Bias controller and current monitor

Analog Devices is introducing what it claims is the first device to combine avalanche photodiode bias control and current monitoring on a single chip.


Analog Devices is introducing what it claims is  the first device to combine avalanche photodiode (APD) bias control and current monitoring on a single chip for space-constrained optical transceiver modules.


For optical network designers who need to ensure the responsivity of a temperature-sensitive APD, the ADL5317 accurately sets the bias voltage over a 6-V to 72-V range, while simultaneously monitoring current over a six-decade range.


The device supports next-generation optical networks operating at typical data rates of 10 Gits/sec and above and its linear interface reduces the noise normally found in APD modules.


As data rates grow to 10 Gbit/sec and beyond, systems are increasingly transitioning from PIN diodes to higher performing APDs which improve receiver sensitivity and increase link reach. For an APD to work accurately in receiver designs, continuous voltage correction and bias control are required.


The 3V linear bias control interface of the ADL5317 allows optical designers to use a fixed high-voltage switcher, lowering the supply decoupling and low-pass filtering requirements of traditional APD biasing designs that are prone to switching noise created by PWM-based DC-to-DC converters.


It mirrors photodiode current (5:1 ratio) over six decades with a linearity of 0.5% from 50nA to 1mA and 1% from 5nA to 5mA, enabling high-side current measurement when used with optical power measurement devices, such as ADI’s AD8304, AD8305, ADL5306 and ADL5310 translinear log amps.


Features such as over-current protection and over-temperature shutdown protect the expensive APD from damage caused by excessive input current and die temperature, shutting down the bias controller until temperature falls below 120 degrees Celsius and current levels fall below acceptable levels.


The ADL5317 APD bias controller is sampling now in a 3 mm × 3 mm LFCSP (lead frame chip-scale package) and is priced at $4.10 per unit in 1,000-piece quantities. Full production will begin in June 2005.