Voltage-to-Voltage Sigmoid Neuron Activation Function Design for Artificial Neural Networks

An Artificial Neural Network (ANN) involves a complex network of interconnected nodes called artificial neurons (AN); the AN sums N weighted inputs and send thought the result to a non-linear activation function (AF). In this work, a modified version of the sigmoid activation function is proposed. To obtain a voltage-to-voltage (V-V) transfer function required by an specific ANN. The proposed solution uses a pseudo-differential pair configuration at the input as voltage to current converter. The proposed circuit is designed using a commercial PDK in 180nm (TSMC) and is simulated in Virtuoso (Cadence). This specific design enable to obtain the desired steepness of the sigmoid function by means of the proper transistor sizing. Simulation results of our specific design show that we can reach an average relative error of only 1.09 % for steepness of 1 as compared to the exact mathematical function, and a power consumption of 6.77 mu W for steepness of 10.