Electronic Circuts

An electronic circuit is a closed path or paths formed by the interconnection of electronic components through which an electric current can flow.

Physically, an electronic circuit can be as small as a pin point or cover many miles. They are constructed by connecting electronic components together with conductors, which allow electricity to flow between the components. Integrated circuits are small circuits constructed from a piece of semiconductor housed in a protective package. While larger circuits may be built by assembling electronic components onto a printed circuit board (PCB), which is used to mechanically support and electrically connect the components. Integrated circuits are typically used as components in larger circuits built onto PCBs. When components are connected using wire as the conductor, the circuit may be extended to cover or connect a large area.

Breadboards, perfboards or stripboards are common for testing new designs. They allow the designer to make quick changes to the circuit during development.

Electronic circuits can display highly complex behaviors, even though they are governed by the same laws of physics as simpler circuits.

An electronic circuit can usually be categorized as an analog circuit, a digital circuit, or a mixed-signal circuit (a combination of analog circuits and digital circuits).

Analog circuits

Analog electronic circuits are those in which signals may vary continuously with time to correspond to the information being represented. Electronic equipment like voltage amplifiers, power amplifiers, tuning circuits, and radios are largely analog (with the exception of their control sections, which may be digital, especially in modern units).

There are two main types of analog circuits: series and parallel. A string of Christmas lights is a good example of a series circuit: if one goes out, they all do. In a parallel circuit, each bulb is connected to the power source separately, so if one goes out the rest still remain shining.

The basic components of analog circuits are resistors, capacitors, inductors, memristors and transistors. They may be thought of as having active independent power sources and dependent power sources. An alternative model is to take independent power sources and induction as basic electronic units; this allows modeling frequency dependent negative resistors, gyrators, negative impedance converters, and dependent sources as secondary electronic components.

Digital circuits

In digital electronic circuits, electric signals take on discrete values, which are not dependent upon time, to represent logical and numeric values. These values represent the information that is being processed. The transistor is one of the primary components used in digital circuits, and combinations of these can be used to create logic gates. These logic gates may then be used in combination to create a desired output from an input.

Larger circuits may contain several complex components, such as FPGAs or microprocessors. These along with several other components may be interconnected to create a large circuit that operates on large amount of data.

Examples of electronic equipment which use digital circuits include digital wristwatches, calculators, PDAs, and computers.

Mixed-signal circuits

Typically, mixed-signal chips perform some whole function or sub-function in a larger assembly such as the radio subsystem of a cell phone, or the read data path and laser sled control logic of a DVD player. They often contain an entire system-on-a-chip.

Examples of mixed-signal integrated circuits include data converters using delta-sigma modulation, analog-to-digital converter/digital-to-analog converter using error detection and correction, and digital radio chips. Digitally controlled sound chips are also mixed-signal circuits. With the advent of cellular technology and network technology this category now includes cellular telephone, software radio, LAN and WAN router integrated circuits.

Because of the use of both digital signal processing and analog circuitry, mixed-signal ICs are usually designed for a very specific purpose and their design requires a high level of expertise and careful use of computer aided design (CAD) tools. Automated testing of the finished chips can also be challenging. Teradyne and Agilent are the major suppliers of the test equipment for mixed-signal chips.

The particular challenges of mixed signal include:
CMOS technology is usually optimal for digital performance and scaling while bipolar transistors are usually optimal for analog performance, yet until the last decade it has been difficult to either combine these cost-effectively or to design both analog and digital in a single technology without serious performance compromises. The advent of technologies like high performance CMOS, BiCMOS, CMOS SOI and SiGe have removed many of the compromises that previously had to be made.
Testing functional operation of mixed-signal ICs remains complex, expensive and often a "one-off" implementation task
Systematic design methodologies comparable to digital design methods are far more primitive in the analog and mixed-signal arena. Analog circuit design can not generally be automated to nearly the extent that digital circuit design can. Combining the two technologies multiplies this complication.
Fast-changing digital signals send noise to sensitive analog inputs. One path for this noise is substrate coupling. A variety of techniques are used to attempt to block or cancel this noise coupling, such as fully differential amplifiers[4], P+ guard-rings [5], differential topology, on-chip decoupling, and triple-well isolation[6].