140dB Range (1nA to 10mA) Logarithmic Current-to-Voltage Converter
140dB Range (1nA to 10mA) Logarithmic Current-to-Voltage Converter

The SGM834A is a single-supply logarithmic current-to- voltage converter for measuring the low frequency current signals over a large range from 1nA to 10mA. With capabilities such as photodiode adaptive biasing, active-shielding (guard driving), output buffer amplifier conditioning and voltage reference on a single chip, this device is optimized for measuring the power of optical signals by using a photodiode operating in the photo current mode. The measured current is converted and compressed to a logarithmic voltage by using transistor I-V characteristics and a compensation circuit.

The SGM834A operates with a single 3V to 5.5V supply and is equipped with a disable input to shut down the device. The input current (IPD) is converted to an internal 40μA/dec logarithmic scaled current that is injected into an internal 5kΩ resistance to provide an output voltage with 10mV/dB (or 200mV/dec) logarithmic slope on the VLOG output pin. This slope can be reduced by an external shunt resistor. The intercept point (the output voltage corresponding to the selected intercept current) and the scale (to change the slope) can be adjusted by the on-chip buffer amplifier.

This device is available in a Green TSSOP-14 package and is specified over a temperature range of -40 to +85.



  • Patents Pending Proprietary Circuits

  • Seven Full Decades Range

  • 3V to 5.5V Single-Supply Operation

  • Low Power and Temperature Stable

  • Precise Trimmed Scaling

  • 10mV/dB Logarithmic Slope at VLOG Pin

  • 100pA Basic Logarithmic Intercept

  • Simple Slope and Intercept Adjustments

  • 15V/μs Slew Rate

  • 3.3mA (TYP) Quiescent Current (Enabled)

  • 9μA (TYP) Shutdown Current (Disabled)

  • Available in a Green TSSOP-14 Package


High Accuracy Optical Power Measurement

Wide Range Baseband Log Data Compression

Versatile Detector for Automatic Power Control Loops

Part Number Status Package Pins Pb-Free Temp Range
SGM834AYTS14G/TR Production TSSOP-14 14 Y -40℃ to +85℃ Samples