The process of creating a circuit to accomplish a particular task. When designing a circuit, one should consider how it should work, the target specifications, efficiency, cost effectiveness, code compliance, and ethics.
Introduction
The process of circuit design can cover systems ranging from complex electronic systems all the way down to the individual transistors within an integrated circuit.
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 design automation, 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.
Process
Formal circuit design usually involves a number of stages. Sometimes, a design specification is written after liaising with the customer. A technical proposal may be written to meet the requirements of the customer specification. The next stage involves synthesising on paper a schematic circuit diagram, an abstract electrical or electronic circuit that will meet the specifications. A calculation of the component values to meet the operating specifications under specified conditions should be made. Simulations may be performed to verify the correctness of the design.
Specifications
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. 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.
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.
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.
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.
Validation and Testing
Once a circuit has been designed, it must be both verified 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.
