Abstract:
Apparatus and methods for filtering spurious output transitions with an adaptive filtering circuit which tracks the memory architecture and form factors with a reduced speed penalty. The filtering is selectable by a fuse option.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a divisional of U.S. patent application Ser. No. 11/127,526 (allowed), filed May 12, 2005 and titled, “METHOD AND APPARATUS FOR FILTERING OUTPUT DATA” which is commonly assigned and incorporated by reference in its entirety herein, and which claims priority to Italian Patent Application Serial No. RM 2004A000554, filed Nov. 8, 2004, which is commonly assigned. 
     
    
     FIELD  
       [0002]     The present invention relates generally to memories and in particular the present invention relates to memory data output.  
       BACKGROUND  
       [0003]     A critical parameter in memories and particularly nonvolatile memories like flash memories is the access time to access data. When reading randomly from a memory core such an access is defined as an asynchronous access, (defined as T ace , data valid from a chip enable complement CE* transition). When reading data there can be spurious glitches on the data connections (DQs), which can usually be filtered out at the expense of increasing data access time.  
         [0004]     Referring to  FIGS. 1 and 2 , which are a block diagram of a memory and a timing diagram of data passing from the memory, the access time T ace  is driven by three main circuit blocks, the memory core  102 , data path component  104 , and output buffer component  106 . Memory core  102  contains a memory array  108 , sense amplifiers  110 , address transition detector (atd) and read timer  112 , and latch  114 . Data path component  104  contains data path driver  116  and latch  118 . Output buffer component  106  contains output buffers  120 . The memory core  102  with the sense amplifiers  110 , sets the amount of time needed from supply of signal CE*=0 to select the addressed location, to sense the data from the array  108  and have the data ready and presented at the memory bank boundary. The data path circuit  104  controls data propagation through the memory  100  up to the pad area and the output buffers  120  are used to drive the output load.  
         [0005]     Typically, the output buffers  120  are set as pass through buffers at the beginning of the read phase, allowing an immediate transition as soon as the internal data is read from the array  108  and propagated through the data path  104 . The delay, as shown in  FIG. 2 , is Δτ0. Such approach has the side effect of making the output buffers transparent to any transition of the data path even when the data are not valid yet. The architecture of the data path drives the timing and number of such undesired spurious transitions ( FIGS. 1-2 ).  
         [0006]     In working with very fast memories, it is desirable to decrease the time data takes to propagate from the sense amplifiers to the output buffers. One way to do this is to keep all data communications from the sense amplifiers to the output buffers transparent. When new data is detected at the sense amplifiers, it propagates to the output buffers. This allows for a minimum time delay from the sense amplifiers to the output buffers. However, the sense amplifiers in reading data from the array generate spurious data outputs before stabilization to valid data. This spurious data output propagates to the output buffers as noise before stabilization. There is a minimum time delay Δτ0 that data takes to move from the input of the data path driver  116  to the output from data path latch  118 . When access time T ace  is set for the device  100 , then, the specification for the device indicates that the data are not valid until expiration of the minimum access time T ace . Spurious data cannot be considered good data until the access time expires. While such an approach is very fast, the transitions in the spurious data greatly increase memory power consumption because of the switching of the output buffers. This current consumption without information is inconvenient for customers and consumes power, which is in increasingly short supply in today&#39;s memories.  
         [0007]     To avoid the spurious output switching of the configuration shown in  FIG. 1 , a conventional approach to the problem of spurious output transitions is shown in  FIG. 3 , and is based on the use of a second atd and read timer circuit  202  which takes the same inputs as the atd and read timer  112  of memory  100 , to generate a signal (sa_latch_filter in  FIG. 3 ) to mask all of the internal data path transitions immediately before the output buffer drivers  120 . This signal enables the output buffers  120  only after the data are stable, by opening keeping latch  118  closed until the signal has propagated through atd and read timer  202 , and opening latch  118  at that time. The calculated time is longer than Tace minimum by a margin, Tm. The margin Tm is added to the minimum Tace to cover the time needed to enable the latch.  
         [0008]     The approach of  FIG. 3  uses the margin Tm to allow the signal to cut all of the undesired spurious data transitions. This time Tm must allow sufficient propagation time based on the maximum expected time to eliminate all possibility of spurious transitions. Defining the value for Tm requires an accurate evaluation of two parameters, the addressed data sensing time and the data propagation delay to the output buffers. Both parameters depend upon process spread, architecture, layout and memory size, and therefore some estimation is required. To avoid the possibility of invalid data at the output buffers, the margin Tm is increased to a safe time. The uncertainty about these parameters evaluation drives the Tm value up.  
         [0009]     For the reasons 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 apparatus and techniques for filtering spurious data output but increasing speed of access. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0010]      FIG. 1  is a block diagram of a memory of the prior art;  
         [0011]      FIG. 2  is a timing diagram for operation of the memory of  FIG. 1 ;  
         [0012]      FIG. 3  is a block diagram of another memory of the prior art;  
         [0013]      FIG. 4  is a timing diagram for operation of the memory of  FIG. 3 ;  
         [0014]      FIG. 5  is a block diagram of a memory according to one embodiment of the present invention;  
         [0015]      FIG. 6  is a timing diagram for operation of the memory of  FIG. 5 ; and  
         [0016]      FIG. 7  is a block diagram of a memory and system according to another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0017]     In the following detailed description of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present invention.  
         [0018]     The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.  
         [0019]     The embodiments of the present invention utilize the same signal already used for sense amplifier temporization in a memory to identify the time at which data read from the memory are valid at the sense amplifier output. The signal is propagated from the active sense amplifier to output buffers through a path that mimics the read data path of the memory. Due to the paths being the same, the signal activation is contemporaneous to the presence of valid data along all data paths, so the signal indicating that reading of the output data path will result in valid data being read is contemporaneous with arrival of valid data. The paths are identical, and therefore the smallest additional margin time is achieved, but all spurious transitions are complete.  
         [0020]     Referring to  FIG. 5 , a memory  300  according to one embodiment if the present invention is shown. Memory  300  comprises memory core  302 , data path component  304 , and output buffer  306 .  
         [0021]     Memory core  302  comprises a memory array  308 , sense amplifiers  310 , address transition detector (atd) and read timer  312 , and latch  314 . Data path component  304  comprises data path driver  316 , latch  318 , and matched path  320 . Matched path  320  comprises in one embodiment a second data path driver  322  identical to data path driver  316 , and logic  324  for enabling new_salatch_filter signal for control of latch  318 . Output buffer component  306  comprises output buffers  326 . The memory core  302  with the sense amplifiers  310 , sets the amount of time needed from supply of signal CE*=0 to select the addressed location, to sense the data from the array  308  and have the data ready and presented at the memory bank boundary. The data path circuit  304  controls data propagation through the memory  300  up to the pad area and the output buffers  326  are used to drive the output load.  
         [0022]     In operation, atd and read timer  312  receives a chip enable signal CE* and an address. The address is also received at array  308 . Sense amplifier  310  senses the data at the received address and feeds the data to latch  314 . Latch  314  is enabled by a signal, sa_latch, from atd and read timer  312 . This same signal, sa_latch, is propagated ultimately to latch  318  to enable the data to be sent to the output buffer component  306  using a path  320  that is matched to the path the data follows through the data path component  304 . The two paths, data through the data path driver  316 , and the sa_latch signal through an identical data path driver  322  data path to output, are matched with the same propagation delay. When the data is valid in the memory core, it takes a certain amount of time to propagate, but the same latch signal that enables data to be fed from the memory core  302  is fed in parallel through matched path  320 , the valid data and the signal new_salatch_filter arrive at the latch  318  simultaneously. This assures that all data spurious commutations are masked, but no extra delay is present beyond the small delay for enabling the latch  318 . In the memory  300 , logic  324  accepts as input the sa_latch_logic_in signal from data path driver  322 , and determines on the basis of the status of a signal from fuse  330  whether to delay the opening of latch  318  or to operate the memory  300  as a standard unfiltered memory such as that shown in  FIG. 1 .  
         [0023]     The memory embodiment  300  is configured to allow one of two configurations. The output buffers  326  can be set either as pass through buffers, or as filtered output buffers, depending on the signal from logic  324 . The configurations allow a choice as to whether to use the memory  300  in a very fast but noisy configuration, or in a fast non-noisy configuration that is significantly faster than a conventional filtered approach. In one embodiment, the option is set during programming, at the factory, and cannot be changed. In one embodiment, the configuration is enabled by a non-volatile bit, realized with a FAMOS cell fuse, allowing the selection of the filtered or unfiltered output depending upon the specific customer need and access time specification.  
         [0024]     The new_salatch_filter signal and the valid data reach the pad area simultaneously, and the memory  300  requires no additional margin on top of the margin it already has at the sense amplifier level. Fuse  330  is used to set the new_salatch_filter signal (to enable use of the filtered data path) as active, thus allowing the device to be set into the two different configurations. The first configuration is “mask signal active” in which no spurious transitions are present on the output buffers and the asynchronous access time penalty is very short. The second configuration is “mask signal inactive” in which spurious transitions are present on the output buffers but asynchronous access time is at a minimum.  
         [0025]     The matched path  320  consumes very little real estate within the memory since only one matched path is needed for an entire memory.  
         [0026]     The embodiments of the present invention overcome the criticalities with memory circuits by using a signal generated from the last event of the sensing phase and propagated to the output buffers with a path which tracks the data path. This reduces the delay time and still filters the output so that the output data does not have bad data prior to the valid point.  
         [0027]     In one embodiment, once the active mask signal is enabled, the memory operates in the masking configuration permanently. However, it should be understood that the nonvolatile bit such as fuse  330  is capable of being reprogrammed at a later time provided the option is left to reprogram the bit. This is within the scope of the present invention.  
         [0028]     The embodiments of the present invention shown in  FIGS. 5-6  are self-adapting to the conditions in which the memory operates. When a different signal is used to generate a delay such as that shown in  FIG. 3 , with two atd and read timer circuits, one circuit allowing for masking of spurious data, and one propagating data through the memory, two different signals in two different parts of the device are used. Those two signals may act differently with power supply or temperature changes. Any differences between devices and locations within the device, including but not limited to sensitivity, location, and temperature, have different delay potentials. Further, power supply changes could also affect the signals differently. The present embodiments use the same signal, which ensures that changing conditions affect each path the same, so the delay in the two circuits is the same.  
         [0029]     A memory suitable for use with the embodiments of the present invention is shown in  FIG. 4 , which is a functional block diagram of a memory device  400 , such as a flash memory device, of one embodiment of the present invention, which is coupled to a processor  410 . The memory device  400  and the processor  410  may form part of an electronic system  420 . The memory device  400  has been simplified to focus on features of the memory that are helpful in understanding the present invention. The memory device includes an array of memory cells  430 . The memory array  430  is arranged in banks of rows and columns.  
         [0030]     An address buffer circuit  440  is provided to latch address signals provided on address input connections A 0 -Ax  442 . Address signals are received and decoded by row decoder  444  and a column decoder  446  to access the memory array  430 . It will be appreciated by those skilled in the art, with the benefit of the present description, that the number of address input connections depends upon the density and architecture of the memory array. That is, the number of addresses increases with both increased memory cell counts and increased bank and block counts.  
         [0031]     The memory device reads data in the array  430  by sensing voltage or current changes in the memory array columns using sense/latch circuitry  450 . The sense/latch circuitry, in one embodiment, is coupled to read and latch a row of data from the memory array. Data input and output buffer circuitry  460  is included for bi-directional data communication over a plurality of data (DQ) connections  462  with the processor  410 , and is connected to write circuitry  455  and read/latch circuitry  450  for performing read and write operations on the memory  400 .  
         [0032]     Command control circuit  470  decodes signals provided on control connections  472  from the processor  410 . These signals are used to control the operations on the memory array  430 , including data read, data write, and erase operations. Matched path circuitry  480  is connected to the address circuitry  440  and to read/latch  450  and I/O circuitry  460 . The matched path circuitry in one embodiment includes the fuse  330  described above. It should be understood that the flash memory device  400  has been simplified to facilitate a basic understanding of the features of the memory. A more detailed understanding of internal circuitry and functions of flash memories are known to those skilled in the art.  
         [0033]     Advantages of the embodiments of the present invention include a reduced speed penalty on access time when in filtered configuration (compared to previous filtered configuration); self adaptation to the data path architecture (i.e., when shrinking to a new technology node or when increasing the memory size) that does not require a new reassessment of the delays, since the paths will propagate at their minimum times and valid data will arrive at the output buffers at the same time the new_sa_latch_filter signal enabling the latch arrives; and configurable use with a fuse allowing the customer to decide at the factory level whether the customer requires a minimum access time at the penalty of spurious data, or a reduced speed penalty over traditional filtered approaches and valid data.  
       CONCLUSION  
       [0034]     Circuits and methods have been described that include using a signal generated from the last event of a sensing phase, propagated to the output buffers with a patch which tracks the data path. The feature is enabled in one embodiment by a non-volatile bit, allowing the selection of the filtered or not filtered output depending upon the specific customer need and access time specification.  
         [0035]     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.