If you ever need to do TRL calibration, you will find AtaiTec’s patent-pending In Situ De-embedding (ISD) technique most useful. Compared to more than seven test coupons on a TRL calibration board, ISD needs only one through trace. TRL requires that the calibration board and DUT test fixture have identical characteristic impedance, which is an impossible feat to achieve. In addition, TRL does not remove coupling among lead-in traces. The result is that the S parameters of DUT after TRL calibration are almost always non-causal and are difficult to correlate with simulation. ISD addresses all of these issues with a very simple procedure: (a) measure the through trace test coupon (which only needs to have similar, but not identical, behavior as the DUT test fixture); (b) measure DUT + test fixture; and (c) run ISD software.
In this example, the DUT is a mezzanine connector. A test fixture and 2x thru coupon were built. Zoom in to see more details:
The SMA and lead-in traces were de-embedded with the same exact differential impedance from DUT + test fixture in 4-port VNA measurement, as shown below in time-domain differential impedance profile.
The non-causal response after TRL, which is attributed to the impedance variation between TRL calibration board and actual DUT test fixture, is clearly seen in the following figure. ISD is free of causality error. Note the big difference in return loss, too.
Click HERE for more details and zoom in below to see how ISD can be more accurate, simpler to operate, and less expensive than TRL and bare board de-embedding.
ISD vs. AFR
See the ISD advantages:
- Gives more accurate and causal results
- Uses standard substrates, etching tolerances and connectors for the test fixture and coupons
- Extracts crosstalk from a single trace test coupon
- Extracts small DUT from a large board
- De-embeds asymmetric structures
- Runs in batch to stack up multiple jobs
Zoom in the following to see the comparison between ISD and AFR in de-embedding a resonator structure:
See additional comparison between ISD and AFR in de-embedding a USB Type-C connector: