AbstractsEngineering

The performance of certain high-gain amplifiers, such as those used in null detectors, can be greatly improved by using a nonlinear element in a feedback loop. With the addition of nonlinear feedback, it is possible to obtain an amplifier that can handle a large dynamic range of input signals without saturating or blocking. The desired characteristic of the amplifier is a voltage gain that varies instantaneously and inversely with input signal amplitude. Thus, for small input signals, the voltage gain is maximum and as the input signal amplitude increases, the voltage gain decreases to unity or less. The characteristics of a number of suitable nonlinear elements are investigated and a mathematical function is derived to describe them. The variation in voltage gain of an amplifier with a single nonlinear feedback loop is investigated, both theoretically and experimentally, and the results are in good agreement. Several single-loop nonlinear feedback amplifiers can be connected in cascade to obtain the equivalent of nonlinear elements that are not available. This method is used in an example of an approximation of a logarithmic function.