Derivative measurement by frequency mixing
AssigneeBell Telephone Laboratories, Incorporated
InventorThomas L. Paoli
Life of this patent
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Abstract
A dual-frequency technique for electronically measuring high-order derivatives by frequency mixing is described. The technique utilizes an ac modulation at two distinct but synchronous frequencies to produce a derivative signal at a useful difference frequency, which is unique to the order of the derivative being measured. By appropriate selection of the frequencies, significant advantages are obtained compared to the conventional method in which derivatives are measured at harmonics of a single frequency. The technique is illustrated with a practical measurement of the second derivative of the electrical characteristic of a silicon rectifier diode.
Claims5
A method of generating the n-th order (n .gtoreq. 2) derivative of a parameter of a nonlinear device comprising the steps of:
- applying to the device a first sinusoidal signal at a first frequency f.sub.1
- applying to the device a second sinusoidal signal at a second frequency f.sub.2 phase-locked to the first signal at f.sub.1, and
- detecting a third signal corresponding to a difference frequency f.sub.d of f.sub.1 and f.sub.2, the third signal being proportional to the n-th order derivative.
A method of generating the n-th order derivative of voltage with respect to current of a nonlinear device comprising the steps of:
- applying to the device a first sinusoidal current at a first frequency f.sub.1,
- applying to the device a second sinusoidal current at a second frequency f.sub.2 phase-locked to the first current at f.sub.1, and
- detecting the resulting voltage signal across the device at a difference frequency f.sub.d of f.sub.1 and f.sub.2, the amplitude of the signal being proportional to the desired n-th derivative.
Dependencies are inferred from the claim text.