How does the launch connector affect the signal integrity of a high speed PCB test coupon?
PCB Test Coupon Launch
The launch connector is often the limiting factor in high-frequency PCB measurement accuracy, and a poor launch can make a good trace appear bad.
| Parameter | Option A | Option B | Option C |
|---|---|---|---|
| Performance | High | Medium | Low |
| Cost | High | Low | Medium |
| Complexity | High | Low | Medium |
| Bandwidth | Narrow | Wide | Moderate |
| Typical Use | Lab/military | Consumer | Industrial |
Sampling and Quantization
(1) The 2x-thru method is the most practical and widely used de-embedding technique: fabricate a "thru" coupon with two launches connected back-to-back (no trace between them). Measure the 2x-thru S-parameters on the VNA. The de-embedding algorithm (AFR, or MATLAB/Python script) splits the 2x-thru into two halves (one per launch). This launch model is subtracted from all subsequent measurements using the same launch. (2) This method assumes: both launches are identical (symmetric). The launches do not significantly interact with each other (the thru length should be > 10 mm to avoid near-field coupling). The method is frequency-limited by the loss and reflection of the launches themselves (if the launch S11 > -8 dB, the de-embedding becomes unreliable). (3) Software: Keysight ADS AFR (Automatic Fixture Removal), Ansys Circuit, and open-source Python libraries (scikit-rf) support 2x-thru de-embedding.
Dynamic Range Considerations
When evaluating how does the launch connector affect the signal integrity of a high speed pcb test coupon?, engineers must account for the specific requirements of their target application. The optimal choice depends on the frequency range, power level, environmental conditions, and cost constraints of the overall system design.
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
Clock and Timing
When evaluating how does the launch connector affect the signal integrity of a high speed pcb test coupon?, engineers must account for the specific requirements of their target application. The optimal choice depends on the frequency range, power level, environmental conditions, and cost constraints of the overall system design.
Frequently Asked Questions
How far can I trust my edge launch measurement?
A well-designed SMA edge launch: reliable to 15-18 GHz. 2.92 mm (K connector) edge launch: reliable to 35-40 GHz. 2.4 mm edge launch: reliable to 45-50 GHz. Beyond these limits: the launch becomes too lossy and reflective for useful measurement. For higher frequencies: use GSSG probes or waveguide-to-microstrip transitions.
How many test coupons should I include on a PCB panel?
Minimum: one coupon per impedance class (single-ended 50 ohm, differential 100 ohm) per signal layer. Recommended: 3-5 coupons per Class/layer (allows statistical analysis). Include: a thru coupon (for de-embedding), a long trace (6-12 inches for loss measurement), and a short trace (1-2 inches as a reference). Place coupons at the panel edge and center (to check uniformity across the panel).
What is the cost of a GSSG probe measurement?
Probe station + probes: $50,000-200,000 (one-time purchase). Per-measurement cost: minimal (probes are reusable). For labs that do not own probes: outsource to a PCB characterization service (e.g., Wild River Technology, Isola). Cost: $500-2,000 per board measured. The probe measurement provides the highest accuracy and is the reference for validating edge launch measurement quality.