High-side monitor

Analog Devices has introduced a high-side monitor that provides a compact solution for the problem of interfacing an optical power monitoring device, such as a logarithmic amplifier, to the cathode-side of a PIN photodiode.

The ADL5315 mirrors the current at the cathode at a 1:1 ratio over a six-decade range  from 3 nA to 3mA, producing an output equal to the reference current monitored. The company claims that competing optical current monitors have much higher mirror ratios over narrower ranges, rendering proportional outputs at very low input currents impossible, while discrete solutions are more complex to implement and may require significantly more board space.

The new chip also sports a linearity of only 1% over the operating range. In PIN photodiode modules where only the cathode is available for connection, this high linearity allows the device to be paired with linear or logarithmic amplifiers to form a complete, precise optical power measurement system.