Impact of multi threshold transistor in positive feedback source coupled logic (PFSCL) fundamental cell

In this paper, a new fundamental cell in positive feedback source coupled logic is presented, which is an improvement over the existing fundamental cell employed in digital circuit design in various high resolution mixed-signal integrated circuits. The operation of the existing fundamental cell relies on using large sized transistor in its centre branch, resulting in significantly larger implementation area. The proposed fundamental cell incorporates multi-threshold transistor in the center branch thereby allowing designer to use reduce its dimension and hence the area. The impact of the proposed modification is examined by configuring the cell as two input exclusive OR (XOR2) gate. The behaviour is analysed in terms of static and propagation delay parameters which are modelled and a design procedure is also elaborated. The theoretical prepositions are verified by designing and simulating for various operating conditions using model parameters of 180 nm CMOS technology node. A maximum error of 27% is observed between the simulated and predicted parameters. The process variation study through Monte Carlo analysis and PVT variations identifies the proposed fundamental cell based circuit as less prone to variations in comparison to existing fundamental cell based counterparts. A full adder, as an application of the proposed fundamental cell, shows a significant (66%) area reduction while delay, power and PDP are within 4% of their corresponding values for the existing one.