An electronic circuit is an electrical circuit that also contains active electronic devices such as transistors or vacuum tubes.
Electronic circuits can display highly complex behaviors, even though they are governed by the same laws as simple electrical circuits.
Electronic circuits can usually be categorized as analog, digital, or mixed-signal (a combination of analog and digital) electronic circuits.
Analog circuits
Analog electronic circuits are those in which electric signals vary continuously to correspond to the information being represented. Electronic equipment like voltage amplifiers, power amplifiers, tuning circuits, radios, and televisions are largely analog (with the exception of their control sections, which may be digital, especially in modern units).
The basic units of analog circuits are passive (resistors, capacitors, inductors) and active (independent power sources and dependent power sources). Components such as transistors may be represented by a model containing passive components and dependent sources. Another classification is to take impedance and independent sources and opamp as basic electronic components; this allows us to model 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 to represent logical and numeric values that represent the information to be processed. Transistors are used primarily as switches to make logic gates. Examples of electronic equipment which use digital circuits include digital wristwatches, calculators and PDAs, and microprocessors.
The term "circuitry" refers to collections of analog or digital circuits that are configured to perform a specific task. By comparison, a digital microcontroller that may be programmed to perform any variety of tasks is not considered to be circuitry.
Mixed-signal circuits
Mixed-signal or hybrid circuits contain elements of both analog and digital circuits. Examples include comparators, timers, PLLs, ADCs (analog-to-digital converters), and DACs (digital-to-analog converters).
An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources, and switches.
An electrical circuit is a network that has a closed loop, giving a return path for the current. A network is a connection of two or more components, and may not necessarily be a circuit.
Electrical networks that consist only of sources (voltage or current), linear lumped elements (resistors, capacitors, inductors), and linear distributed elements (transmission lines) can be analyzed by algebraic and transform methods to determine DC response, AC response, and transient response.
A network that also contains active electronic components is known as an electronic circuit. Such networks are generally nonlinear and require more complex design and analysis tools
To design any electrical circuit, either analog or digital, electrical engineers need to be able to predict the voltages and currents at all places within the circuit. Linear circuits, that is, circuits with the same input and output frequency, can be analyzed by hand using complex number theory. Other circuits can only be analyzed with specialized software programs or estimation techniques.
Circuit simulation software such as VHDL allows engineers to design circuits without the time, cost and risk of error involved in building circuit prototypes.
Electrical laws
A number of electrical laws apply to all electrical networks. These include
Kirchhoff's current law: The sum of all currents entering a node is equal to the sum of all currents leaving the node.
Kirchhoff's voltage law: The directed sum of the electrical potential differences around a circuit must be zero.
Ohm's law: The voltage across a resistance is equal to the product of the resistance and the current flowing through it.
Norton's theorem: Any network of voltage and/or current sources and resistors is electrically equivalent to an ideal current source in parallel with a single resistor.
Thévenin's theorem: Any network of voltage and/or current sources and resistors is electrically equivalent to a single voltage source in series with a single resistor.
See also Analysis of resistive circuits.
Other more complex laws may be needed if the network contains nonlinear or reactive components. Non-linear self-regenerative heterodyning systems can be approximated. Applying these laws results in a set of simultaneous equations that can be solved either by hand or by a computer.
Network simulation software
More complex circuits can be analyzed numerically with software such as SPICE or symbolically using software such as SapWin.
Linearization around operating point
When faced with a new circuit, the software first tries to find a steady state solution, that is, one where all nodes conform to Kirchhoff's Current Law and the voltages across and through each element of the circuit conform to the voltage/current equations governing that element.
Once the steady state solution is found, the operating points of each element in the circuit are known. For a small signal analysis, every non-linear element can be linearized around its operation point to obtain the small-signal estimate of the voltages and currents. This is an application of Ohm's Law. The resulting linear circuit matrix can be solved with Gaussian elimination.
Piecewise-linear approximation
Software such as the Simulink toolbox PLECS uses piecewise-linear approximation of the equations governing the elements of a circuit. The circuit is treated as a completely linear network of ideal diodes. Every time a diode switches from on to off or vice versa, the configuration of the linear network changes. Adding more detail to the approximation of equations increases the accuracy of the simulation, but also increases its running time
Analogue electronics (or analog in American English) are those electronic systems with a continuously variable signal. In contrast, in digital electronics signals take only one of two different levels. The term "analog" describes the proportional relationship between a signal and a voltage or current that represented the signal.
An analogue signal uses some property of the medium to convey the signal's information. For example, an aneroid barometer uses angular position as the signal to convey pressure information. Electrical signals may represent information by changing their voltage, current, frequency, or total charge. Information is converted from some other physical form ( such as sound, light, temperature, pressure, position) to an electrical signal by a transducer.
The signals take any value from a given range, and each unique signal value represents different information. Any change in the signal is meaningful, and each level of the signal represents a different level of the phenomenon that it represents. For example, suppose the signal is being used to represent temperature, with one Volt representing one degree Celsius. In such a system 10 Volts would represent 10 degrees, and 10.1 Volts would represent 10.1 degrees.
Another method of conveying an analog signal is to use modulation. In this, some base carrier signal has one of its properties altered: amplitude modulation (AM) involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation (FM) changes the frequency. Other techniques, such as changing the phase of the carrier signal are also used. In an analog sound recording, the variation in pressure of a sound striking a microphone creates a corresponding variation in the current passing through it or voltage across it. An increase in the volume of the sound causes the fluctuation of the current or voltage to increase proportionally while keeping the same waveform or shape.
Mechanical, pneumatic, hydraulic and other systems may also use analog signals.
Inherent noise
The primary disadvantage of analog signaling is that any system has noise; that is, random disturbances or variations in it. Since all variations of an analog signal are significant, any disturbance is equivalent to a change in the original signal and so appears as noise. As the signal is copied and re-copied, or transmitted over long distances, these random variations become dominant and lead to signal degradation. Electrically these disturbances are reduced by shielding, and using low noise amplifiers.
The effects of random noise can make signal loss and distortion impossible to recover, since amplifying the signal to recover attenuated parts of the signal often generates more noise and amplifies the noise as well.
Analogue vs. digital electronics
Since the information is encoded differently in analog and digital electronics, the way they process a signal is consequently different. All operations that can be performed on an analog signal such as amplification, filtering, limiting, and others, can also be duplicated in the digital domain.
The first electronic devices invented and mass produced were analog. The use of microelectronics has reduced the cost of digital techniques and now make digital methods feasible and cost-effective.
The main differences between analog and digital electronics are listed below:
Noise
Because of the way information is encoded in analog circuits, they are much more susceptible to noise than digital circuits, since a small change in the signal can represent a significant change in the information present in the signal and can cause the information present to be lost. Since digital signals take only one of two different values, a disturbance would have to be about one-half the magnitude of the digital signal to cause an error; this property of digital circuits can be exploited to make signal processing noise-resistant. In digital electronics, because the information is quantized, as long as the signal stays inside a range of values, it represents the same information. Digital circuits use this principle to regenerate the signal at each logic gate, lessening or removing noise.
Precision
A number of factors affect how precise a signal is, mainly the noise present in the original signal and the noise added by processing. See Signal-to-noise ratio. Fundamental physical limits such as the shot noise in components limits the resolution of analog signals. In digital electronics additional precision is obtained by using additional digits to represent the signal; the practical limit in the number of digits is determined by the performance of the analog to digital converters, since digital operations can usually be performed without loss of precision.
Design Difficulty
Digital systems are much easier and smaller to design than comparable analog circuits. This is one of the main reasons why digital systems are more common than analog. An analog circuit must be designed by hand, and the process is much less automated than for digital systems. Also, because the smaller the integrated circuit (chip) the cheaper it is, and digital systems are much smaller than analog, digital is cheaper to manufacture.
An electronic circuit is an electrical circuit that also contains active electronic devices such as transistors or vacuum tubes.
Electronic circuits can display highly complex behaviors, even though they are governed by the same laws as simple electrical circuits.
Electronic circuits can usually be categorized as analog, digital, or mixed-signal (a combination of analog and digital) electronic circuits.
Analog circuits
Analog electronic circuits are those in which electric signals vary continuously to correspond to the information being represented. Electronic equipment like voltage amplifiers, power amplifiers, tuning circuits, radios, and televisions are largely analog (with the exception of their control sections, which may be digital, especially in modern units).
The basic units of analog circuits are passive (resistors, capacitors, inductors) and active (independent power sources and dependent power sources). Components such as transistors may be represented by a model containing passive components and dependent sources. Another classification is to take impedance and independent sources and opamp as basic electronic components; this allows us to model 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 to represent logical and numeric values that represent the information to be processed. Transistors are used primarily as switches to make logic gates. Examples of electronic equipment which use digital circuits include digital wristwatches, calculators and PDAs, and microprocessors.
The term "circuitry" refers to collections of analog or digital circuits that are configured to perform a specific task. By comparison, a digital microcontroller that may be programmed to perform any variety of tasks is not considered to be circuitry.
Mixed-signal circuits
Mixed-signal or hybrid circuits contain elements of both analog and digital circuits. Examples include comparators, timers, PLLs, ADCs (analog-to-digital converters), and DACs (digital-to-analog converters).
An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources, and switches.
An electrical circuit is a network that has a closed loop, giving a return path for the current. A network is a connection of two or more components, and may not necessarily be a circuit.
Electrical networks that consist only of sources (voltage or current), linear lumped elements (resistors, capacitors, inductors), and linear distributed elements (transmission lines) can be analyzed by algebraic and transform methods to determine DC response, AC response, and transient response.
A network that also contains active electronic components is known as an electronic circuit. Such networks are generally nonlinear and require more complex design and analysis tools
To design any electrical circuit, either analog or digital, electrical engineers need to be able to predict the voltages and currents at all places within the circuit. Linear circuits, that is, circuits with the same input and output frequency, can be analyzed by hand using complex number theory. Other circuits can only be analyzed with specialized software programs or estimation techniques.
Circuit simulation software such as VHDL allows engineers to design circuits without the time, cost and risk of error involved in building circuit prototypes.
Electrical laws
A number of electrical laws apply to all electrical networks. These include
Kirchhoff's current law: The sum of all currents entering a node is equal to the sum of all currents leaving the node.
Kirchhoff's voltage law: The directed sum of the electrical potential differences around a circuit must be zero.
Ohm's law: The voltage across a resistance is equal to the product of the resistance and the current flowing through it.
Norton's theorem: Any network of voltage and/or current sources and resistors is electrically equivalent to an ideal current source in parallel with a single resistor.
Thévenin's theorem: Any network of voltage and/or current sources and resistors is electrically equivalent to a single voltage source in series with a single resistor.
See also Analysis of resistive circuits.
Other more complex laws may be needed if the network contains nonlinear or reactive components. Non-linear self-regenerative heterodyning systems can be approximated. Applying these laws results in a set of simultaneous equations that can be solved either by hand or by a computer.
Network simulation software
More complex circuits can be analyzed numerically with software such as SPICE or symbolically using software such as SapWin.
Linearization around operating point
When faced with a new circuit, the software first tries to find a steady state solution, that is, one where all nodes conform to Kirchhoff's Current Law and the voltages across and through each element of the circuit conform to the voltage/current equations governing that element.
Once the steady state solution is found, the operating points of each element in the circuit are known. For a small signal analysis, every non-linear element can be linearized around its operation point to obtain the small-signal estimate of the voltages and currents. This is an application of Ohm's Law. The resulting linear circuit matrix can be solved with Gaussian elimination.
Piecewise-linear approximation
Software such as the Simulink toolbox PLECS uses piecewise-linear approximation of the equations governing the elements of a circuit. The circuit is treated as a completely linear network of ideal diodes. Every time a diode switches from on to off or vice versa, the configuration of the linear network changes. Adding more detail to the approximation of equations increases the accuracy of the simulation, but also increases its running time
Analogue electronics (or analog in American English) are those electronic systems with a continuously variable signal. In contrast, in digital electronics signals take only one of two different levels. The term "analog" describes the proportional relationship between a signal and a voltage or current that represented the signal.
An analogue signal uses some property of the medium to convey the signal's information. For example, an aneroid barometer uses angular position as the signal to convey pressure information. Electrical signals may represent information by changing their voltage, current, frequency, or total charge. Information is converted from some other physical form ( such as sound, light, temperature, pressure, position) to an electrical signal by a transducer.
The signals take any value from a given range, and each unique signal value represents different information. Any change in the signal is meaningful, and each level of the signal represents a different level of the phenomenon that it represents. For example, suppose the signal is being used to represent temperature, with one Volt representing one degree Celsius. In such a system 10 Volts would represent 10 degrees, and 10.1 Volts would represent 10.1 degrees.
Another method of conveying an analog signal is to use modulation. In this, some base carrier signal has one of its properties altered: amplitude modulation (AM) involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation (FM) changes the frequency. Other techniques, such as changing the phase of the carrier signal are also used. In an analog sound recording, the variation in pressure of a sound striking a microphone creates a corresponding variation in the current passing through it or voltage across it. An increase in the volume of the sound causes the fluctuation of the current or voltage to increase proportionally while keeping the same waveform or shape.
Mechanical, pneumatic, hydraulic and other systems may also use analog signals.
Inherent noise
The primary disadvantage of analog signaling is that any system has noise; that is, random disturbances or variations in it. Since all variations of an analog signal are significant, any disturbance is equivalent to a change in the original signal and so appears as noise. As the signal is copied and re-copied, or transmitted over long distances, these random variations become dominant and lead to signal degradation. Electrically these disturbances are reduced by shielding, and using low noise amplifiers.
The effects of random noise can make signal loss and distortion impossible to recover, since amplifying the signal to recover attenuated parts of the signal often generates more noise and amplifies the noise as well.
Analogue vs. digital electronics
Since the information is encoded differently in analog and digital electronics, the way they process a signal is consequently different. All operations that can be performed on an analog signal such as amplification, filtering, limiting, and others, can also be duplicated in the digital domain.
The first electronic devices invented and mass produced were analog. The use of microelectronics has reduced the cost of digital techniques and now make digital methods feasible and cost-effective.
The main differences between analog and digital electronics are listed below:
Noise
Because of the way information is encoded in analog circuits, they are much more susceptible to noise than digital circuits, since a small change in the signal can represent a significant change in the information present in the signal and can cause the information present to be lost. Since digital signals take only one of two different values, a disturbance would have to be about one-half the magnitude of the digital signal to cause an error; this property of digital circuits can be exploited to make signal processing noise-resistant. In digital electronics, because the information is quantized, as long as the signal stays inside a range of values, it represents the same information. Digital circuits use this principle to regenerate the signal at each logic gate, lessening or removing noise.
Precision
A number of factors affect how precise a signal is, mainly the noise present in the original signal and the noise added by processing. See Signal-to-noise ratio. Fundamental physical limits such as the shot noise in components limits the resolution of analog signals. In digital electronics additional precision is obtained by using additional digits to represent the signal; the practical limit in the number of digits is determined by the performance of the analog to digital converters, since digital operations can usually be performed without loss of precision.
Design Difficulty
Digital systems are much easier and smaller to design than comparable analog circuits. This is one of the main reasons why digital systems are more common than analog. An analog circuit must be designed by hand, and the process is much less automated than for digital systems. Also, because the smaller the integrated circuit (chip) the cheaper it is, and digital systems are much smaller than analog, digital is cheaper to manufacture.
