Implementation of functional components of the Locomotion Processing Unit

A Locomotion Processing Unit (LPU) processes sensory feedback and intrinsic feed forward control to produce a stimulation pattern for producing walking movements. The aim of the LPU is to emulate the functionality of the biological central pattern generator (CPG). The concept of the LPU has been previously described and this work presents experimental results of the sensory feedback comparators, an integrate-and-fire neuron, and a current stimulator implemented in a 0.5 micron VLSI process. The sensory feedback comparators were tested by setting a threshold voltage and sweeping the input to observe when the output changed its binary value. The bias current to the integrate-and-fire neuron was varied to generate spiking frequencies between 5Hz and 1kHz. The parameters (pulse width, amplitude, and waveform) of the current stimulator were programmed and for each waveform type the amplitude was measured up to 100μA (peak to peak). In addition, the LPU current outputs were tested through a phantom material to estimate its performance in an in vivo experiment.