Circuit design - AbsoluteAstronomy.com

The process of circuit design can cover systems ranging from complex electronic systems all the way down to the individual transistor

Transistor

A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

s within an integrated circuit

Integrated circuit

An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

. For simple circuits the design process can often be done by one person without needing a planned or structured design process, but for more complex designs, teams of designers following a systematic approach with intelligently guided computer simulation are becoming increasingly common.

In integrated circuit

Integrated circuit

design automation

Electronic design automation

Electronic design automation is a category of software tools for designing electronic systems such as printed circuit boards and integrated circuits...

, the term "circuit design" often refers to the step of the design cycle which outputs the schematics of the integrated circuit. Typically this is the step between logic design and physical design

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...

.

Formal circuit design usually involves the following stages:

sometimes, writing the requirement specification after liaising with the customer
writing a technical proposal to meet the requirements of the customer specification
synthesising on paper a schematic
Schematic
A schematic diagram represents the elements of a system using abstract, graphic symbols rather than realistic pictures. A schematic usually omits all details that are not relevant to the information the schematic is intended to convey, and may add unrealistic elements that aid comprehension...

circuit diagram
Circuit diagram
A circuit diagram is a simplified conventional graphical representation of an electrical circuit...

, an abstract electrical or electronic circuit that will meet the specifications
calculating the component values to meet the operating specifications under specified conditions
performing simulations to verify the correctness of the design
building a breadboard
Breadboard
A breadboard is a construction base for prototyping of electronics. The term is commonly used to refer to solderless breadboard ....

or other prototype version of the design and testing against specification
making any alterations to the circuit to achieve compliance
choosing a method of construction as well as all the parts and materials to be used
presenting component and layout information to draughtspersons, and layout and mechanical engineers, for prototype production
testing or type-testing a number of prototypes to ensure compliance with customer requirements
signing and approving the final manufacturing drawings
post-design services (obsolescence of components etc.)

Specification

The process of circuit design begins with the specification, which states the functionality that the finished design must provide, but does not indicate how it is to be achieved .http://www.informit.com/articles/article.aspx?p=392278 The initial specification is basically a technically detailed description of what the customer wants the finished circuit to achieve and can include a variety of electrical requirements, such as what signals the circuit will receive, what signals it must output, what power supplies are available and how much power it is permitted to consume. The specification can (and normally does) also set some of the physical parameters that the design must meet, such as size, weight, moisture resistance, temperature range, thermal output, vibration tolerance and acceleration tolerance.

As the design process progresses the designer(s) will frequently return to the specification and alter it to take account of the progress of the design. This can involve tightening specifications that the customer has supplied, and adding tests that the circuit must pass in order to be accepted. These additional specifications will often be used in the verification of a design. Changes that conflict with or modify the customer's original specifications will almost always have to be approved by the customer before they can be acted upon.

Correctly identifying the customer needs can avoid a condition known as 'design creep' which occurs in the absence of realistic initial expectations, and later by failing to communicate fully with the client during the design process. It can be defined in terms of its results; "at one extreme is a circuit with more functionality than necessary, and at the other is a circuit having an incorrect functionality". (DeMers, 1997) Nevertheless some changes can be expected and it is good practice to keep options open for as long as possible because it's easier to remove spare elements from the circuit later on than it is to put them in.

Design

The design process involves moving from the specification at the start, to a plan that contains all the information needed to be physically constructed at the end, this normally happens by passing through a number of stages, although in very simple circuit it may be done in a single step. http://www.informit.com/content/images/chap1_0131433474/elementLinks/01fig01.gif The process normally begins with the conversion of the specification into a block diagram of the various functions that the circuit must perform, at this stage the contents of each block are not considered, only what each block must do, this is sometimes referred to as a "black box" design. This approach allows the possibly very complicated task to be broken into smaller tasks which may either by tackled in sequence or divided amongst members of a design team.

Each block is then considered in more detail, still at an abstract stage, but with a lot more focus on the details of the electrical functions to be provided. At this or later stages it is common to require a large amount of research or mathematical modeling into what is and is not feasible to achieve.http://www.seas.upenn.edu/~ee205/Labs97S/Lab4.html The results of this research may be fed back into earlier stages of the design process, for example if it turns out one of the blocks cannot be designed within the parameters set for it, it may be necessary to alter other blocks instead. At this point it is also common to start considering both how to demonstrate that the design does meet the specifications, and how it is to be tested ( which can include self diagnostic

On Board Diagnostics

On-Board Diagnostics, or OBD, in an automotive context, is a generic term referring to a vehicle's self-diagnostic and reporting capability. OBD systems give the vehicle owner or a repair technician access to state of health information for various vehicle sub-systems...

tools ).http://www.besttest.com/Courses/DFTBIST.cfm

Finally the individual circuit components are chosen to carry out each function in the overall design, at this stage the physical layout and electrical connections of each component are also decided, this layout commonly taking the form of artwork for the production of a printed circuit board

Printed circuit board

A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...

or Integrated circuit. This stage is typically extremely time consuming because of the vast array of choices available. A practical constraint on the design at this stage is that of standardization, while a certain value of component may be calculated for use in some location in a circuit, if that value cannot be purchased from a supplier, then the problem has still not been solved. To avoid this a certain amount of 'catalog engineering' can be applied to solve the more mundane tasks within an overall design.

Costs

Proper design philosophy and structure incorporates economic and technical considerations and keeps them in balance at all times, and right from the start. Balance is the key concept here; just as many delays and pitfalls can come from ill considered cost cutting as with cost overruns. Good accounting tools (and a design culture that fosters their use) is imperative for a successful project. "Manufacturing costs shrink as design costs soar," is often quoted as a truism in circuit design, particularly for ICs.

Verification and testing

Once a circuit has been designed, it must be both verified

Formal verification

In the context of hardware and software systems, formal verification is the act of proving or disproving the correctness of intended algorithms underlying a system with respect to a certain formal specification or property, using formal methods of mathematics .- Usage :Formal verification can be...

and tested. Verification is the process of going through each stage of a design and ensuring that it will do what the specification requires it to do. This is frequently a highly mathematical process and can involve large-scale computer simulations of the design. In any complicated design it is very likely that problems will be found at this stage and may involve a large amount of the design work be redone in order to fix them.

Testing is the real-world counterpart to verification, testing involves physically building at least a prototype of the design and then (in combination with the test procedures in the specification or added to it) checking the circuit really does do what it was designed to.

Prototyping

Prototyping is a means of exploring ideas before an investment is made in them. Depending on the scope of the prototype

Prototype

A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...

and the level of detail required, prototypes can be built at any time during the project. Sometimes they are created early in the project, during the planning and specification phase, commonly using a process known as breadboard

Breadboard

A breadboard is a construction base for prototyping of electronics. The term is commonly used to refer to solderless breadboard ....

ing; that's when the need for exploration is greatest, and when the time investment needed is most viable. Later in the cycle packaging mock-ups are used to explore appearance and usability, and occasionally a circuit will need to be modified to take these factors into account.

Results

As circuit design is the process of working out the physical form that an electronic circuit will take, the result of the circuit design process is the instructions on how to construct the physical electronic circuit. This will normally take the form of blueprints describing the size, shape, connectors, etc., in use, and artwork or CAM

Computer-aided manufacturing

Computer-aided manufacturing is the use of computer software to control machine tools and related machinery in the manufacturing of workpieces. This is not the only definition for CAM, but it is the most common; CAM may also refer to the use of a computer to assist in all operations of a...

file for manufacturing a printed circuit board

Printed circuit board

or Integrated circuit

Integrated circuit

Documentation

Any commercial design will normally also include an element of documentation, the precise nature of this documentation will vary according to the size and complexity of the circuit as well as the country in which it is to be used. As a bare minimum the documentation will normally include at least the specification and testing procedures for the design and a statement of compliance with current regulations. In the EU this last item will normally take the form of a CE Declaration

CE mark

CE marking is a mandatory conformity mark for products placed on the market in the European Economic Area . With the CE marking on a product the manufacturer ensures that the product conforms with the essential requirements of the applicable EC directives...

listing the European directives complied with and naming an individual responsible for compliance.http://www.ita.doc.gov/td/tic/ce_mark/ceFAQ.htm

Specification

Design

Costs

Verification and testing

Prototyping

Results

Documentation

See also

Sources