An Energy Efficient $V_{\rm PP}$ Generator With Fast Ramp-Up Time for Mobile DRAM

An energy efficient
V
_PP
generator with fast ramp-up time for mobile DRAM is presented in this paper. Instead of using a fixed pumping clock frequency as in the conventional
V
_PP
generator, the proposed
V
_PP
generator adopts a voltage-controlled oscillator (VCO) and uses variable pumping frequencies to improve the ramp-up time as well as energy efficiency. Numerical results show that the VCO based
V
_PP
generators achieve energy savings of up to 34% with 40% improvement on ramp-up time when compared to the conventional ring oscillator (RO) based design. Our proposed
V
_PP
generator, which uses a three-stage voltage doubler as a charge pump, was implemented and fabricated in CMOS 0.13 μm process. The
V
_PP
generator chip's core occupies 0.6 mm
²
area and consumes 1162 nJ (average power of 47.8 mW during 24 μs ramp-up time) while generating 3.0 V output voltage with 1.0 nF load capacitor, 2.0 mA current load and 1.2 V supply voltage.