Digital-to-analog converter: description, operating principle, application.

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 an analog signal recording can be a gramophone record. Photos, first black and white, and, then, and color - also an example of recording an analog signal.

A digital-to-analog converter almost always stands after an analog-to-digital converter (ADC), about which it is useful to say a few words, in order to understand the problem solved by the devices we are considering.

The ADC converts an analog signal to a digital one. Usually the number that corresponds to the value of the signal at the time of its measurement is represented by a binary code. Each measurement is performed at a certain frequency, called the quantization frequency.

The minimum quantization frequency is theoretically justified, ensuring undisturbed signal reconstruction. This signal is without distortion and must restore the converter of the digital signal to analog output. The quantization frequency must be at least two maximum frequencies of the converted signal. For example, for an undistorted conversion of a sound 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 operation and lifetime 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, conversion accuracy and timing.

The dynamic range is defined for the input and output of the DAC, as the ratio of the maximum value at the input (at the 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 set by the ADC, by means of which the signal was converted.

The basic value, which characterizes the speed of the DAC, is the conversion time. Here you have to choose: a longer conversion time - a more accurate DAC, but less of its speed, and vice versa.

Let us consider some principles of the "digit-analogue" transformation, without giving formulas and schemes. There are two principles of transformation - sequential and parallel.

The sequence of digital codes on the input digital-to-analog converter converts 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. Therefore, at the output of the low-pass filter, an analog signal is obtained, according to the pulses arriving at the input with a variable period.

Parallel conversion is performed, for example, by using resistances connected in parallel to a stable power supply. The number of resistances is equal to the bit rate of the incoming code. The magnitude of the resistance in the high-order discharge is 2 times less than in the preceding lower order. In the chain of each resistance there is a key. The input code controls the keys - where 1, the current passes. Therefore, in 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.