Digital Converter:

ADCs offer a significantly broader set of design trade-offs. The speed, precision, and accuracy of analog-to-digital conversion methods vary greatly. Analogue-to-Digital Converters (ADCs) enable microprocessor-controlled circuits, such as Arduinos, Raspberry Pis, and other digital logic circuits, to connect with the outside world. In the real world, analog signals have constantly changing values that come from a variety of sources and sensors that can monitor sound, light, temperature, or movement, and many digital systems interact with their surroundings by measuring the analog signals from such transducers.

While analog signals can be continuous and provide an endless number of voltage values, digital circuits function with binary signals that only have two discrete states, a logic "1" (HIGH) or a logic "0" (LOW) (LOW). So an electronic circuit that can convert between the two domains of continuously changing analog signals and discrete digital signals is required, and this is where Analogue-to-Digital Converters (A/D) come in.

Basically, an analog-to-digital converter takes a snapshot of an analog voltage at one instant in time and produces a digital output code that represents this analog voltage. The number of binary digits or bits used to represent this analog voltage value depends on the resolution of an A/D converter.

For example, a 4-bit ADC will have a resolution of one part in 15, (2⁴ – 1) whereas an 8-bit ADC will have a resolution of one part in 255, (2⁸ – 1). Thus an analog to digital converter takes an unknown continuous analog signal and converts it into an “n”- bit binary number of 2ⁿ bits.

But first, let us review the distinctions between an analog (or analog) signal and a digital signal, as illustrated:

Analogue and Digital Signals

As we can see, as the potentiometer's wiper terminal is spun between 0 and VMAX, it creates a continuous output signal (or voltage) with an endless variety of output values relative to the wiper position. There is no abrupt or step change between the two voltage levels as the potentiometer's wiper is moved from one position to the next, resulting in a continuously changing output voltage. Temperature, pressure, liquid levels, and light intensity are all examples of analogue signals.

The potentiometer wiper has been replaced in a digital circuit by a single rotary switch that is connected in turn to each junction of the series resistor chain, forming a basic potential divider network. The output voltage, VOUT, changes swiftly as the switch is spun from one position (or node) to the next, as shown, in discrete and distinct voltage increments representing multiples of 1.0 volts on each switching operation or step.

So, for example, the output voltage will be 2 volts, 3 volts, 5 volts, and so on, but NOT 2.5 volts, 3.1 volts, or 4.6 volts. Finer output voltage levels could be easily created by employing a multi-positional switch and increasing the number of resistive elements inside the potential divider network, resulting in an increase in the number of discrete switching steps.

The main distinction between an analog signal and a digital signal is that an "Analogue" quantity changes continuously over time, whereas a "Digital" quantity has discrete (step-by-step) values. "HIGH" to "LOW" or "LOW" to "HIGH"

So, how can we convert a signal with an unlimited number of values to one with unique values or steps for usage by a digital circuit?

Analogue-to-Digital Converter:

The process of converting an analog voltage signal to an equivalent digital signal can be accomplished in a variety of ways, and while many analog-to-digital converter chips, such as the ADC08xx series, are available from various manufacturers, it is possible to build a simple ADC using discrete components.

Parallel encoding, also known as flash, simultaneous, or multiple comparator converters, is a basic and straightforward method in which comparators detect distinct voltage levels and output their switching state to an encoder.

Parallel "Flash" A/D converters provide an equivalent output code for a specific n-bit resolution by using a series of interconnected but equally spaced comparators and voltage references generated by a series network of precision resistors.

The advantage of parallel or flash converters is that they are simple to build and do not require any timing clocks because any analog voltage applied to the comparator inputs is compared to a reference voltage. Take a look at the comparator circuit below.