Impedance matching test method for memory chip

Abstract

The application relates to the technical field of data storage, and discloses a memory chip impedance matching test method, which comprises the following steps: performing different impedance value matching tests on three dimensions of CA-odt, DQ-odt and SOC-odt of a memory chip to obtain different impedance combinations; performing impedance verification on the memory chip according to the different impedance combinations; screening the memory chips outside the range of the different impedance combinations, determining that the memory chips outside the range of the different impedance combinations are memory chips with obvious impedance difference, i.e. memory chips with poor impedance matching; screening the memory chips within the range of the different impedance combinations, recording the impedance combinations passing all test items, and determining the effective working range of different impedance values of each dimension. The application ensures that the memory chip has sufficient impedance matching tolerance under specific mainboard design and load conditions, thereby guaranteeing the stability of long-term operation of the system.

Description

Technical Field

[0001] This invention relates to the field of data storage technology, and in particular to an impedance matching test method for memory chips. Background Technology

[0002] Impedance matching testing of memory chips is a core technology for ensuring signal integrity in high-speed digital systems. With data transfer rates exceeding 6400MT / s for memory technologies such as DDR5 and LPDDR5, signal integrity has become a critical factor affecting system stability and performance. Impedance mismatch can lead to signal reflection, ringing, and timing deviations, severely impacting system reliability. In modern servers, high-performance computing, and mobile devices, accurate impedance matching testing is not only a necessary step in product verification but also a fundamental guarantee for achieving high-quality signal transmission.

[0003] The impedance of existing memory chips is set according to the average impedance of a certain number of chips (e.g., 5000 chips of the same capacity). However, some memory chips have special impedances, resulting in poor impedance matching. Existing technology cannot quickly, accurately, and effectively eliminate memory chips with poor impedance matching. Summary of the Invention

[0004] This invention provides an impedance matching test method for memory chips, which can solve the technical problem that existing technologies cannot quickly, accurately, and effectively eliminate memory chips with poor impedance matching.

[0005] To solve the above-mentioned technical problems, one technical solution adopted by the present invention is: to provide an impedance matching test method for a memory chip, the method comprising:

[0006] Different impedance matching tests were performed on the memory chip in three dimensions: CA-odt, DQ-odt, and SOC-odt, to obtain different impedance combinations.

[0007] Impedance verification of memory chips is performed based on different impedance combinations;

[0008] Screen memory chips outside the range of different impedance combinations to identify those with significant impedance differences, i.e., memory chips with poor impedance matching.

[0009] Screen memory chips within a range of different impedance combinations, record the impedance combinations that pass all test items, and determine the effective operating range of different impedance values ​​for each dimension.

[0010] The beneficial effects of this invention are: by actively and systematically exploring the boundaries of memory interface impedance matching, rather than simply verifying a set of nominal values, the safe operating area of ​​impedance is precisely defined through multi-dimensional parameter scanning and functional testing. It can effectively identify chips with subtle impedance defects that might have slipped through simple tests. It ensures that memory chips have sufficient impedance matching tolerance under specific motherboard design and load conditions, thereby guaranteeing the long-term stability of the system. The large amount of accumulated test data can provide valuable reference for the ODT circuit design and PCB design of next-generation memory interfaces. Attached Figure Description

[0011] Figure 1 This is a flowchart illustrating the impedance matching test method for a memory chip according to the first embodiment of the present invention. Detailed Implementation

[0012] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0013] The terms "comprising" and "having," and any variations thereof, used in this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0014] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0015] Figure 1 This is a schematic flowchart of the impedance matching test method for a memory chip according to the first embodiment of the present invention. Figure 1 As shown, the method includes:

[0016] Step S1: Perform matching tests on the memory chip at three dimensions: CA-odt (the chip's command pin, through which the main controller sends data), DQ-odt (the data pin end (close to the chip), and SOC-odt (referring to the CPU's SOC end), to obtain different impedance combinations.

[0017] Step S2: Perform impedance verification on the memory chip according to different impedance combinations;

[0018] Step S3: Screen memory chips outside the range of different impedance combinations, and determine that memory chips outside the range of different impedance combinations are memory chips with significant impedance differences, that is, memory chips with poor impedance matching.

[0019] Step S4: Screen memory chips within the range of different impedance combinations, record the impedance combinations that pass all test items, and determine the effective operating range of different impedance values ​​for each dimension (e.g., DQ-ODT can work normally between 48 ohms and 80 ohms).

[0020] Impedance matching is performed on the memory chip across three dimensions: CA-odt (the chip's command pin, through which the main controller sends data), DQ-odt (the data pin, which is closer to the chip), and SOC-odt (the CPU's SOC pin). Impedance values ​​include 40, 48, 60, 80, 120, and 240 ohms (standard impedance). The impedance value is varied for each dimension to obtain different impedance combinations. For example, the impedances for the three dimensions might be 40 ohms, 48 ​​ohms, and 60 ohms. After setting the impedance, read and write tests are performed on the memory chip to check if it is functioning correctly. All impedance combinations that enable the memory chip to function correctly are obtained. For example, the first impedance combination for the three dimensions might be 40, 48, and 60 ohms; the second might be 48, 60, and 80 ohms; and the third might be 80, 120, and 24 ohms. The range of impedances for each dimension is then determined to define the range of impedance combinations. This range is used to verify the chip, screening out chips that are outside the impedance combination range to identify chips with significant impedance differences, i.e., chips with poor impedance matching.

[0021] In LPDDR5 memory systems, CA-odt, DQ-odt, and SOC-odt constitute a complete impedance matching system. CA-odt (Chip Command On-Die Termination) corresponds to the impedance of the chip's command address pin, through which the controller sends control commands and address information. In LPDDR5, the CA bus uses the LVSTL (Low Voltage Short Cut Termination Logic) standard, with a VDDQ voltage of 0.5V and a maximum VOH value of approximately 300mV in the write direction. DQ-odt (Data Pin On-Die Termination) refers to the impedance of the data pin, responsible for data signal transmission. The LPDDR5 interface contains 32 DQ pins, grouped in 8-bit groups, each group equipped with two differential lines, RDQS and WCK. SOC-odt (System-on-Chip On-Die Termination) is the impedance of the CPU's SOC terminal, representing the interface characteristics between the system-on-a-chip and the memory.

[0022] According to the JEDEC standard, the target impedance requirements for LPDDR5 are: 40Ω for DQ / CA / CS signals, 75Ω for DQS / CLK differential signals, and 65Ω for WCK signals. These standard values ​​are determined based on signal integrity theory, aiming to ensure optimal power transfer and minimal reflection during signal transmission. The basic principle of impedance matching is to make the characteristic impedance of the transmission line equal to the load impedance, thereby achieving complete signal transmission and avoiding energy reflection.

[0023] In actual testing, the impedance characteristics of these three dimensions interact with each other, forming a complex coupling relationship. For example, when the CA-odt impedance changes, it not only affects the transmission quality of the command signal but also influences nearby data signals through electromagnetic coupling. Therefore, a single-dimensional testing method cannot comprehensively evaluate the impedance characteristics of a memory chip; a three-dimensional collaborative testing approach is necessary.

[0024] The test scheme selected six standard impedance values: 40, 48, 60, 80, 120, and 240 ohms. These values ​​cover the commonly used impedance range for memory chips. The selection of these specific values ​​was based on the following criteria: 40 ohms is the standard single-ended impedance requirement for LPDDR5; 48, 60, and 80 ohms represent typical variations around the standard value, simulating the effects of manufacturing process deviations and environmental temperature changes; and 120 and 240 ohms represent larger impedance deviations, used to test the chip's ability to operate under extreme conditions.

[0025] The test matrix employs a fully combinatorial design, meaning that the six impedance values ​​in each dimension are combined to form 6×6×6=216 different impedance configurations. The advantage of this design method is that it comprehensively covers all possible impedance combinations, ensuring the completeness and reliability of the test. In actual testing, each combination needs to be tested independently, and the corresponding signal quality parameters are recorded.

[0026] The construction of the test matrix also needs to consider the actual electrical connection topology. In LPDDR5 systems, commonly used topologies include Star, Fly-by, and hybrid types. For Star topologies, theoretically, the impedance relationship Z2 = 2 × Z1 needs to be satisfied. In actual engineering implementations, a driver impedance of 34Ω, an SOC package impedance of 40Ω ± 10%, a PCB trunk impedance of 30Ω ± 15%, and a PCB branch impedance of 60Ω ± 10% are used. Fly-by topologies, due to their shorter branches, have a relatively uniform overall impedance, typically using a driver impedance of 34Ω, an SOC package impedance of 45Ω ± 10%, and a PCB impedance of 45Ω ± 10%.

[0027] The accuracy of impedance testing directly affects the reliability of the test results, thus requiring sophisticated testing equipment. Core testing equipment includes vector network analyzers (VNAs), such as the Keysight E5071C, which covers a frequency range of 9kHz to 8.5GHz, provides 8-bit accuracy, and can meet various testing needs from low to high frequencies. Time domain reflectometers (TDRs), such as the T3SP series, have a typical rise time of 30ps, support S-parameter measurements up to 15GHz, and a 50,000-point memory capacity, allowing testing of devices up to 50 meters long.

[0028] For dedicated testing of memory chips, a high-speed memory testing system is required, such as the Advantest T5835, which supports data rates up to 5.4Gbps and can test 768 devices simultaneously with an overall timing accuracy of ±50ps. These devices can simulate the real-world operating environment of memory and accurately measure signal quality under different impedance configurations.

[0029] Controlling the testing environment is crucial to ensuring the accuracy of test results. According to industry standards, the testing environment should be controlled at a temperature of 23±2℃ and a relative humidity of 50±5% RH. For automotive-grade chips, the testing temperature range needs to be extended to -40℃ to 125℃. The importance of environmental control lies in the fact that for every 10℃ increase in temperature, the mean time between failures (MTBF) of electronic components decreases by 30%-50%, and chip performance degrades by 25%. Simultaneously, excessively low humidity (<30% RH) can lead to electrostatic discharge (ESD) accumulation exceeding 10kV, potentially damaging sensitive components such as MOSFETs.

[0030] The design of the test fixture also needs to meet stringent technical requirements. The impedance of the test point must match the transmission line; LPDDR4X typically uses a 40Ω or 48Ω single-ended impedance. The capacitance introduced by the test point should be less than 0.5pF, and the inductance less than 1nH to avoid affecting signal integrity. In terms of physical layout, miniature test points (diameter ≤ 0.6mm) should be used. The test points should be connected to the signal lines via short stakes with a length ≤ 50mil (1.27mm), and teardrop pads should be used to reduce impedance abrupt changes.

[0031] ZQ calibration is a core technology in memory chip impedance testing. Its purpose is to adjust the internal pull-up and pull-down resistor values ​​to match a specific standard impedance using an external, precise 240Ω standard resistor. In DDR3 and DDR4, the ZQ pin of each DRAM is connected to an external 240Ω resistor with an accuracy of ±1%. The calibration process is achieved by comparing the VOH signal with an internally generated reference voltage (VDDQ / 2). P-channel tuners are individually tuned using the VOH signal until the XRES voltage equals the reference voltage.

[0032] In LPDDR5, ZQ calibration technology has been further developed. The ZQCAL (Impedance Calibration) process for LPDDR5X memory is used to calibrate the impedance of the output driver and on-chip termination (ODT) of the memory interface. After calibration, the internal register stores the calibration result and uses this value for impedance control of the output driver and ODT. This calibration mechanism can compensate for the effects of process, voltage, and temperature (PVT) variations on impedance characteristics, ensuring optimal signal integrity under different operating conditions.

[0033] Impedance measurement employs a four-wire method, which eliminates the influence of contact resistance and achieves an accuracy of ±0.1mΩ. This method is particularly suitable for testing low-resistance solder joints, such as the power pins of LPDDR chips. For high-speed signals, a TDR (Time Domain Reflectometer) is also required to measure the transmission line impedance, requiring an accuracy of 50Ω ±5% to identify impedance abrupt changes. The calibration of the test equipment is also strictly regulated: the TDR is calibrated every 6 months, and the network analyzer every 3 months. Calibration items include "impedance accuracy," "time reference," and "frequency accuracy." After calibration, verification is performed using a standard impedance board to ensure that the test value deviates from the standard value by ≤±1Ω.

[0034] Impedance verification involves not only measuring electrical parameters but also conducting comprehensive functional tests to verify the actual performance of the memory chip under different impedance combinations. Functional tests verify the logic functions and protocol compatibility of the memory chip under normal operating conditions, such as the eMMC5.1 protocol for eMMC and the JEDEC standard for LPDDR5.

[0035] The testing system employs ATE (Automatic Test Equipment), integrating multi-channel signal sources and high-speed digital interfaces, supporting parallel testing, and achieving a throughput of over 1000 chips per hour. A protocol analyzer is used to verify high-speed interfaces, such as UFS 3.1's 11.6Gbps rate, detecting bit error rate (BER < 10^-12) and timing tolerances. These test devices can simulate real-world system operating environments, comprehensively evaluating the functional integrity of memory chips under different impedance configurations.

[0036] Functional verification testing includes several key components. The first is signal integrity testing, which assesses signal quality through eye diagram analysis. The wider the "eye" of the eye diagram is open, the better the signal quality. Eye width represents effective timing margin; the receiver needs to sample data within the time window when the eye is open. Eye height represents effective voltage margin; a higher eye means a larger difference between the logic high and low levels of the signal.

[0037] Secondly, timing characteristic testing is performed, including the measurement of key timing parameters such as tRP (row precharge time), tRCD (row-to-column address latency), tWR (write recovery time), and tRAS (row activation time). These parameters directly affect memory access speed and system performance, and require precise measurement and optimization under different impedance configurations.

[0038] To ensure the reliability and repeatability of test results, a standardized test procedure needs to be established. The test procedure includes five main stages: initial calibration, parameter setting, data acquisition, result analysis, and report generation. In the initial calibration stage, an external 240Ω resistor is connected to the ZQ pin to calibrate the driver output impedance using the formula Z_driver = R_ext × N, where N is the calibration code scaling factor.

[0039] During the parameter setting phase, the impedance values ​​of CA-odt, DQ-odt, and SOC-odt need to be configured sequentially according to the test matrix. Testing for each impedance combination includes: measuring the actual impedance value of each pin to verify if it is within the allowable deviation range of the target value (usually ±5%); performing signal integrity testing, including measurements of eye diagram quality, jitter, noise, and other parameters; executing functional tests to verify basic functions such as data read / write, refresh, and self-refresh; and recording operating parameters such as power consumption and temperature.

[0040] In terms of quality control, a multi-layered verification mechanism needs to be established. First, equipment calibration verification ensures the accuracy and stability of the testing equipment. Second, environmental monitoring involves real-time monitoring of environmental parameters such as temperature, humidity, and voltage to ensure that testing conditions meet requirements. Third, data verification involves real-time analysis of the collected data to identify outliers and perform repeat tests. Finally, cross-validation involves independently measuring key parameters using different testing equipment to ensure consistency of results.

[0041] The determination of out-of-range chips is based on multiple technical standards, mainly including three dimensions: impedance deviation, signal integrity, and functional performance. Regarding impedance deviation, according to JEDEC standards and engineering practice, when the measured impedance value deviates from the target value by more than ±5%, it can be determined as an impedance anomaly. For example, for a standard impedance of 40Ω, the measured value should be within the range of 38Ω to 42Ω; anything outside this range is considered an out-of-range chip.

[0042] The criteria for determining signal integrity are more complex, primarily determined through eye diagram analysis and bit error rate (BER) testing. When the eye diagram height is below 155mV (as required by the JEDEC standard) or the eye diagram width is less than the specified timing margin, it indicates a signal quality problem. Regarding BER, a BER exceeding 10^-12 indicates a functional malfunction. Furthermore, the impact of signal reflection must be considered; a reflection coefficient exceeding the -15dB tolerance threshold indicates a severe impedance mismatch problem.

[0043] In actual testing, the effects of temperature and voltage changes on impedance characteristics also need to be considered. According to the 10°C rule, the performance of electronic components decreases by 25% for every 10°C increase in temperature. Therefore, when testing under different temperature conditions (such as 25°C, 85°C, and -40°C), the judgment criteria need to be adjusted accordingly. For automotive-grade chips, due to their wider operating temperature range (-40°C to 125°C), the judgment criteria need to be even more stringent.

[0044] Analysis of a large amount of test data reveals several typical anomaly patterns for out-of-range chips. The first type is single-dimensional anomaly, where impedance deviation occurs only in one of the following dimensions: CA-odt, DQ-odt, or SOC-odt. For example, a chip might have a CA-odt of 45Ω (deviation +12.5%), while its DQ-odt and SOC-odt are within the normal range. This situation is typically caused by manufacturing process deviations, such as uneven metal layer thickness or variations in contact resistance.

[0045] The second type is the two-dimensional anomaly, where impedance deviations occur simultaneously in two dimensions. Common combinations include both CA-odt and DQ-odt being excessively high or low. This situation may be related to the overall chip design or process control. Correlation analysis revealed a positive correlation between CA-odt and DQ-odt, with a correlation coefficient of approximately 0.6–0.8, indicating that they may be influenced by common factors.

[0046] The third type is the three-dimensional anomaly, where all three dimensions deviate from the normal range. This situation is relatively rare, but the most serious, and usually indicates a systemic defect in the chip, such as a design error, material problem, or uncontrolled manufacturing process.

[0047] In addition to impedance deviations, it is also necessary to analyze the functional characteristics of abnormal chips. For example, some chips may experience data read / write errors under specific impedance combinations, manifesting as fixed-mode bit errors; other chips may exhibit timing violations, such as tRCD or tRP exceeding specification requirements; and some chips may experience stability issues under high load conditions, such as frequent refresh failures or self-refresh errors.

[0048] For chips outside the selected range, in-depth fault location and root cause analysis are required. First, TDR testing is used to accurately locate impedance anomalies. The picosecond-level pulses of the TDR can precisely pinpoint impedance anomalies, such as impedance jumps at the connection between the gold fingers and the PCB. In actual testing, impedance values ​​are often found to deviate from the nominal 50Ω ± 10%, which can cause signal reflection to exceed the -15dB tolerance threshold.

[0049] During fault localization, the following factors are considered: the connection quality within the chip package, including the length, width, and contact resistance of the bonding lines; the impedance continuity of the PCB traces, especially at vias, pads, and trace width variations; the connector contact quality, such as the plating thickness, surface roughness, and contact pressure of the gold fingers; and power integrity, including the configuration of decoupling capacitors, the impedance of the power plane, and the noise level.

[0050] Root cause analysis employed FMEA (Failure Mode and Effects Analysis) combined with advanced technologies such as neural networks and genetic algorithms. Research indicates that an optimization framework integrating FMEA, Taguchi methods, neural networks, and genetic algorithms (FMEA-TSTM-NNGA) can effectively identify and optimize key factors affecting impedance characteristics. The analysis process included: identifying potential failure modes, assessing the severity, probability of occurrence, and detection difficulty of failures; determining key process parameters using Design of Experiments (DOE) methods; and establishing a predictive model to optimize the combination of process parameters.

[0051] Determining the effective working range for each dimension requires a multi-dimensional statistical analysis method. First, the stability parameters for each impedance combination are calculated, including the proportion of non-conforming samples, the total sample size, the impedance mean, and the impedance variance. The impedance mean μ reflects the average level of the chip impedance under this combination, and the impedance variance... It reflects the degree of dispersion of the impedance value.

[0052] The formula for calculating the quality evaluation coefficient λ is: λ = μ × (1-f) / λ is the proportion of non-conforming samples. This coefficient comprehensively considers three factors: impedance mean, pass rate, and dispersion, and can comprehensively evaluate the quality of the impedance combination. A higher λ value indicates that the impedance combination has better working performance.

[0053] Correlation analysis can reveal the relationships between different dimensions. Correlation analysis provides a numerical measure of the degree to which a change in one variable can be attributed to another. The study found that the correlation coefficient between CA-odt and DQ-odt is approximately 0.7, indicating a strong positive correlation between the two. In contrast, the correlation between SOC-odt and the other two dimensions is relatively weak, with correlation coefficients ranging from approximately 0.3 to 0.4, suggesting that SOC-odt is primarily influenced by system design.

[0054] When determining the effective operating range, the impact on production yield also needs to be considered. By analyzing the yield distribution under different impedance combinations, the optimal impedance range can be determined. For example, when DQ-odt is between 48 ohms and 80 ohms, the yield exceeds 95%, while outside this range, the yield drops sharply.

[0055] Based on a yield rate threshold method, a yield rate ≥ 95% is set as the lower limit of the effective operating range. By statistically analyzing the yield rate distribution under different impedance values, the effective range for each dimension can be determined. For example, when DQ-odt is between 48 ohms and 80 ohms, the yield rate reaches 96.5%, while below 48 ohms or above 80 ohms, the yield rate drops to 85% and 88%, respectively.

[0056] The performance-based approach is based on signal integrity. By analyzing key performance indicators such as eye diagram quality, bit error rate, and timing margin, the impedance range that meets design requirements is determined. For example, when DQ-odt is between 50 ohms and 70 ohms, the eye diagram height reaches above 180mV, meeting JEDEC standard requirements; outside this range, the eye diagram height drops below 155mV, approaching the critical value.

[0057] The process method is based on manufacturing capability. By analyzing the capability indices (Cp and Cpk) of the manufacturing process, the impedance range that the process can stably control is determined. When Cp ≥ 1.33 and Cpk ≥ 1.0, it indicates that the process capability is sufficient, and the corresponding impedance range can be determined as the effective operating range.

[0058] For the DQ-odt dimension, comprehensive analysis shows that its effective operating range is 48 ohms to 80 ohms. This range not only ensures good signal integrity and functional performance, but also takes into account the feasibility of manufacturing processes, thus possessing high engineering practical value.

[0059] Leveraging the parallel processing capabilities of modern test equipment, multiple chips or channels can be tested simultaneously. For example, Teradyne's Magnum V system offers up to 20,480 digital channels, each with a processing capacity of 1600 Mbps. Parallel testing can reduce test time to 1 / 10 or even 1 / 100 of its original value.

[0060] By analyzing historical data from testing equipment, we can predict equipment failure and performance degradation trends, enabling proactive maintenance and calibration. This not only reduces equipment downtime but also ensures the long-term stability of test results.

[0061] Based on machine learning technology, algorithms can be developed that can dynamically adjust testing strategies according to test results. For example, when a high yield rate is found for a certain impedance combination, the number of tests for that combination can be reduced; conversely, when an abnormal pattern is found, the test density for related combinations can be increased.

[0062] Step S1 includes:

[0063] Test configuration and initialization on an Automated Test Equipment (ATE) or System-Level Testing (SLT) platform;

[0064] The resistance values ​​of CA-ODT and DQ-ODT are dynamically configured by writing to the mode register (MRS) of the memory chip, while the SOC-ODT value is set by configuring the CPU's internal registers. (JEDEC standards (such as DDR4 / 5) define selectable ODT resistance levels, such as 40, 48, 60, 80, 120, 240 ohms, etc., and modern memory controllers and chips support dynamic switching of these levels.)

[0065] The three ODT dimensions mentioned above correspond to three key interface points in the collaborative operation of the memory subsystem. The goal of impedance matching is to ensure that signals are effectively absorbed at the end of the transmission path, preventing signal distortion caused by reflections. CA-ODT (Command / Address Bus Termination Resistor): The CA bus is unidirectional, issued by the memory controller (usually integrated within the CPU's SoC) and sent to the memory chips. The ODT resistor is typically placed inside the CA pin on the memory chip side. Its function is to ensure that command and address signals are cleanly terminated at the memory chip end, preventing reflected signals from interfering with subsequent commands. Matching considerations: The CA bus typically uses a fly-by topology to connect multiple memory chips, and the signal arrival time at different chips varies slightly. Therefore, optimizing the CA-ODT is crucial to ensuring that all chips can correctly receive instructions. DQ-ODT (Data Bus Termination Resistor): The DQ bus is bidirectional and used for read and write data transmission. The ODT resistor is on the memory chip side. During data writing, the memory controller sends data; at this time, the DQ-ODT on the memory chip side should be enabled to optimize the received signal quality. Matching considerations: The DQ signal has the highest rate and is most sensitive to integrity. Improper DQ-ODT settings can lead to data eye diagram closure and increased bit error rate. SOC-ODT (Memory Controller Termination Resistor): This ODT is located on the data pin inside the CPU / SOC. It mainly functions during data reading, when the memory chip becomes the transmitter and the CPU becomes the receiver. Enabling the SOC-ODT can effectively terminate the data signal from the memory chip, improving read stability.

[0066] ATE platforms (such as Advantest T5835 and Teradyne UltraFLEX) require dedicated test fixtures to achieve electrical connection with memory chips. Key configuration points include: precisely aligning the ATE's digital and analog measurement channels with the memory chip's CA (command address) pins, DQ (data) pins, ZQ (calibration) pins, and power supply pins (VDD, VDDQ), with an error controlled within ±0.1mm to avoid signal attenuation due to contact misalignment. Calibration is performed to ensure the channel output impedance deviates from the memory chip's target impedance by ≤±1%. For example, when testing a 40Ω ODT, the ATE channel impedance should be stable at 40±0.4Ω. The memory chip's power supply parameters are set according to JEDEC standards (DDR5 standard VDD=1.1V, VDDQ=1.1V), and the command / data signal delay is calibrated using the ATE's timing generator (tCK clock cycle deviation ≤±5ps) to ensure matching with the memory chip's timing characteristics.

[0067] The SLT platform is built on an actual system motherboard (such as a motherboard equipped with an Intel 12th generation Core or AMD Ryzen processor). Key configuration points include: installing the memory chip to be tested into the motherboard memory slot, ensuring the gold finger contact pressure meets specifications (typically 20-30N), and connecting the CPU power supply, motherboard power supply, and debugging interfaces (such as JTAG, SPI) to ensure the system can boot normally and enter test mode. A high-speed signal acquisition card (such as the Keysight UXR series) is connected via the PCIe interface for real-time monitoring of the CA and DQ bus signal waveforms; a power monitoring module is also connected to record the power consumption changes of the memory chip during testing, avoiding the impact of power supply fluctuations on impedance test results. The SLT platform must be placed in a constant temperature and humidity chamber, controlling the temperature at 23±2℃ and the humidity at 50±5% RH (automotive-grade testing requires extending to -40℃~125℃), and disabling dynamic frequency adjustment (such as Intel XMP, AMD EXPO) through the motherboard BIOS to ensure the memory operates at a fixed frequency (such as DDR5-4800), eliminating interference from frequency fluctuations on impedance characteristics.

[0068] Both ATE and SLT platforms require software-level loading and initialization of the test protocol to ensure compliant instruction interaction with the memory chip: Load the JEDEC DDR4 / 5 test protocol stack, and send a "reset command (RESET#)" through the ATE test program (such as Advantest TestBuilder) to initialize the memory chip; then execute the ZQ calibration command (ZQCL) to calibrate the chip's internal ODT resistor network using an external 240Ω standard resistor (accuracy ±1%), establishing a baseline for subsequent dynamic configuration. Enter "test mode" through the motherboard BIOS or a dedicated debugging tool (such as the Intel Platform Debug Toolkit), disable the operating system's memory management functions, and directly send initialization commands through the CPU's memory controller; simultaneously configure the CPU's "memory controller mode register" to switch the SOC's ODT control permissions to "manual configuration mode" to prevent automatic system adjustments from interfering with the test. After initialization, the chip status is confirmed by reading the "Status Register (SR)" of the memory chip. For example, if the SR [0] bit of the DDR5 chip is "0", it means that the initialization is successful, and if the SR [5] bit is "1", it means that the ZQ calibration is completed. If the status is abnormal, the reset and calibration process needs to be repeated until the test requirements are met.

[0069] According to the JEDEC DDR4 / 5 standard, the resistance values ​​of CA-ODT and DQ-ODT are configured through the mode register (MRS) of the memory chip, while the resistance value of SOC-ODT is configured through the internal register of the CPU. All three support dynamic switching of standard levels such as 40, 48, 60, 80, 120, and 240Ω. The configuration process must follow strict instruction timing and bit definition rules.

[0070] The Mode Register (MRS) of the memory chip is the core of controlling the ODT resistance value. Different types of MRS correspond to different functions. MRS1 is responsible for CA-ODT configuration, and MRS2 is responsible for DQ-ODT configuration. The configuration process needs to be executed after the memory chip initialization is completed.

[0071] Taking DDR5 memory chips as an example, the MRS instruction format consists of "command cycle (CMD) + address cycle (ADDR)", where specific bits of the address lines (A0-A17) are used to define the ODT resistance value. The core bit definitions are as follows:

[0072] CA-ODT Configuration (MRS1): The resistance value is defined by the two-bit combination A10 and A11. The correspondence between the bit combination and the resistance value conforms to the JEDEC JESD79-5 standard.

[0073]

[0074] DQ-ODT Configuration (MRS2): Resistance values ​​are defined using the three-position combination of A4, A5, and A6, supporting a wider range of resistance options.

[0075]

[0076] The execution process of MRS configuration: On ATE and SLT platforms, the execution of MRS configuration must follow strict timing requirements (DDR5 standard tMRD (MRS instruction cycle) ≥ 4 tCK cycles). The specific steps are as follows: The test software of the ATE / SLT platform generates the corresponding MRS instruction (including CMD and ADDR signals) according to the target resistance value. For example, when configuring DQ-ODT to 40Ω, A6=1, A5=0, A4=1 of the MRS2 instruction, and other irrelevant address bits are set to default values ​​(such as A0-A3=0). The platform synchronizes with the memory chip through the clock signal (CK / CK#) to ensure that the MRS instruction is sent on the rising edge of CK, and the instruction duration meets the tMRD requirement (such as tCK=0.416ns for DDR5-4800, tMRD≥1.664ns, i.e., at least 4 CK cycles). First, send the MRS command (CMD line output "0011", DDR5 standard), then send the corresponding ADDR signal in subsequent address cycles to complete the writing to the MRS register. After configuration, confirm the resistance value is effective by using the "Read MRS Register" command (supported by some chips, or verified by indirect impedance measurement) – for example, on the ATE platform, measure the actual impedance of the DQ pin with an impedance analyzer; the deviation from the target value must be ≤ ±5%, otherwise, re-execute the configuration process.

[0077] The resistance value of the SOC-ODT is controlled by the internal register of the CPU's memory controller. The register address and bit definition vary between different manufacturers (Intel, AMD), but they all follow the resistance value requirements of the JEDEC standard. Configuration needs to be achieved through a dedicated debugging interface or software tool.

[0078] Each memory channel corresponds to an independent ODT control register, where Bits 3-0 define the resistance range of the SOC-ODT. Connect the CPU's JTAG interface via the Intel Platform Debug Toolkit (PDT) and enter "Memory Controller Configuration Mode" as follows: Select the target memory channel (e.g., Channel 0) and locate the ODT ControlRegister (address 0x400). Based on the target resistance value (e.g., 40Ω), set Bits 3-0 to "0110", leaving other irrelevant bits (e.g., Bits 4-31) at their default values ​​(0). After writing to the register, execute the "Register Synchronization" command to ensure the configuration takes effect. Use the PDT's "Impedance Measurement Tool" to read the actual impedance at the SOC terminal and verify that it matches the target value (deviation ≤ ±5%).

[0079] AMD CPU SOC-ODT Register Configuration (Taking Ryzen 7000 Series as an Example): The memory controller of the AMD Ryzen 7000 series (Zen 4) controls the SOC-ODT through the "DRAM ODT Control" register (address: 0xC0010050-0xC001005F). The key configuration points are as follows:

[0080] Register bit definitions: Bits 5-2 define the SOC-ODT resistance value, supporting JEDEC standard settings.

[0081]

[0082] Configure via the AMD Debug Tool (ADT) or the motherboard BIOS's "Advanced Memory Settings" interface, following these steps: In the BIOS, enter the "MIT (Memory Smart Tweaker)" menu and select "DRAM ODT Configuration". Disable the "Auto ODT" function and switch to "Manual" mode. In the "SOC ODT Resistance" option, select the target resistance value (e.g., 40Ω). Save the BIOS settings and restart the system. After entering SLT test mode, measure the impedance at the CPU memory controller output terminal using a high-speed signal acquisition card to verify the configuration's effectiveness.

[0083] In actual testing, the configurations of CA-ODT, DQ-ODT, and SOC-ODT must be executed in a coordinated manner to ensure that the impedance combination of the three meets the requirements of the test matrix. The core control logic is as follows: first configure SOC-ODT (CPU register), then configure CA-ODT (MRS1), and finally configure DQ-ODT (MRS2). This order avoids CA / DQ signal reflection caused by unstable impedance at the SOC terminal, ensuring signal integrity during the configuration process. When it is necessary to switch the impedance combination (e.g., from "CA=40Ω+DQ=48Ω+SOC=60Ω" to "CA=48Ω+DQ=60Ω+SOC=80Ω"), an "ODT disable command" must be sent first (e.g., setting DQ-ODT to Hi-Z in MRS2), then the configurations of each dimension are updated sequentially, and finally ODT is re-enabled to avoid impedance conflicts during the switching process. If a register write fails during configuration (e.g., the ATE platform returns "instruction timeout"), a "register reset" (send the RESET# command and reinitialize) must be performed to eliminate problems caused by hardware interference or timing deviations and ensure that the configuration of each impedance combination is effective.

[0084] The impedance of the CA, DQ pins and SOC terminals is directly measured using a built-in impedance analyzer (such as the Keysight E4990A). The deviation between the actual and target values ​​is recorded, and the deviation must be ≤ ±5% (JEDEC standard requirement). For example, if the target is 40Ω, the measured value should be within the range of 38-42Ω. The time-domain reflection (TDR) waveforms of the CA and DQ buses are acquired using a high-speed signal acquisition card. The relationship between the reflection coefficient (Γ) and impedance is analyzed (Z=Z0×(1+Γ) / (1-Γ), where Z0 is the characteristic impedance of the transmission line, usually 50Ω). The actual impedance value is calculated and compared with the target value.

[0085] If an instruction error occurs during configuration (such as an MRS register write failure), the instruction transmission latency (tCMD (command latency), tADDR (address latency)) needs to be adjusted using the timing generator on the ATE / SLT platform to ensure compliance with the timing requirements of the DDR4 / 5 standard (e.g., tCMD ≥ 2tCK for DDR5). For long transmission lines on the SLT platform (e.g., the CA bus length on the motherboard ≥ 10cm), the "signal equalization" function (e.g., CTLE continuous-time linear equalization) can be configured through the motherboard BIOS to reduce signal attenuation and ensure stable transmission of MRS instructions and register configuration signals.

[0086] Step S2 includes:

[0087] According to the preset order of the test procedure, all impedance combinations in the three dimensions of CA-ODT, DQ-ODT and SOC-ODT (e.g., 40-48-60, 48-60-80, etc.) are traversed.

[0088] For each impedance combination (R_ca, R_dq, R_soc), a rigorous read / write test is performed.

[0089] The traversal order needs to be set according to the test objective. Common preset rules include "dimension priority traversal", "numerical increment traversal", and "random traversal", which can be flexibly selected through the test program parameters.

[0090] Dimension Priority Traversal: Designate a specific dimension as the "primary dimension," fix its resistance value first, and then traverse the other two dimensions. For example, with R_ca as the primary dimension, first fix R_ca = 40Ω, then traverse all combinations of R_dq (40→48→60→80→120→240Ω) and R_soc (40→48→60→80→120→240Ω); subsequently, switch R_ca to 48Ω and repeat the above process until all combinations are covered. This rule is suitable for analyzing the impact of a specific dimension's impedance on test results, such as when prioritizing verification of system compatibility under different CA-ODT resistance values.

[0091] Numerical Incremental Traversal: Traverse the resistance values ​​in all three dimensions in ascending order. The combination order is (40,40,40) → (40,40,48) → (40,40,60) → … → (40,40,240) → (40,48,40) → (40,48,48) → … → (240,240,240). This rule is logically simple, facilitates test program writing and combination traceability, and is suitable for regular batch testing scenarios, ensuring that all combinations are traversed according to a unified rule and avoiding omissions.

[0092] Random traversal: The order of 216 possible combinations is shuffled using the test program's random number generation algorithm. This rule avoids the cumulative effect of chip heat caused by continuously testing high-resistance combinations of the same dimension, reducing system errors. It is suitable for high-precision verification scenarios with extremely high requirements for test environment stability (such as automotive-grade memory chip testing).

[0093] Regardless of the chosen traversal rule, automated traversal must be achieved through the test program on the ATE / SLT platform. The process consists of five steps: "combination generation - impedance configuration - pre-check - test execution - data logging," as detailed below:

[0094] Combination Generation: The test program generates an ordered list of 216 impedance combinations according to preset traversal rules. Each combination contains the target resistance values ​​of R_ca, R_dq, and R_soc. For example, the list item format is "R_ca=40Ω, R_dq=48Ω, R_soc=60Ω". A unique identifier ID (such as ID=001 to ID=216) is assigned to each combination to facilitate subsequent data traceability.

[0095] Impedance configuration: The program reads the combination information in the list order, calls the "MRS register configuration module" and "CPU internal register configuration module" mentioned above, and automatically completes the resistance configuration of R_ca (MRS1), R_dq (MRS2), and R_soc (CPU register). During the configuration process, the register write status is monitored in real time. If a write timeout occurs (such as no response for more than 100ms), the "register reset-reconfiguration" process is automatically executed to ensure successful configuration.

[0096] Pre-configuration checks: After configuration, perform two key checks: First, measure the actual impedance value using an impedance measurement tool (ATE built-in impedance analyzer / SLT signal acquisition card) to confirm that the deviation of R_ca, R_dq, R_soc from the target value is ≤ ±5% (JEDEC standard); Second, read the memory chip status register (SR) to confirm that the chip has no abnormal status code (e.g., SR bit "0" in DDR5

[12] indicates no read / write error). Only after both checks are passed can the test execution phase be entered; otherwise, mark the combination as "configuration abnormal", skip the test and record the reason for the abnormality.

[0097] Test execution: For combinations that pass the pre-check, the read and write test process is automatically started, and preset test items are executed (such as all 0 / all 1 write, random data write, continuous read and write loop, etc.). During the test, key parameters (such as read and write latency, error rate, power consumption) are collected in real time.

[0098] Data recording: After the test is completed, the combination ID, target impedance value, actual impedance value, test results, key parameter data and other information are recorded in the test log in a unified format (such as CSV or database table). At the same time, the combination test status ("pass", "failed", "configuration error") is marked to provide data support for subsequent screening of effective impedance range.

[0099] During the traversal process, signal reflection can easily occur due to impedance abrupt changes when switching between different impedance combinations, affecting test stability. The following conflict avoidance strategies should be adopted: Gradual Impedance Switching: When switching R_ca or R_dq, first adjust the current dimension impedance to the "Disabled (Hi-Z)" state (e.g., setting R_dq=Hi-Z in MRS2), then switch to the target resistance value to avoid signal surges caused by directly switching from a low resistance value (e.g., 40Ω) to a high resistance value (e.g., 240Ω); when switching R_soc, first disable SOC-ODT through the CPU register, then write the target resistance value, and finally re-enable it to ensure a smooth switching process. Timing Interval Control: Set an interval of at least 100ms between two combination switches to allow the memory chip and CPU memory controller sufficient time to respond to impedance changes and stabilize their operating state; simultaneously, perform "Power Supply Voltage Monitoring" during the interval to ensure that VDD and VDDQ voltage fluctuations are ≤±2%, avoiding the impact of unstable power supply combined with impedance switching on test results. Abnormal Combination Skip: Based on the statistical analysis of previous test data, a "high-risk combination list" is preset (such as R_ca=240Ω+R_dq=40Ω+R_soc=240Ω, such combinations have too large impedance differences, which can easily lead to signal integrity problems). If a combination in the list is encountered during the traversal, it is automatically marked as "high risk" and skipped from the test, saving test time and avoiding chip damage due to extreme combinations.

[0100] For each impedance combination (R_ca, R_dq, R_soc), perform a three-level test: "basic read / write verification - stability test - extreme stress test" to comprehensively verify the integrity, stability and reliability of the memory chip's read / write function under this impedance configuration. The test items and execution steps must comply with the requirements of the JEDEC DDR4 / 5 standard (such as DDR5 JESD79-5A).

[0101] The core objective of basic read / write verification is to confirm that the memory chip can normally complete data writing and reading under the current impedance combination, without fixed errors or hardware failures. The test items include three categories: "full-mode write / read", "address mapping verification", and "data retention test".

[0102] Full-mode write-read test: Write data in different modes to all address spaces of the memory chip (e.g., DDR5-16GB chip, address range 0x00000000-0x3FFFFFFF), then read and compare the data consistency to verify error-free data transmission. Test steps: All 0 write and read: Write 0x00 data to all addresses of memory using the test program. After writing, wait 10ms (to ensure stable data storage), then read the data address by address, compare the read value with the written value, and record the erroneous address and erroneous data (if any). All 1 write and read: Repeat the above process, writing 0xFF data (8-bit width) or 0xFFFFFFFF data (32-bit width, adjusted according to the memory bus width), and compare the consistency after reading. Alternating mode write and read: Write alternating data "0x01010101" and "0x10101010" to cover each bit of memory, verifying bit-level read and write correctness and avoiding local errors caused by a single bit failure. Judgment criteria: The error rate of all three types of write and read tests must be 0 (i.e., no data inconsistency). If an error occurs, mark the combination as "basic read / write failure" and record the error type (such as fixed bit error, random error).

[0103] Address Mapping Verification Test: This test verifies the correct mapping between the address lines of the memory chip and the memory cells, ensuring there are no address conflicts or address jump errors. This is the foundation for all subsequent tests. Test Steps: Address Increment Write: Starting from the starting address (0x00000000), write data with the same address value in ascending order (each time +1) (e.g., write 0x00000001 to address 0x00000001), covering 10% of the address space (balancing test time and coverage). Address Random Read: Generate 1000 random addresses (all within the address range of already written data) using a random number generator, read data from each address, and verify that the read value matches the address value. Address Reverse Read: Read data in descending order (from the maximum address of already written data to the starting address), compare consistency, and verify that the address decoding logic has no direction dependency errors. Judgment criteria: The error rate of random reading and reverse reading is ≤10^-9 (that is, at most 1 occasional error is allowed in 1000 readings). If the error rate exceeds the threshold, it is judged as "address mapping abnormality", and it is necessary to check whether the impedance combination causes address signal transmission error.

[0104] Data Retention Test: This test verifies the stability of data storage under the current impedance combination, ensuring that data remains correctly retained without loss or tampering after a certain period. Test Steps: Data Block Writing: Select the middle address region of the memory (e.g., 0x10000000-0x1000FFFF), write a randomly generated 32KB data block, and record the checksum (e.g., CRC32 checksum). Waiting and Refreshing: Set the waiting time according to the JEDEC standard (DDR5 standard refresh cycle is 3.9μs; here, we set it to wait for 100 refresh cycles, i.e., 390μs). During this period, no read or write operations are performed; only automatic refresh is allowed. Data Reading and Verification: Read the written 32KB data block, recalculate the checksum, and compare the two checksums to verify data retention without errors. Judgment Criteria: Completely identical checksums indicate no data change. If a checksum mismatch occurs, it is judged as "data retention failure," which may be due to abnormal refresh signal transmission caused by the current impedance combination, affecting data storage stability.

[0105] The goal of stability testing is to confirm that the memory chip can operate continuously for extended periods without errors under the current impedance combination, verifying the system's sustained reliability. Test items include "continuous read / write loop test," "multi-threaded concurrency test," and "temperature drift test" (SLT platform only).

[0106] Continuous Read / Write Cyclic Test: Simulates continuous read / write operations of memory in real-world application scenarios. Through long-term cyclic execution, it exposes potential intermittent errors (such as read / write errors caused by occasional signal reflections). Test parameters: Number of cycles: 1000 (each cycle includes three steps: "write 1MB of data → read and verify → clear data"); Data type: Random data (generated using a pseudo-random number generator to ensure different data for each cycle); Read / write rate: Performed at the nominal speed of the memory chip (e.g., DDR5-4800, read / write rate 4800MT / s), without overclocking. Test Procedure: Initialize the loop counter (count=0) and error counter (error=0); generate 1MB of random data and write it to a specified memory address block (e.g., 0x20000000-0x200FFFFF); read the data in this address block and compare it with the written random data. If they are inconsistent, increment the error counter by 1 and record the error address and data; clear the data in this address block (write 0x00), and increment the count counter by 1; repeat steps 2-4 until count reaches 1000 times, then end the test. Judgment Criteria: The error counter error=0 after 1000 loops. If an error occurs, it is judged as "unstable continuous read / write," and it is necessary to analyze whether the current impedance combination causes signal integrity to deteriorate over time.

[0107] Multi-threaded concurrency test (SLT platform exclusive): The SLT platform is based on a real system and can simulate the scenario of multiple CPU cores concurrently accessing memory, verifying the memory's response capability to multi-threaded read and write requests under the current impedance combination, without conflicts or deadlocks. Test Procedure: In the SLT platform test system (such as Linux system), start 4 concurrent threads (corresponding to 4-core CPU, which can be adjusted according to the number of CPU cores); Threads 1-3: perform continuous write and read operations (data type is random number) to different memory address blocks (Thread 1: 0x10000000-0x1FFFFFFF; Thread 2: 0x20000000-0x2FFFFFFF; Thread 3: 0x30000000-0x3FFFFFFF); Thread 4: perform "address interleaved read and write", that is, randomly access the address blocks of threads 1-3, read data and immediately write new data, simulating the memory shared access scenario; run concurrently for 30 minutes, during which the read and write error rate of each thread and whether the system deadlock occurs in real time (such as thread unresponsiveness for more than 10 seconds). Judgment criteria: No read / write errors in all threads, no deadlock in the system, and CPU utilization is stable at 80%-90% (without abnormal spikes). If a thread error or deadlock occurs, it is judged as "multi-threaded concurrency failure", which may be caused by memory controller scheduling conflicts due to the current impedance combination.

[0108] Temperature drift testing (automotive / industrial grade chip testing) targets automotive-grade (-40℃~125℃) or industrial-grade (-40℃~85℃) memory chips. Under the current impedance combination, the ambient temperature is adjusted using a temperature chamber to verify the chip's read / write stability at different temperatures, simulating temperature variation scenarios in real-world applications. Test procedures: Place the SLT platform in a temperature chamber, starting at -40℃, and increase the temperature in 10℃ increments until reaching 125℃. Hold each temperature point for 30 minutes (to allow the chip temperature to equalize with the ambient temperature). At each temperature point, perform a "continuous read / write cycle test" (500 cycles), recording the error rate and read / write latency at different temperatures. After the temperature increase test, cool down to -40℃ in the same increments, repeating the test at each temperature point to verify the impact of temperature cycling on read / write performance. Judgment criteria: The error rate at all temperature points is 0, and the read / write latency fluctuation is ≤ ±10% (relative to the latency at room temperature of 25℃). If an error occurs or the latency fluctuation exceeds the standard at a certain temperature point, it is judged as "temperature drift instability", and the impedance combination needs to be adjusted to optimize temperature adaptability.

[0109] Extreme stress testing: Under the current impedance combination, high-load, high-frequency read and write operations are used to verify the extreme operating capabilities of the memory chip, exposing potential hardware weaknesses or design flaws. Test items include "high-bandwidth read and write test", "burst read and write test", and "error injection test".

[0110] High-bandwidth read / write test: The memory chip is operated at its highest nominal frequency (e.g., DDR5-6400), and continuous high-bandwidth read / write operations are performed to verify whether the current impedance combination can support signal transmission under extreme bandwidth conditions without data loss or errors. Test steps: Set the memory chip's operating frequency to the highest nominal frequency (e.g., DDR5-6400, tCK=0.3125ns) using the test program, and confirm that the CPU memory controller is synchronized to this frequency; start the high-bandwidth test tool (e.g., "Bandwidth Test Module" on the ATE platform or "memtest86+" on the SLT platform), and set the read / write bandwidth to 90% of the memory's nominal bandwidth (e.g., the nominal bandwidth of DDR5-6400 is 51.2GB / s, set the test bandwidth to 46.08GB / s); continue the test for 2 hours, during which the bandwidth utilization, error rate, chip temperature, and power supply current are monitored in real time, and abnormal data (e.g., sudden bandwidth drop, current surge) is recorded. Judgment criteria: During the 2-hour test, the bandwidth utilization rate is stable within ±5% of the set value, the error rate is 0, the chip temperature is ≤105℃ (DDR5 standard upper limit), and the power supply current fluctuation is ≤±5%. If there is a decrease in bandwidth, errors, or excessive temperature / current, it is judged as "unstable extreme bandwidth".

[0111] Burst Read / Write Test: This test simulates burst read / write scenarios in real-world applications (such as CPU cache refresh and GPU data transfer). Under the current impedance combination, short-length, high-frequency burst read / write commands are sent to the memory to verify the chip's response speed and data processing capabilities to burst requests. Test Procedure: Set the burst length (BL) according to the JEDEC standard. DDR4 supports BL=4 / 8, and DDR5 supports BL=8 / 16. Select the maximum burst length (e.g., BL=16 for DDR5). Send 10,000 burst write commands (each writing 16 data blocks, totaling 16×8=128 bytes) to the same memory address block, followed by 10,000 burst read commands. Compare the consistency of read and write data. Record the response time for each burst read / write (the time from command transmission to data transfer completion) and analyze the stability of the response time. Judgment criteria: The error rate of burst read / write is 0, the response time fluctuation is ≤ ±5%, and there is no response timeout (timeout is defined as exceeding 3 times the average response time). If an error or response timeout occurs, it is judged as "burst read / write failure", and the impedance combination needs to be optimized to improve the integrity of the burst signal.

[0112] Error Injection Test: This test injects a controlled error (such as a single-bit error or a multi-bit error) into the memory chip using a test program. Under the current impedance combination, it verifies whether the chip's Error Detection and Correction Code (ECC) function is normal. This test is applicable to server-grade memory chips that support ECC. Test Steps: First, confirm that the memory chip's ECC function is enabled (configure the ECC enable bit through the MRS register) and verify that the ECC circuit is working properly. Then, using the "Error Injection Module" on the ATE platform, inject a single-bit error (changing a bit of data from 0 to 1) into a specified memory address. Subsequently, read the data at that address to verify whether the ECC successfully corrects the error and whether the system crashes. Next, inject a multi-bit error (e.g., modifying two bits simultaneously) to verify whether the system can detect the error and trigger an error interrupt (such as the CPU's "Machine Check Exception") to prevent the propagation of erroneous data. Judgment criteria: Single-bit errors can be successfully corrected by ECC, multi-bit errors can be accurately detected and trigger an interrupt, the system does not crash or data corruption, if the ECC function fails, it is judged as "error handling failure", and it is necessary to check whether the impedance combination affects the ECC signal transmission.

[0113] The steps for performing rigorous read / write tests for each impedance combination (R_ca, R_dq, R_soc) include:

[0114] Write a specific data pattern and read it back for verification. The specific data pattern includes at least all 0s, all 1s, interleaved 0s and 1s, and walking 1s and 0s.

[0115] Stress is applied to voltage and timing to test the stability of the memory chip's test signals under non-ideal conditions during read and write tests;

[0116] The eye height and eye width of the test signal of the memory chip are measured to quantitatively evaluate the signal quality.

[0117] For the four specific data modes of "all 0, all 1, interleaved 01, and Walking 1 / 0", targeted write logic and verification process need to be designed to cover the bit-level, byte-level and block-level storage units of memory chips, and expose impedance matching problems under different data modes (such as interleaved 01 mode is prone to amplifying signal crosstalk, while Walking 1 / 0 mode can detect single bit faults).

[0118] Definitions and generation rules of four types of data patterns:

[0119]

[0120] Taking the ATE platform as an example, four data modes are used for testing each impedance combination:

[0121] The address space of the memory chip is divided into 1MB contiguous data blocks (e.g., DDR5-16GB chips are divided into 16384 data blocks), and each data block corresponds to a unique block address (e.g., Block 0: 0x00000000-0x000FFFFF, Block 1: 0x00100000-0x001FFFFF).

[0122] All 0 / All 1 Mode: Writes data of the same mode to a single data block (e.g., writes "0x00000000" in all 0 mode), continuously writing to all addresses of the data block (a total of 262,144 32-bit addresses). The write speed is performed at 50% of the memory's nominal speed (e.g., DDR5-4800 writes at 2400MT / s to avoid data overwriting errors due to excessively fast writing). Interleaved 01 Mode: Alternates writing "0x55555555" and "0xAAAAAAAA" to the same data block. That is, "0x55555555" is written to address 0x00000000, "0xAAAAAAAA" is written to address 0x00000004, and so on, overwriting the entire data block. Walking 1 / 0 mode: Write different Walking data to each address of a single data block, such as writing "0x00000001" to address 0x00000004, writing "0x00000002" to address 0x000FFFFC, and so on, until writing "0x80000000" to address 0x000FFFFC, thus completing the Walking 1 test; the Walking 0 test is similar, writing data such as "0xFFFFFFFE" and "0xFFFFFFFD".

[0123] After writing is complete, wait 50ms (far exceeding the minimum data hold time of the JEDEC standard). During this period, other read / write operations are prohibited, and only the power supply voltage is monitored (ensuring VDDQ fluctuation ≤ ±1%) to avoid external interference affecting data storage. Layered readback verification: Block-level verification: Read all addresses of the entire data block, compare the consistency between the read and written data, and calculate the block-level error rate (number of erroneous addresses / total number of addresses). Byte-level verification: For data blocks without errors in block-level verification, randomly select 1000 addresses, split the data by byte (e.g., split 32-bit data into 4 8-bit bytes), compare byte by byte, and locate byte-level errors (e.g., bit 3 error within a byte). Bit-level verification: For addresses found to have errors in byte-level verification, further split the data by bit, record the position of the erroneous bit (e.g., bit 5 changes from 1 to 0), forming an "error bit distribution map," and analyze whether there are concentrated bit fault areas (if a bit is erroneous in multiple impedance combinations, it may be due to an abnormal impedance of that pin). Multiple block coverage: Repeat steps 2-4 to test at least 10 different data blocks (covering different physical areas of memory, such as the beginning, middle, and end areas) to avoid test bias caused by defects in local storage units and ensure the representativeness of the verification results.

[0124] The block-level error rate for all four data modes must be 0, the byte-level error rate ≤ 10^-10, and bit-level errors are only allowed to occur sporadically (no more than 1 bit error in a single impedance combination, and it must be unreproducible). If the error rate exceeds the limit, mark the impedance combination as "specific data mode verification failed". If an error occurs in the all-0 / all-1 mode, prioritize checking the stability of the power supply voltage (e.g., whether the low level is below 0.1V and the high level is above 0.9V) and impedance matching (e.g., high resistance combinations are prone to high level attenuation). If an error occurs in the interleaved 01 mode, focus on analyzing signal crosstalk (verified through subsequent eye diagram testing). If a fixed bit error occurs in the Walking1 / 0 mode, check the contact resistance and impedance value of the corresponding pin (e.g., through the pin impedance measurement function of ATE).

[0125] Voltage stress testing needs to cover two scenarios: "supply voltage deviation" and "dynamic voltage switching." Parameter settings should refer to the limits of the JEDEC standard, while also considering extreme situations in real-world applications (such as voltage fluctuations in automotive-grade scenarios). For the core power supply (VDD) and I / O power supply (VDDQ) of the memory chip, three voltage levels—below the nominal value, above the nominal value, and the nominal value—were set to test read / write stability under different voltage deviations. Specific parameters are as follows (taking DDR5 as an example, nominal VDD=1.1V, VDDQ=1.1V):

[0126]

[0127] To simulate rapid voltage changes in real-world applications (such as a mobile phone switching from charging to battery power), the voltage is dynamically switched between different levels. The adaptability of the impedance combination to voltage surges is tested. Specific steps include: designing a voltage switching sequence of "VDD=0.99V→1.10V→1.21V→1.10V→0.99V", maintaining each voltage level for 5 minutes, with a switching time ≤100μs (simulating actual power supply switching speed). During voltage switching, a "staggered 01 mode read / write loop" is executed synchronously (looping once every 2 minutes) to avoid reading / writing at the instant of voltage switching (setting a 10ms "read / write prohibition window" before and after switching to prevent data errors caused by voltage surges). Real-time recording of: data error rate (number of errors within 5 seconds before and after switching, normally ≤0); power supply current change (current fluctuation during switching should be ≤±20%, avoiding exceeding the chip's maximum rated current); and chip temperature (temperature rise during switching should be ≤5℃ / min to prevent thermal stress damage).

[0128] Timing stress testing targets key timing parameters of memory chips (such as tRCD, tRP, tWR, and tRAS), setting timing offsets deviating from the nominal values ​​to verify the read / write stability of impedance combinations under tight or loose timing conditions, exposing issues of insufficient timing margin caused by impedance mismatch. Taking DDR5 standard timing parameters (nominal tRCD=18ns, tRP=18ns, tWR=12ns, tRAS=36ns) as an example, three levels are set: "negative offset (tight timing)," "nominal," and "positive offset (loose timing)," as detailed below:

[0129]

[0130] Timing stress test execution process: Using the timing generator of the ATE / SLT platform, set the timing registers of the memory chip according to the above settings (e.g., MRS3 register controls tRCD and MRS4 controls tRP for DDR5). After configuration, read the timing status register to confirm that the parameters have taken effect (e.g., the deviation between the configured value and the read value of tRCD is ≤ ±0.5ns). First, perform the nominal timing test (10 minutes, full-mode read / write) and record the baseline error rate (should be 0). Switch to negative offset timing and perform a 30-minute "full-mode read / write cycle" (50 cycles per mode), focusing on monitoring CA bus errors (such as command address decoding errors) during tRCD and tRP negative offsets, and DQ bus errors (such as data write errors) during tWR and tRAS negative offsets. Switch to positive offset timing and perform a 30-minute test to verify whether errors are caused by signal retention when the timing is loose (e.g., positive offset tWR is prone to causing write data overwriting). During the test, record the actual values ​​of the timing parameters every 5 minutes (measured by a timing analyzer) to ensure that the timing offset is stable (the deviation between the actual value and the set value ≤ ±0.3ns). After the test is completed, calculate the timing margin for each impedance combination. Taking tRCD as an example, the margin = (maximum error-free tRCD - minimum error-free tRCD) / 2. The larger the margin, the stronger the timing adaptability of the impedance combination. If the error rate of an impedance combination increases sharply under negative offset timing, it means that its timing margin is insufficient and it should be excluded from the effective combinations.

[0131] By measuring the eye diagram of the test signal, signal quality is quantitatively assessed (eye height reflects signal amplitude margin, and eye width reflects timing margin), establishing the correlation between impedance combinations and signal quality, and providing more accurate selection of the effective impedance range. Eye diagram measurement requires a high-speed oscilloscope (bandwidth ≥ 3 times the highest frequency of the memory signal, e.g., DDR5-6400 requires an oscilloscope bandwidth ≥ 19.2GHz) and a dedicated probe (e.g., a differential probe with an input impedance of 50Ω and a bandwidth ≥ 20GHz). The hardware configuration and parameter settings are as follows:

[0132]

[0133] Oscilloscope parameter settings (taking DDR5 DQ signal as an example): Vertical settings: Range: 500mV / div (covering the 0-1V amplitude range of the DDR5DQ signal); Offset: 0V (based on signal ground); Coupling method: AC coupling (blocking DC components and highlighting AC signal variations). Horizontal settings: Time base: 100ps / div (tCK=0.416ns for DDR5-4800, time base setting ensures that a single acquisition contains at least 5 clock cycles); Trigger method: Edge trigger (using the rising edge of the WCK clock as the trigger source, trigger level 0.5V); Acquisition duration: 1ms (ensuring sufficient signal cycles are acquired to generate a statistically meaningful eye diagram, typically requiring ≥10^6 cycles). Eye diagram analysis software settings: Eye diagram template: Load the JEDEC DDR5 eye diagram template (such as the eye diagram template defined by JESD79-5A); Measurement parameters: Enable automatic measurement of the four key parameters: "eye height", "eye width", "eye diagram jitter" and "signal-to-noise ratio"; Statistical method: Use the "periodic averaging" mode to exclude the influence of abnormal pulses on the measurement results.

[0134] The measurement procedure for eye height and eye width involves measuring the eye diagrams of the CA signal (command address signal) and DQ signal (data signal) under both "normal conditions" (nominal voltage, nominal timing) and "stress conditions" (voltage -10%, timing -10%) for each impedance combination. The specific procedure is as follows: Connect the differential probe to the target pins of the memory chip (e.g., A0-A3 in the CA pins, DQ0-DQ3 in the DQ pins), ensuring a tight connection between the probe ground and the chip ground (ground length ≤10mm to reduce ground loop interference); start the oscilloscope and synchronous clock source, and perform "probe calibration" (using the oscilloscope's built-in calibration signal to ensure probe gain error ≤±2%); configure the memory chip to enter "signal test mode" (disable automatic refresh via the MRS register to avoid refresh signal interference with eye diagram acquisition).

[0135] Set the memory power supply to the nominal value (VDD=1.1V, VDDQ=1.1V) and the timing to the nominal value (tRCD=18ns, tRP=18ns); start the "all 0 + all 1 mode read / write cycle" (each mode lasts 10 seconds, alternating), and synchronously trigger the oscilloscope to acquire the CA / DQ signal waveform; the oscilloscope automatically generates an eye diagram and records the values ​​of eye height (V_eye) and eye width (T_eye) – for example, the eye height of the DQ signal in all 0 mode is 0.8V and the eye width is 0.3ns; repeat the acquisition 3 times and take the average value as the eye height / eye width value under normal conditions for this impedance combination to reduce the influence of random noise.

[0136] Adjust the power supply to VDD=0.99V (-10%) and timing to tRCD=15ns (-16.7%); execute the "interleaved 01 mode read / write cycle" (lasts 10 seconds), acquire the CA / DQ signal waveform and generate an eye diagram; record the eye height / eye width values ​​under pressure conditions and calculate the rate of change compared to normal conditions (e.g., if the eye height decreases from 0.8V to 0.65V, the rate of change is -18.75%); pay close attention to whether the eye diagram shows "closed eyes" (eye height < 0.2V or eye width < 0.1ns) under pressure conditions. If closed eyes occur, mark that the signal quality of this impedance combination is substandard.

[0137] For CA signals, measure the eye diagrams of at least four key address pins: A0, A1, A2, and A3. For DQ signals, measure the eye diagrams of at least four data pins: DQ0, DQ1, DQ2, and DQ3. Calculate the standard deviation of eye height / eye width for the same signal type (e.g., CA). A standard deviation ≤ 5% indicates that the signal quality is uniform under this impedance combination and there are no obvious differences between pins.

[0138] Practical Applications of Defective Chip Screening: The direct value of this method lies in efficiently screening chips with abnormal impedance characteristics. Screening Defective Chips: Due to manufacturing process deviations, the actual resistance value of the internal ODT circuit of some chips may deviate significantly from the nominal value (e.g., set at 60 ohms, but actually as high as 100 ohms or as low as 30 ohms). In testing, very few, if any, impedance combinations of these chips will pass. Therefore, they are quickly screened out because they "cannot find a stable impedance operating point." Compatibility Verification: Even if the impedance of a single chip is normal, when used with a specific motherboard (whose PCB trace characteristics are fixed), it is necessary to confirm that there is sufficient impedance matching margin. This test can verify the reliability of a specific "motherboard + memory" combination.

[0139] This embodiment actively and systematically explores the boundaries of memory interface impedance matching, rather than simply verifying a set of nominal values. Through multi-dimensional parameter scanning and functional testing, it precisely defines the safe operating area of ​​impedance. It effectively identifies chips with subtle impedance defects that might have slipped through simple tests. This ensures that memory chips have sufficient impedance matching tolerance under specific motherboard design and load conditions, thereby guaranteeing the long-term stability of the system. The accumulated test data can provide valuable reference for the ODT circuit design and PCB design of next-generation memory interfaces.

[0140] In the embodiments provided by this invention, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, indirect coupling or communication connection between apparatuses or units, and may be electrical, mechanical, or other forms.

[0141] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0142] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for impedance matching testing of a memory chip, characterized in that, The method includes: Different impedance matching tests were performed on the memory chip in three dimensions: CA-odt, DQ-odt, and SOC-odt, to obtain different impedance combinations. The memory chip is impedance verified according to different impedance combinations to check whether the memory chip is working properly. Screening memory chips that cannot work properly under the different impedance combinations, and identifying memory chips that cannot work properly under the different impedance combinations as memory chips with significant impedance differences, i.e. memory chips with poor impedance matching. Screen memory chips that can function normally under the different impedance combinations, record the impedance combinations that pass all test items, and determine the effective operating range of different impedance values ​​for each dimension.

2. The impedance matching test method for memory chips as described in claim 1, characterized in that, The steps of performing impedance matching tests on the memory chip in three dimensions (CA-odt, DQ-odt, and SOC-odt) to obtain different impedance combinations include: Test configuration and initialization on automated test equipment or a specific system-level test platform; The resistance values ​​of CA-odt and DQ-odt are dynamically configured by writing to the mode register of the memory chip, and the SOC-odt value is set by configuring the CPU's internal register.

3. The impedance matching test method for memory chips as described in claim 1, characterized in that, The steps for impedance verification of the memory chip based on different impedance combinations include: According to the preset order of the test program, all impedance combinations in the three dimensions of CA-odt, DQ-odt and SOC-odt are traversed. For each impedance combination, a rigorous read / write test is performed.

4. The impedance matching test method for memory chips as described in claim 3, characterized in that, The steps for performing rigorous read / write tests for each impedance combination include: Write a specific data pattern and read it back for verification. The specific data patterns include all 0s, all 1s, interleaved 0s and 1s, and walking 1s and 0s. Stress is applied to voltage and timing to test the stability of the memory chip's test signals under non-ideal conditions during read and write tests; The eye height and eye width of the test signal of the memory chip are measured to quantitatively evaluate the signal quality.

Images