Abstract: Phase shift is added between a uttering clock signal and a data bit stream clocked by the clock signal. The phase shift is adjusted until half the data bits are captured (counted) over a measurement period. Adding this amount of phase shift between the clock and data signals centers the average clock edge placement. In a particular embodiment, counters, each having N bits where N is an integer, are used to count clock pulses and data bits. When one counter is full and the most-significant bit on the other counter goes high, the phase shift between the data and clock signal places the average clock edge at the data bit edge.

Abstract: Cross-correlation of delay line characteristics is described. An integrated circuit for cross-correlation testing includes: a first ring oscillator and a second ring oscillator. The first ring oscillator includes a first test circuit, and the second ring oscillator includes a second test circuit. The first test circuit is coupled via first programmable interconnects to first ring oscillator circuitry, and the second test circuit is coupled via second programmable interconnects to second ring oscillator circuitry. The first test circuit includes a first programmable delay line, and the second test circuit includes a second programmable delay line. The first test circuit and the second test circuit are configured to provide separately controllable outputs for cross-correlation as between the first programmable delay line and the second programmable delay line.

Abstract: First and second clock signals are provided to first and second sequential circuits, where the first and second clock signals are inversely coupled to logic high and low levels for clocking of the first and second sequential circuits. A third sequential circuit is clocked responsive to a first output from the first sequential circuit and receives first signature data. A fourth sequential circuit is clocked responsive to a second output from the second sequential circuit and receives second signature data. A third output from the third sequential circuit is monitored responsive to the first signature data and the first output. A fourth output from the fourth sequential circuit is monitored responsive to the second signature data and the second output. Whether the first clock signal and the second clock signal are phase aligned may be determined responsive to the third output and the fourth output.

Abstract: A system and method for measuring the timing requirements of a sequential logic element of a programmable logic device. The sequential logic element has a first data terminal, an output terminal, and a clock terminal. A first synchronous element is coupled to the data terminal through a first delay element. The first synchronous element is clocked by a clock signal and receives an alternating test signal. A second synchronous element is coupled to the clock terminal through a second delay element of an input-output block. The second synchronous element is also clocked by the clock signal and receives the alternating test signal. The output terminal of the sequential logic element is monitored by a tester or by logic configured in the fabric of the programmable logic device to determine when the logic state changes as the delay of the first or second delay element is selectively varied.