Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range

The MAX4207 logarithmic amplifier computes the log ratio of an input current relative to a reference current (externally or internally generated) and provides a corresponding voltage output with a default -0.25V/decade scale factor. The device operates from dual ±2.7V to ±5.5V supplies and is capable of measuring five decades of input current across a 10nA to 1mA range.

The MAX4207's uncommitted op amp can be used for a variety of functions, including filtering noise, adding offset, and adding additional gain. A 0.5V reference is also included to generate an optional precision current reference using an external resistor, which adjusts the log intercept of the MAX4207. The output-offset voltage and the adjustable scale factor are also set using external resistors.

The MAX4207 is available in a space-saving 16-pin thin QFN package (4mm x 4mm x 0.8mm), and is specified for operation over the -40°C to +85°C extended temperature range.

Applications

* Analog Signal Processing * Medical Instrumentation * Photodiode Current Monitoring * Portable Instrumentation

* ±2.7V to ±5.5V Dual-Supply Operation

* 5 Decades of Dynamic Range (10nA to 1mA)

* Monotonic Over a 1nA to 1mA Range

* -0.25V/Decade Internally Trimmed Output Scale Factor

* Adjustable Output Scale Factor

* Adjustable Output Offset Voltage

* Internal 10nA to 10µA Reference Current Source

* Input Amplifiers Summing Nodes at Ground

* Small 16-Pin Thin QFN Package (4mm x 4mm x 0.8mm)

* -40°C to +85°C Operating Temperature Range

* Evaluation Kit Available (Order MAX4206EVKIT)