EXPERIMENTAL INVESTIGATION OF THE MINIMUM SIGNAL FOR RELIABLE OPERATION OF DRAM SENSE AMPLIFIERS

Reliable operation of a DRAM sense amplifier requires a minimum input voltage. It depends mainly on mismatches in device parameters such as process tolerances in gate length, different bit-line capacitances, and on the shape of the trigger pulses activating the sense amplifier. The minimum sense signal has been investigated experimentally by using a test structure that is basically a modified cross-coupled sense amplifier with 16-Mb DRAM feature sizes. Measured 5-sigma values of 27 mV correspond to variation in gate length, whereas 10 mV are found for bit-line capacitance asymmetries. The way that the minimum sense signal is affected by different trigger-pulse slopes was investigated. Finally, a simple but illustrative analysis of the effect of device mismatches is developed and the measured values are compared with theoretical limits.