without loss of precision. The ADC takes an analogue signal and changes it into a series of binary numbers. The ADC may be used in simple digital display devices, e. g., thermometers or light meters but it may also be used in digital sound recording and in data acquisition. However, a digital-to-analogue converter (DAC) is used to change a digital signal to an analogue signal. A DAC takes a series of binary numbers and converts it to an analogue signal. It is common to find a DAC in the gain-control system of an op-amp which in turn may be used to control digital amplifiers and filters. Design difficulty Analogue circuits are typically harder to design, requiring more skill than comparable digital systems to conceptualize. An analogue circuit is usually designed by hand because the application is built into the hardware. Digital hardware, on the other hand, has a great deal of commonality across applications and can be mass produced in a standardised form. Hardware design consists largely of repeated identical blocks and the design process can be highly automated. This is one of the main reasons that digital systems have become more common than analogue devices. However, the application of digital hardware is a function of the software/firmware and creating this is still largely a labour-intensive process. Since the early 2000s, there were some platforms that were developed which enabled analogue design to be defined using software - which allows faster prototyping. Furthermore, if a digital electronic device is to interact with the real world, it will always need an analogue interface. For example, every digital radio receiver has an analogue preamplifier as the first stage in the receive chain. Design of analogue circuits has been greatly eased by the advent of software circuit simulators such as SPICE. IBM developed their own in-house simulator, ASTAP, in the 1970s which used an unusual (compared to other simulators) sparse matrix method of circuit analysis. Circuit classification Analogue circuits can be entirely passive, consisting of resistors, capacitors and inductors. Active circuits also contain active elements such as transistors. Traditional circuits are built from lumped elements – that is, discrete components. However, an alternative is distributed-element circuits, built from pieces of transmission line. See also Analogue chip Analogue computer Analogue verification Comparison of analogue and digital recording Digital data – for a comparison with analogue References Analog circuits Electronic engineering