Precision logarithmic and log ratio amplifier with scale factor of 0.5-V/decade

The LOG104 is a versatile integrated circuit that computes the logarithm or log ratio of an input current relative to a reference current.

The LOG104 is tested over a wide dynamic range of input signals. In log ratio applications, a signal current can come from a photodiode, and a reference current from a resistor in series with a precision external reference.

The output signal at VOUT is trimmed to 0.5V per decade of input current, allowing seven decades of input current, dynamic range.

Low DC offset voltage and temperature drift allow accurate measurement of low-level signals over a wide environmental temperature range. The LOG104 is specified over the temperature range –5°C to +75°C, with operation over –40°C to +85°C.