Accession Number : ADD006541

Title :   Logarithmic Lock-In Amplifier.

Descriptive Note : Patent Application,

Corporate Author : DEPARTMENT OF THE ARMY WASHINGTON DC

Personal Author(s) : Hartman,Richard L

Report Date : 21 Dec 1978

Pagination or Media Count : 6

Abstract : A technique for automatically varying the gain of a lock-in-amplifier with logarithmically responding diodes placed in the feedback network so that the output is proportional to the logarithm of the input. Measurement of low or high level signals without manual changes of gain is then provided. The lock-in-amplifier is a combination of narrow band preamplification, phase sensitive detection, and DC amplification. It is typically used to detect very low level signals submerged in noise. The disadvantage is that in many measurements there are large and small signals. If the gain level is set to detect the small signals, the large ones overload the system. If the gain is set to detect large signals, the small ones are lost. Trial and error repetitions are required to correctly adjust. A solution to this is to use a logarithmic amplifier. Many such slow responding amplifiers could be used after the lock-in, but then the dynamic range of the system is low. A logarithmic preamplifier can be used, but then it must be a very low noise amplifier, and the very low noise amplifier in the lock-in is wasted.

Descriptors :   *Patent applications, *Logarithmic amplifiers, Diodes, Feedback

Subject Categories : Electrical and Electronic Equipment
      Cybernetics

Distribution Statement : APPROVED FOR PUBLIC RELEASE