Place and route

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Place and route is a stage in the design of printed circuit boards, integrated circuits, and field-programmable gate arrays. As implied by the name, it is composed of two steps, placement and routing. The first step, placement, involves deciding where to place all electronic components, circuitry, and logic elements in a generally limited amount of space. This is followed by routing, which decides the exact design of all the wires needed to connect the placed components. This step must implement all the desired connections while following the rules and limitations of the manufacturing process.

Printed circuit board board to support and connect electronic components

A printed circuit board (PCB) mechanically supports and electrically connects electronic components or electrical components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it.

Field-programmable gate array array of logic gates that are reprogrammable

A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturing – hence the term "field-programmable". The FPGA configuration is generally specified using a hardware description language (HDL), similar to that used for an Application-Specific Integrated Circuit (ASIC). Circuit diagrams were previously used to specify the configuration, but this is increasingly rare due to the advent of electronic design automation tools.

In electronic design, wire routing, commonly called simply routing, is a step in the design of printed circuit boards (PCBs) and integrated circuits (ICs). It builds on a preceding step, called placement, which determines the location of each active element of an IC or component on a PCB. After placement, the routing step adds wires needed to properly connect the placed components while obeying all design rules for the IC. Together, the placement and routing steps of IC design are known as place and route.

Contents

Place and route is used in several contexts:

Electronic component basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields

An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not to be confused with electrical elements, which are conceptual abstractions representing idealized electronic components.

Integrated circuit electronic circuit manufactured by lithography; set of electronic circuits on one small flat piece (or "chip") of semiconductor material, normally silicon

An integrated circuit or monolithic integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material that is normally silicon. The integration of large numbers of tiny transistors into a small chip results in circuits that are orders of magnitude smaller, faster, and less expensive than those constructed of discrete electronic components. The IC's mass production capability, reliability, and building-block approach to circuit design has ensured the rapid adoption of standardized ICs in place of designs using discrete transistors. ICs are now used in virtually all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other digital home appliances are now inextricable parts of the structure of modern societies, made possible by the small size and low cost of ICs.

Integrated circuit layout representation of an integrated circuit in terms of planar geometric shapes which correspond to the patterns of metal, oxide, or semiconductor layers that make up the components of the integrated circuit

Integrated circuit layout, also known IC layout, IC mask layout, or mask design, is the representation of an integrated circuit in terms of planar geometric shapes which correspond to the patterns of metal, oxide, or semiconductor layers that make up the components of the integrated circuit.

These processes are similar at a high level, but the actual details are very different. With the large sizes of modern designs, this operation is usually performed by electronic design automation (EDA) tools.

Electronic design automation (EDA), also referred to as electronic computer-aided design (ECAD), is a category of software tools for designing electronic systems such as integrated circuits and printed circuit boards. The tools work together in a design flow that chip designers use to design and analyze entire semiconductor chips. Since a modern semiconductor chip can have billions of components, EDA tools are essential for their design.

In all these contexts, the final result when placing and routing is finished is the layout, a geometric description of the location and rotation of each part, and the exact path of each wire connecting them.

Occasionally some people call the entire place-and-route process layout.

Printed circuit board

The design of a printed circuit board comes after the creation of a schematic and generation of a netlist. The generated netlist is then read into a layout tool and associated with part footprints from a library. Placing and routing can now start.

Circuit diagram graphical representation of an electrical circuit

A circuit diagram is a graphical representation of an electrical circuit. A pictorial circuit diagram uses simple images of components, while a schematic diagram shows the components and interconnections of the circuit using standardized symbolic representations. The presentation of the interconnections between circuit components in the schematic diagram does not necessarily correspond to the physical arrangements in the finished device.

In electronic design, a netlist is a description of the connectivity of an electronic circuit. In its simplest form, a netlist consists of a list of the electronic components in a circuit and a list of the nodes they are connected to. A network (net) is a collection of two or more interconnected components.

Placing and routing is generally done in two steps. Placing the components comes first, then routing the connections between the components. The placement of components is not absolute during the routing phase, as it may still be changed by moving and rotating, especially with designs using more complex components such as FPGAs or microprocessors. Their large number of signals, and their signal integrity needs may require optimization of the placement. [1]

Signal integrity

Signal integrity or SI is a set of measures of the quality of an electrical signal. In digital electronics, a stream of binary values is represented by a voltage waveform. However, digital signals are fundamentally analog in nature, and all signals are subject to effects such as noise, distortion, and loss. Over short distances and at low bit rates, a simple conductor can transmit this with sufficient fidelity. At high bit rates and over longer distances or through various mediums, various effects can degrade the electrical signal to the point where errors occur and the system or device fails. Signal integrity engineering is the task of analyzing and mitigating these effects. It is an important activity at all levels of electronics packaging and assembly, from internal connections of an integrated circuit (IC), through the package, the printed circuit board (PCB), the backplane, and inter-system connections. While there are some common themes at these various levels, there are also practical considerations, in particular the interconnect flight time versus the bit period, that cause substantial differences in the approach to signal integrity for on-chip connections versus chip-to-chip connections.

The resulting design is then output in RS-274X Gerber format to load in the CAM system of the manufacturer.

Gerber format file format

The Gerber format is an open ASCII vector format for 2D binary images. It is the de facto standard used by printed circuit board (PCB) industry software to describe the printed circuit board images: copper layers, solder mask, legend, drill data, etc.

Field-programmable gate array

The process of placing and routing for an FPGA is generally not performed by a person, but uses a tool provided by the FPGA Vendor or another software manufacturer. The need for software tools is because of the complexity of the circuitry within the FPGA and the function the designer wishes to perform. FPGA designs are described using logic diagrams containing digital logic and hardware description languages such as VHDL and Verilog. These will then be put through an automated place-and-route procedure to generate a pinout, which will be used to interface with the parts outside of the FPGA. [1]

Integrated circuits

The IC place-and-route stage typically starts with one or more schematics, HDL files, or pre-routed IP cores, or some combination of all three. It produces an IC layout that is automatically converted to a mask work in the standard GDS II or the OASIS format. [2]

History

The final layout of early ICs and PCBs was stored as a tape-out of Rubylith on transparent film.

Gradually, electronic design automation automated more and more of the place-and-route work. At first, it merely sped up the process of making many small edits without spending a lot of time peeling up and sticking down the tape. Later design rule checking sped up the process of checking for the most common sorts of errors. Later auto routers speed up the process of routing.

Some people hope that further improvements in autoplacers and autorouters will eventually produce good layouts without any human manual intervention. Further automation leads to the idea of a silicon compiler.

Related Research Articles

Very Large Scale Integration process of creating an integrated circuit by combining thousands of transistors into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed

Very-large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining millions of transistors or devices into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The microprocessor is a VLSI device. Before the introduction of VLSI technology most ICs had a limited set of functions they could perform. An electronic circuit might consist of a CPU, ROM, RAM and other glue logic. VLSI lets IC designers add all of these into one chip.

In computer engineering, a hardware description language (HDL) is a specialized computer language used to describe the structure and behavior of electronic circuits, and most commonly, digital logic circuits.

Application-specific integrated circuit Integrated circuit customized (typically optimized) for a specific task

An application-specific integrated circuit is an integrated circuit (IC) customized for a particular use, rather than intended for general-purpose use. For example, a chip designed to run in a digital voice recorder or a high-efficiency bitcoin miner is an ASIC. Application-specific standard products (ASSPs) are intermediate between ASICs and industry standard integrated circuits like the 7400 series or the 4000 series.

Schematic capture stage of electronic circuit design

Schematic capture or schematic entry is a step in the design cycle of electronic design automation (EDA) at which the electronic diagram, or electronic schematic of the designed electronic circuit is created by a designer. This is done interactively with the help of a schematic capture tool also known as schematic editor.

CADSTAR

CADSTAR is a Windows-based electronic design automation (EDA) software tool for designing and creating schematic diagrams and printed circuit boards (PCBs). It provides engineers with a tool for designing simple or complex, multilayer PCBs. CADSTAR spans schematic capture, variant management, placement, automatic and high-speed routing, signal integrity, power integrity, EMC analysis, design rule checks and production of manufacturing data.

In electronic design a semiconductor intellectual property core, IP core, or IP block is a reusable unit of logic, cell, or integrated circuit layout design that is the intellectual property of one party. IP cores may be licensed to another party or can be owned and used by a single party alone. The term is derived from the licensing of the patent and/or source code copyright that exist in the design. IP cores can be used as building blocks within application-specific integrated circuit (ASIC) designs or field-programmable gate array (FPGA) logic designs.

Standard cell group of transistor and interconnect structures that provides a boolean logic function; used to design application-specific integrated circuits with mostly digital-logic features

In semiconductor design, standard cell methodology is a method of designing application-specific integrated circuits (ASICs) with mostly digital-logic features. Standard cell methodology is an example of design abstraction, whereby a low-level very-large-scale integration (VLSI) layout is encapsulated into an abstract logic representation. Cell-based methodology — the general class to which standard cells belong — makes it possible for one designer to focus on the high-level aspect of digital design, while another designer focuses on the implementation (physical) aspect. Along with semiconductor manufacturing advances, standard cell methodology has helped designers scale ASICs from comparatively simple single-function ICs, to complex multi-million gate system-on-a-chip (SoC) devices.

OrCAD electronic design automation software

OrCAD Systems Corporation was a software company that made OrCAD, a proprietary software tool suite used primarily for electronic design automation (EDA). The software is used mainly by electronic design engineers and electronic technicians to create electronic schematics, perform mixed-signal simulation and electronic prints for manufacturing printed circuit boards. OrCAD was taken over by Cadence Design Systems in 1999 and was integrated with Cadence Allegro since 2005.

XCircuit

XCircuit is a Unix/X11 and Windows program for drawing publication-quality electrical circuit schematic diagrams and related figures and the production of circuit netlists through schematic capture. XCircuit regards circuits as inherently hierarchical and writes both PostScript output and hierarchical SPICE netlists. Circuit components are saved in and retrieved from libraries which are fully editable. XCircuit does not separate artistic expression from circuit drawing; it maintains flexibility in style without compromising the power of schematic capture.

Integrated circuit design Engineering process for electronic hardware

Integrated circuit design, or IC design, is a subset of electronics engineering, encompassing the particular logic and circuit design techniques required to design integrated circuits, or ICs. ICs consist of miniaturized electronic components built into an electrical network on a monolithic semiconductor substrate by photolithography.

Placement is an essential step in electronic design automation — the portion of the physical design flow that assigns exact locations for various circuit components within the chip's core area. An inferior placement assignment will not only affect the chip's performance but might also make it non-manufacturable by producing excessive wire-length, which is beyond available routing resources. Consequently, a placer must perform the assignment while optimizing a number of objectives to ensure that a circuit meets its performance demands. Together, the placement and routing steps of IC design are known as place and route.

The Layout Versus Schematic (LVS) is the class of electronic design automation (EDA) verification software that determines whether a particular integrated circuit layout corresponds to the original schematic or circuit diagram of the design.

Electronic circuit electrical circuit with active components such as transistors, valves and integrated circuits; electrical network that contains active electronic components, generally nonlinear and require complex design and analysis tools

An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow. To be referred to as electronic, rather than electrical, generally at least one active component must be present. The combination of components and wires allows various simple and complex operations to be performed: signals can be amplified, computations can be performed, and data can be moved from one place to another.

Physical design (electronics)

In integrated circuit design, physical design is a step in the standard design cycle which follows after the circuit design. At this step, circuit representations of the components of the design are converted into geometric representations of shapes which, when manufactured in the corresponding layers of materials, will ensure the required functioning of the components. This geometric representation is called integrated circuit layout. This step is usually split into several sub-steps, which include both design and verification and validation of the layout.

In the automated design of integrated circuits, signoff checks is the collective name given to a series of verification steps that the design must pass before it can be taped out. This implies an iterative process involving incremental fixes across the board using one or more check types, and then retesting the design. There are two types of sign-off's: front-end sign-off and back-end sign-off. After back-end sign-off the chip goes to fabrication. After listing out all the features in the specification, the verification engineer will write coverage for those features to identify bugs, and send back the RTL design to the designer. Bugs, or defects, can include issues like missing features, errors in design, etc. When the coverage reaches a maximum% then the verification team will sign it off. By using a methodology like UVM, OVM, or VMM, the verification team develops a reusable environment. Nowadays, UVM is more popular than others.

In electronic design automation, parasitic extraction is calculation of the parasitic effects in both the designed devices and the required wiring interconnects of an electronic circuit: parasitic capacitances, parasitic resistances and parasitic inductances, commonly called parasitic devices, parasitic components, or simply parasitics.

Pulsonix Software für Schaltplan Erstellung und Leiterplatten Design

Pulsonix is an electronic design automation (EDA) software suite for schematic capture and PCB design. It is produced by WestDev, which is headquartered in Gloucestershire, England, with additional sales and distribution offices overseas. It was first released in 2001, and runs on Windows.

References

  1. 1 2 "FPGA/PCB Co-Design Increases Fabrication Yields". Printed Circuit Design and Fabrication. Retrieved 2008-07-24.
  2. A. Kahng, J. Lienig, I. Markov, J. Hu: "VLSI Physical Design: From Graph Partitioning to Timing Closure", Springer (2011), ISBN   978-90-481-9590-9, pp. 7-11.