Logarithmic current amplifier

1,110,354. Logarithmic circuits; neutron detectors. ATOMENERGI A.B. 18 Feb., 1966 [19 Feb., 1965], No. 7356/66. Heading G4G and G6P. [Also in Divisions G1 and H3] In a neutron dosimeter a detector comprising a chamber filled with boron trifluoride containing electrodes supplied with a high voltage is surrounded by a screen of polyethylene/boron plastic approximating the neutron response characteristics of the human body, and delivers pulses corresponding to the arrival of neutrons which are amplified and applied to a discriminator selecting pulses exceeding a given amplitude which are transformed to pulses of constant duration and amplitude which are integrated in capacitance C 1 and resistance R 1 with dividers D 1 , D 2 , Dg setting quiescent conditions, and the integrand voltage is applied to a feedback amplifier comprising PNP transistor To in common base connection with input to its emitter, and its collector connected to the base of a common emitter NPN transistor T 2 . The amplified output at the collector thereof is connected to the emitter of a NPN grounded base feedback transistor T 1 whose collector is connected to the amplifier input. It is shown that the loop gain is constant, and the amplified output proportional to the logarithm of the input is applied to the collector of NPN transistor T 3 in a chain of emitter followers T 3 , T 4 , T 5 . A similar chain of transistors T 6 , T 7 , T 8 is provided with a variable direct voltage from potentiometer R, applied across diode connected transistor T 9 , and the emitters of transistors T 6 , T 6 are interconnected by resistance R 3 in series with meter M reading neutron dosage. Temperature drift is connected by giving R 3 a positive temperature coefficient and adjusting R 7 to a critical value. A mathematical analysis is given.