Low-Power Encoding for PAM-3 DRAM Bus

TL;DR

The experimental results show the proposed PAM3-DBI, PAM3-MF, and PAM3-SORT algorithms can reduce termination power for high-speed memory links significantly by 41% to 90% for benchmark programs.

Abstract

The 3-level pulse amplitude modulation (PAM-3) signaling is expected to be widely used in memory interfaces for its greater voltage margins compared to PAM-4. To maximize the benefit of PAM-3, we propose three low-power data encoding algorithms: PAM3-DBI, PAM3-MF, and PAM3-SORT. With the DRAM memory traces from the gem5 computer architecture simulator running benchmarks, we evaluate the energy efficiency of our three PAM-3 encoding techniques. The experimental results show the proposed algorithms can reduce termination power for high-speed memory links significantly by 41% to 90% for benchmark programs.

Figures (9)

• Figure 1: PAM-3 signal modulation method. Each column of binary symbols 000, 001, 010, ..., 111 from three 8-bit word lines (X, Y, and Z) are mapped to PAM-3 signals [-1, -1], [-1, 0], [-1, +1], ..., [+1, +1] of two PAM-3 lines.
• Figure 2: An example for the definition of notation cnt(Z).
• Figure 3: An example operation of the helper procedure, MF_Convert, used in PAM3-MF encoding (Algorithm \ref{['alg:PAM3-MF']}), where the given signal to be swapped with +1 signal is -1.
• Figure 4: An example process of sorting signals from the least frequent one to the most frequent one, assigning a permutation number for the sorted signals, and applying a helper procedure, Sort_Convert, to convert the data for the given permutation number to achieve the minimum power consumption. (The permutation [0, 1, -1] is assigned the permutation number 3 in this example.)
• Figure 5: The distribution of each PAM-3 signal (-1, 0, or 1) from the memory traces of MiBench programs executed on x86 ISA and from random bits.