A 4-Mb pseudo SRAM operating at 2.6+or-1 V with 3- mu A data retention current

Abstract

A 4-Mb pseudo static RAM (PSRAM) suitable for universal battery usage is described. The wide voltage range, 2.6+or-1 V, is set to target the power supply voltage of the PSRAM considering various voltage levels and charging-discharging characteristics of batteries. A double-to-single automatically switchable booster is developed to provide the wide voltage range operation. To reduce the power dissipation of data retention for battery usage a low-power back-bias generator with a new substrate-level sensor and a temperature-dependent self-refresh timer with a unique internal refresh control scheme are demonstrated. A PSRAM operation ranging from 1 V to more than 5 V was obtained and a 3- mu A data retention current was realized at room temperature in contrast with 7 mu A at 70 degrees C and V/sub cc/ of 2.6 V. This PSRAM allows a 20-Mbyte RAM disk to retain data for two months with a single lithium battery.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>