Description
The LSP2961 is a single-channel precision logarithm and log ratio integrated circuit powered by +5 V and –5 V power supplies. The voltage output of the amplifier is a logarithmic function of the ratio of a reference current (IREF) over the input current (IIN). The scale factor is set internally to 1 V/decade, and is further adjustable by adding an external resistor. The input dynamic range for the amplifier is a six decade (1 nA to 1 mA) minimum, with seven-decade (1 nA to 10 mA) and eight-decade (100 pA to 10 mA) operation available with increased conformity error. The amplifier has an internal trimmed reference 1 µA ± 5% current source that is also externally adjustable using an external resistor. The output offset voltage is 100 mV maximum and can be nulled using an external potentiometer.

FEATUREs
■ Seven decades (1 nA to 10 mA) typical input range
■ Internal scale factor K = 1 ± 2% (K externally adjustable):
   OUTPUT = K x log IREF/IIN
■ Internal trimmed reference current (IREF = 1 µA ± 5%, externally adjustable)
■ Maximum ±100 mV output offset (externally adjustable)
■ Minimal external components
■ ±5 V power supply
■ TSSOP small package

APPLICATIONs
■ Optical light density measurement
■ Log, log ratio computation
■ Data linearization