In the collaborative operation of test fixtures and Pb test benches, signal transmission interference is a core challenge affecting test accuracy. Interference may originate from electromagnetic radiation, power supply noise, ground loops, or crosstalk between signal lines, leading to test data fluctuations, false triggers, or signal distortion. To systematically reduce interference, a comprehensive approach is needed, encompassing hardware design, wiring optimization, shielding measures, and power management.
At the hardware design level, components with strong anti-interference capabilities should be prioritized. For example, using low-noise operational amplifiers, high-speed optocoupler isolation chips, and high-precision ADCs/DACs can reduce signal distortion during transmission. Simultaneously, the interface circuit of the test fixture should be designed in differential transmission mode, utilizing the opposite current directions of the two lines to cancel external magnetic field interference. For high-frequency signals, impedance matching networks should be added at the interface to avoid oscillations caused by signal reflection. Furthermore, filter capacitors and ferrite beads should be integrated on critical signal paths to form a low-pass filter effect, suppressing the intrusion of high-frequency noise.
Wiring optimization is a crucial aspect of reducing interference. Signal lines and power lines must be strictly separated, avoiding parallel routing, and maintaining a perpendicular angle when crossing to reduce coupling capacitance. For long-distance transmission, twisted-pair cables or coaxial cables are preferred. Twisted-pair cables cancel electromagnetic induction through their twisted structure, while coaxial cables rely on shielding layers to block radiated interference. For multi-layer PCB designs, signal layers should be adjacent to power or ground layers to utilize the capacitance effect of the reference plane to absorb high-frequency noise. Simultaneously, signal line lengths must be controlled to avoid antenna effects, especially avoiding line lengths approaching a quarter of the signal wavelength.
Shielding measures can significantly reduce spatial radiated interference. Test fixture housings should be made of highly conductive metal materials, such as aluminum alloy or galvanized steel, ensuring structural continuity and preventing gaps or openings from becoming electromagnetic leakage paths. For high-frequency signal transmission paths, shielding covers or conductive rubber can be used for partial wrapping. The shielding layer must be grounded at one end to prevent ground loop interference. Furthermore, electromagnetic absorption materials, such as ferrite tiles or conductive foam, can be deployed around the Pb test bench to further attenuate environmental electromagnetic noise.
Power management directly affects signal stability. The test system must be equipped with an independent linear power supply or a high-precision switching power supply to avoid noise superposition caused by sharing power with other equipment. The power input should integrate a common-mode choke and X/Y capacitors to form a π-type filter network, suppressing conducted interference from the power grid. For analog signal power supply, an LDO linear regulator or low-noise DC-DC converter should be used, along with a decoupling capacitor array to ensure power supply ripple is less than one percent of the signal amplitude. Furthermore, the power supplies for digital and analog circuits should be isolated using ferrite beads or 0-ohm resistors to prevent digital noise from coupling to the analog signal through the power supply path.
Grounding design is the core method for eliminating common-mode interference. The test system should adopt a single-point grounding strategy, converging all grounding paths to the same reference point to avoid potential differences caused by ground loops. For high-frequency signals, multi-point grounding is required to reduce grounding impedance, but it must be ensured that the potentials of each grounding point are consistent. Grounding wires should be as short and thick as possible to reduce parasitic inductance; copper foil or grounding busbars can be used to improve conductivity if necessary. In addition, the test fixture and the metal casing of the Pb test bench must be reliably connected via low-impedance wires to form a Faraday cage effect, shielding against external electromagnetic interference.
Software algorithms can help improve test robustness. Digital filtering techniques, such as moving average filtering, median filtering, or Kalman filtering, can effectively suppress random noise in signals. For periodic interference, synchronous sampling or lock-in amplification techniques can be used to extract specific frequency components. Furthermore, the test program must integrate self-testing and calibration functions to monitor signal quality in real time and trigger alarms or automatic retest mechanisms when interference exceeds limits, ensuring data reliability.
Environmental control and operating procedures are equally important. The test site should be far away from high-power electrical equipment, such as frequency converters, welding machines, or high-voltage switchgear, to avoid strong electromagnetic field radiation. Test cables must be fixed in place, avoiding arbitrary bending or tangling to prevent changes in characteristic impedance due to cable deformation. Operators must wear anti-static wrist straps to prevent damage to sensitive components from electrostatic discharge. Regular maintenance and calibration of the test system to ensure the stable performance of each module are also necessary measures to guarantee test accuracy.
