Substrate bias generator for dynamic RAM having variable pump current level

摘要

A dynamic MOS read/write memory has a substrate bias generator circuit which includes, in this example, four separate pump circuits. A first of these operates only during power-up to quickly produce the desired back bias; this pump circuit uses a high frequency oscillator and a low impedence drive, and cuts off to save power as soon as the necessary bias is reached. A second generates a smaller sustaining current, using a lower frequency oscillator and higher impedance drive; this functions to compensate for leakage during idle periods. The third and fourth pump circuits are driven by &upbar& R and &upbar& C, so these occur only when needed, and at a rate dependent upon the actual operating condition of the memory.