Experiments with field programmable analog arrays in active noise control

Smart materials usually need a control system to accomplish the smart behavior. A widely used control system principle is analog or digital feedback control. Smart material applications benefit from short control latency, and an analog controller usually has the shortest possible processing delay. Its drawback is the lack of flexibility for adjustable or adaptive solutions. For this purpose digitally adjustable analog controllers can be used. They can be implemented in various ways. Implementation in this study focuses to the Field Programmable Analog Array (FPAA), which is based on switched capacitor technology. With FPAAs not only the filter parameters are digitally adjustable but the filter structure may be modified during the operation. With these properties FPAAs can be used as low latency feedback controllers. Base filter structures in FPAAs are often rudimentary, such as biquad filters, but they can be cascaded for more complex arrangements. An FPAA realisation of a controller is presented. Moreover, the developed feedback controller is evaluated in an active noise control test setup. The results show that the FPAAs can be successfully used in feedback control applications. However, the switched capacitor technology sets limits to performance of practical controller due to the switching noise and the clock feed-through in practical implementations, and implications of this are also discussed.