John J. Pickerd

Interpolation procedure for cascading S-parameters to prevent aliasing

This paper describes a methodology for re-sampling S-parameters in a manner that prevents aliasing when combining multiple S-parameter sets. In high speed serial data link systems, S-parameters are often used to describe the characteristic behavior [1, 2]. A complex system may be composed of multiple subsystems. Each subsystem can be represented by one S-parameter set. There is a need to combine these S-parameter sets to obtain the model for the complete system. It is required that S-parameter data covers a specific bandwidth of interest. It is also required that the S parameter data has frequency resolution that is fine enough to prevent aliasing [3]. This means that the frequency resolution needs to be fine enough to provide a time interval long enough to cover the impulse response duration plus the reflections duration. Even though all the S-parameter data for an individual block may have appropriate frequency resolution, the same frequency resolution may become inadequate when combining them together in a cascade.

Optical reference receiver calibration for real time oscilloscopes

The filter is applied to the acquired waveform data from the O/E converter. This is done at the maximum real time sample rate of the oscilloscope. Lower frequency standards are highly over sampled. Therefore, floating point math is used for the filter convolution. This over sampling allows the bandwidth of the oscilloscope channel to operate as an anti-alias filter. From this point the filtered data is placed into a waveform database to create the source for the eye diagram that will appear on screen with the optical mask standard.