Design of Stage-Selective Negative Voltage Generator to Improve On-Chip Power Conversion Efficiency for Neuron Stimulation

Dedicated to neuron stimulation circuits, a stage-selective negative voltage generator is proposed to enhance the overall power efficiency. Since the supplied voltage of the stimulus driver is subject to applications and treatments, an extensive output requirement of supply is demanded to achieve energy-efficient stimulation. The charge pump is implemented as a negative voltage generator for on-chip design. In a limited area, excess power loss is eliminated by reconfiguring the cascaded architecture and clocks. Digitally programmable voltage levels can be outputted by varying the number of stages dynamically. The function of stage selection is achieved by the proposed stage-selective scheme. With appreciate control, the stage-selective negative voltage generator can maintain higher power efficiency under different output voltage levels and loading conditions. The technique improves 40% power conversion ratio at most but only leads to an increment of 8% in area occupation. The measured output voltage covers from -0.3 V to -9.3 V within a maximum 5.5-mA output current, which is verified in a 0.25-μm BCD process.