analog and digital circuitry

[PG1995]

Hi

As far as I know there are two kinds of circuitries in electronics: analog, digital. I have a little bit of knowledge of analog circuitry (at least I understand the big picture). For instance, this circuit is analog one. Where does one use a digital circuit, like under what requirements? Can every circuit be made in two ways - i.e. in an analog way, or, in a digital way? Can you transform the linked circuit into a digital one?

Could you please provide me with some simple circuit which can be built both analog-ally and digitally in Multisim10 or Circuit Wizard format (otherwise, a simple image will also do)? Many, many thanks.

Regards
PG

 

[crutschow]

You are really rather trying to combine apples and oranges and get what, applanges?

Analog circuits are continuous in nature with no discrete levels. Thus the circuit you show is analog since it varies as the sine-wave input varies on a continuous basis. It's a power rectifier circuit and can not be readily changed to digital, although switching regulators are a type of digital power circuit.

Digital circuits are used in all modern computers and most signal processing. Digital circuits have discrete steps. The typical digital circuit is binary and is either 1 (on) or 0 (off). If it's been generated by a transistor the transistor is fully on or fully off. There is no in between. In a computer the digital words are represented by a series of ones and zeros. The common minimum word is a byte or 8-bits. Modern PCs use a word length of 64-bits or 8 bytes. The big advantage of a digital circuit is that once the information or signal is digitized it suffers no degradation from noise or other factors and can be stored indefinitely. Think TiVo or digital cameras.

In modern electronics the analog audio or video signal is usually converted to discrete steps using an analog-to-digital converter. It takes a series of samples at equal points along the analog waveform and each sample is converted into a digital word. The length of the digital word determines the resolution of the samples. For example 8-bits would give 256 steps, so the minimum sample resolution would be 1/256 of the full-scale voltage range of the particular converter you are using. How rapidly you take each sample determines the upper frequency limit of the analog signal you are digitizing. The Nyquist rule is that you need at least two times the number of samples as the highest analog frequency of interest.

The closest I can think of to a circuit that can be made both analog or digital is a simple common-emitter transistor. If the collector if an NPN is biased at about 1/2 the supply voltage with collector resistor to V+ than it can amplify small analog signals applied to the base. If you apply a larger square-wave to the base then the transistor will turn on and off generating a (digital) square-wave.

 

[cr0sh]

Technically, there's no such thing as a "digital circuit". Rather, they are composed of analog circuits driven to "extremes" (ie, transistors, rather than smoothly amplifying an analog signal, are instead driven to "saturation" to represent a "HIGH" level). We can pretend such circuits aren't analog - but the analog nature of the circuits begins to show up when driving them at higher frequencies (or closer tolerances), for instance...