Linear trans-impedance amplifier with functional active loads for analog optical communication systems

We developed a CMOS-based trans-impedance amplifier (TIA) circuits for analog optical communication systems. Our TIA structure is based on common-source configuration and a novel functional active load (FAL). Proposed FAL structure is composed the two PMOSs that have the symmetric structure. In those schemes, transfer curve of TIA can be tuned by the gate voltage of FAL in the way to improve linearity. In analog optical transceiver, TIA employing the FAL can suppress the nonlinearity originated from various sources. Because the nonlinearity deteriorate analog communication systems, enhancement of linearity is crucial to improve the analog transceiver performances. In this work, we have designed the TIA with FAL in a 0.18 mu m CMOS technology. The linearity of TIA is controlled by the variation of transfer curve with the change of the FAL bias voltage. As of the simulation results, the IIP3 level of the TIA employing FAL is enhanced by 3.4 dB with the V-g variation in FAL.