PATENT DOCUMENT

Publication Number: US-8988957-B2
Application Number: US-201213670813-A
Country: US
Kind Code: B2

Title: Sense amplifier soft-fail detection circuit

Abstract:
A sense amplifier test circuit that may allow for detecting soft failures may include a voltage generator circuit, a sense amplifier, and a detection circuit. The voltage generator may be operable to controllably supply different differential voltages to the sense amplifier, and the detection circuit may be operable to detect an analog voltage on the output of the sense amplifier.

Claims:
What is claimed is: 
     
       1. An apparatus, comprising:
 a voltage generator circuit configured to generate a plurality of differential voltages; 
 a sense amplifier configured to receive a given one of the plurality of differential voltages and generate an output signal in response to receiving an enable signal; 
 a load circuit coupled to the output of the sense amplifier and configured to detect an analog voltage level of the output signal in response to receiving the enable signal; and 
 an output circuit configured to generate a data output signal dependent upon the output of the load circuit and the output of the sense amplifier. 
 
     
     
       2. The apparatus of  claim 1 , wherein the load circuit comprises a voltage reference and a comparator circuit configured to compare the output signal to the reference voltage. 
     
     
       3. The apparatus of  claim 1 , wherein the output circuit comprises a multiplex circuit configured to select the output of the sense amplifier as the data output signal responsive to a hard fail test mode signal. 
     
     
       4. The apparatus of  claim 1 , wherein the load circuit comprises a dynamic circuit configured to discharge a dynamic node in response to the output signal reaching the analog voltage level. 
     
     
       5. The apparatus of  claim 4 , wherein the dynamic circuit comprises a pull-down device, and a keeper device, wherein the transconductance values of the pull-down device and the keeper device are such that the dynamic node discharges in response to the output signal reaching the analog voltage level. 
     
     
       6. A method, comprising:
 designing a sense amplifier test circuit including one or more sense amplifier circuits; 
 fabricating the sense amplifier test circuit on a semiconductor manufacturing process; 
 measuring a minimum differential voltage requirement for each one of the one or more sense amplifier circuits included in the sense amplifier test circuit; 
 analyzing the measured minimum differential voltage requirements; and 
 modifying the design of the sense amplifier dependent upon the analysis. 
 
     
     
       7. The method of  claim 6 , wherein the sense amplifier test circuit further includes one or more detection circuits, wherein each detection circuit is coupled to the output of a respective one of the one or more sense amplifiers. 
     
     
       8. The method of  claim 7 , wherein measuring the minimum differential voltage requirement comprises detecting a soft failure for each one of the one or more sense amplifier circuits. 
     
     
       9. The method of  claim 6 , wherein analyzing the measured minimum differential voltage requirements comprises performing a curve fit of the measured minimum differential voltage requirements to a pre-determined probability density function. 
     
     
       10. The method of  claim 9 , wherein analyzing the measure minimum differential voltage requirements further comprises estimating the yield of the sense amplifier circuit. 
     
     
       11. A system, comprising:
 one or more sense amplifier circuits; 
 a voltage generator circuit configured to selectably supply a differential voltage of a plurality of differential voltages to at least some of the one or more sense amplifier circuits; and 
 one or more detection circuits, wherein each of the one or more detection circuits is coupled to a respective one of the one or more sense amplifiers circuits; 
 wherein each of the one or more sense amplifier circuits is configured to generate an output signal that is dependent upon the applied differential voltage in response to receiving an enable signal; and 
 wherein each of the one or more detections circuits is configured to detect an analog voltage level on the output signal of the respective sense amplifier. 
 
     
     
       12. The system of  claim 11 , wherein the voltage generator circuit comprises one or more resistive voltage dividers configured to generate the plurality of differential voltages. 
     
     
       13. The system of  claim 11 , wherein the voltage generator circuit comprises a one or more voltage reference circuits configured to generate the plurality of differential voltages. 
     
     
       14. The system of  claim 11 , wherein each one of the detection circuits comprises a dynamic circuit configured to discharge a dynamic node in response to the detection of the analog voltage level. 
     
     
       15. The system of  claim 11 , further comprising one or more latches, wherein each one of the latches is configured to store an output of a respective one of the one or more detection circuits. 
     
     
       16. A memory, comprising:
 a plurality of memory cells; 
 a voltage generator circuit configured to generate a plurality of differential voltages; 
 a plurality of sense amplifier circuits; and 
 a plurality of test circuits, wherein each test circuit of the plurality of test circuits is coupled to a respective one of the plurality of sense amplifiers. 
 
     
     
       17. The memory of  claim 16 , wherein each of the plurality of test circuits comprises a load circuit configured to detect an analog voltage level on an output of the respective one of the plurality of sense amplifiers. 
     
     
       18. The memory of  claim 17 , wherein the load circuit comprises a dynamic circuit configured to discharge a dynamic node in response the output of the respective one of the plurality of sense amplifiers achieving the analog voltage level. 
     
     
       19. The memory of  claim 16 , wherein the voltage generator circuit is further configured to selectably apply a differential voltage of the plurality of differential voltages to each of the plurality of sense amplifiers in response to receiving a test signal. 
     
     
       20. A method, comprising:
 selecting a first differential voltage level; 
 activating a sense amplifier circuit configured to receive the selected first differential voltage; 
 detecting, by a detection circuit, an analog voltage level on an output of the sense amplifier; 
 determining a soft failure dependent upon the detected analog voltage; 
 storing the differential voltage level dependent upon the determination; and 
 selecting a second differential voltage level dependent upon the determination. 
 
     
     
       21. The method of  claim 20 , wherein the second differential voltage level is lower than the first differential voltage level. 
     
     
       22. The method of  claim 20 , wherein detecting the analog voltage level comprises comparing a voltage level on the output of the sense amplifier to a pre-determined reference voltage level. 
     
     
       23. The method of  claim 20 , wherein detecting the analog voltage level comprises discharging a dynamic circuit node in response the output of the sense amplifier reaching a pre-determined voltage level. 
     
     
       24. The method of  claim 21 , wherein determining a soft failure comprises selecting between the output of the sense amplifier and an output of the detection circuit.

Description:
BACKGROUND 
     1. Technical Field 
     This invention is related to the field of memory implementation, and more particularly to the implementation of sense amplifiers. 
     2. Description of the Related Art 
     Computing systems may include one or more systems on a chip (SoC), which may integrate a number of different functions, such as, graphics processing, and memories onto a single integrated circuit. With numerous functions included in a single integrated circuit, chip count may be kept low in mobile computing systems, such as tablets, for example, which may result in a smaller form factor for such mobile computing systems. 
     Memories typically include a number of data storage cells composed of interconnected transistors. Such data storage cells may be constructed according to a number of different circuit design styles. For example, the data storage cells may be implemented as a single transistor coupled to a capacitor to form a dynamic storage cell. Alternatively, cross-couple inverters may be employed to form a static storage cell, or a floating gate MOSFET may be used to create a non-volatile storage cell. 
     During the semiconductor manufacturing process, variations in lithography, transistor dopant levels, etc., may result in different electrical characteristics between storage cells and sense amplifiers that are intended to have identical characteristics. Additional variation in electrical characteristics may occur due to aging effects within the transistors as the device is repeatedly operated. These differences in electrical characteristics between transistors can result in data storage cells that output different small signal voltages for the same stored data, and sense amplifiers that respond differently to the same differential input voltage level. 
     In some cases, the variation of a given sense amplifier may result in the sense amplifier not being able to properly sense the data state of a selected storage cell. Such sense amplifiers may be identified as failures during testing and may require re-design in order to achieve manufacturing yield goals. 
     SUMMARY OF THE EMBODIMENTS 
     Various embodiments of circuit for testing a sense amplifier circuit on an integrated circuit are disclosed. Broadly speaking, a circuit and a method are contemplated in which a sense amplifier may receive a differential voltage and may generate an output in response to receiving an enable signal. The output of the sense amplifier may be coupled to a load circuit which may detect an analog voltage level. And an output circuit may select between the output of the sense amplifier and the output of the load circuit to provide a data output signal. 
     In one embodiment, the load circuit may include a dynamic circuit which may discharge a dynamic node in response to the output of the sense amplifier reaching the analog voltage level. The output circuit may include a multiplex circuit configured to select as the data output signal the output of the load circuit in response to a soft fail test mode enable signal. 
     In a further embodiment, a voltage generator circuit may generate a plurality of differential voltages that may be selectably applied to the sense amplifier. The voltage generator circuit may include a plurality of resistive voltage dividers to generate the plurality of differential voltages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description makes reference to the accompanying drawings, which are now briefly described. 
         FIG. 1  illustrates an embodiment of a system on a chip. 
         FIG. 2  illustrates an embodiment of a memory. 
         FIG. 3  illustrates an embodiment of a memory sub-array. 
         FIG. 4  illustrates an embodiment of a sense amplifier. 
         FIG. 5  illustrates possible waveforms for the operation of a sense amplifier. 
         FIG. 6  illustrates an embodiment of a sense amplifier test module. 
         FIG. 7  illustrates a block diagram of a sense amplifier test circuit. 
         FIG. 8  illustrates an embodiment of a sense amplifier load circuit with dedicated feedback inverter. 
         FIG. 9  illustrates a flowchart of an example method of designing a sense amplifier. 
         FIG. 10  illustrates a flowchart of an example method for detecting soft failures in a sense amplifier. 
     
    
    
     While the disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the disclosure to the particular form illustrated, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include,” “including,” and “includes” mean including, but not limited to. 
     Various units, circuits, or other components may be described as “configured to” perform a task or tasks. In such contexts, “configured to” is a broad recitation of structure generally meaning “having circuitry that” performs the task or tasks during operation. As such, the unit/circuit/component can be configured to perform the task even when the unit/circuit/component is not currently on. In general, the circuitry that forms the structure corresponding to “configured to” may include hardware circuits. Similarly, various units/circuits/components may be described as performing a task or tasks, for convenience in the description. Such descriptions should be interpreted as including the phrase “configured to.” Reciting a unit/circuit/component that is configured to perform one or more tasks is expressly intended not to invoke 35 U.S.C. §112, paragraph six interpretation for that unit/circuit/component. More generally, the recitation of any element is expressly intended not to invoke 35 U.S.C. §112, paragraph six interpretation for that element unless the language “means for” or “step for” is specifically recited. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     A system on a chip (SoC) may include one or more functional blocks, such as, e.g., a microcontroller or a memory, which may integrate the function of a computing system onto a single integrated circuit. Prior to the inclusion of a memory in an SoC design, some or all of circuits, such as sense amplifiers, for example, included in the memory made be fabricated on a test chip or process control module to gather data regarding the performance and yield of the circuits. The embodiments illustrated in the drawings and described below may provide techniques for testing sense amplifiers to determine failure limits of the sense amplifiers and provide data necessary to estimate memory yield for a given sense amplifier design. 
     A block diagram of an SoC is illustrated in  FIG. 1 . In the illustrated embodiment, the SoC  100  includes a processor  101  coupled to memory block  102 , and analog/mixed-signal block  103 , and I/O block  104  through internal bus  105 . In various embodiments, SoC  100  may be configured for use in a mobile computing application such as, e.g., a tablet computer or cellular telephone. 
     Memory block  102  may include any suitable type of memory such as a Dynamic Random Access Memory (DRAM), a Static Random Access Memory (SRAM), a Read-only Memory (ROM), Electrically Erasable Programmable Read-only Memory (EEPROM), or a FLASH memory, for example. It is noted that in the embodiment of an SoC illustrated in  FIG. 1 , a single memory block is depicted. In other embodiments, any suitable number of memory blocks may be employed. 
     Analog/mixed-signal block  103  may include a variety of circuits including, for example, a crystal oscillator, a phase-locked loop (PLL), an analog-to-digital converter (ADC), and a digital-to-analog converter (DAC) (all not shown). In other embodiments, analog/mixed-signal block  103  may be configured to perform power management tasks with the inclusion of on-chip power supplies and voltage regulators. Analog/mixed-signal block  103  may also include, in some embodiments, radio frequency (RF) circuits that may be configured for operation with cellular telephone networks. 
     I/O block  104  may be configured to coordinate data transfer between SoC  101  and one or more peripheral devices. Such peripheral devices may include, without limitation, storage devices (e.g., magnetic or optical media-based storage devices including hard drives, tape drives, CD drives, DVD drives, etc.), audio processing subsystems, or any other suitable type of peripheral devices. In some embodiments, I/O block  104  may be configured to implement a version of Universal Serial Bus (USB) protocol or IEEE 1394 (Firewire®) protocol. 
     I/O block  104  may also be configured to coordinate data transfer between SoC  101  and one or more devices (e.g., other computer systems or SoCs) coupled to SoC  101  via a network. In one embodiment, I/O block  104  may be configured to perform the data processing necessary to implement an Ethernet (IEEE 802.3) networking standard such as Gigabit Ethernet or 10-Gigabit Ethernet, for example, although it is contemplated that any suitable networking standard may be implemented. In some embodiments, I/O block  104  may be configured to implement multiple discrete network interface ports. 
     Turning to  FIG. 2 , a memory is illustrated according to one of several possible embodiments. In some embodiments, memory  200  may correspond to memory block  102  as depicted in  FIG. 1 . The illustrated embodiment includes data I/O ports  208  denoted as “dio,” an address bus input  211  denoted “add,” mode selection input  210  denoted as “mode,” and clock input  209  denoted as “clk.” 
     In the illustrated embodiment, memory  200  includes sub-arrays  201   a ,  201   b , and  201   c , timing and control unit  202 , and address decoder  203 . Timing and control unit  202  is coupled to provide a decoder enable signal  205  to address decoder  203 , and control signals  204  to sub-arrays  201   a - 201   c . In some embodiments, control signals  204  may include a sense amplifier enable signal and an output enable signal. 
     Sub-arrays  201   a ,  201   b , and  201   c  may include, as described below in more detail, one or more data storage cells each of which may be configured to store data or output stored data when selected, sense amplifiers, multiplex circuitry, and input/output circuitry. In other embodiments, additional sub-arrays may be included in memory  200 . 
     Timing and control unit  202  may include a variety of circuits including delay chains, latches, and flip-flops that may be configured to implement a state machine capable of controlling memory  200 . In some embodiments, timing and control unit  202  may provide synchronous operation with respect to clock input  209 , while in other embodiments, timing and control unit  202  may employed self-timed circuits. 
     Address decoder  203  is coupled to provide row selection signals  206  and column selection signals  207 , in response to the assertion of decoder enable signal  205  and dependent upon the address value encoded on address bus input  211 . In some embodiments, address decoder  203  may be configured to latch values on address bus input  211  prior to the generation of row selection signals  206  and column selection signals  207 . In other embodiments, column selection signals  207  may be differentially encoded. 
       FIG. 3  illustrates an embodiment of a memory sub-array which may, in some embodiments, correspond to sub-arrays  201   a - 201   c  as depicted in  FIG. 2 . In the illustrated embodiment, sub-array  300  includes a data output  310  denoted as “dout,” an output enable input  309  denote as “oe,” and a sense amplifier enable input  308  denoted as “sae.” The illustrated embodiment also includes one or more column selection input  307  denoted as “cs” and one or more row selection inputs denoted as “rs.” 
     In the illustrated embodiment, columns  301   a ,  301   b ,  301   c , and  301   d  are coupled to the inputs of column multiplexer  302  through bit lines  305 . The differentially encoded output of column multiplexer  302  is coupled to the differential inputs of sense amplifier  303 , and the output of sense amplifier  303  is coupled to the input of output circuit  304 . 
     Each column  301  may include one or more data storage cells, whose outputs are coupled to a common pair (a true bit line and a complement bit line) of bit lines  305 . The data storage cells may be configured such that in response to the assertion of one of row selection inputs  306 , a selected one of the data storage cells may output its stored data onto the pair of bit lines. In some embodiments, the data storage cells may be static storage cells, while in other embodiments, the data storage cells may be dynamic storage cells, single-bit or multi-bit non-volatile storage cells, or mask programmable read-only storage cells. It is noted that in some embodiments, the data storage cells may transmit data in a single-ended fashion. In such cases, only a single bit line per column may be required. 
     In some embodiments, column multiplexer  302  may contain one or more pass gates controllable by column selection inputs  307 . The input of each pass gate may be coupled to either the true or complement bit line output from one of columns  301   a ,  301   b ,  301   c , or  301   d . The output of each pass gate coupled to a true bit line may be coupled to the true output of column multiplexer  302  in a wired-OR fashion, and the output of each pass gate coupled to a complement bit line may be coupled to the complement output of column multiplexer  302  in a wired-OR fashion. In other embodiments, column multiplexer  302  may contain one or more logic gates configured to perform the multiplexer selection function. 
     It is noted that a pass gate (also referred to as a “transmission gate”) may include an n-channel metal-oxide-semiconductor field-effect transistor (MOSFET) and a p-channel MOSFET connected in parallel. In other embodiments, a single n-channel MOSFET or a single p-channel MOSFET may be used as a pass gate. It is further noted that, in various embodiments, a “transistor” may correspond to one or more transconductance elements such as a junction field-effect transistor (JFET), for example. 
     As will be described in more detail below, sense amplifier  303  may use a latch based amplification technique. In other embodiments, sense amplifier  303  may use analog amplification techniques. In cases where the data storage cells of columns  301   a - 301   d  transmit data in a single-ended fashion, sense amplifier  303  may be configured to amplify the singled-ended data. 
     Output circuit  304  may be configured to convert the differentially encoded output of sense amplifier  303  into single-ended data prior to output on data output  310 . In some embodiments, output enable input  309  may control the impedance of output circuit  304 , allowing for a high impedance state such that multiple circuits may be coupled to data output  310  in a wired-OR fashion. 
     It is noted that the sub-array illustrated in  FIG. 3  is merely an example. In other embodiments, different circuit blocks and arrangement of circuit blocks are possible and contemplated. 
       FIG. 4  illustrates a sense amplifier according to one of several possible embodiments that may be coupled to receive differentially encoded data from the output of a column multiplexer as described above in reference to  FIG. 3 . In the illustrated embodiment, sense amplifier  400  includes true amplifier input  414  denoted as “input_t,” complement amplifier input  413  denoted as “input_c,” and sense amplifier enable input  415  denoted as “sae.” Sense amplifier  400  further includes true output  412  and complement output  411  denoted as “saout_t” and “saout_c,” respectively. 
     In the illustrated embodiment, true amplifier input  414  controls gain device  406 , and complement amplifier input  413  controls gain device  405 . Gain device  406  is coupled to pull-down device  416 , feedback device  404 , and pre-charge device  410 . Gain device  405  is coupled to pull-down device  416 , feedback device  403 , and pre-charge device  409 . Pre-charge devices  409  and  410 , and pull-down device  416  are controlled by sense amplifier enable input  415 . 
     Feedback device  404  is further coupled, through node  418 , to pull-up device  402 , pre-charge device  408 , and inverter  420 , which is coupled to true output  412 . Feedback device  403  is further coupled, through node  417 , to pull-up device  401 , pre-charge device  407 , and inverter  419 , which is coupled to complement output  411 . Pull-up device  402  and feedback device  404  are controlled by node  417 , and pull-up device  401  and feedback device  403  are controlled by node  418 . Pre-charge devices  407  and  408  are controlled by sense amplifier enable input  415 . 
     It is noted that static complementary metal-oxide-semiconductor (CMOS) inverters, such as those shown and described herein, may be a particular embodiment of an inverting amplifier that may be employed in the circuits described herein. However, in other embodiments, any suitable configuration of inverting amplifier that is capable of inverting the logical sense of a signal may be used, including inverting amplifiers built using technology other than CMOS. Moreover, it is noted that although pre-charge devices, feedback devices, pull-up devices, and pull-down devices may be illustrated as individual transistors, in other embodiments, any of these devices may be implement using multiple transistors or other suitable circuit elements. 
     Turning to  FIG. 5 , possible waveforms resulting from the operation of sense amplifier  400  are depicted. Referring collectively to  FIG. 4  and  FIG. 5 , both true amplifier input  414  (waveform  501 ) and complement amplifier input  413  (waveform  502 ) are initially high, and sense amplifier enable input  415  is low (waveform  503 ), which turns on pre-charge devices  407 ,  408 ,  409 , and  410 , thereby pre-charging nodes  417 ,  418 ,  422 , and  423 . In response to the pre-charged voltage level on nodes  417  and  418 , true output  412  (waveform  504 ) and complement output  411  (waveform  505 ) are both low. 
     At some time later, complement amplifier input  413  (waveform  502 ) begins to discharge resulting from a selected data storage cell discharging its respective complement bit line, while true amplifier input  414  (waveform  501 ) remains high. As complement amplifier input  413  (waveform  502 ) discharges, a difference develops between true amplifier input  414  and complement  413 , corresponding to the data stored in the selected data storage cell. 
     It is noted that “low” refers to a voltage at or near ground and that “high” refers to a voltage level sufficiently large to turn on a n-channel MOSFET and turn off a p-channel MOSFET. In other embodiments, different technology may result in different voltage levels for “low” and “high.” 
     When a sufficient difference in voltage level between true amplifier input  414  and complement amplifier input  413  has developed, sense amplifier enable input  415  (waveform  503 ) is transitioned high, which causes pull-down device  416  to turn on, discharging node  421 . At the same time, in response to sense amplifier enable input  415  switching high, pre-charge devices,  407  through  410  turn off. The high level on true amplifier input  414  causes gain device  406  to turn on, discharging node  422 . Since there is a lower voltage on complement amplifier input  413 , gain device  405  does not conduct as much as gain device  406 , thereby causing node  423  to discharge a slower rate than that of node  422 . Regenerative feedback through feedback devices  403  and  404 , and pull-up devices  401  and  402 , cause node  417  to discharge from its pre-charge state. Inverter  420  then causes true output  412  to transition high (waveform  504 ). During the period of time the regenerative feedback is being established, node  418  may partially discharge before returning to its pre-charged level. Inverter  419  may generate a momentary signal on complement output  411  (waveform  505 ) in response to the partial discharge of node  417 . Although the previous description of the operation of sense amplifier  400  describes sensing a logical 1, the operation of sense amplifier is fundamentally the same when sensing a logical 0. 
     The proper operation of sense amplifier  400  is dependent upon the relative transconductance values of gain devices  405  and  406 , and those of feedback devices  403  and  404 . During manufacture in a semiconductor process, differences in lithography, random dopant fluctuations, variations in stress and strain, may result in different transconductance values between two devices intended to have identical values (commonly referred to as “matched devices”), such as, e.g., gain devices  405  and  406 . 
     Differences in matched devices, may cause a sense amplifier to preferentially detect one logical data state over another. This phenomenon is commonly referred to as “offset” and may require a larger than desired differential voltage in order to overcome the offset of the sense amplifier. In cases where the input differential voltage is insufficient to overcome any offset within a sense amplifier, an incorrect data state may be generated by the sense amplifier, resulting in what is commonly referred to as a “hard failure.” 
     When the input differential voltage is close to a level that may cause a hard failure, a momentary analog voltage level, such as was previously described in regards to waveform  505  of  FIG. 5 , may appear on the high side of the amplifier. The momentary analog voltage level is commonly referred to as a “glitch.” Depending on the voltage level of the glitch, noise sensitive circuits coupled to the output of the sense amplifier may interpret the glitch as a change in logical state and react accordingly, resulting in what is commonly referred to as a “soft failure.” 
     Both types of failures may be detrimental to the operation of a memory. In some embodiments, test circuits may be employed to gather data on one or more sense amplifiers to determine how frequently each type of failure occurs. Such data may be used to modify the design of the sense amplifiers for further revisions of a memory circuit. 
     Turning to  FIG. 6 , an embodiment of a sense amplifier test circuit is illustrated. The illustrated embodiment includes sense amplifier enable input  614  denoted as “sae,” control input  615  denoted as “control,” and test outputs  610  through  613  denoted as “data_a,” “data_b,” “data_c,” and “data_d,” respectively. In some embodiments, sense amplifier enable input  614  may correspond to sense amplifier enable input  415  of sense amplifier  400  as depicted in  FIG. 4 . 
     In the illustrated embodiments, differential voltage generator  601  is coupled to sense amplifiers  602 ,  604 ,  606 , and  608 , which are controlled by sense amplifier enable input  614 . Sense amplifier  602  is further coupled to detection circuit  603 , and sense amplifier  604  is further coupled to detection circuit  605 . Additionally, sense amplifier  606  is further coupled to detection circuit  607 , and sense amplifier  608  is further coupled to detection circuit  609 . Each of detection circuits  603 ,  605 ,  607 , and  609  are controlled by control input  615 , and coupled to test outputs  610  through  613 , respectively. It is noted that although four sense amplifiers and four detection circuits are illustrated, in other embodiments, different numbers and configurations of sense amplifiers and detection circuits are possible. 
     Differential voltage generator  601  may be configured to provide a range of differential voltages to sense amplifiers  602 ,  604 ,  606 , and  608 . In some embodiments, differential voltage generator  601  may include one or more resistive voltage dividers configured to generate the range of differential voltages. In other embodiments, differential voltage generator  601  may include one or more voltage reference circuits, such as a bandgap reference circuit, for example, configured to generate the range of differential voltages. 
     Sense amplifiers  602 ,  604 ,  606 , and  608  may be configured to employ a latch-based amplification method such as sense amplifier  400  as depicted in  FIG. 4 , for example. In other embodiments, sense amplifiers  602 ,  604 ,  606 , and  608  may include analog amplification circuits such as a differential amplifier configured to provide either a single-ended or differential output. 
     Detection circuits  603 ,  605 ,  607 , and  609 , as described in more detail below, may be configured to detect either hard sense amplifier failures of soft sense amplifier failures dependent upon control input  615 . In some embodiments, control input  615 , may include multiple signals configured to operate one or more multiplex circuits included in detection circuits  603 ,  605 ,  607 , and  609 . 
     Sense amplifier test circuit  600  may, in some embodiments, be included in a process control module that may be fabricated in conjunction with integrated circuits to monitor process parameters such as, e.g., metal layer resistances, inter-metal dielectric thickness, and the like. In other embodiments, all or portions of sense amplifier test circuit  600  may be included in an integrated circuit such as, SoC  100  as depicted in  FIG. 1 , for example. In some embodiments, test outputs  610  through  613  may be stored in latches and flip-flops (not shown) and accessed through a scan chain or similar test circuit. 
     Data resulting from the operation of sense amplifier test circuit  600  may be used to perform statistical analysis on the differential voltage input requirements of sense amplifiers  602 ,  604 ,  606 , and  608 , such as, curve fitting to various probability density functions, calculation of a probability of encountering a hard or soft failure, etc. In some embodiments, test conditions, such as, e.g., power supply voltage, temperature, etc., may be varied and data gather to determine the effect of such test conditions on sense amplifier performance. 
     An embodiment of a detection circuit according one of several embodiments is illustrated in  FIG. 7 . The illustrated embodiment includes a true sense amplifier data input  707  denoted as “sadata_t,” a complement sense amplifier data input  708  denoted as “sadata_c,” a hard failure detection selection input  709  denoted as “hfsel,” a true data selection input  710  denoted as “tsel,” a sense amplifier enable input  711  denoted as “sae,” and a test data output  706  denoted as “out.” 
     In the illustrated embodiment, true sense amplifier data input  707  is coupled to load circuit  701  and multiplex circuit  703 . The output of load circuit  701  is coupled to multiplex circuit  703 , and the output of multiplex circuit  703  is coupled to multiplex circuit  705  via true data output signal  712 . Complement sense amplifier input  708  is coupled to load circuit  702  and multiplex circuit  704 . The output of load circuit  702  is coupled to multiplex circuit  704 , and the output of multiplex circuit  704  is coupled to multiplex circuit  705  via complement data output signal  713 . 
     Multiplex circuits  703 ,  704 , and  705  may include a plurality of tri-state buffers whose outputs are coupled together in a wired-OR fashion, and whose control input is dependent upon one of the selection inputs  709  or  710 . In some embodiments, multiplex circuits  703 ,  704 , and  705  may include a plurality of logic gates configured to implement the desired multiplex function. Although multiplex circuits  703 ,  704 , and  705  are illustrated as multiplex circuits in  FIG. 7 , in other embodiments, any suitable output circuit configured to generate an output dependent on one or more data inputs (e.g., true sense amplifier data  707 , and the output of load circuit  701 ) responsive to a selection input such as, e.g., hard fail detection selection input, may be employed. 
     Load circuits  701  and  702  may be configured to detect an analog voltage level on sense amplifier data inputs  707  and  708 , respectively. In some embodiments, load circuits  701  and  702  may include a voltage comparator and a reference circuit. In other embodiments, load circuits may include a dynamic circuit, as described below in more detail, configured to discharge a pre-charged dynamic node upon the detection of a pre-determined analog voltage level on the sense amplifier data inputs  707  and  708 . 
     During operation, sense amplifier enable input  711  is transition from low to high, thereby activating load circuits  701  and  702 , which respond to the voltages on true sense amplifier data input  707  and complement sense amplifier data input  708 , respectively. When one of the load circuits receives a sufficiently high voltage level from its corresponding sense amplifier data input, the load circuit generates a high logic level output. Dependent on the voltage levels present on the sense amplifier data inputs, one or both of the load circuits may generate a high logic level output. 
     To detect a soft failure in the sense amplifier coupled to the input of detection circuit  700 , hard failure selection input  709  is set to a low logic level, which causes multiplex circuits  703  and  704  to select for output to multiplex circuit  705 , the outputs of load circuit  701  and  702 , respectively. The state of true data selection input  710  is dependent upon the polarity of data to be sensed. For example, when the data to be sensed is a logical 1, true sense amplifier data  707  will transition to a high logic level and complement sense amplifier data  708  may transition to an analog voltage level. The output of load circuit  701  will be a high logic level in response to the high logic level on true sense amplifier data  707 . The output of load circuit  702  may transition to a high logic level is the analog voltage level present on complement sense amplifier data  708  is sufficiently large, thereby denoting a soft failure. True data selection input  710  is accordingly set low so that test data output  706  outputs the generated high logic level from load circuit  702 . In the case when a logical 0 is to be sensed, the logical sense of true data selection input  710  is reversed so that a sufficiently large analog voltage level on true sense amplifier data  707  will result in a high logic level on test data output  706 . 
     It is noted that the detection circuit illustrated in  FIG. 7  is merely an example. In other embodiments, different circuit blocks and connectivity between blocks is possible and contemplated. 
     An embodiment of a sense amplifier load circuit is illustrated in  FIG. 8 . In some embodiments, load circuit  800  may correspond to load circuits  701  and  702  as depicted in reference to  FIG. 7 . The illustrated embodiment includes sense amplifier enable input  804  denoted as “sae,” sense amplifier data input  805  denoted as “sa_data,” and load circuit output  807  denoted as “load_out.” 
     In the illustrated embodiment, sense amplifier enable  804  controls pre-charge device  801 , which is coupled, through dynamic node  810 , to pull-down device  803 , keeper device  802 , inverter  806 , and inverter  809 . Inverter  809  is further coupled to load circuit output  807 . Pull-down device  803  is controlled by sense amplifier data  805 , and keeper device  802  is controlled by the output of inverter  806  through node  808 . In various embodiments, additional inverters or buffers (not shown) may be coupled the output of inverter  809  that may provide additional gain for driving larger capacitive loads. 
     During operation, sense amplifier enable  804  and sense amplifier data  805  are both initially low causing dynamic node  810  to be pre-charged high. The high logic level on dynamic node  810  is inverted by inverters  806  and  809 , resulting in a low logic level on node  808  and load circuit output  807 , respectively. When sense amplifier enable is set high, pre-charge device  801  turns off. At this point, the operation of load circuit  800  is dependent upon the voltage level on sense amplifier data  805 . When the voltage level reaches a sufficiently large level, pull-down device  803  sinks a current from dynamic node  810  larger than the current being sourced to load circuit output  807  by keeper device  802 , resulting in the voltage level on dynamic node  810  to drop. When the voltage level on dynamic node  810  drops below the switching threshold of inverter  806 , the output of inverter  806  transitions from a low logic level to a high logic level, turning off keeper device  802 . In a similar fashion, when the voltage level on dynamic node  810  drops below the switching threshold of inverter  809 , load circuit output  807  may transition to a high logic level. Load circuit  800  will remain in this state until both sense amplifier data  805  and sense amplifier enable input  804  return to a low logic level, resulting in the pre-charging of dynamic node  810 . 
     The voltage level that triggers the discharge of dynamic node  810  is dependent upon the relative transconductance values of pull-down device  803  and keeper device  802 . In some embodiments, pull-down device  803  and keeper device  802  may be MOSFETs, and their respective transconductance values may be adjusted by varying the physical dimensions (device width and channel length) of the devices. In other embodiments, pull-down device  803  and keeper device  802  may be each be implemented as a plurality of devices in series to reduce the device&#39;s transconductance value. 
     It is noted that the load circuit depicted in  FIG. 8  is merely an example. In other embodiments, different configurations of devices are possible. 
     Turning to  FIG. 9 , a flowchart of a method for designing a sense amplifier is illustrated. The method begins in block  901 . An initial design for a sense amplifier is then generated (block  902 ). Generating the initial design may include such steps as schematics capture, mask design and physical verification, circuit extraction, and electrical simulation. The designed sense amplifier may then be included in a process control module or test chip along with supporting test circuits such as, sense amplifier test circuit  600  as depicted in  FIG. 6 , for example. The process control module may then be fabricated (block  903 ). 
     Once the process control module has been fabricated, the included sense amplifiers are tested and the variation in required input differential voltage levels may be measured for both hard failures and soft failures (block  904 ). In some embodiments, the variation may be measured under a variety of test conditions, such as, e.g., power supply voltage. The measured data may then be analyzed using statistical techniques (block  905 ). The statistical analysis may include curve fitting of the data to a known statistical distribution, such as, e.g., a Gaussian distribution, the calculation of probabilities for encountering hard or soft failures, and an estimation of the yield impact the sense amplifier design may have on a memory circuit in which the sense amplifier design is employed. The sense amplifier circuit may be then re-designed based upon the results of the analysis of the measured data (block  906 ). Device sizes, mask design of the circuit, etc., may be changed during the re-design process in order to achieve desired performance and yield goals. The method then concludes in block  907 . It is noted that the method illustrated in  FIG. 9  is merely an example, and that in some embodiments, some or all of the operations illustrated in  FIG. 9  may occur in a different order, or may occur concurrently rather than sequentially. 
     A flowchart of a method to operate the test circuit illustrated in  FIG. 6  to gather data on sense amplifier soft failures is illustrated in  FIG. 10 . Referring collectively to  FIG. 6  and the flowchart of  FIG. 10 , the method begins in block  1001 . Differential voltage generator  601  is then operated to provide a maximum differential voltage (block  1002 ). Sense amplifiers  602 ,  604 ,  606 , and  608  are then activated (block  1003 ), and their respective outputs detected by detection circuits  603 ,  605 ,  607 , and  609  (block  1004 ). The method then depends on whether or not a soft failure was detected for one or more of sense amplifiers  602 ,  604 ,  606 , and  608  (block  1005 ). When a soft failure is detected, the differential voltage that triggered the soft failure is recorded (block  1008 ), and the method concludes (block  1009 ). 
     When no soft failure is detected, differential voltage generator  601  is operated to reduce the differential voltage being supplied to sense amplifiers  602 ,  604 ,  606 , and  608  (block  1006 ). The operation then depends on a comparison of the differential voltage to a pre-determined minimum differential voltage (block  1007 ). When the differential voltage less than or equal to the pre-determined minimum differential voltage, the differential voltage is recorded (block  1008 ). The operation then concludes in block  1009 . 
     When the differential voltage is greater than the pre-determined minimum differential voltage, sense amplifiers  602 ,  604 ,  606 , and  608  are re-activated (block  1003 ), and the operation proceeds from block  1003  are described above. It is noted that operations illustrated in  FIG. 10  are executed in a sequential fashion. In some embodiments, the operations may occur concurrently or in a different order than the example method illustrated in  FIG. 10 . 
     Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.

Metadata:
Filing Date: 20121107
Publication Date: 20150324
Grant Date: 20150324
Priority Date: 20121107
Inventors: HESS GREG M
BURNETTE, II JAMES E
Assignee: APPLE INC
CPC Classifications: [{"code": "H01L2924/0002", "inventive": false, "first": false, "tree": "[]"}, {"code": "G11C29/026", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L22/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L2924/0002", "inventive": false, "first": false, "tree": "[]"}, {"code": "G11C29/026", "inventive": true, "first": false, "tree": "[]"}, {"code": "G11C29/026", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2924/0002", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L22/12", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 50622236