This article summarizes two experiments utilizing building blocks to ﬁnd analog electronic circuits on a CMOS Field Programmable Transistor Array (FPTA). The FPTA features 256 programmable transistors whose channel geometry and routing can be conﬁgured to form a large variety of transistor level analog circuits. The transistor cells are either of type PMOS or NMOS and are arranged in a checkerboard pattern. Two case studies focus on improving artiﬁcial evolution by using a building block library of four digital gates consisting of a NOR, a NAND, a buﬀer and an inverter. The methodology is applied to the design of the more complex logic gates XOR and XNOR as well as to the evolution of circuits discriminating between square waves of diﬀerent frequencies.