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For example, a chip designed to run in a digital voice recorder or a high-efficiency Bitcoin miner is an ASIC. ASIC has grown from 5,000 logic gates to over 100 million. FPGA to be used in many different applications. The initial ASICs used gate array technology. An early successful commercial application was the gate array circuitry found in the 8-bit ZX81 and ZX Spectrum low-end personal computers, introduced in 1981 and 1982. O solution aimed at handling the computer’s graphics. Customization occurred by varying the metal interconnect mask.
Gate arrays had complexities of up to a few thousand gates. Later versions became more generalized, with different base dies customised by both metal and polysilicon layers. Some base dies include RAM elements. In the mid-1980s, a designer would choose an ASIC manufacturer and implement their design using the design tools available from the manufacturer.
While third-party design tools were available, there was not an effective link from the third-party design tools to the layout and actual semiconductor process performance characteristics of the various ASIC manufacturers. Most designers ended up using factory-specific tools to complete the implementation of their designs. By the late 1990s, logic synthesis tools became available. Such tools could compile HDL descriptions into a gate-level netlist.
A team of design engineers starts with a non-formal understanding of the required functions for a new ASIC, usually derived from requirements analysis. This process is analogous to writing a computer program in a high-level language. Suitability for purpose is verified by functional verification. Logic synthesis transforms the RTL design into a large collection of lower-level constructs called standard cells. 2 input nor, 2 input nand, inverters, etc. The standard cells are typically specific to the planned manufacturer of the ASIC.
The gate-level netlist is next processed by a placement tool which places the standard cells onto a region representing the final ASIC. It attempts to find a placement of the standard cells, subject to a variety of specified constraints. The routing tool takes the physical placement of the standard cells and uses the netlist to create the electrical connections between them. Given the final layout, circuit extraction computes the parasitic resistances and capacitances. In the case of a digital circuit, this will then be further mapped into delay information, from which the circuit performance can be estimated, usually by static timing analysis. These steps, implemented with a level of skill common in the industry, almost always produce a final device that correctly implements the original design, unless flaws are later introduced by the physical fabrication process. The significant difference is that standard-cell design uses the manufacturer’s cell libraries that have been used in potentially hundreds of other design implementations and therefore are of much lower risk than full custom design.
Microscope photograph of a gate-array ASIC showing the predefined logic cells and custom interconnections. Gate-array design is a manufacturing method in which the diffused layers, i. The physical design process then defines the interconnections of the final device. Often difficulties in routing the interconnect require migration onto a larger array device with consequent increase in the piece part price. These difficulties are often a result of the layout software used to develop the interconnect. In their frequent usages in the field, the terms “gate array” and “semi-custom” are synonymous.