A Fine-Grained, Uniform, Energy-Efficient Delay Element for FD-SOI Technologies

Abstract

Contemporary digitally controlled delay elements trade off power overheads and delay quantization error. This paper proposes a new delay element that provides a balanced design that yields low power with low delay quantization error. The proposed element has a quasi linear delay characteristic, with uniform delay differences between adjacent codewords. The element employs and leverages the advantages offered by a 28nm FD-SOI technology, using its back body biasing feature to add an extra dimension to its programmability. To do so, a novel generic delay shift block is proposed, which enables incorporating both fine and coarse delays in a single delay element that can be easily integrated into digital systems, an advantage over hybrid delay elements that rely on analog design.

Synthesis of All-Digital Delay Lines

“…DLs have three interesting properties that simplify delay analysis: (1) the nets do not have glitches, (2) the time windows of the nets do not overlap, and (3) all nets have single fanout 4 . In this way, simple delay models can be used and crosstalk can be ignored by simply isolating or shielding the DL.…”

“…• All the wires must have the same width. 4 Property (3) is not fully complied when synthesizing configurable DLs with muxes (see section V). • Large spacing rules between wires are defined.…”

“…Another interesting and area-efficient solution commonly used for delay lines is shown in Fig. 10 (e.g., [4]). For N codewords, this scheme requires M = log 2 N 2-input muxes.…”

“…The main goal of a variability-tracking DL is to have a circuit that generates a delay highly correlated with the longest timing path of the system. DLs are often used for post-silicon tuning [1]- [4], thus enabling the reduction of guardband margins.…”

“…On the analog side, voltage-controlled delay elements are typically used [9]- [11]. Digitally-controlled delay elements are also possible, for example, by interleaving multiplexers in the DL [4], [12].…”