| 摘要 |
PURPOSE:To provide a micro-current logarithmic amplifier which has logarithmic computers of stable output straightness and temperature property in a signal area where a measured input current is at a low level, one pico-ampere or lower. CONSTITUTION:A micro-current logarithmic amplifier is such that a measured input current is input to one of two sets of logarithmic computers which provides log diodes 1a, 1b for negative feedback circuits in computation amplifiers 2a, 2b and a reference current is input to the other to use an output difference between both logarithmic computers for an output signal. The logarithmic computer (1a, 2a) for measurement, the logarithmic computer (1b, 2b) for comparison, a temperature compensating resistance 9, a temperature sensor 15 and a heating element 14 are stored in a heat insulating metal case of good heat conductivity and electric conductivity. The temperature of the heat insulating case 13 is based on the detected temperature of the temperature sensor 15 and the heating element 14 is controlled by the output of the temperature control circuit 16 to keep the ambient temperature of the logarithmic computers constant. A linearizer 12 is provided for an output circuit in the micro-current logarithmic amplifier to compensate the nonlinear form of the logarithmic computers.
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