Method for characterizing interconnect timing characteristics using reference ring oscillator circuit
First Claim
1. A method of determining timing characteristics of a test interconnect structure, said method comprising the steps of:
- a) determining timing characteristics of reference logic units and reference interconnect structures that comprise a reference ring oscillator circuit using direct measurement;
b) measuring a first frequency of oscillation of said reference ring oscillator circuit;
c) inserting said test interconnect structure onto one of said reference interconnect structures of said reference ring oscillator circuit;
d) measuring a second frequency of oscillation of said reference ring oscillator circuit having said test interconnect structure inserted therein;
e) subtracting the period of said first frequency from the period of said second frequency to determine a first time value; and
f) based on said first time value and determined timing characteristics of said one of said reference interconnect structures, determining said timing characteristics of said test interconnect structure.
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Abstract
A reference ring oscillator circuit (RROC) is used to determine timing characteristics of a test interconnect structure in an integrated circuit. The RROC includes an odd number of inverters coupled together in a ring manner and has defined test segments at which a test interconnect can be loaded. Reference timing characteristics of the unloaded RROC are determined according to a calibration method including the steps of: (a) directly measuring signal propagation delay through each segment of the RROC; (b) modeling each test segment using an RC tree type reference circuit model having reference elements; (c) simulating the reference circuit model to provide a functional relationship between two reference capacitors; (d) defining upper and lower bounds for propagation delay through the test segment in terms of the reference elements; (e) determining values for the reference capacitor elements; and (f) measuring a reference frequency of oscillation of the unloaded RROC.
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Citations
18 Claims
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1. A method of determining timing characteristics of a test interconnect structure, said method comprising the steps of:
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a) determining timing characteristics of reference logic units and reference interconnect structures that comprise a reference ring oscillator circuit using direct measurement; b) measuring a first frequency of oscillation of said reference ring oscillator circuit; c) inserting said test interconnect structure onto one of said reference interconnect structures of said reference ring oscillator circuit; d) measuring a second frequency of oscillation of said reference ring oscillator circuit having said test interconnect structure inserted therein; e) subtracting the period of said first frequency from the period of said second frequency to determine a first time value; and f) based on said first time value and determined timing characteristics of said one of said reference interconnect structures, determining said timing characteristics of said test interconnect structure. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of determining timing characteristics of a test interconnect structure, said method comprising the steps of:
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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. - View Dependent Claims (11)
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12. A method of determining timing characteristics associated with an interconnect structure of a field programmable gate array, said method comprising the steps of:
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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. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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Specification