The DS1865 from Maxim is an IC for optical control, calibration and monitoring. It integrates GPON power-levelling functionality, a large bias APC (average-power-control) loop, video amplifier control and SFF-8472 diagnostic and alarm features, making it ideal for BPON (broadband passive optical network) and GPON (gigabit passive optical network) triplexer applications.
Usually a laser diode driver intended for GPON transceiver applications needs to include the laser-bias APC loop or lookup table (LUT), some fault management circuitry to meet eye safety requirements and other control functionality. These additional features add extra complexity to a design and are expensive to implement in the high-speed processes required to meet the GPON specifications. The DS1865 controller, however, is optimised to work with the MAX3643 burst-mode laser driver for a compact GPON system solution. By implementing all control, monitoring and fault management functions using low-cost CMOS technology, the DS1865 minimises the total solution cost for a GPON transceiver.
This device also integrates several analog functions that make the device's performance the best in its class, according to the manufacturer. An integrated 13-bit ADC includes input scaling, which provides 29 dB of dynamic range. The built-in temperature sensor is factory-calibrated and is said to have 50% less error than competing solutions. A tracking error lookup table enables compensation for laser-monitor diode error that occurs across temperature. This feature further increases the accuracy of the laser power control.
The DS1865 includes a 13-bit laser-bias DAC, claimed to be more than four times better than existing solutions, to control the video amplifier and a second DAC to control the boost converter (MAX5026) for the APD (avalanche photodiode) bias. The APD bias can be controlled across temperature to ensure operation in the correct gain range. The RF output power of the video amplifier (MAX3654) is controlled using the MAX4003 to sense the output RF power, an op-amp to make a feedback loop, and the DS1865's DAC output to provide a set point for the control loop.
With all this built-in capability, the DS1865 simplifies GPON transceiver design in several ways. The APC loop controls the laser's bias across temperature and ageing, thus removing the requirement for a laser-bias LUT. The modulation control DAC and APC loop have eight bits of resolution, and another three levels of scaling: +0 dB, -3 dB, and -6 dB. This scaling ability allows a single register to control the ONU (optical network unit) power level. The DS1865 memory map conforms to the SFF-8472 specification.
The DS1865 is available in a 28-pin 5 mm x 5 mm TQFN package and operates from a 2,85 V to 5,5 V power supply over a -40°C to +95°C temperature range.
Also available is the DS1863 burst-mode PON controller, which does not include the additional DACs for video amplifier and APD bias control. The DS1863 is available in a 16-pin TSSOP package.
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