Logarithmic amplifiers are characterized by the fact that they have a logarithmic characteristic curve and their amplification is logarithmic. Due to the logarithmic characteristic, signals with low level values are amplified more than signals with high amplitudes. They compress signals with high amplitudes and amplify those with small and smallest amplitudes.
The dynamic range of logarithmic amplifiers can span many decades, eight or more. This means that logarithmic amplifiers can handle input voltages between nanovolts (nV) and volts (V). The logarithmic characteristics of these amplifiers are determined by electronic components with logarithmic characteristics. The curved characteristic of diodes or transistors can follow a logarithmic function and be used as a working characteristic. Depending on the amplifier concept, these components determine the level-dependent gain in the feedback ofoperational amplifiers.
Other concepts work similar to analog computers with several amplifier stages connected in series, each taking over a part of the logarithmic function. The number of amplifier stages determines the dynamic range of the amplifier. This concept is mainly used in RF technology and IF amplifiers.
Logarithmic amplifiers are used wherever the smallest levels have to be amplified disproportionately, while large levels have to be amplified only slightly or not at all. For example, in RF technology and optoelectronics for the detection of very small voltages.