Characteristic impedance and signal loss measurements of head-to-preamplifier interconnects

The use of scattering parameters (S-parameters) to characterize high frequency interconnects has widely been used in the signal integrity field and is now being accepted into the disk drive arena as the preferred modeling tool for write and read path interconnects. The motivating factor for the shift from traditional lumped circuit models to S-parameter models has been the increase in data rates which exceed 1 GB/s. S-parameter models are convenient because they can be used directly in several high end spice circuit simulators as "black box" models. This paper will describe recent measurement techniques which make vector (VNA) network analyzer measurements possible for various interconnect structures up to 8.5 GHz. This paper will verify the results using time domain reflectometry (TDR) measurements of the same interconnect structures. Specific examples on signal losses, impedance, and coupling will be shown. Advances in achieving a broad range of differential impedances while maintaining high bandwidth will be demonstrated with idealized test structures.