Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein:
According to the present invention, existing state elements within the design of an integrated circuit are selectively used to produce a repeatable, substantially random series of preferably binary digits that is used as an identification for the integrated circuit. The random nature of the series is produced by subjecting one or more state elements to a specific protocol of voltage or frequency fluctuations. Small differences in the state elements from one integrated circuit to another cause the identification to differ from one integrated circuit to another. These small differences are caused by slight and minute differences in materials and processing that are used during the fabrication of the integrated circuits, even as between integrated circuits that are fabricated on the same wafer. While these differences in the state elements, such as voltage threshold, are typically too small to cause a given integrated circuit to malfunction or not perform according to specification, they can be used for the purposes as described herein.
With reference now to
It is appreciated that the flip flop 10 is merely one example of a state element, or in other words, a state holding device, and that any such state element could be used as a part of the preferred embodiments of the invention as described herein. For example, any accessible storage element will suffice if it can be stated properly. Some examples are scan flip-flops, memory arrays, and JTAG boundary scan cells.
Advances in structural testing of integrated circuits have made it possible to gain direct access to these state elements. Specifically in the case of the flip flops 10, it is routine to daisy chain these elements into what is called a scan chain. Binary streams of data can be shifted into and out of these scan chains, making it possible to access the binary state of any given flip flop in the design.
In standard CMOS technology, flip flops 10 are created using a feedback network such as that shown in the logic diagram of
The method 100 of using the state elements to obtain a unique device identifier is depicted in
In step 102, a power sequence is preferably followed that results in the states changing in a manner according to the specific processing that the devices in the state element have undergone. This sequence can be either very simple or more complex. On the simple end, the sequence can be a full power down where supply voltage is taken fully to zero volts, followed by a full power up. On the more elaborate end, it can be a sequence of partial power down and time dependant power up ramps, for example. All such power sequences are anticipated.
In step 103, under full power up conditions, the modified binary data is accessed via scan chains or other structural approaches to obtain the unique device identifier.
Another variation is the way in which the part is stated. Any way that random values can be applied to the state elements will generate a unique signature. Some examples are powering the part up from an off-state, and reducing the voltage at a known state.
The foregoing description of preferred embodiments for this invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.