A technique for real-time measurement of Nth-order derivatives d/sup N/V/dI/sup N/

A technique for the measurement of device derivatives d/sup N/V/dI/sup N/ of arbitrary order N described. Measurement is accomplished by injecting a test current composed of the sum of N square waves into the rest device, and then multiplying the corresponding voltage change by the product of those same square waves, followed by low-pass filtering. The algorithm is implemented in real time using a mixture of analog and digital circuitry, and its application to semiconductor laser control in high-speed optical communications is described.<
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