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Linear Circuits

March 14th Fact-of-the-Day

Any circuit that has a ratio of output-signal to input-signal (called a transfer function) that is not a function of any input signal characteristic, such as, for example, frequency, phase or amplitude, is by definition a linear circuit. Circuits that meet that requirement are unable to alter the shape of an input wave in any way. Therefore, comparison of input and output waveshapes is the prime test for circuit linearity. Note, however, that the shape of a wave is unrelated to its constant amplitude or to any constant time-shift. Therefore, a circuit can change the amplitude of a signal and still be linear, so long as the amplitude difference does not depend on any input signal characteristic. Likewise, a circuit can advance or retard an output signal with respect to an input signal and still be linear, so long as the input/output signal timing does not depend on any characteristic of the input signal. ©2005 Martek International All rights reserved.


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