The DS1865 integrates GPON power-leveling functionality, a laser bias average-power-control (APC) loop, video amplifier control, and SFF-8472 diagnostic and alarm features. These capabilities make the DS1865 a solution for all BPON and GPON triplexer applications. In the past a laser-diode driver intended for GPON transceiver applications needed 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 added extra complexity to a design and were expensive to implement in the high-speed processes required to meet the GPON specifications.
The DS1865 controller, however, is optimized to work with the (MAX3643) burst-mode laser driver for a compact GPON system solution. An integrated 13-bit ADC includes input scaling, which provides 29dB of dynamic range. The built-in temperature sensor is factory-calibrated and has 50% less error than competing solutions. A tracking error lookup table enables compensation for laser-monitor diode error that occurs across temperature. This latter feature further increases the accuracy of the laser power control. The DS1865 includes a 13-bit laser-bias DAC, to control the video amplifier and a second DAC to control the boost converter (MAX5026) for the APD bias. The APD bias can be controlled across temperature to ensure that the APD operates 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 aging, 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: +0dB, -3dB, and -6dB. This scaling ability allows a single register to control the ONU power level. The DS1865 memory map conforms to SFF-8472 specification, making this device simple to use and design in.
The DS1865 is available now in a 28-pin 5mm x 5mm TQFN. It operates from a 2.85V to 5.5V power supply over a -40°C to +95°C temperature range. An evaluation kit is available. 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. An evaluation kit is available.
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