A high-performance wordline voltage-generating system for low-power low-voltage flash memory

Abstract

Wordline (WL) voltage-generating system is a crucial block in flash memory. It generates a voltage higher than the supply voltage for reading, programming and erasing in flash memory. However, operation accuracy is deteriorated by the excessive overshoot and ripple voltage. Moreover, current consumption in standby mode shortens the life of memory. The paper presents a high-performance wordline voltagegenerating system in 55nm CMOS technology. In active mode, a variable stage and frequency charge pump system is proposed to suppress overshoot and ripple of WL voltage (VWL) when the supply voltage ranges from 1.5 V to 2.1 V. To cut down standby current, an ultra-low power voltage reference circuit operating in subthreshold region is introduced. When recovering from standby mode, a standby recovery management circuit is utilized to minimize WL voltage setup time. The ripple voltage is 3 mV at 30 pF load with 20 MHz pumping frequency in active mode in post-simulation. The WL voltage setup time when recovery from standby mode is equal to 13.7 ns, even though the average standby current is less than 0.98 μA typically.