120 Dual Logarithmic Converter

The ADL5310 is a low-cost dual logarithmic amplifier that converts input current over a wide dynamic range to a linear-in-dB output voltage. It is optimized for the determination of optical power in wide-ranging optical communication system applications including control circuitry for lasers, optical switches, attenuators, and amplifiers, as well as general system monitoring. The device is equivalent to a dual AD8305 with enhanced dynamic range (120 dB). While the ADL5310 contains two independent signal channels with individually-configurable transfer function constants (slope and intercept), internal bias circuitry is shared between channels for improved power consumption and channel matching. Dual converters in a single compact LFCSP package yield space-efficient solutions for measuring gain or attenuation across optical elements. Only a single supply is required, while optional dual supply operation offers added flexibility.

The ADL5310 employs an optimized translinear structure, which utilizes the accurate logarithmic relationship between a bipolar transistor's base-emitter voltage and collector current, with appropriate scaling by precision currents to compensate the inherent temperature dependence. Input and reference current pins sink current ranging from 3 nA to 3 mA (limited to ±60 dB between input and reference) into a fixed voltage defined by the VSUM potential, which is internally set to 500 mV but may be externally-grounded for dual-supply operation and additional applications requiring voltage inputs.

* Optimized for fiber optic photodiode interfacing

* Measures current over 6 decades

Law conformance 0.3 dB from 3 nA to 3 mA

* Single- or dual-supply operation (3 V to ±5.5 V total)

* Nominal slope of 10 mV/dB (200 mV/decade)

* Nominal intercept of 300 pA (set by external resistor)

Optional adjustment of slope and intercept

* Full log-ratio capabilities

* Temperature stable

* Rapid response time for a given current level

* Miniature 24-lead chip scale package

(LFCSP 4 mm × 4 mm)

* Low power: <10 mA quiescent current