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

Analog signals are characterized by manytechnical 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 can be a gramophone record. Photos, first black and white, and, then, and color - also an example of recording an analog signal.

The digital-to-analog converter is practicallyalways stands after the analog-to-digital converter (ADC), which is useful to say a few words, so that the problem solved by the devices we are considering is more understandable.

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 frequency is theoretically justifiedquantization, ensuring undistorted signal recovery. 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.

It is now clear that the D / A 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 theindicators, 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 determined 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 value,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 quantity that characterizesthe 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.

Sequence of digital input codesThe D / A 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,with the help of resistors connected in parallel to a stable power source. 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.