Implementation of Hyperbolic Tangent Function Using Improved STAM Algorithm

STAM (Symmetric Table Lookup Addition Method) algorithm is an efficient approach to implement non-linear function approximation with hardware, in which only lookup tables and addition are involved, and size of table could be reduced remarkably due to symmetry of the second term of Taylor series. Nevertheless, the dominant memory occupier is the first term, which still uses relatively big table. An improved method based on differential decomposition was brought forth aiming at relieving the problem, and hyperbolic tangent sigmoid function was implemented on FPGA using the improved algorithm. Experiment results showed that 17% to 30% of memory was saved after improvement.