LOGARITHMIC AMPLIFIER CIRCUIT

PURPOSE:To improve the temperature characteristics and to extend the operating temperature range by providing a function generating circuit generating a function in response to a base-emitter voltage in a logarithmic amplifier amplifying an input signal based on the logarithmic characteristic between a collector current and the base-emitter voltage of a transistor. CONSTITUTION:The temperature characteristic of the logarithmic amplifier circuit is caused by a characteristic of an element and depends nearly on a value of a base-emitter voltage VBE. That is, the effect of an ambient temperature T appears at the diode characteristic of the element, especially in a reverse saturation current Ic. Although the Ic is neglected normally because it is sufficiently small, but since the difference between the actually measured value and the theoretical value is reflected on the VBE via the current Ic, a circuit generating an optional function is added, where the temperature compensation circuit is activated when the VBE reaches a prescribed value or below. For example, a temperature compensation circuit 1d comprising is provided, and the logarithmic amplifier circuit is constituted by adding its input to an output terminal of a logarithmic converting operational amplifier of a logarithmic converting circuit 1a and its output to an input terminal of an output buffer 1b.