Analog signals are characterized by many technical parameters, one of which is the oscillation frequency. For example, a person’s ear hears signals having a frequency in the range of 1 to 22 kHz, and visible light contains frequencies measured in billions of hertz. An example of recording an analog signal is a phonograph record. Photographs, initially black and white, and then color, are also an example of recording an analog signal.
A digital-to-analog converter almost always stands after an analog-to-digital converter (ADC), which is useful to say a few words to make it easier to understand the task that the devices under consideration solve.
The ADC converts an analog signal to a digital one. Typically, the number that corresponds to the magnitude of the signal at the time of measurement is represented by a binary code. Each measurement is performed at a specific frequency, called the quantization frequency.
Theoretically substantiated the minimum quantization frequency, providing undistorted signal recovery. This signal is without distortion and should restore the converter of the digital signal to analog at the output. The quantization frequency must be at least two maximum frequencies of the converted signal. For example, for undistorted conversion of an audio signal, a quantization frequency of 44 kHz is sufficient.
Now it is clear that the digital-to-analog converter has a binary code sequence at the input, which it must convert to the corresponding analog signal.
Reliability in work and service life are also included in the indicators, but these parameters do not depend on the principle of the DAC, but rather on the element base and build quality. Regardless of the principle of conversion, digital-to-analog converters are distinguished by characteristics such as dynamic range, accuracy of conversion and time indicators.
The dynamic range is determined for the input and output of the DAC, as the ratio of the maximum value at the input (output) to the minimum input (output) value.
One of the time parameters is the inverse of the quantization frequency, called the quantization period. It is clear that for the DAC, this value is determined by the ADC with which the signal was converted.
The main quantity characterizing the speed of the DAC is the conversion time. Here you have to choose: longer conversion time - a more accurate DAC, but its performance is less, and vice versa.
Consider some of the principles of the digital-to-analogue conversion, without giving formulas and schemes. There are two principles of conversion - serial and parallel.
The digital-to-analog converter converts the sequence of digital codes at the input into a sequence of rectangular pulses at the output. The pulse width and the subsequent interval to the next pulse are determined depending on the value of the incoming binary code. Consequently, at the output of the low-pass filter, an analog signal is obtained by the pulses received at the input with a variable period.
Parallel conversion is performed, for example, by means of resistances connected in parallel to a stable power source. The number of resistances is equal to the bit depth of the code input. The resistance value in the high order is 2 times less than in the previous low order. Each resistance circuit has a key. The input code controls the keys - where 1, current flows. Therefore, in the circuits the current will be determined by the weight of the discharge, and the digital-to-analog converter at the output has a total current that will correspond to the recorded binary code.