Samsung has introduced yet another extension to the LPDDR5 specification at the International Solid-State Circuits Conference (ISSCC), increasing data transfer rates to 12,700 MT/s (12.7 GT/s). To increase the speed, Samsung had to add four-phase self-calibration and AC-coupled transceiver equalization to its DRAM chips, which it calls its LPDDR5-Ultra-Pro DRAM.
World's fastest LPDDR5X
Samsung's highest-speed LPDDR5X, with a data transfer rate of 12,700 MT/s, is a 16 Gb memory IC with an industry-standard voltage of 1.05V made using the company's 5th Generation 10nm-class DRAM fabrication process. 16 Gb device capacity may not be too impressive on the mobile devices front, considering Samsung announced 24 Gb LPDDR5X ICs in 2023 and then launched 32Gb LPDDR5X ICs in 2024. However, 16 Gb could be quite a decent capacity for applications that do not demand the highest memory densities. This is perhaps why Samsung's ISSCC paper mentions AI, AR, VR, and server applications, whereas the company's presentation mentions LPCAMM2 modules aimed at PCs and servers (well, edge servers).
The LPDDR5 specification was introduced in 2019 with the plan to extend the data transfer rate to 6,400 MT/s. In 2021, JEDEC published an extended version of the spec — dubbed LPDDR5X — that pushed the speed to 8,533 MT/s. But that was not enough for at least some LPDDR5X users, so Micron, Samsung, and SK hynix further increased the data transfer rate of LPDDR5X to 9,600 MT/s in 2023, and then Samsung followed up with 10,700 MT/s in 2024 (which it has yet to ship). Now, Samsung has taken another step and introduced LPDDR5-Ultra-Pro memory with a 12,700 MT/s data transfer rate.
Enabling such an extreme data transfer rate required Samsung to implement a four-phase self-calibration loop and AC-coupled transceiver equalization. These two features are not defined in the LPDDR5X specification and are vendor-specific circuit-level design techniques used to meet or exceed the official JEDEC LPDDR5X data rate and power requirements.
Four-phase self-calibration loop
A four-phase self-calibration loop is a circuit-based solution that ensures four internal clock phases (0°, 90°, 180°, and 270°) remain properly aligned in high-speed memory interfaces. In LPDDR5X DRAM, clock signals are divided and distributed to create these four phases, which drive data transfers at multi-GT/s speeds. Even slight mismatches between these phases — called phase skew — can affect the timing margin and degrade performance. The calibration loop measures each pair of phases (e.g., 0° vs. 180°, 90° vs. 270°) and automatically compensates for any offset.
Samsung's implementation of the four-phase self-calibration loop uses two calibration steps: flip and unflip. By flipping which signal is fed to the circuit under test (e.g., swapping 0° and 180°) and comparing the results against the unflipped measurement, the calibration logic isolates and corrects the true clock-phase misalignment. The final calibration codes are then applied to shift or adjust each phase as needed to preserve clean, evenly spaced clock edges inside the chip.
AC-coupled transceiver equalization
At high-speed data transmission rates, signals are prone to attenuation and inter-symbol interference (ISI) along the channel. AC-coupled transceiver equalization addresses signal issues in high-speed DRAM components: on a high level, it boosts the clock signal, equalizes the receiver, and pre-emphasizes the transmitter.
Samsung's implementation involves three complementary blocks: an AC-coupled booster (ACCB) in the clock buffer, an AC-coupled equalizer (ACCE) on the receive side, and an AC-coupled pre-emphasis (ACCP) on the transmit side. Each applies extra high-frequency gain at various points in the path, ensuring that attenuated clock edges are restored and timing integrity is maintained. According to Samsung, the net effect is more robust data transmission and reception at speeds exceeding 10,000 MT/s per pin.
Measurements
Based on the company's own measurements, at its maximum rate of 12,700 MT/s, Samsung's LPDDR5-Ultra-Pro DRAM memory chip operates reliably at 1.05 volts. Even at 10,700 MT/s, it maintains stability above 0.9 volts, according to measurements conducted by Samsung. The read and write margins at peak speed measure 0.71 and 0.68 unit intervals, respectively, demonstrating robust signal integrity. These values confirm the effectiveness of Samsung's calibration and equalization techniques.
