SLLSEK1B July 2014 – March 2018 ONET2804T
The first stage of the signal path is a transimpedance amplifier which converts the photodiode current into a voltage. If the input signal current exceeds a certain value, the transimpedance gain is reduced by means of a nonlinear AGC circuit to limit the signal amplitude.
The second stage is a limiting voltage amplifier that provides additional limiting gain and converts the single ended input voltage into a differential data signal. The output stage provides CML outputs with an on-chip 50Ω back-termination to VCC.
The TIA has adjustable gain, amplitude, bandwidth and input threshold and they can be globally controlled through pad settings or each channel can be individually controlled through the 2-wire interface. The default mode of operation is pad control where the state (OPEN, HI or LO) of the AMPL, BW, GAIN and TRSH pads sets the respective parameter. To enable 2-wire control, the I2CENA pad should be set HIGH and the functionality of each channel can be controlled individually through the 2-wire interface.