LPDDR3 is optimized for battery life and portability. DDR3L-RS is a low IDD6 version of the DDR3L die and offers a balance in price versus performance, along with improved standby power.
LPDDR3 increases performance to 1600 Mb/s (versus 1066 Mb/s for LPDDR2). Additional changes include write leveling, C/A (command/address) training, and a lower I/O capacitance limit to improve timing.
LPDDR4 increases data rate to 3200Mbps ~ 4266Mbps/pin, using LVSTL(Low Voltage Swing Terminated Logic). Die organization has changed from x32 1ch (LPDDR3) to x16/x8 2ch, and added x16/x8 1ch. There are other new features on LPDDR4 for higher speed, lower power consumption.