Performance of low loss, high speed interconnects for multi-GHz digital systems

Preliminary frequency-, time-, and digital-domain testing and electromagnetic simulations indicate that the striplines and microstrip lines of Honeywell's thin-film multilayer (TFML) technology are suitable for high-performance digital systems that require operation at frequencies greater than 1 GHz. The return loss was typically -20 dB, which indicates the ability to design and fabricate controlled impedance lines with Honeywells' TFML technology. The 1- and 2-GHz digital-domain test measurements did not appear to be affected significantly by the reflections. The insertion loss of approximately -2.5 dB/in. at 9 GHz is acceptable for relatively short signal interconnect lines which, in any event, are required to minimize interchip propagation delays in a functioning system. Predictions from the Mayo electromagnetic modeling package show excellent agreement with measured signal and crosstalk waveforms. The crosstalk between adjacent lines is less than -20 dB even when the coupled line length is very long (>6 in.). Vias and via pads show negligible effects on insertion and return losses up to a frequency of 9 GHz. Large impedance mismatches severely affect the return losses, and therefore should be avoided. Stubs in the interconnect must be kept smaller than 1/4 of the smallest wavelength within the signal bandwidth.