Measurement and analysis of packages with differential signaling scheme

The characterization of packages with differential input lines involves the implementation of mixed mode S-parameters based on the even and odd modes of propagation. The device under test is a 100 I/O quad flat package with a differential signaling scheme. Under simplified assumptions of uncoupled transmission test system, this analysis can be performed using the conventional vector network analyzer and specially designed calibration and test fixtures; making use of conversion equations from a single mode measurement to a mixed mode calculation. The calibration is a standard "short open load thru" (SOLT) calibration, with specially designed fixtures to de-embed the effects of the test network used. Consideration is given to the co-efficients of calibration as expected frequency of operation extends up to 26GHz at which the parasitics of the vias are suspected to cause some distortion. The test fixture is the unpowered IC under consideration that has an unpowered terminal impedance of 52 ohms. With the provisions above, a comprehensive model of the package can be determined.