Abstract:
A power saving method for a semiconductor memory is provided. The power saving method for a semiconductor memory including the steps of receiving a plurality of address codes, each of which has a first part code and a second part code; and activating a first boost process when the first part code of a currently received address code is different from the first part code of a last received address code, otherwise a second boost process is activated.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a power saving method and circuit for a semiconductor memory, in particular, to a power saving word line boost method and a decoder for implementing the method. 
     BACKGROUND OF THE INVENTION 
     Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and Flash memory, wherein the ROM and the Flash memory are also resided in non-volatile memory. 
     For a conventional Flash memory device, a plurality of one-transistor core cells may be formed on a semiconductor substrate in which each cell is comprised of a P-type conductivity substrate, an N-type conductivity source region formed integrally with the substrate, and an N-type conductivity drain region also formed integrally within the substrate. A floating gate is separated from the substrate by a thin dielectric layer. A second dielectric layer separates a control gate from the floating gate. A P-type channel region in the substrate separates the source and drain regions. One type of architecture used for Flash memories is typically referred to as a NOR Flash memory architecture which is an array of Flash EEPROM cells which are divided into a plurality of sectors. Further, the memory cells within each sector are arranged in rows of wordlines and columns of bit lines intersecting the rows of wordlines. To sum up, a typical flash memory comprises a memory array, which includes a large number of memory cells divided in sectors. The flash memory is differentiated from other non-volatile memory in that flash memory cells can be erased and reprogrammed in blocks instead of one byte at a time. 
     Furthermore, for the cells in the Flash memory, each of the flash memory cells is connected with a row or X-decoder but a column or Y-decoder is shared by multiple memory cells. An example of a typical memory cell architecture is illustrated in  FIG. 1 , which is a diagram illustrating an conventional architecture of a plurality of memory cells corresponded with a plurality of decoders for a semiconductor memory. This architecture uses an X-decoder for each cell of memory.  FIG. 1  shows two columns of memory cells. Each column is comprised of eight flash memory array cells  100 - 115 . Each memory array cell  100 - 115  has a dedicated X-decoder  1101 - 1115  respectively, and each column of cells is shared a Y-decoder  131 - 132  respectively. 
     In order for memory manufacturers to remain competitive, memory designers must constantly increase the density, shrank the entire size, reduce the power consumption and enhance read speed of flash memory devices. In particular, there has arisen a need to provide a way of reducing the power consumption or the capacitive loading in Flash memory X-decoder in order to produce accurate voltage control at selected wordlines. 
     For the requirements stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a memory decoding architecture that reduces power consumption for reading operation in a semiconductor memory. Hence a novel power saving method and decoder for a semiconductor memory is thus provided. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to propose a power saving method and circuit for a semiconductor memory. The present invention provides a power saving word line boost scheme. Read speed and power consumption are respectively improved and reduced by dividing loading and recycling the boosted well power. 
     According to the first aspect of the present invention, a power saving method for a semiconductor memory including the steps of providing a memory array having a plurality of memory cells divided into a plurality of sectors, wherein a part of the plurality of sectors arranged in the same row is disposed on a well region; receiving a plurality of the address codes, each of which has a first part code and a second part code, wherein the first part code is addressed for the well region; and activating a first boost process when the first part code of a currently received address code is different from the first part code of a last received address code, otherwise a second boost process is activated. 
     Preferably, the semiconductor memory is a Flash memory. 
     Preferably, the first boost process is used to boost the well region for which the first part code of the currently received address code is addressed. 
     Preferably, the second boost process is used to maintain a voltage of the well region by a small boost. 
     According to the second aspect of the present invention, a power saving method for a semiconductor memory including the steps of receiving a plurality of address codes, each of which has a first part code and a second part code; and activating a first boost process when the first part code of a currently received address code is different from the first part code of a last received address code, otherwise a second boost process is activated. 
     Preferably, the semiconductor memory is a Flash memory. 
     Preferably, a plurality of well regions is addressed by the first part of the address code. 
     Preferably, the first boost process is used to boost a well region for which the first part code of the currently received address code is addressed. 
     Preferably, the second boost process is used to maintain a voltage of the well region by a small boost. 
     According to the third aspect of the present invention, a power saving circuit for reducing power consumption for a semiconductor memory including a circuit receiving a plurality of address codes, each of which has a first part code and a second part code; and wherein a first boost process is activated when the first part code of a currently received address code is different from the first part code of a last received address code, otherwise a second boost process is activated. 
     Preferably, the semiconductor memory is a Flash memory. 
     Preferably, a plurality of well regions is addressed by the first part of the address code. 
     Preferably, the first boost process is used to boost a well region for which the first part code of the currently received address code is addressed. 
     Preferably, the second boost process is used to maintain a voltage of the well region by a small boost. 
     The foregoing and other features and advantages of the present invention will be more clearly understood through the following descriptions with reference to the drawings: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an conventional architecture of a plurality of memory cells corresponded with a plurality of decoders for a semiconductor memory; 
         FIG. 2  is a diagram illustrating a power saving architecture of a memory cell for a semiconductor memory; and 
         FIG. 3  is a flow chart illustrating the process for implementing the power saving method for a semiconductor memory. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for the aspect of illustration and description only, it is not intended to be exhaustive or to be limited to the precise form disclosed. 
     For the sake of reducing the power consumption for a semiconductor memory, if we charge/discharge the well loading in each read operation, it will consume too much un-necessary current. Since it is understood that usually a plurality of one-transistor core cells may be formed on a semiconductor substrate in which each cell is comprised of a P-type conductivity substrate, an N-type conductivity source region formed integrally with the substrate, and an N-type conductivity drain region also formed integrally within the substrate. And a P-type channel region in the substrate separates the source and drain regions. Thus the plurality of memory sectors arranged in the same row would share with the identical well region. Furthermore, in accordance with the characteristics of code with “local of reference”, it is inspired therefrom that the well loading could only be re-setup when there are many address changes. 
     In order to further demonstrate the power saving method, a preferred embodiment is provided as follows. Please refer to the  FIG. 2 , which is a diagram illustrating a power saving architecture of a memory cell for a semiconductor memory. It is demonstrated in  FIG. 2  a scramble of 32Mbit array with 16I/O and 64sectors with capacity 0.5Mbit/sector for a flash memory where X decoder was showed only. A memory array  20  disclosed in  FIG. 2  includes a plurality of memory cells  21 , a plurality of sectors  22 , a plurality of well regions  23 , a row-decoder  24  and a column decoder  25 . Wherein the memory array  20  is a 32 Mbit array including four memory cells  21 , each of which is then divided into sixteen sectors  22 . Each of the totally sixty-four sectors  22  has the capacity of 0.5 Mbit/sector and is numbered from Sec  0  to Sec  63  herein. The respective address signals inputted into the row-decoder  24  from top to bottom is A 0 -A 15  and the respective address signals inputted into the column decoder  25  from left to right is A 16 -A 19 . 
     Since for each read operation, when address signals A 16 -A 19  are changed, it means that the row address is correspondingly changed. Otherwise when the address signals A 16 -A 19  are not changed, it means that the row address is not changed and the sectors arranged in the same row could keep sharing the same well region. Thus once it is detected that the current received address signals A 16 -A 19  are different from the last received address signals A 16 -A 19 , a well boost would be activated for activating a well region whose type is different from the present well region. Otherwise, the current received address signals A 16 -A 19  are the same with the last received address signals A 16 -A 19 , an internal read operation is triggered, that is the voltage of the well region would be maintained by a small boost, so as to trigger an internal read operation. 
     For the preceding mentioned method, it could be able to be generalized in  FIG. 3 , which is a flow chart illustrating the process for implementing the power saving method for a semiconductor memory. Following steps are included in  FIG. 3 : an address trigger detection (ATD) process  31 , a well boost process  32  for activating a well region, and a small boost  33  for activating an internal read operation. First, the address signals A 16 -A 19  are inputted into the ATD process  31 . If the current received address signals A 16 -A 19  are different from a last received address signals A 16 -A 19 , the well boost process  32  would be activated for activating a well region, otherwise a small boost  33  for activating an internal read operation keeps performing. 
     To sum up the aforementioned method, since the power demanding for internal read operation is smaller than that for well boost and the well boost process is not activated for every read operation on the basis of the method, the demanding for power consumption is thus well reduced. Hence, the present power saving method for a semiconductor and the decoder presented by the present application indeed achieve the anticipated effect. The present invention not only bears a novelty and a progressive nature, but also bears a utility. 
     While the invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention need not to be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims that are to be accorded with the broadest interpretation, so as to encompass all such modifications and similar structures. According, the invention is not limited by the disclosure, but instead its scope is to be determined entirely by reference to the following claims.