifier stage  438 . As previously mentioned, the amplifier stage  438  produces an output with a voltage of approximately VDD. 
   Specifically, as shown in  FIG. 4 , the storage cell  428  is coupled to the amplifier stage  438  at the gate-inputs of the NMOS transistors  442  and  447 . Thus, if a logical “1” is at the node  426 , then the NMOS transistor  442  will be activated and the PMOS transistor  446  will also be activated. Accordingly, current will flow from the VDD line  407  through the PMOS transistor  446  to the configuration output  465 . Conversely, the cross-coupled PMOS transistor  441  will ensure that the output  460  will be pulled low (i.e., grounded through the NMOS transistor  442 . 
   As previously mentioned, the amplifier stage  438  leaks less current than its counterpart in the prior art (buffers  140  and  145 ) because the output voltage only passes through a low impedance PMOS transistor. However, the Normal State has even lower current leakage. 
   3. Normal State (EN-bar=0, WL_EN=0) 
   As shown in  FIG. 5 , when the input signal at the input Not_Enable  520  has a logical “0” and the signal at the input Word_Line_Enable  530  has a logical “0,” the NMOS transistor  540  is turned on and current flows from the VDD line  507  through the VDDcell line  506 . Because the signal at the output of the inverter  535  is a logical “1,” both the PMOS transistors  545  and  555  are turned off and the word line  505  has a logical “0.” When the PMOS transistors  545  and  555  are off, the word line  505  is not enabled for reading or writing the contents of the storage cell  528  in the memory circuit  500 . Moreover, because the NMOS transistor  540  connects the VDDcell line  506  to the VDD line  507 , the VDDcell line  506  has a reduced voltage of approximately one NMOS threshold below the full supply voltage VDD. 
   Therefore, the memory circuit  500  is used in the current arrangement (of a configurable IC, for instance) but the memory circuit  500  is not currently being accessed by a read or write operation through the word line  505 . However, the memory circuit  500  is outputting a value stored in the storage cell  528  to the configuration outputs  560  and  565 . This is the normal active state of the memory circuit  500 . 
   As more specifically shown in  FIG. 4 , during the Normal State, the VDDcell line  406  is activated but the word line  405  is de-activated. Since the word line  405  is de-activated, the pass gates  420  and  425  are turned off. When the pass gates  420  and  425  are turned off, the bit lines  410  and  415  are not used to write to, and are not used to read from, the storage cell  428 . However, since the VDDcell line  406  is activated, (a reduced) power is supplied to the storage cell  428  to maintain a value stored in the storage cell  428 . Since the cell operates at the reduced voltage (which in some embodiments is less than VDD by an NMOS threshold), the electronic components of the cell  428  leak exponentially less current than the prior art cell. Further, the value stored in the storage cell  428  is applied to the amplifier stage  438  through the NMOS transistors  442  and  447 . 
   Accordingly, the amplifier stage  438  outputs the value stored in the storage cell  428  at a voltage approximately equal to VDD (from the VDD line  407 ). As mentioned above, the voltage signal from the VDD line  407  through the PMOS transistors  441  and  446  to the configuration outputs  460  and  465  is roughly equal to the full supply voltage VDD. In this manner, the voltage signal from the storage cell  428  that is approximately equal to VDDcell is amplified (level-converted) for output at the amplifier stage  438  to a value that is approximately equal to VDD. As previously mentioned, the voltage on the VDDcell line  406  can be less than the voltage on the VDD line  407  by one or more NMOS thresholds because the NMOS transistors  442  and  447  of the amplifier stage  438  do not require full swing. Thus, the amplifier stage  438  converts (amplifies) the voltage level from the storage cell  428  before outputting the voltage signal at the configuration outputs  460  and  465 . Therefore, in the Normal State, the storage cell  428  can operate at a reduced voltage to minimize leakage while maintaining and outputting a stable configuration output value at approximately the full supply voltage VDD. 
   4. Table Showing Inputs, Outputs, and States 
   Table 1 summarizes the three states for the memory circuit  500  in relation to the input values for the control circuit  501 . Table 1 also shows the values of the VDDcell line  506  and the word line  505  for the three states according to one embodiment of the present invention. For instance, the VDDcell line  506  is approximately equal to VDD (the full supply voltage) which allows typical reading and/or writing operations during the Read/Write State. During the Read/Write State the word line  505  is also approximately equal to VDD. During the Normal State, however, the word line  505  is de-activated and the VDDcell line  506  is about one NMOS threshold below VDD. As described above, reducing the VDDcell voltage by only one NMOS threshold is sufficient to result in a significant reduction in current leakage. 
   III. Performance and Advantages 
   As mentioned in relation to  FIG. 4 , the voltage within the cell (VDDcell) can be reduced from about 1.0V to about 0.8V or approximately one NMOS threshold, in some embodiments. In other embodiments VDDcell may be reduced by a plurality of NMOS thresholds to further reduce current leakage through the electronic components (e.g., the MOS transistors) of the memory circuit storage cell. 
   Some embodiments use 90 nm electronic components. At 90 nm the sub threshold leakage and the gate leakage are roughly equal. Since gate leakage is more sensitive to voltage reductions, some embodiments provide greater reduction in the gate leakage for 90 nm components. For 65 nm components, gate leakage is often worse than sub threshold leakage. Thus, a greater improvement in overall leakage reduction may occur for electronic components using 65 nm technologies. 
   Some embodiments allow the reduced voltage to be used for a set of cells that are similar to the cell  428  in  FIG. 4 , to reduce the power consumed and leaked by the entire set of memory cells. For instance, the invention also allows an entire row of cells to be powered down at a time. This feature can be useful, for instance, in an FPGA where the whole array may not be needed for some arrangements of the FPGA. Thus, the present invention allows for additional power savings by allowing unused parts of the array to be powered off. The invention has been described in relation to FPGA&#39;s and configuration cells. However, one of ordinary skill in the art will recognize that the invention would be useful in a variety of memory and other applications where reduced power consumption and lower leakage are desirable. 
   The foregoing has described a reduced power cell. One of ordinary skill will also recognize that the invention can be embodied in other specific forms without departing from the spirit of the invention, even though the invention has been described with reference to numerous specific details. In view of the foregoing, one of ordinary skill in the art would understand that the invention is not to be limited by the foregoing illustrative details, but rather is to be defined by the appended claims. 
   
     
       
             
             
             
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               State 
               EN-bar 520 
               WL EN 530 
               VDDcell 406 
               Word Line 405 
             
             
                 
             
           
           
             
               Disabled 
               1 
               0 
               0 
               0 
             
             
               Read/Write 
               0 
               1 
               (VDD) 
               (VDD) 
             
             
               Normal 
               0 
               0 
               (VDD-1Vth) 
               0