Apparatus and method for processing acquired signals for measuring the impedance of a device under test

The method of processing a plurality of acquired samples from a device under test having a signal source coupled to a passive circuit device (PCD) comprising the steps of:

• acquiring a plurality of samples in the time domain from the signal source via a signal path including a plurality of impedance loads selectively coupled in the signal path;
• converting the plurality of samples in the time domain from the signal source to a spectral domain representation for each selected impedance load of the plurality of impedance loads;
• characterizing transfer parameters of the signal source within a spectral domain from the spectral domain representation for each selected impedance load of the plurality of impedance loads;
• retrieving a stored value representing a reference impedance Zref associated with the transfer parameters;
• processing the transfer parameters of the signal source with the reference impedance (Zref) in the spectral domain to effect thereby a representation of the signal source impedance (Zeqsource) as a function of frequency;
• coupling the signal source to the passive circuit device;
• acquiring a plurality of samples in the time domain from the passive circuit device via a signal path including a plurality of impedance loads selectively coupled in the signal path;
• converting the plurality of samples in the time domain from the passive circuit device to a spectral domain representation for each selected impedance load of the plurality of impedance loads;
• characterizing transfer parameters of the passive circuit device combined with the signal source within a spectral domain from the spectral domain representation for each selected impedance load of the plurality of impedance loads;
• processing the transfer parameters of the combined signal source and the passive circuit device with the reference impedance (Zref) in the spectral domain to effect thereby a representation of the combined signal source and passive circuit device impedance (Zeqcomb) as a function of frequency.
• processing the representations of the signal source impedance (Zeqsource) and the combined signal source impedance and passive circuit device impedance (Zeqcomb) in the spectral domain to effect thereby a representation of the passive circuit device impedance (ZeqPCD) as a function of frequency.

A signal analysis system for processing acquired time domain digital samples of a test signal from a device under test to represent an impedance of the device under test comprising:

• a digitizing instrument having a memory for storing transfer parameters associated with the digitizing instrument and acquiring time domain digital samples of an incoming test signal;
• a test probe providing the incoming test signal to the digitizing instrument, the test probe having associated with it a memory for storing transfer parameters associated with the probe, and a controllable impedance device having selectable impedance loads selectively coupled to the device under test;
• and
• a controller having associated memory communicating with the digitizing instrument and the test probe for selectively coupling impedance loads in the controllable impedance device to the device under test and receiving the acquired time domain digital samples of the incoming test signal and converting the time domain digital samples to a spectral domain representation for each selected impedance load, and characterizing the transfer parameters of the device under test within a spectral domain from the spectral domain representations for each selected impedance load, the controller retrieving a stored value representing a reference impedance Zref associated with the transfer parameters and computing at least a first impedance (Zeq) of the device under test as a function of frequency using the characterized transfer parameters of the device under test and the reference impedance (Zref).