Field Programmable Analog Arrays (FPAAs)

Many attempts have been made to apply rapid-prototyping techniques known from the digital domain to analog designs. The goal of the presented work is to develop an FPAA, which is suitable for reconfigurable implementation of analog continuous-time (CT) high-frequency filters on an integrated circuit.

The proposed FPAA structure consists of a two-dimensional array of CABs, which include digitally configurable transconductors. The arrangement in a hexagonal layout allows reconfigurable routing of analog signals throughout the chip. Series and parallel connection as well as feedback of any order is provided by the structure.

It can be shown that a large number of different filter types with different orders can be synthesized on the FPAA, for example low-pass filters, variable gain amplifiers or band-pass filters. The circuit can instantaneously be adapted to a wide range of varying needs in analog filtering and maximum achievable bandwidths are in the range of 200 MHz. A test-chip has been designed and manufactured in a 130nm CMOS technology. Experiments show good compliance with the simulation results and prove the feasibility of the structure.

It is not only possible to apply classical filter synthesis to achieve a configuration, but the FPAA also provides a platform for evolutionary experiments by usage of genetic algorithms with hardware in the loop. An embedded hardware platform with fast DACs and ADCs, as well as an FPGA has been developed, which is capable of evaluating a transfer function of the chip and running a genetic algorithm for automated synthesis of filters with reconfigurable analog hardware in the loop.