Digital IP Protection Using Threshold Voltage Control

This paper proposes a method to completely hide the functionality of a digital standard cell. This is accomplished by a differential threshold logic gate (TLG). A TLG with $n$ inputs implements a subset of Boolean functions of $n$ variables that are linear threshold functions. The output of such a gate is one if and only if an integer weighted linear arithmetic sum of the inputs equals or exceeds a given integer threshold. We present a novel architecture of a TLG that not only allows a single TLG to implement a large number of complex logic functions, which would require multiple levels of logic when implemented using conventional logic primitives, but also allows the selection of that subset of functions by assignment of the transistor threshold voltages to the input transistors. To obfuscate the functionality of the TLG, weights of some inputs are set to zero by setting their device threshold to be a high $V_t$. The threshold voltage of the remaining transistors is set to low $V_t$ to increase their transconductance. The function of a TLG is not determined by the cell itself but rather the signals that are connected to its inputs. This makes it possible to hide the support set of the function by essentially removing some variable from the support set of the function by selective assignment of high and low $V_t$ to the input transistors. We describe how a standard cell library of TLGs can be mixed with conventional standard cells to realize complex logic circuits, whose function can never be discovered by reverse engineering. A 32-bit Wallace tree multiplier and a 28-bit 4-tap filter were synthesized on an ST 65nm process, placed and routed, then simulated including extracted parastics with and without obfuscation. Both obfuscated designs had much lower area (25%) and much lower dynamic power (30%) than their nonobfuscated CMOS counterparts, operating at the same frequency

Boundary Element Method Macromodels for 2-D Hierarchical Capacitance Extraction †

A 2-D hierarchical field solution method was recently introduced for capacitance extraction for VLSI interconnect modeling. In this paper, we present several extensions to the method including a Boundary Element Method (BEM) formulation for creating macromodels, which provides a better trade-off between accuracy and efficiency, as well as parameterized elements, which allow the analysis of gridless designs with reasonable accuracy and a small library size. 1

A Synthesis Flow Toward Fast Parasitic Closure for Radio-Frequency Integrated Circuits

An electrical and physical synthesis flow for high-speed analog and radio-frequency circuits is presented in this paper. Novel techniques aiming at fast parasitic closure are employed throughout the flow. Parasitic corners generated based on the earlier placement statistics are included for circuit resizing to enable parasitic robust designs. A performance-driven placement with simultaneous fast incremental global routing is proposed to achieve accurate parasitic estimation. Device tuning is utilized during layout to compensate for layout induced performance degradations. This methodology allows sophisticated macromodels of performances versus device variables and parasitics to be used during layout synthesis to make it truly performance-driven. Experimental results of a 4GHz LNA and a mixer demonstrate fast parasitic closure with this methodology