TECHNICAL RESOURCES

EMI Filter
Selection Guide.

Define the electrical problem, preserve the wanted signal, and select a filter architecture that fits the interface.

01 / DEFINE THE REQUIREMENT

Start with the measured noise.

Provide the failing frequency bands, measured levels, applicable limits, and required margin. Include the test setup and operating mode so the filter can be evaluated against the actual interface.

Noise and acceptance limits

Conducted or radiated issue, affected circuits, and suspected coupling path.
Frequency sweep, limit line, detector and bandwidth settings, and worst-case operating mode.
Required attenuation at each critical frequency, including design margin.

Signals that must pass

Signal type, bandwidth, data rate, rise/fall times, and allowable distortion.
DC operating voltage, steady-state current, and transient conditions by contact.
Source/load characteristics and circuits that must remain unfiltered.

02 / ELECTRICAL SELECTION

Choose values and topology together.

Insertion loss depends on the filter and its source/load environment. Compare curves under stated measurement conditions, then validate the candidate in the intended circuit. A 50-ohm characterization is useful for comparison but may not represent the system impedances.

Capacitance and signal loading

Select capacitance around the noise band and allowable loading on each signal. Review tolerance, temperature, and DC-bias behavior. For digital interfaces, consider edge rate as well as data rate.

C and Pi configurations

Evaluate C or Pi filtering against the required frequency response, impedances, current, and space. More filter elements do not automatically improve the installed result; evaluate resonance and signal behavior as part of the circuit.

Electrical ratings

Specify working voltage, transients, current, allowable voltage drop, and thermal conditions. Where an inductive element is used, include its current-dependent behavior in the review.

Mixed circuit requirements

Identify contact-by-contact capacitance, unfiltered circuits, and any TVS or resistor requirements. Treat transient protection and EMI attenuation as separate requirements that must both be verified.

Technical reference: Knowles — insertion loss and source/load impedance.

03 / MECHANICAL INTEGRATION

Match the filter to the assembly.

Review the shell, insert arrangement, mounting, termination, available depth, and ground path before fixing the electrical design. Grounding, layout, and parasitic effects influence installed performance.

Connector-level filtering

For an integrated connector interface, discuss planar array, Pi tube, or chip-on-flex construction with RCV. Provide the required contact map and mechanical envelope.

Explore filtered connectors →

Filtering an existing interface

For a retained connector, provide internal dimensions and contact geometry to assess a press-in insert. Confirm fit and the contact-to-shell grounding arrangement.

Explore press-in filters →

Multiple circuits or interfaces

Where filtering belongs at an enclosure or subsystem assembly, define circuit count, mounting, interconnections, and service access for a custom module.

Explore filter modules →

Board and flex interfaces

Include PCB spacing, tail dimensions, hole patterns, and flex routing constraints. Review contact support and assembly sequence alongside the filter design.

Explore flex interconnects →

04 / ENGINEERING REVIEW

Send a complete starting point.

Connector part number, series, shell, contact arrangement, keying, and drawing revision.
Contact-by-contact electrical requirements and proposed filter values, if known.
Noise plots, applicable limits, measurement conditions, and signal constraints.
Assembly drawings, grounding approach, and available mechanical envelope.
Environmental requirements, test methods and revisions, acceptance criteria, and required records.
Prototype and production quantities, schedule, and qualification milestones.

Compare candidate performance in the representative assembly and across relevant operating modes before finalizing the configuration.

Review testing and environmental requirements →

ENGINEERING SUPPORT

Bring the data.
Define the filter.

Discuss Your Requirements →