A circuit board crystal frequency online accurate measurement method

Abstract

The application belongs to the technical field of online accurate measurement method, and particularly relates to a circuit board crystal frequency online accurate measurement method, which builds a measurement system, the measurement system comprises a spectrum analyzer, a rubidium atomic frequency standard and an inductive input probe, the output end of the rubidium atomic frequency standard is connected to the external reference frequency input end of the spectrum analyzer, and the inductive input probe is connected to the radio frequency input end of the spectrum analyzer; the rubidium atomic frequency standard, the spectrum analyzer and the measured circuit board are preheated, and after the frequency is stable, the measurement step is entered; the frequency reference mode of the spectrum analyzer is set as an external reference, the center frequency is set as the nominal frequency of the measured crystal, and the sweep width, the reference level and the attenuation parameters are set.

Description

Technical Field

[0001] This invention belongs to the technical field of online accurate measurement methods, and particularly relates to an online accurate measurement method for circuit board crystal oscillator frequency. Background Technology

[0002] Traditional circuit board crystal oscillator frequency measurement often employs contact-based measurement or offline disassembly testing methods. These methods require soldering test points or removing the crystal oscillator, which can easily damage the circuit board and components. Furthermore, real-time online measurement is not possible under normal operating conditions, making it difficult to reflect the actual operating frequency of the crystal oscillator. Simultaneously, conventional measurement equipment relies on internal reference sources, resulting in limited frequency stability and measurement accuracy. It is also susceptible to environmental temperature, circuit load, and interference signals, leading to significant measurement deviations and failing to meet the requirements for high-precision, non-invasive online testing.

[0003] Existing non-contact measurement solutions generally suffer from problems such as low signal acquisition efficiency, weak anti-interference ability, and poor measurement repeatability. Furthermore, the lack of standardized preheating procedures, environmental control, and instrument parameter configuration specifications leads to insufficient consistency in measurement results. This makes it difficult to achieve stable and accurate frequency detection for crystal oscillators in a wide range of 10kHz-100MHz, thus restricting the testing efficiency and quality control level in circuit board production and maintenance. Summary of the Invention

[0004] In view of the aforementioned problems, and in conjunction with the first aspect of the present invention, embodiments of the present invention provide a method for accurate online measurement of circuit board crystal oscillator frequency, the method comprising: The steps include: setting up a measurement system, which includes a spectrum analyzer, a rubidium atomic frequency standard and an inductive input probe; connecting the output of the rubidium atomic frequency standard to the external reference frequency input of the spectrum analyzer; and connecting the inductive input probe to the radio frequency input of the spectrum analyzer. The rubidium atomic frequency standard, spectrum analyzer and the circuit board under test are powered on and preheated. After the frequency stabilizes, the measurement step begins. Set the frequency reference mode of the spectrum analyzer to external reference, set the center frequency to the nominal frequency of the crystal oscillator under test, and set the sweep width, reference level and attenuation parameters. The inductive input probe is brought close to the crystal oscillator on the circuit board under test, and the crystal oscillator radiation signal is picked up by electromagnetic induction. Activate the peak search and frequency mark counting functions of the spectrum analyzer, read the frequency mark count value, and obtain the measured frequency of the crystal oscillator under test.

[0005] Preferably, the rubidium atom frequency standard outputs a standard 10MHz sine wave signal with an amplitude ≥0dBm and an impedance of 50Ω, providing a 10MHz standard signal for the spectrum analyzer. -10 External reference frequency for class stability.

[0006] Preferably, the inductive input probe consists of a BNC RF cable, a Q9 connector, and an inductive coil; the inductive coil is wound with 0.5mm diameter copper enameled wire, with a coil diameter of approximately 10mm, and the two ends of the coil are respectively connected to the core wire and the shielding layer of the BNC RF cable.

[0007] Preferably, the number of turns of the induction coil is set according to the frequency range: 3-5 turns for 10kHz-10MHz, 2 turns for 10MHz-50MHz, and 1 turn for 50MHz-100MHz.

[0008] Preferably, the preheating step satisfies the following conditions: rubidium atomic frequency standard preheating for ≥30 minutes with the lock indicator light constantly on, spectrum analyzer preheating for ≥20 minutes, and the circuit board under test preheating for ≥4 hours after power-on.

[0009] Preferably, the parameters of the spectrum analyzer are configured as follows: the center frequency is set to the nominal frequency of the crystal oscillator under test, the sweep width is set to 1kHz, the reference level is set to -50dBm, the attenuator is set to automatic or fixed at 10dB, and the resolution bandwidth and video bandwidth are set to automatic.

[0010] Preferably, the measurement environment is controlled at a temperature of 24.7±0.5℃ and a humidity of 47%±5%RH, and all equipment is reliably grounded to suppress interference.

[0011] Preferably, the spectrum analyzer has external reference frequency input, peak search and frequency standard counting functions, frequency resolution ≤1Hz, and amplitude measurement dynamic range ≥80dB.

[0012] Preferably, the measurement method enables non-contact, online, and loadless measurement of crystal oscillator frequencies within the range of 10kHz-100MHz, without desoldering the crystal oscillator or interrupting the normal operation of the circuit board under test.

[0013] Based on the above, the rubidium atomic frequency standard provides 10 for the spectrum analyzer. -10 A high-stability external reference frequency, combined with a dedicated inductive probe for non-contact signal pickup, enables high-precision online measurement of crystal oscillator frequencies from 10kHz to 100MHz without desoldering or interrupting circuit board operation. Frequency resolution is within 1Hz, significantly improving measurement accuracy and consistency. Standardized preheating procedures, environmental temperature and humidity control, and unified instrument parameter configuration effectively suppress errors caused by temperature drift, power frequency interference, and impedance mismatch, greatly reducing measurement uncertainty.

[0014] This method employs a load-free, non-contact testing approach, avoiding electrical load and physical damage to the circuit under test. It is suitable for rapid testing scenarios in mass production and on-site maintenance. The entire system is easy to set up, operates in a standardized manner, and has strong repeatability. It improves testing efficiency while ensuring measurement accuracy, meeting the needs of online calibration, quality screening, and fault diagnosis of crystal oscillator frequencies in high-precision electronic equipment. It has good engineering practicality and promotional value. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the circuit board crystal oscillator frequency measurement principle of the online accurate measurement method for circuit board crystal oscillator frequency provided in this embodiment of the invention; Figure 2 This is a circuit board crystal oscillator frequency measurement diagram provided by the online accurate measurement method for circuit board crystal oscillator frequency according to an embodiment of the present invention. Detailed Implementation

[0016] The following is a detailed introduction to the method for accurate online measurement of the crystal oscillator frequency of this circuit board.

[0017] The circuit board crystal oscillator frequency measurement system consists of a spectrum analyzer, a rubidium atomic frequency standard, and an inductive input probe.

[0018] The spectrum analyzer used is the Agilent E4440A model, the rubidium atomic frequency standard used is the Symmetricom 8040C model, and the inductive input probe is self-made, consisting of a BNC RF cable and an inductive probe.

[0019] The rubidium atom frequency standard output is connected to the external input of the frequency reference of the spectrum analyzer, serving as the external reference frequency of the spectrum analyzer to improve the frequency measurement accuracy of the spectrum analyzer, which can reach the 10-10 level. The inductive input probe is connected to the input terminal of the spectrum analyzer.

[0020] Before starting the measurement, the spectrum analyzer and rubidium atomic frequency standard are powered on and warmed up, while the crystal oscillator of the circuit board under test is powered on. The measurement begins after the frequency stabilizes.

[0021] During measurement, set the frequency reference of the spectrum analyzer to external input, the reference level to -50dBm, the center frequency to the frequency of the crystal oscillator being measured (e.g., 25MHz), the sweep width to 1kHz, and other settings to automatic. Place the induction probe as close as possible to the crystal oscillator being measured. The spectrum analyzer will perform a peak search using the frequency standard. Activate the frequency standard counter function and read the frequency standard count value, which is the measured value of the crystal oscillator frequency.

[0022] The specific measurement is shown in the diagram below. The output of the rubidium atom frequency standard (model 8040C) is connected to the reference frequency input of the spectrum analyzer (model E4440A) via a BNC RF cable. The induction input probe is connected to the input terminal of the spectrum analyzer via an adapter. The induction probe consists of a BNC RF cable, a Q9 connector, and an induction coil. The induction coil is made of copper enameled wire of appropriate diameter (e.g., 0.5mm) wound with an appropriate number of turns (generally 1 to 5 turns depending on the measurement frequency; for example, only 2 turns are needed when measuring a 25MHz crystal oscillator). The coil diameter is approximately 10mm. The two ends of the coil are connected to the core wire and the shielding layer of the BNC RF cable, respectively, and then wrapped with insulating tape. During measurement, the induction coil should be as close as possible to the crystal oscillator being measured. The crystal oscillator frequency test range is 10kHz to 100MHz. The measurement method is described in [link to measurement instructions]. Figure 1 .

[0023] Product Name: 560 Simplified Version Board Model: V560-SIMPLE (Simplified Version V2.0); Test environment: 24.7℃, 47%RH, preheating for 4 hours.

[0024] This measurement system consists of three parts: a high-precision spectrum analyzer, a rubidium atomic frequency standard, and an inductive input probe. The three parts work together to achieve non-contact, online, and high-precision frequency measurement of the circuit board crystal oscillator without disassembling the crystal oscillator or interrupting the normal operation of the circuit board.

[0025] Spectrum analyzer; Preferred model: Agilent E4440A (supports frequency coverage of 10kHz~100MHz, which meets the measurement range of this method).

[0026] Key requirements: It should have external reference frequency input, peak search, and frequency standard counting functions; frequency resolution ≤ 1Hz; and amplitude measurement dynamic range ≥ 80dB.

[0027] Rubidium atomic frequency standard; Preferred model: Symmetricom 8040C.

[0028] Core function: Provides 10 -10 The ultra-high stability reference frequency, which replaces the built-in crystal oscillator of the spectrum analyzer, eliminates the frequency error of the analyzer itself from the source, and is the key to achieving high-precision measurement.

[0029] Output requirements: Standard 10MHz sine wave, amplitude ≥0dBm, impedance 50Ω.

[0030] Inductive input probe (homemade); Composition: BNC RF cable, Q9 connector, induction coil, insulation protective layer.

[0031] Core principle: Non-contact pickup of radio frequency signals radiated by crystal oscillator through electromagnetic induction, without electrical connection, load, or interference with the circuit under test.

[0032] To avoid measurement errors caused by signal reflection and impedance mismatch, strictly follow the connection order below: Connect the 10MHz reference output of the rubidium atomic frequency standard (8040C) to the External Reference In interface of the spectrum analyzer (E4440A) using a 50Ω BNC RF cable.

[0033] Connect the homemade inductive input probe to the RF Input terminal of the spectrum analyzer using a short-distance, low-loss BNC RF cable.

[0034] The circuit board under test is powered on normally, the crystal oscillator is kept working continuously, and no desoldering or rewiring operations are performed.

[0035] All equipment is reliably grounded to avoid power frequency interference and electrostatic interference affecting the measurement results.

[0036] Insufficient preheating is a major source of frequency measurement error and must be strictly controlled. Rubidium atomic frequency standard: Power on and warm up for ≥30 minutes until the LOCK light on the front panel is constantly on, confirming that the frequency is locked and stable.

[0037] Spectrum analyzer: After a warm-up period of ≥20 minutes, the internal circuit temperature is balanced, minimizing amplitude and frequency drift.

[0038] Test circuit board: Power-on preheating for ≥4 hours (taking V560-SIMPLE simplified version V2.0 board as an example), the crystal oscillator reaches thermal stability, and the frequency drift is ≤±1ppm.

[0039] Stable environment: Temperature controlled at 24.7±0.5℃ and humidity at 47%±5%RH to avoid sudden temperature changes that could cause the crystal oscillator frequency to shift.

[0040] Before each measurement, set the following parameters consistently to ensure that the measurement conditions are consistent: Frequency reference mode: Set to External to force the use of the rubidium atom standard as a reference.

[0041] Center Freq: Set to the nominal frequency of the crystal oscillator being tested (e.g., 12.288MHz, 25MHz, 32MHz).

[0042] Sweep width (Span): Set to 1kHz (narrow sweep width facilitates precise locking of crystal oscillator signal peaks).

[0043] Reference Level: Set to -50dBm (to accommodate weak signals picked up by the sensor and avoid overload).

[0044] Attenuator: Automatic or fixed 10dB to ensure signal linearity.

[0045] Resolution bandwidth (RBW) and video bandwidth (VBW): Set to automatic; the instrument optimizes the signal-to-noise ratio.

[0046] Trigger mode: Runs freely, no external trigger required.

[0047] Manufactured according to the following specifications, suitable for measuring crystal oscillators from 10kHz to 100MHz: Coil conductor: 0.5mm diameter copper enameled wire, with good conductivity and low loss.

[0048] Number of coil turns: 10kHz~10MHz: 3~5 cycles; 10MHz~50MHz: 2 cycles (e.g., 25MHz crystal oscillator); 50MHz~100MHz: 1 revolution; Coil size: approximately 10mm in diameter, circular in shape, to ensure uniform induction efficiency.

[0049] Wiring method: Connect the BNC cable core and shielding layer to both ends of the coil respectively to avoid short circuit.

[0050] Protective measures: Wrap completely with insulating tape to prevent short circuits, oxidation, and mechanical damage.

[0051] It should be noted that, in order to simplify the description of the present invention and thus help to understand one or more embodiments of the invention, multiple features may sometimes be grouped into one embodiment, drawing or description thereof in the foregoing description of the embodiments of the present invention.

[0052] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for accurate online measurement of circuit board crystal oscillator frequency, characterized in that: Includes the following steps: A measurement system is constructed, which includes a spectrum analyzer, a rubidium atomic frequency standard, and an inductive input probe. The output terminal of the rubidium atomic frequency standard is connected to the external reference frequency input terminal of the spectrum analyzer, and the inductive input probe is connected to the radio frequency input terminal of the spectrum analyzer. The rubidium atomic frequency standard, spectrum analyzer and the circuit board under test are powered on and preheated. After the frequency stabilizes, the measurement step begins. Set the frequency reference mode of the spectrum analyzer to external reference, set the center frequency to the nominal frequency of the crystal oscillator under test, and set the sweep width, reference level and attenuation parameters. The inductive input probe is brought close to the crystal oscillator on the circuit board under test, and the crystal oscillator radiation signal is picked up by electromagnetic induction. Activate the peak search and frequency mark counting functions of the spectrum analyzer, read the frequency mark count value, and obtain the measured frequency of the crystal oscillator under test.

2. The method of claim 1, wherein the method comprises the steps of: a) applying a voltage to the crystal oscillator; b) measuring the current through the crystal oscillator; c) determining the frequency of the crystal oscillator from the measured current; and d) repeating steps a) through c) at least once. The rubidium atomic frequency standard outputs a standard 10MHz sinusoidal wave signal with amplitude ≥ 0dBm and impedance 50Ω, which provides a 10 -10 external reference frequency for the grade stability.

3. The method of claim 1, wherein the method comprises the steps of: a) applying a voltage to the crystal oscillator; b) measuring the current through the crystal oscillator; c) determining the frequency of the crystal oscillator from the measured current; and d) repeating steps a) through c) at least once. The inductive input probe consists of a BNC RF cable, a Q9 connector, and an inductive coil. The inductive coil is wound with 0.5mm diameter copper enameled wire, with a coil diameter of approximately 10mm. The two ends of the coil are connected to the core wire and the shielding layer of the BNC RF cable, respectively.

4. The method for accurate online measurement of circuit board crystal oscillator frequency according to claim 1, characterized in that: The number of turns of the induction coil is set according to the frequency range: 3-5 turns for 10kHz-10MHz, 2 turns for 10MHz-50MHz, and 1 turn for 50MHz-100MHz.

5. The method for accurate online measurement of circuit board crystal oscillator frequency according to claim 1, characterized in that: The preheating steps meet the following requirements: rubidium atomic frequency standard preheating for ≥30 minutes with the lock indicator light constantly on, spectrum analyzer preheating for ≥20 minutes, and the circuit board under test preheating for ≥4 hours after power-on.

6. The method of claim 1, wherein the method comprises the steps of: a) applying a voltage to the crystal oscillator; b) measuring the current through the crystal oscillator; c) determining the frequency of the crystal oscillator from the measured current; and d) repeating steps a) through c) at least once. The parameters of the spectrum analyzer are configured as follows: the center frequency is set to the nominal frequency of the crystal oscillator under test, the sweep width is set to 1kHz, the reference level is set to -50dBm, the attenuator is set to automatic or fixed 10dB, and the resolution bandwidth and video bandwidth are set to automatic.

7. The method of claim 5, wherein the method comprises the steps of: a) applying a voltage to the crystal oscillator; b) measuring the current through the crystal oscillator; c) determining the frequency of the crystal oscillator from the measured current; and d) repeating steps a) through c) at least once. The measurement environment is controlled at a temperature of 24.7±0.5℃ and a humidity of 47%±5%RH. All equipment is reliably grounded to suppress interference.

8. The method of claim 1, wherein the method comprises: a) applying a voltage to the circuit board; b) measuring the voltage; c) measuring the current; d) calculating the impedance; e) calculating the frequency; and f) repeating steps a) through e) at least once. The spectrum analyzer has external reference frequency input, peak search and frequency standard counting functions, frequency resolution ≤1Hz, and amplitude measurement dynamic range ≥80dB.

9. The method for accurate online measurement of circuit board crystal oscillator frequency according to claim 1, characterized in that: The measurement method enables non-contact, online, and loadless measurement of crystal oscillator frequencies within the range of 10kHz-100MHz, without desoldering the crystal oscillator or interrupting the normal operation of the circuit board under test.

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