An analog-to-digital converter is an electronic device, component, or part of a device for converting analog input signals into a digital data stream, which can then be further processed or stored. A variety of conversion processes are in use. The counterpart is the digital-to-analog converter (DAC).
Analog-to-digital converters are elementary components of almost all devices of modern communication and consumer electronics such as mobile phones, digital cameras, or camcorders. In addition, they are used for data acquisition in research and industrial production plants, in machines and technical everyday objects such as motor vehicles or household appliances.
An ADC converts a time and value continuous input signal (analog signal) into a discrete-time and discrete-value sequence of digitally represented values. Due to a finite number of possible output values, quantization always takes place. The result of an AD conversion can be imagined in a signal-time diagram in a sequence of dots with stepped horizontal and vertical distances. The main parameters of an ADC are its bit depth and its maximum sampling rate. The conversion time is usually much smaller than the reciprocal of the sampling rate.
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Even the bit depth of an AD converter limits the maximum possible accuracy with which the input signal can be converted. The usable accuracy is lower due to further sources of error of the ADC. In addition to methods that are as fast as possible, there are also slow methods for suppressing interference coupling.
There are a large number of methods that can be used to convert analog signals into digital signals. The following are the most important principles. In all examples, the electrical voltage is used as the input variable. The internal process of an implementation is controlled by the building blocks themselves. For cooperation with a computer, an ADC can be equipped with a start input for the request for a new conversion, with a busy output for reporting the ongoing implementation and with bus-compatible data outputs for reading out the resulting digital value.
Important Parameters Related to Analog-to-Digital Converter (ADC)
- Sample Rate—Indication of the frequency of conversion.
- Resolution—Width of the steps (also known as the number of steps or number of digits) used to represent the output signal.
- Zero point error – The converter characteristic curve (without taking into account the gradation) is shifted. The digital value differs from the correct value by a constant amount.
- Sensitivity error, gain error – The converter characteristic (without taking into account the gradation) is twisted (slope error). The digital value differs from the correct value by a constant percentage of the input variable.
- Integral nonlinearity – The error caused by the fact that a converter characteristic taken as linear is not rectilinear (without taking into account the gradation).
- Differential nonlinearity – deviation of the width of the implementation stages from each other
- Quantization characteristic curve – Graphical representation of the relationship between the digital output values and the analog input values, e.g. following a linear or logarithmic curve.
- Quantization error – Deviation of the output signal from the functional (continuous) curve due to the limited resolution.
- Missing code – When a continuous increase in the input signal does not result in consecutively numbered values of the output code, but a value is skipped; possible with a differential nonlinearity of more than 1 LSB.
- Latency – Propagation delay from the acquisition of the input signal to the provision of the associated output signal.
- Signal-to-noise ratio in dB
- Dynamic range in dB
- Dynamic parameters
- Intermodulation interference in dB
- Operating current – the faster the conversion electronics have to work, the higher their supply current (self-heating) becomes.
