How to Design EMC Protection for the Sensitive Audio Output Path of an Audiometer While Ensuring High-Fidelity Signal?

The core of protection design lies in achieving a balance between signal integrity and anti-interference capability. It is essential to integrate specialized EMI filters with ultra-low capacitance, such as models with capacitance below 1pF, at the entry points of critical audio pathways like the headphone interface. These filters effectively attenuate common-mode RF interference in the MHz to GHz frequency range while having minimal impact on the audio signal bandwidth within 20kHz. Additionally, TVS or ESD protection devices with extremely fast response times and low clamping voltages must be deployed at the post-filter stage or in parallel to provide a discharge path for electrostatic discharge away from precision operational amplifiers. In PCB layout, protection devices must be placed close to the interface, audio traces should be in differential pair form with strictly controlled impedance, and they must be kept away from digital noise sources.