There were some errors in the previously obtained transfer function of the part where TIA was in series with the Whitening Filter. So, below is the updated transfer function plot.

Attachment 1: The circuit diagram

The usual transimpedance configuration was made using the OP27 IC. There are two TIA as we will be using two PD in our final circuit. The two TIA are connected to Whitening Filter respectively. The Whitening filter has a gain of 10. Apart from that, the output of the two TIA is connected to a differential circuit and whose output is in turn connected to another independent whitening filter.

Attachment 2: The Transfer Function

The transfer function of the transimpedance amplifier, Differential Circuit(at both its input nodes), Whitening Filter was analyzed by using the SR785 spectrum analyzer. A 1V source was applied at the input of a 10k resistor which was in turn connected in series with the respective circuit under consideration. The averaging mode is RMS and the input ground node is floating. The input is AC coupled.

The terminology used in the graph:

TIA- Transfer function of the transimpedance amplifier

Differential at node1- TF of Differential circuit by providing source at node1

Differential at node2- TF of Differential circuit by providing source at node2

Whitening Filter- TF of Whitening filter by providing source at node1

TIA and Whitening filter- TF of transimpedance amplifier in series with the Whitening filter, and the source were at node1 of the TIA.