A 5Gb/s/pin 16Gb LPDDR4/4X Reconfigurable SDRAM with Voltage-High Keeper and a Prediction-based Fast-tracking ZQ Calibration

Abstract

A 5Gb/s/pin 16Gb LPDDR4/4X reconfigurable SDRAM with a self-mode detection scheme, a voltage-high keeper (VHK) for un-terminated load and a prediction-based fast-tracking ZQ algorithm is implemented in 10nm class ($2^{nd}$ generation) DRAM process. Providing a reconfigurable LVSTL with a mode detection scheme to support two different DRAM interface standards (LPDDR4/4X) depending on I/O supply voltage $(V_{DDQ})$, a proposed design can maintain the system compatibility and longevity to the legacy controller and the PHY structure. The VHK for LPDDR4 enables the 3.2Gb/s operation in the un-terminated load similar to LPDDR4X by alleviating the inter symbol interference (ISI) through the controlled leakage current. In a ZQ calibration, the proposed ZQ algorithm achieves fast ZQ code searching, the calibration time can be reduced by 30% in PVT variation. Moreover, an internal ZQ calibration (IZQC) is newly adopted to minimize the variation of the driver strength to PVT variation.