SLLSEK1B July 2014 – March 2018 ONET2804T
Figure 42 shows the ONET2804T being used in a 4 x 25 Gbps fiber optic receiver with pin control and Figure 45 shows the device being used with 2-wire control. The ONET2804T converts the electrical current generated by the PIN photodiode into a differential output voltage. The FILTER inputs provide a DC bias voltage for the PIN that is low pass filtered. Because the voltage drop across the photodiode FET is sensed and used by the bias circuit, the photodiode must be connected to the FILTER pads for the bias to function correctly.
The RSSI outputs are used to mirror the photodiode output current and can be connected via resistors to GND. The voltage gain can be adjusted for the intended application by choosing the external resistor; however, for proper operation of the ONET2804T, ensure that the voltage at RSSI never exceeds VCC - 0.65 V. If the RSSI outputs are not used while operating with internal PD bias they should be left open.
The OUT+ and OUT– pins are internally terminated by 50 Ω pull-up resisters to VCC. The outputs must be AC coupled, for example by using 0.1 µF capacitors, to the succeeding device.