Logarithmic amplification circuit for obtaining output voltage corresponding to difference between logarithmically amplified values of two input currents

Abstract From the Canadian patent

A logarithmic amplification circuit is provided with a first transistor having its collector supplied with a first input current, a second transistor having its collector supplied with a second input current and being differentially connected to the first transistor a, comparing circuit for receiving the first and second input currents to supply a signal corresponding to a difference between the two input currents to a base of the second transistor, and first and second constant current circuits for supplying respective collectors of the first and the second transistors with equivalent compensating current. An output voltage corresponding to a difference between a logarithmically amplified …