Pulse per second batch calibration test system, device and method

Abstract

The invention relates to the technical field of electronic measurement and test, and discloses a pulse per second batch calibration test system, device and method, and the system comprises a main control unit located outside an environment test box and a test terminal board located inside the environment test box, and the main control unit and the test terminal board are connected through a transmission wire harness. The test terminal board is provided with a reference anchor point channel, and the input and output ends of the reference anchor point channel are respectively connected with a downlink and an uplink to cooperate with the main control unit to form a closed-loop detection loop; and the main control unit sends a detection pulse sequence by using the second pulse idle gap and receives feedback, and determines a phase pre-correction value according to the calculated one-way physical transmission delay so as to adjust the second pulse emission time. By monitoring the physical delay change of the transmission wiring harness in real time and performing dynamic phase pre-correction, the transmission delay drift error caused by the temperature circulation of the environmental test box is effectively eliminated, and the second pulse signal reaching the test seat is ensured to always keep high-precision synchronization with the standard moment.

Description

Technical Field

[0001] This invention relates to the field of electronic measurement and testing technology, specifically to a second pulse batch calibration test system, apparatus, and method. Background Technology

[0002] High-precision time and frequency products require rigorous frequency-temperature characteristic testing during production to calibrate their output frequency stability under different temperature environments. A typical testing procedure involves placing a batch of products under test inside an environmental test chamber, while the high-precision test management host and main control unit are located outside the chamber, connected by a transmission harness passing through the chamber wall. During testing, the external main control unit sends second pulse signals to the internal products under test via the transmission harness, serving as a synchronization reference for the products under test to calibrate their own frequency or perform phase comparisons.

[0003] In actual wide-temperature-range cycling tests, the temperature inside the environmental test chamber undergoes a wide range of changes, from extremely low to extremely high temperatures. The transmission harness connecting the main control unit and the product under test (DUT), as the physical medium for signal transmission, is affected by temperature changes. The dielectric constant of its insulation layer, as well as the physical length and resistivity of the conductor, all alter the signal propagation speed within the transmission harness. This means that, as the temperature inside the environmental test chamber rises and falls, the physical transmission delay of the second pulse signal from the outside to the DUT is not a constant value, but rather exhibits a dynamic drift characteristic that fluctuates with temperature.

[0004] Existing batch testing systems typically employ static compensation, which involves measuring the transmission harness delay once at room temperature and using it as a fixed deduction throughout the entire testing process. This method ignores the thermal drift effect of the transmission harness delay under varying temperature conditions. When the environmental test chamber is at extreme high or low temperatures, a significant deviation will occur between the actual transmission delay and the preset static delay value, causing the phase of the second pulse signal arriving at the device under test (DUT) port to be out of sync with the standard time. This synchronization error is directly introduced into the frequency measurement data of the DUT, affecting the accuracy of the final calculated frequency compensation parameters and making it difficult to meet the nanosecond-level or even higher precision synchronization testing requirements of highly stable time-frequency devices. Summary of the Invention

[0005] The purpose of this invention is to provide a batch calibration test system, apparatus and method for second pulses, which solves the problem that when batch frequency and temperature characteristic tests are carried out in an environmental test chamber, the physical transmission delay drift caused by changes in ambient temperature in the long-distance transmission harness results in the inability of the second pulse signal reaching the test terminal board to maintain high-precision phase synchronization.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A batch calibration test system, apparatus, and method for second pulses, including:

[0008] The first aspect of this invention provides a second pulse batch calibration test system, which mainly solves the transmission delay drift problem when multiple products under test are tested synchronously at the frequency in an environmental test chamber.

[0009] The system comprises a main control unit located outside the environmental test chamber and a test terminal board located inside the environmental test chamber. The main control unit and the test terminal board are connected via a transmission harness; the main control unit is also communicatively connected to the test management host. The test terminal board is equipped with multiple test sockets for parallel access to the product under test (DUT), and a reference anchor point channel not connected to the DUT. The input end of the reference anchor point channel is connected to a downlink signal link from the transmission harness, and the output end is connected to an uplink feedback link leading to the transmission harness, forming a closed-loop detection circuit with the main control unit via the transmission harness.

[0010] In the physical layer design of the test terminal board, the trace length between the output pin of the fan-out buffer and the input pin of the signal loopback driver of the reference anchor channel is specified to be equal to the trace length between the output pin of the fan-out buffer and the input pad of the test socket. The signal loopback driver and the fan-out buffer are connected to the same voltage regulator output and share the power supply filter capacitor. Their thermal pads are connected through a grounded copper foil to ensure a consistent thermal environment.

[0011] The main control unit sends a sequence of probe pulses to the test terminal board and receives feedback signals returned via the reference anchor point channel. Based on the calculated one-way physical transmission delay, the main control unit determines the phase pre-correction amount and controls the transmission time of the second pulse signal accordingly to achieve signal synchronization at the test socket. The test management host is used to set test parameters and acquire the frequency data output by the product under test.

[0012] A second aspect of the present invention provides a second pulse batch calibration test device as the main control unit in the above system.

[0013] The device includes a burst detector generator, a high-precision time measurement module, a central logic processing module, and a digital delay line module. The burst detector generator generates a sequence of probe pulses during the idle period of the original second pulse signal and transmits it to an external transmission harness via a differential analog front-end interface. The high-precision time measurement module receives the loopback feedback signal through the differential analog front-end interface and measures the time difference between the transmission and reception times of the probe pulse sequence.

[0014] The central logic processing module calculates the phase pre-correction amount based on the measured time difference and converts it into control commands. The digital delay line module responds to these commands, adjusting the transmission delay of the original second pulse signal and outputting a synchronous second pulse signal through the differential analog front-end interface. The digital delay line module employs a hybrid architecture combining coarse and fine adjustments. Coarse adjustment utilizes the system clock counter to achieve an integer multiple delay of the period, while fine adjustment uses programmable delay primitives or carry chain physical transmission delays to construct delay taps.

[0015] A third aspect of the present invention provides a method for batch calibration testing of second pulses, which is applied to the above-mentioned system.

[0016] This method includes system initialization, dynamic calibration, and data processing. During the system power-on initialization phase, the main control unit retrieves the pre-stored system static asymmetric calibration constant. This constant is calibrated using an external standard time measuring instrument under normal temperature conditions, and its value is defined as the difference between the downlink signal link delay and half of the round-trip delay; where the downlink signal link delay refers to the transmission delay of the main control unit's output signal to the test socket.

[0017] During testing, the test management host controls the environmental test chamber to adjust the temperature. The main control unit generates a burst detection pulse sequence using the second pulse signal interval. This sequence is transmitted to the test terminal board via the transmission harness, and then returned to the main control unit via the return line after passing through the reference anchor point channel. The main control unit collects the round-trip time data of the burst detection pulse sequence and performs statistical filtering. The steps of the statistical filtering process are as follows: collect multiple single round-trip times corresponding to a set of continuous detection pulse sequences, remove the maximum and minimum values, and calculate the arithmetic mean of the remaining single round-trip times to obtain the average round-trip time.

[0018] The main control unit calculates the unidirectional physical transmission delay at the current temperature based on the system's static asymmetric calibration constant. The phase pre-correction amount is calculated as the sum of half the average round-trip time and the system's static asymmetric calibration constant. Based on the determined phase pre-correction amount, the main control unit adjusts the transmission time of the next second pulse signal, advancing the transmission time relative to the standard time by the aforementioned phase pre-correction amount. After phase pre-correction, the second pulse signal arrives at the test socket aligned with the standard time, at which point the product under test outputs frequency data.

[0019] The test management host receives the frequency observation values ​​uploaded by the main control unit, calculates the frequency deviation value based on the nominal frequency of the product under test, compares the frequency deviation value with the preset pass / fail threshold range to generate a frequency temperature characteristic curve, and calculates the compensation coefficient based on the curve and writes it into the product under test.

[0020] In summary, the present invention has at least one of the following beneficial technical effects:

[0021] 1. This invention utilizes a reference anchor point channel located on the test terminal board to form a closed-loop detection circuit with the main control unit. Without interfering with the normal downlink transmission of the second pulse, it uses signal gaps to measure the physical delay of the transmission harness in real time, which varies with ambient temperature. By calculating the phase pre-correction amount in real time and dynamically adjusting the transmission time, this system can automatically compensate for the transmission delay drift caused by the long-distance transmission harness during high and low temperature cycles in the environmental test chamber. This ensures that the second pulse signal arriving at the test stand is always synchronized with the standard time, thereby improving the data accuracy of frequency and temperature characteristic tests for batch products.

[0022] 2. This invention employs equal-length traces and thermal coupling in the physical layer design of the test terminal board. The loopback path length of the reference anchor channel is equal to the signal path length of the test channel, and the loopback driver and fan-out buffer share the power network and heat dissipation pads. This ensures that the electrical and thermal characteristics of the reference anchor channel accurately reflect the state of the test channel where the product under test is located, minimizing system errors introduced by differences in board-level traces or local temperature differences, and guaranteeing the representativeness and reliability of the unidirectional physical transmission delay calculation reference.

[0023] 3. The main control unit of this invention adopts a hybrid architecture of digital delay lines combining coarse and fine adjustment. It utilizes a system clock counter to achieve a wide range of delay coverage that is an integer multiple of the period, and uses programmable delay primitives or carry chain physical transmission delays within the FPGA to construct fine adjustment taps. This architecture can directly convert the calculated phase pre-correction amount into high-precision physical transmit delay control commands without relying on expensive external analog delay devices, achieving low-cost, highly integrated, and fast-response nanosecond-level signal synchronization control. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the second pulse batch calibration test system according to an embodiment of the present invention;

[0025] Figure 2 This is a flowchart of the second pulse batch calibration test method according to an embodiment of the present invention;

[0026] Figure 3 This is a perspective view of the environmental test chamber according to an embodiment of the present invention;

[0027] Figure 4 This is a schematic diagram of the internal structure of the environmental test chamber according to an embodiment of the present invention.

[0028] Among them, 100 is the test management host; 200 is the main control unit; 300 is the environmental test chamber; 310 is the test fixture rack; 320 is the air outlet of the circulating air duct; 400 is the test terminal board; 401 is the test socket; and 500 is the transmission harness. Detailed Implementation

[0029] The following is in conjunction with the appendix Figure 1 -Appendix Figure 4 The present invention will be further described in detail below.

[0030] See attached document Figure 1 The present invention provides a batch calibration test system for second pulses. The system adopts a distributed closed-loop control architecture and mainly includes: a test management host 100, a main control unit 200, an environmental test chamber 300, at least one test terminal board 400 located inside the environmental test chamber 300, and a transmission harness 500 connecting the main control unit 200 and the test terminal board 400.

[0031] The test management host 100 is connected to the main control unit 200 via a communication bus. It is used to configure test temperature curves, channel parameters, and calibration thresholds, and to receive final test data to generate reports. The main control unit 200 is located in a normal temperature environment outside the environmental test chamber 300. Its input is connected to an external standard time source to receive raw second pulse signals. The main control unit 200 integrates FPGA control logic and analog front-end circuitry, responsible for signal phase modulation, differential driving, and loop closure measurement.

[0032] The environmental test chamber 300 provides the required variable-temperature testing environment for the product under test (DUT), and its interior includes a mounting bracket for securing the test terminal board 400. The test terminal board 400, which houses the circuitry of the DUT, is placed directly within the variable-temperature environment. The test terminal board 400 contains signal conditioning circuitry and multiple test sockets 401 for parallel connection of multiple DUT clock modules. The transmission harness 500, employing a shielded twisted-pair cable structure, passes through the cable holes in the environmental test chamber 300, establishing an electrical connection between the main control unit 200 and the test terminal board 400, including a downlink signal link and an uplink feedback link.

[0033] The test terminal board 400 is equipped with a reference anchor point channel that is not connected to the product under test. The end of this channel is connected to a simulated load network and directly connected to the uplink feedback link. The main control unit 200 uses this reference anchor point channel and the transmission harness 500 to form a closed-loop detection circuit, monitor the physical delay changes of the transmission link in real time, and achieve signal synchronization at the test base 401 by adjusting the phase of the transmitted signal.

[0034] See attached document Figure 2 This invention provides a method for batch calibration testing of second pulses, comprising the following steps:

[0035] S10, system power-on initialization, the main control unit 200 sends a burst detection pulse sequence under normal temperature conditions, and establishes the initial static delay reference of the transmission link by measuring the loop data of the reference anchor point channel;

[0036] S20, the test management host 100 controls the environmental test chamber 300 to adjust the internal temperature according to the preset curve. During the test, the main control unit 200 generates a burst detection pulse sequence by utilizing the time gap between two adjacent second pulse signals.

[0037] S30, the burst detection pulse sequence is sent by the main control unit 200, transmitted to the test terminal board 400 via the transmission harness 500, and then returned to the main control unit 200 via the return line after passing through the reference anchor point channel and the simulated load network.

[0038] S40, the main control unit 200 collects the round-trip time data of the burst detection pulse sequence, and after statistical filtering, combines it with the initial static delay reference to calculate the one-way physical transmission delay of the signal from the main control unit 200 to the test stand 401 at the current temperature.

[0039] S50, the main control unit 200 determines the phase pre-correction amount based on the calculated one-way physical transmission delay, and controls the internal digital delay line to adjust the transmission time of the next second pulse signal so that the transmission time is advanced by the phase pre-correction amount relative to the standard time.

[0040] S60, the second pulse signal after phase pre-correction is transmitted to the test terminal board 400 and reaches the test socket 401. At this time, the signal phase is aligned with the standard time. The product under test receives the synchronization signal, works and outputs frequency data.

[0041] See attached document Figure 1 The test management host 100, serving as the control center and data processing hub of the entire second pulse batch calibration test system, is typically implemented as an industrial control computer, a general-purpose personal computer, or an embedded workstation. The test management host 100 establishes a bidirectional data connection with the main control unit 200 through a standard digital communication interface. This digital communication interface can specifically employ an Ethernet interface (RJ45) conforming to the IEEE 802.3 standard, using the TCP / IP protocol for data packet transmission; or it can use a Universal Serial Bus (USB) interface or an RS-232 / RS-485 serial communication interface. The underlying drivers and physical layer connection methods of the aforementioned communication interfaces are well-known technologies in this field and will not be elaborated upon here.

[0042] The test management host 100 runs test control software, which constitutes the system's application layer logic and is responsible for connecting discrete test steps into an automated closed-loop process. Specifically, the configuration and interaction process of the test management host 100 with the system can be achieved through the following steps:

[0043] S101, Test Parameter Configuration Phase. The test management host 100 receives the test specification parameters input by the user. These parameters include at least the temperature cycling curve setting and the channel status mask setting. The temperature cycling curve setting includes data from multiple temperature test points, each consisting of a target temperature value, a temperature gradient, and a holding time at that temperature. The channel status mask setting specifies the enabled or disabled state of each test socket 401 on the test terminal board 400. For example, when some test sockets 401 are not connected to the product under test, the test management host 100 generates a corresponding bitmask instruction, instructing the main control unit 200 to ignore the feedback data from the corresponding channel, thereby preventing invalid data from consuming processing bandwidth.

[0044] S102, Command Issuance and Status Synchronization. The test management host 100 encapsulates the above configuration parameters into a control frame and sends it to the main control unit 200. Simultaneously, the test management host 100 directly connects to the environmental test chamber 300 via GPIB bus, Ethernet, or serial port, or indirectly controls the environmental test chamber 300 through the main control unit 200. The test management host 100 continuously reads the real-time internal temperature sensor data of the environmental test chamber 300. When it detects that the internal temperature has reached the target temperature value set in S101 and the preset heat preservation time has been completed, it sends a trigger measurement command to the main control unit 200. This trigger measurement command signifies that the system has entered the steady-state measurement window and initiates the second pulse synchronization and frequency acquisition process.

[0045] S103, Test Data Acquisition and Analysis. After the main control unit 200 completes phase pre-correction and drives the product under test (DUT) to operate, the DUT outputs a frequency signal. This frequency signal is periodically counted by the frequency measurement module integrated within the main control unit 200 (or by an external high-precision frequency meter connected to the test management host 100), and converted into a digital frequency observation value. The test management host 100 receives a data packet containing the channel number, the current temperature value, and the frequency observation value. The test management host 100 parses the data packet and extracts the actual output frequency of each DUT at the current temperature point. .

[0046] S104, Deviation Calculation and Conformity Determination. The test management host 100 calculates the deviation based on the nominal frequency of the product under test. Calculate the frequency deviation value This calculation aims to quantify the degree of frequency drift of the product under test caused by the influence of ambient temperature. The calculation formula is as follows:

[0047] ;

[0048] in, The actual output frequency of the product under test at the current temperature point is expressed in Hertz (Hz). The nominal frequency of the product under test (e.g., 10MHz or 32.768kHz) is expressed in Hertz (Hz). This is a unit conversion factor used to convert calculation results into parts per million (ppm), a unit commonly used in the clock industry.

[0049] The test management host 100 will calculate the frequency deviation value. The result is compared to a preset pass / fail threshold range. This pass / fail threshold range is determined based on the permissible frequency error range specified in the product's datasheet (e.g., ±20 ppm). If the product falls within the threshold range, the channel product is marked as qualified; otherwise, it is marked as unqualified.

[0050] S105, Report Generation and Calibration Data Writing. The test management host 100 summarizes the frequency deviation data at all temperature points and generates a frequency-temperature characteristic curve (FT Curve). For products under test (DUTs) that support digital compensation (such as TCXOs or OCXOs), the test management host 100 calculates the corresponding compensation coefficients based on the FT characteristic curve and a preset compensation algorithm (such as polynomial fitting). Subsequently, the test management host 100 encapsulates the compensation coefficients into a write instruction, which is then transmitted via the main control unit 200 and the transmission harness 500 through the digital communication bus (such as I2C, SPI, or UART) connected to the DUT on the test terminal board 400. This writes the compensation coefficients into the internal non-volatile memory (such as EEPROM) of the DUT, thereby completing the batch calibration operation of the product.

[0051] The main control unit 200, as the core physical actuator of the system, consists primarily of a central logic processing module, a high-precision time measurement module, a digital delay line module, and a differential analog front-end interface. In practical implementation, the central logic processing module, high-precision time measurement module, and digital delay line module are typically integrated within a field-programmable gate array (FPGA) chip, utilizing the FPGA's parallel processing capabilities and dedicated timing resources to achieve nanosecond-level time control.

[0052] The main control unit 200 receives the raw second pulse signal from an atomic clock or satellite time receiver via an external clock interface. This raw second pulse signal serves as the system's absolute time reference. The clock management unit (MMCM / PLL) inside the FPGA performs jitter removal and shaping on the input signal to generate the system's internal synchronization clock domain.

[0053] To achieve fine-tuning of the output signal phase, the main control unit 200 integrates a digital delay line (DDL) module. This DDL module is not merely a simple counter delay, but employs a hybrid architecture combining coarse and fine adjustment. The coarse adjustment section utilizes the high-frequency system clock counter within the FPGA to achieve delays that are integer multiples of the system clock cycle (e.g., 10ns steps at a 100MHz system clock). The fine adjustment section calls upon dedicated programmable delay primitives (e.g., IDELAY / ODELAY elements) within the FPGA I / O module or utilizes the physical propagation delay of the carry chain within the logic array to construct delay taps. By concatenating the coarse adjustment count value with the fine adjustment delay level, this DDL module can cover a delay range from 0 to 1 second, with an adjustment resolution better than 100 picoseconds (ps), thereby ensuring that the phase pre-correction adjustment accuracy meets the testing requirements of high-precision crystal oscillators.

[0054] The main control unit 200 also incorporates a high-precision time measurement module based on Time-to-Digital (TDC) technology. This module utilizes the propagation delay characteristics of the carry chain within the FPGA to construct a delay line array, quantizing the time interval by capturing the signal's propagation position on the delay lines. This TDC module is used to accurately measure the time difference between the emission time of the probe pulse and the return time of the feedback signal from the reference anchor channel, i.e., the round-trip time.

[0055] The adaptive phase pre-correction logic of the main control unit 200 for the signal can be executed through the following steps:

[0056] S201, Probe Pulse Generation. The main control unit 200 monitors the edge of the raw second pulse signal. During the idle time period between two adjacent raw second pulse signals (preferably the dead time after the falling edge of the standard second pulse signal, for example, between 100ms and 900ms of the cycle per second), the burst probe generator inside the FPGA generates a sequence of high-frequency probe pulses. This probe pulse sequence contains a preset number of narrow pulses, whose pulse width and frequency are designed to adapt to the transmission bandwidth of the differential isolation chip, ensuring that the signal is not distorted after transmission through the magnetic isolator and long lines.

[0057] S202, Closed-loop feedback measurement. The probe pulse sequence is sent to the transmission harness 500 via the differential analog front-end interface, loops back through the reference anchor point channel of the test terminal board 400, and is received again by the main control unit 200. The TDC module records the transmission time of each probe pulse. and the corresponding receiving time And calculate the round-trip time. ,in This refers to the pulse number in the sequence.

[0058] S203, Statistical Filtering. To eliminate random jitter noise introduced by isolation chips and drivers in the transmission link, the statistical filter module in the main control unit 200 processes the acquired data. indivual The data is processed. The processing logic includes removing the maximum and minimum values, then calculating the arithmetic mean of the remaining data to obtain the average round-trip time at the current temperature. This statistical filtering process utilizes the physical property that thermal noise follows a Gaussian distribution, and significantly improves the signal-to-noise ratio of the measurement results through multiple sampling and averaging.

[0059] S204, Pre-correction amount calculation. The main control unit 200 calculates the pre-correction amount based on the average round-trip time at the current temperature. and the system static asymmetry calibration constant calibrated at the factory. Calculate the amount of time the pulse signal needs to be transmitted in advance for the next second, i.e., the phase pre-correction amount. .

[0060] Among them, the system static asymmetric calibration constant Characterized the downlink signal link delay under standard ambient temperature. Round trip delay The difference between half of the two, i.e. This constant is used to compensate for fixed system errors introduced by differences in PCB trace lengths and inherent delays of transceiver chips.

[0061] Based on this, the phase pre-correction amount at the current temperature The calculation formula is as follows:

[0062] ;

[0063] in, The average round-trip time at the current temperature; This is the phase pre-correction amount.

[0064] S205, Phase Adjustment and Output. The main control unit 200 will calculate... Convert to configuration parameters for digital delay line modules.

[0065] Because the second pulse signal has a period of A periodic signal (usually 1 second) is generated, and it is physically impossible to output a signal before the original signal arrives; therefore, the so-called advance signal is... In the specific implementation of FPGA, the transmission is achieved by delaying the original second pulse signal relative to the previous second. This is achieved over time. The specific delay is calculated as follows:

[0066] ;

[0067] When the FPGA detects the edge of the original second pulse signal, it starts the timer for a duration of [duration missing]. There is a delay, and an output pulse is generated immediately after the delay ends. From a timeline perspective, the timing of this output pulse is exactly ahead of the theoretical arrival time of the original second pulse signal for the next second. This physically achieves a negative delay effect.

[0068] S206, Differential Drive Output. The phase-adjusted synchronous second pulse signal is sent to the differential analog front-end interface. This interface consists of multiple sets of Low Voltage Differential Signaling (LVDS) drivers. The LVDS driver converts single-ended TTL / CMOS logic levels into differential current signals conforming to the TIA / EIA-644 standard, driving long-distance loads via twisted-pair cables. The LVDS interface utilizes the high common-mode rejection ratio (CMRR) of differential signals, effectively resisting the large current electromagnetic noise generated by compressor start-up and shutdown and fan operation in high and low temperature chambers, ensuring the integrity of the remote signal waveform.

[0069] See attached document Figure 3 and appendix Figure 4 The Environmental Test Chamber 300 serves as the physical platform for verifying the performance of the product under test across the entire temperature range. Specifically, it is implemented as a programmable high and low temperature alternating damp heat test chamber or a walk-in environmental test chamber. The Environmental Test Chamber 300 has a wide range of temperature regulation capabilities, with its temperature control range typically covering -55℃ to +125℃, capable of simulating the working conditions of the clock product under test in industrial or even military-grade environments.

[0070] In this embodiment, the environmental test chamber 300 is not merely an auxiliary device providing the testing environment, but also the physical basis upon which the batch compensation method based on single anchor point feedback of this invention can be established. The core of this physical basis lies in constructing a board-level isothermal zone, that is, ensuring that the temperature of the area where the reference anchor point channel is located on the same test terminal board 400 is highly consistent with the temperature of the area where all the test sockets 401 of the products under test are located, so that the transmission delay drift measured by the reference anchor point channel can represent the common drift of all channels on the board.

[0071] To achieve the above objectives and complete batch adaptation, the internal cavity adaptation and installation structure of the environmental test chamber 300 is achieved through the following technical features:

[0072] S301, Construction of a multi-layer array test fixture. For example... Figure 3As shown, the internal working space of the environmental test chamber 300 is equipped with a test fixture rack 310 made of rigid metal (such as stainless steel). This test fixture rack 310 employs a multi-layer slide rail or multi-layer tray structure for horizontally placing and fixing multiple test terminal plates 400. To avoid temperature gradients caused by heat accumulation between layers, the vertical spacing between the layers of the test fixture rack 310 is configured to be no less than 50 mm (preferably 80 mm to 100 mm). This spacing ensures that the airflow in the circulating air duct can flow uniformly across the upper and lower surfaces of each test terminal plate 400 in a laminar or turbulent manner, placing each test plate in an independent and uniform heat exchange environment.

[0073] S302, thermal balance airflow design. For example... Figure 3 As shown, a circulating air duct outlet 320 is provided on one side of the inner wall of the environmental test chamber 300, equipped with a high-power centrifugal fan and a baffle plate to form a forced air circulation system. During the test, the circulating airflow blown from the circulating air duct outlet 320 continuously sweeps across the test terminal plate 400 and the surface of the product under test. When installing the test terminal plate 400, its long side is kept parallel to the mainstream direction of the circulating airflow to reduce airflow resistance and prevent the formation of a thermal dead zone on the leeward side.

[0074] In addition, the environmental test chamber 300 is equipped with independent multi-point temperature monitoring probes. These probes are attached to key areas of the test terminal board 400 (especially the surface of the crystal oscillator and the reference anchor circuit area) using high-temperature thermally conductive adhesive. The test management host 100 monitors the feedback data from these probes in real time. Only when the temperature difference between the multiple points is less than the preset thermal equilibrium threshold (e.g., ±0.5℃) can the test conditions be determined to be met, thus ensuring the effectiveness of the anchor compensation algorithm.

[0075] S303, Low thermal conductivity cable pass-through interface. One or more standard lead-in holes are provided on the side or rear wall of the environmental test chamber 300. The transmission cable harness 500 passes through these lead-in holes into the chamber and connects to the test terminal board 400. To maintain the stability of the temperature field inside the chamber and prevent external moisture intrusion, the lead-in holes are filled with flexible insulating plugs (such as silicone rubber or high-density sponge). Considering the physical characteristics of cables becoming hard and brittle at low temperatures, such as... Figure 4 As shown, the transmission harness 500 has a service loop of 10cm to 30cm in length inside the housing. This loop structure uses the elastic deformation of the cable itself to absorb the mechanical tension caused by drastic temperature changes (thermal expansion and contraction), preventing the tension from acting directly on the onboard connectors on the test terminal board 400, thus avoiding fatigue fracture of the solder joints or poor contact.

[0076] S304, Electrical Grounding and Electrostatic Protection. The metal enclosure of the environmental test chamber 300 is connected to the laboratory grounding stake via a low-impedance grounding wire. A good conductive connection is maintained between the test fixture frame 310 and the metal enclosure. However, to cut off common-mode interference paths, the mounting holes of the test terminal board 400 are fixed to the test fixture frame 310 using insulating supports made of PTFE or nylon. The height of these insulating supports is set at least 5mm to establish a physical isolation barrier between the signal ground at the bottom of the test terminal board 400 and the metal frame of the environmental test chamber 300. This floating ground design, combined with the magnetically coupled isolation circuit at the system front end, can completely block the high-frequency common-mode leakage current generated during the start-up of the high-low temperature chamber compressor motor and the operation of the frequency converter from coupling to the signal measurement circuit through the frame, thereby controlling the system's noise floor to the microvolt level.

[0077] The transmission harness 500 serves as the physical medium connecting the main control unit 200 under normal temperature conditions and the test terminal board 400 under variable temperature conditions. It not only undertakes the task of signal transmission, but its real-time physical characteristics (especially transmission delay) are also the direct object of detection and compensation by this system.

[0078] To ensure reliable signal transmission over a wide temperature range (e.g., -55°C to +125°C) and consistent bidirectional delay, the electrical characteristics and wiring structure of the transmission harness 500 are achieved through the following technical features:

[0079] S401, selection of cables for weather resistance and phase stability. The transmission harness 500 uses a multi-strand shielded twisted-pair structure. Considering the extreme temperature conditions inside the environmental test chamber 300 and the high-precision calibration requirements, the cable insulation and outer sheath are made of perfluoroethylene propylene (FEP) or polytetrafluoroethylene (PTFE / Teflon). The choice of these fluoropolymer materials is not only to prevent low-temperature brittleness or high-temperature softening, but more importantly, to utilize their extremely low dielectric constant temperature coefficient (TCDk). Within the test temperature range of -40℃ to +85℃, the dielectric constant change rate of FEP material is extremely small (typically less than several hundred ppm), which means that the signal propagation speed during transmission is very low. Temperature variations are kept to a minimum, thus suppressing significant phase drift at the physical medium level. The conductor is preferably made of silver-plated oxygen-free copper wire to reduce skin effect losses during high-frequency signal transmission.

[0080] S402, Differential Characteristic Impedance Control. To match the LVDS interface circuits at both ends of the main control unit 200 and the test terminal board 400, each pair of twisted pairs in the transmission harness 500 is designed to have a specific differential characteristic impedance. In this embodiment, the standard design value of the differential characteristic impedance is 100Ω ± 10%. Specific impedance matching is achieved by controlling the wire diameter, twist pitch, and insulation thickness of the twisted pair. Strict impedance matching minimizes signal reflection and ringing at both ends of the transmission line, ensuring the steepness of the second pulse signal edge, thereby reducing jitter errors in time measurement.

[0081] S403, integrated sheath and thermal tracking symmetrical design. This is the key physical structure supporting the round-trip delay symmetry assumption of this invention. The transmission harness 500 tightly wraps the twisted pair used in the downlink signal link (from the main control to the test board) and the twisted pair used in the uplink feedback link (from the test board to the main control) within the same outer sheath cable, maintaining the same twist pitch.

[0082] This physical structure ensures that the downlink and uplink lines are in the exact same ambient temperature field at all times, and have almost identical changes in physical length (thermal expansion and contraction) and dielectric constant. Although there may be slight differences in static physical length between the downlink and uplink pairs due to manufacturing limitations, thanks to the aforementioned integrated structure, their dynamic characteristics with temperature changes are highly synchronized. That is:

[0083] ;

[0084] Cable transmission delay The physical model can be represented as:

[0085] ;

[0086] in, The physical length of the cable varies with temperature. The dielectric constant varies with temperature. This is the speed of light in a vacuum. Since the uplink and downlink lines use the same material and are in the same thermal environment, its... and The trend of change is consistent, thus ensuring the effectiveness of the algorithm that uses half of the total change in loop delay to accurately estimate the change in unidirectional delay.

[0087] S404, Shielded and Grounded Topology. The transmission harness 500 adopts a double-layer shielding structure of individual pair shielding + overall shielding. Each pair of signal twisted pairs is wrapped with an aluminum foil shielding layer, and the entire cable harness is wrapped with a tinned copper braided mesh. The shielding density of the braided mesh is not less than 85%. At the connector, the shielding layer is connected to the metal shell by a 360-degree wraparound crimping method.

[0088] In terms of electrical connections, the shielding layer of the transmission harness 500 is connected to the chassis ground via a low-impedance path on the main control unit 200 side, while on the test terminal board 400 side, it is not directly connected to digital ground, but rather AC grounded through a high-voltage safety capacitor (Y capacitor). The capacitance value of this capacitor ranges from 1nF to 10nF, and the withstand voltage is not less than 2kV. This strategy of single-ended DC grounding and double-ended AC grounding provides both an electrostatic shielding cage against high-frequency electromagnetic radiation and cuts off ground loop currents caused by ground potential differences in the DC and low-frequency power frequency bands, preventing interference from the high-power equipment of the environmental test chamber 300 from being superimposed on the weak clock measurement signal.

[0089] S405, Interface Connector Definition. Both ends of the transmission harness 500 are terminated with industrial-grade high-density connectors. In the connector pin definition, in addition to the pins allocated to LVDS signal pairs, power transmission pins and digital communication pins are also reserved. The power transmission pins are used by the main control unit 200 to supply power to active devices (such as isolation chips and buffers) on the test terminal board 400, ensuring that the test board does not require a separate external power adapter inside the enclosure. To prevent crosstalk, especially interference from high-frequency clock signals to the power lines, grounding pins are spaced apart between all high-speed differential signal pins, forming a signal isolation wall.

[0090] As the core component directly carrying the product under test, the test terminal board 400 is placed in the harsh temperature-changing environment of the environmental test chamber 300. Its circuit design not only needs to ensure the integrity of the signal at the physical level, but also needs to construct a low-noise, clean floating ground test domain through strict electrical isolation to cut off external interference.

[0091] Considering the impact of high temperature and high humidity on PCB substrates, the printed circuit board substrate of the test terminal board 400 is made of FR4 board material or polyimide material with a high glass transition temperature (High-Tg). Its Tg point is designed to be no less than 170℃ to prevent board warping or delamination during high temperature testing at 125℃, and to ensure the long-term stability of the microstrip line characteristic impedance.

[0092] The signal conditioning and isolation architecture of the test terminal board 400 is implemented through the following circuit modules and physical layout features:

[0093] S501, Differential Receiver with Near-End Impedance Matching. The test termination board 400 has a Low Voltage Differential Signaling (LVDS) receiver chip at its input. The differential input pins of this receiver chip are connected across a 100Ω terminating resistor.

[0094] To minimize signal reflection caused by short-pile effect, the terminating matching resistor is placed on the PCB layout at a distance of less than 2mm from the LVDS receiver input pin.

[0095] The resistor is a low-temperature drift precision metal film resistor, with an optimal accuracy of ±0.1% and a temperature coefficient of less than 10ppm / ℃. The LVDS receiver converts the small-swing differential signal from the 500-channel transmission harness into a single-ended TTL or CMOS logic level signal.

[0096] S502, High CMTI Digital Isolation Barrier. This is a key hardware feature for achieving the ground loop breaking effect of this invention. A high-speed digital isolation chip is positioned after the LVDS receiver and before the signal distribution network.

[0097] Specifically, the power and ground of the input side (primary side) of the isolation chip are connected to the chassis ground network introduced by the transmission harness 500; while the power and ground of the output side (secondary side) of the isolation chip are connected to the onboard independent floating ground network. Through this isolation barrier, the environmental test chamber 300 is blocked from common-mode interference coupled by the chassis and ground potential fluctuations introduced by the long transmission line on the primary side of the isolation chip.

[0098] To prevent clock erroneous triggering due to high-voltage transient interference generated during the start-up and shutdown of the 300 compressor in the environmental test chamber, a high common-mode transient immunity (CMTI) model is selected for this isolation chip, with a CMTI specification designed to be no less than 100kV / μs. Furthermore, considering the requirements for precision calibration, the propagation delay temperature coefficient of this isolation chip must be less than 5ps / ℃ to ensure good linearity of delay changes across the entire temperature range.

[0099] The S503 is a two-stage power supply regulator architecture. The test terminal board 400 integrates an isolated DC-DC power module, converting the input DC power to an intermediate voltage. To further filter out the high-frequency ripple noise generated by the DC-DC switching conversion, a low-dropout linear regulator (LDO) is connected in series at the output of the DC-DC module. This LDO provides a ripple voltage of less than 10μF for the subsequent clock fan-out buffer and the product under test. A clean power supply is provided to prevent power supply noise from coupling into the clock signal and forming phase noise through the power supply rejection ratio (PSRR) characteristic.

[0100] S504, a star clock distribution network. The purified second pulse signal, after isolation and level conversion, is fed into a low-jitter fan-out buffer. This buffer uses a 1-input, 100% output topology, and its output drive is configured as a push-pull output with a fast edge rate. This buffer replicates one second pulse signal into multiple identical drive signals, ensuring that the second pulse signal received by each test socket 401 on the test terminal board 400 has the same drive capability and edge steepness.

[0101] S505, Strictly Equal Length and Interference-Suppressing Routing. To ensure that the physical timing of signal arrival at each test socket 401 of the product under test is strictly consistent, the PCB routing employs a strictly equal-length design. The physical length of the signal transmission path from the output pin of the fan-out buffer to the input pad of each test socket 401 is strictly constrained.

[0102] Let the first The physical length of the traces in each test channel is , No. The physical length of the traces in each test channel is Then the length difference between any two channels The following constraints must be met:

[0103] ;

[0104] in, The maximum allowable trace length error is set to 100 mil (approximately 2.54 mm) in this embodiment.

[0105] To achieve this equal length constraint, for channels with relatively short physical distances, the PCB traces use a serpentine routing method with large arc angles for winding compensation, and the spacing between parallel segments of the serpentine traces is greater than 3 times the trace width (3W rule) to prevent impedance abrupt changes caused by self-inductive coupling.

[0106] All signal traces are designed as microstrip lines with a characteristic impedance of 50Ω, and are accompanied by a complete array of grounded shielded vias on both sides of the traces to form a coaxial shielding structure to prevent crosstalk between channels.

[0107] S506, Test Holder 401 Thermal Conductive Coupling Design. Test Holder 401 is a high-temperature resistant, open-top aging test holder. On the PCB layout, Test Holders 401 are arranged uniformly in a matrix. In the PCB area directly beneath each Test Holder 401, an array of thermally conductive vias running from the top to the bottom layer is provided, connected to a large area of ​​grounded copper foil. This design utilizes the high thermal conductivity of copper to rapidly conduct heat from the ambient airflow to the product under test (DUT) inside the Test Holder 401, ensuring that the DUT's case temperature can quickly and without lag follow the temperature changes within the environmental test chamber 300, thereby improving the accuracy of the temperature-frequency response curve measurement.

[0108] To achieve real-time closed-loop monitoring of transmission link delay, the test terminal board 400, in addition to the conventional test channels for connecting the product under test (DUT), also integrates one or more dedicated reference anchor channels. These reference anchor channels are not connected to the actual DUT, but rather serve as a physical loopback device to reflect the received second pulse signal back to the main control unit 200 in real time.

[0109] The physical construction of the reference anchor point channel and the same-source power supply feedback logic are achieved through the following technical features:

[0110] S601, Physical Topology and Equal-Length Layout of the Anchor Channel. The physical location and routing parameters of the reference anchor channel on the circuit board are designed to represent the average physical characteristics of all conventional test channels. Specifically, the input of the reference anchor channel is connected to a separate output pin of the fan-out buffer. More importantly, the PCB trace length from the output pin of the fan-out buffer to the input pin of the reference anchor channel loopback driver is... Designed to have the same trace length as standard test channels (That is, the length from the fan-out buffer to the test socket 401) is strictly equal, and its length tolerance is controlled within ±50mil (approximately 1.27mm).

[0111] This equal-length design ensures that the microstrip line transmission delay contained in the reference anchor channel is physically consistent with the transmission delay of the actual path under test, enabling the reference anchor channel to serve as a specimen to reflect the delay changes of the entire PCB board in real time at the current temperature.

[0112] S602, a co-source power supply and thermal coupling architecture. This is the key design of this invention to eliminate temperature drift differences in onboard active devices. The reference anchor channel is mainly composed of a signal loopback driver. Electrically, the power supply pin (VCC) of this signal loopback driver and the power supply pin of the aforementioned fan-out buffer are physically connected to the output of the same low-dropout linear regulator (LDO), sharing the same set of power supply filter capacitors.

[0113] In terms of physical layout, the signal loopback driver is placed within a range of 5mm to 10mm from the edge of the fanout buffer chip. The thermal pads of the two are connected by the same large-area grounded copper foil inside the PCB, forming a thermal coupler.

[0114] This design, featuring a co-source power supply and a close-proximity layout, leverages the physical characteristic of semiconductor device propagation delay varying with voltage and temperature. When the LDO output voltage drifts or the local ambient temperature fluctuates, the fan-out buffer (downlink path device) and the signal loopback driver (uplink feedback device) experience identical voltage and temperature changes, thus minimizing the propagation delay drift of both. Maintaining a high degree of linear correlation provides a physical basis for subsequent common-mode error cancellation.

[0115] S603, Equivalent Load Matching. To ensure signal integrity when the fan-out buffer drives the reference anchor channel as it does when driving the actual product under test, an equivalent load network is configured at the input of the reference anchor channel. This network consists of surface-mount capacitors and resistors, and its equivalent capacitance to ground is [value missing]. Designed to have a nominal capacitance value relative to the clock input pin of the product under test. Equal (for example, for a common temperature-controlled crystal oscillator OCXO, this capacitance value is set to 15pF ± 5%). Precise load matching ensures that the signal rise slope on the reference anchor channel is completely consistent with the actual test channel, avoiding time shifts at signal threshold crossover points due to different capacitive load effects.

[0116] S604, Differential Loopback Driver Model. The signal loopback driver receives a single-ended TTL / CMOS level signal from the fan-out buffer and converts it into a Low Voltage Differential (LVDS) signal. This LVDS signal is directly connected to the uplink feedback pair in transmission harness 500.

[0117] At this time, the total physical circuit delay measured by the main control unit 200 It can be defined at the physical level by the following formula:

[0118] ;

[0119] Expanded to the sum of all physical delays:

[0120] ;

[0121] in, For transmission harness 500 at the current temperature The following delay; To delay the propagation of digital isolation chips; For the propagation delay of the fan-out buffer; The propagation delay of the reference anchor point channel loopback driver; This represents the propagation delay of the microstrip line at the PCB level (due to the design of equal length, this value represents the board-level delay of the signal reaching the test socket).

[0122] S605, Calibration of the system calibration constant. This is to obtain the system static asymmetric calibration constant from the formulas in Section 2. The system needs to be calibrated once at room temperature (e.g., 25°C) before leaving the factory. The calibration steps are as follows:

[0123] Start the main control unit 200 to output a second pulse signal.

[0124] Using a high-precision oscilloscope (bandwidth not less than 1GHz) probe, point-test any signal input pin of test socket 401 on the test terminal board 400, and measure its downlink signal link delay relative to the original second pulse signal, denoted as . .

[0125] Meanwhile, the TDC module inside the main control unit 200 measures the round-trip delay of the loop returned through the reference anchor point channel, denoted as... .

[0126] Based on the pre-correction formula principle defined in Section 2, calculate the system's static asymmetric calibration constant. :

[0127] ;

[0128] The static asymmetric calibration constant of this system This characterizes the inherent structural asymmetry of the system's uplink and downlink (e.g., the downlink passes through a fan-out buffer, while the uplink passes through a loopback driver, resulting in different inherent delays). This constant is permanently stored in the non-volatile memory (such as EEPROM) of the main control unit 200. In subsequent actual high and low temperature tests, regardless of... How can the system consistently utilize [this technology] despite drastic temperature changes? This allows for accurate estimation of the current unidirectional delay, thereby enabling adaptive compensation across the entire temperature range.

Claims

1. A batch calibration and testing system for second pulses, characterized in that, include: The main control unit (200) located outside the environmental test chamber (300) and the test terminal board (400) inside are connected to the test terminal board (400) via a transmission harness (500). The main control unit (200) is also connected to the test management host (100). The test terminal board (400) is equipped with multiple test sockets (401) for parallel access to the product under test and a reference anchor point channel; The reference anchor point channel input end is connected to the downlink signal link from the transmission harness (500), and the output end is connected to the uplink feedback link to the transmission harness (500), thereby forming a closed-loop detection circuit with the main control unit (200). The main control unit (200) is used to send a probe pulse sequence and receive a feedback signal, determine the phase pre-correction amount based on the calculated one-way physical transmission delay, and control the second pulse signal transmission time to achieve signal synchronization at the test stand (401). The test management host (100) is used to set parameters and obtain frequency data of the product under test.

2. The second pulse batch calibration test system according to claim 1, characterized in that, The test terminal board (400) integrates a fan-out buffer and a signal loopback driver; The trace length of the reference anchor channel from the output pin of the fan-out buffer to the input pin of the signal loopback driver is equal to the trace length from the output pin of the fan-out buffer to the input pad of the test socket (401); The signal loopback driver and the fan-out buffer are connected to the same voltage regulator output terminal and share the power filter capacitor. The thermal pads of the signal loopback driver and the fan-out buffer are connected through grounded copper foil.

3. The second pulse batch calibration test system according to claim 1, characterized in that, The environmental test chamber (300) is provided with a test fixture rack (310) for stacking and fixing multiple test terminal boards (400), and the inner wall is provided with a circulating air duct outlet (320). The transmission harness (500) encloses the twisted pair used in the downlink signal link and the twisted pair used in the uplink feedback link within the same outer sheath cable; The transmission harness (500) is connected to the chassis ground on the shielding layer on the side of the main control unit (200), and connected to the digital ground on the shielding layer on the side of the test terminal board (400) through a high-voltage safety capacitor.

4. A batch calibration and testing device for second pulses, characterized in that, The second pulse batch calibration test system applied to any one of claims 1 to 3 includes: A burst detection generator is used to generate a sequence of detection pulses during the idle period of the original second pulse signal and drive it to an external transmission harness (500) through a differential analog front-end interface. A high-precision time measurement module is used to receive the loopback feedback signal through the differential analog front-end interface and measure the time difference between the transmission and reception times of the probe pulse sequence. The central logic processing module is used to calculate the phase pre-correction amount based on the time difference and convert the phase pre-correction amount into control commands. The digital delay line module is used to adjust the transmission delay of the original second pulse signal in response to the control command, and output a synchronous second pulse signal through the differential analog front-end interface.

5. The second pulse batch calibration test device according to claim 4, characterized in that, The digital delay line module adopts a hybrid architecture that combines coarse and fine tuning; The coarse adjustment uses the system clock counter to achieve an integer multiple delay of the period, and the fine adjustment uses programmable delay primitives or carry chain physical transmission delay to construct delay taps; The central logic processing module converts the phase pre-correction amount into the count value and delay level of the digital delay line module.

6. The second pulse batch calibration test device according to claim 4, characterized in that, The central logic processing module calculates the phase pre-correction amount based on the time difference in the following way: The average round-trip time is obtained by calculating the arithmetic mean of the time differences. Retrieve the pre-stored system static asymmetric calibration constants; The phase pre-correction amount is obtained by summing half of the average round-trip time with the static asymmetric calibration constant of the system.

7. A batch calibration test method for second pulses, characterized in that, The second pulse batch calibration test system applied to any one of claims 1 to 3 includes: Upon system power-on initialization, the main control unit (200) retrieves the pre-stored system static asymmetric calibration constants; The test management host (100) controls the environmental test chamber (300) to adjust the temperature, and the main control unit (200) generates a burst detection pulse sequence using the second pulse signal gap; The burst detection pulse sequence is transmitted to the test terminal board (400) via the transmission harness (500), and then returned to the main control unit (200) via the return line after passing through the reference anchor point channel. The main control unit (200) collects round-trip time data of burst detection pulse sequences and calculates the one-way physical transmission delay at the current temperature in combination with the static asymmetric calibration constant of the system. The main control unit (200) determines the phase pre-correction amount based on the one-way physical transmission delay and adjusts the next second pulse signal transmission time so that the transmission time is ahead of the standard time by the phase pre-correction amount; After the phase pre-correction second pulse signal arrives at the test stand (401) and is aligned with the standard time, the product under test outputs frequency data to the test management host (100).

8. The batch calibration test method for second pulses according to claim 7, characterized in that, After acquiring the round-trip time data of the burst detection pulse sequence, the main control unit (200) also performs a statistical filtering process: The main control unit (200) collects multiple round-trip times corresponding to a continuous sequence of probe pulses; The main control unit (200) removes the maximum and minimum values ​​from the multiple single round-trip times; The main control unit (200) calculates the average round-trip time by arithmetically averaging the remaining single round-trip time.

9. The batch calibration test method for second pulses according to claim 7, characterized in that, The system static asymmetric calibration constant is calibrated through the following steps: Under normal temperature conditions, the downlink signal link delay from the output signal of the main control unit (200) to the test socket (401) on the test terminal board (400) is measured using an external standard time measuring instrument; The round-trip delay of the measurement signal returning to the main control unit (200) via the transmission harness (500) and the reference anchor point channel; Calculate the difference between the downlink signal link delay and half of the loop round-trip delay, and use the difference as the system static asymmetric calibration constant.

10. The batch calibration test method for second pulses according to claim 7, characterized in that, After the product under test outputs frequency data to the test management host (100), the following steps are performed: Receive the frequency observation value uploaded by the main control unit (200), and calculate the frequency deviation value based on the nominal frequency of the product under test; The frequency deviation value is compared with a preset qualified threshold range to generate a frequency temperature characteristic curve; The compensation coefficient is calculated based on the frequency-temperature characteristic curve, and the compensation coefficient is written into the product under test.

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