An analog-to-time converter with positive feedback for amplifying miniature neural recordings

This paper presents an analog-to-time converter to handle analog signals in neural recording circuits. The subthreshold MOS operation allows weak input voltages to be exponentially amplified with reduced power dissipation, which is suitable from the implantable applications. The regenerative positive-feedback circuits then translates the analog information to a time-delay in logarithmic manner, which can attain a linear conversion between overall input and output. The capability of processing weak neural activities prevents large gain setting of preamplifier. To demonstrate the concept, a prototype is implemented with 0.35μm CMOS technology. With input ranging from 415 to 485mV, the output delay varies from 11.6 to 6.96μs. The power dissipation is 0.58mW from a 3.3V supply.