Charge pump circuit for depletion-mode oxide TFTs

Abstract

A chrage pump circuit suitable for depletion-mode oxide thin-film transistors (TFTs) is presented. In this circuit, negative gate-to-source bias is applied to turn off the n-type oxide TFTs because they have negative threshold voltages (V(T)). For this operation, two different supply voltages are used, i.e. V(DD) and V(DD)/2. Spice simulation shows that the power efficiency is about 70% in generating V(DD) x 2 output voltage with 50 mA load current. The output voltages of the fabricated circuits are comparable to those of the simulation results.