Method for characterizing interconnect timing characteristics using reference ring oscillator circuit

A method of determining timing characteristics of a test interconnect structure, said method comprising the steps of:

• configuring a programmable integrated circuit to implement a reference ring oscillator circuit (RROC), said RROC comprising an odd number (x) of segments coupled in a ring manner wherein each segment comprises a reference interconnect structure which couples a pair of inverters;
• measuring a reference frequency of oscillation of said RROC;
• determining capacitance values for reference capacitors of a first segment of said x segments by direct measurement;
• inserting said test interconnect structure onto said first segment;
• measuring a test frequency of oscillation of said RROC having said test interconnect structure inserted therein;
• subtracting the period of said reference frequency from the period of said test frequency to determine a time value;
• adding said time value to a measured signal propagation delay through said first segment to provide a calculated signal propagation delay;
• and
• determining capacitance of said test interconnect structure based on determined values for said reference capacitors of said first segment and said calculated signal propagation delay.

A method of determining timing characteristics associated with an interconnect structure of a field programmable gate array, said method comprising the steps of:

• a) constructing a ring oscillator circuit having x segments, each segment comprising a reference interconnect structure, wherein x is an odd number;
• b) determining capacitance values associated with inverter stages and reference interconnect structures of said ring oscillator circuit based on direct measurement of signal propagation delays within each segment of said x segments;
• c) measuring a first frequency of oscillation of said ring oscillator circuit;
• d) inserting a test interconnect structure onto one of said reference interconnect structures of said ring oscillator circuit;
• e) measuring a second frequency of oscillation of said reference ring oscillator circuit having said test interconnect structure inserted therein;
• f) subtracting the period of said first frequency from the period of said second frequency to determine a time value;
• and
• g) based on said time value and determined capacitance values of said one of said reference interconnect structures, determining said timing characteristics of said test interconnect structure.