What is Analog-to-Digital and Digital-to-Analog Converters (ADC and DAC)?
Analog-to-digital and digital-to-analog converters. The first converts the analog signal into a digital value of the amplitude, the second performs the inverse conversion. In the English language literature, the terms ADC and DAC are used, and the combined converter is called a codec (codec).
The working principle of the ADC is to measure the level of the input signal and output the result in digital form. As a result of ADC operation, a continuous analog signal is converted to a pulse signal, with a simultaneous measurement of the amplitude of each pulse. The DAC receives a digital value of the amplitude at the input and outputs voltage or current pulses of the required magnitude at the output, which the integrator (analog filter) located behind it converts into a continuous analog signal.
In order for the ADC to function properly, the input signal must not change during the conversion time, so a sample hold circuit is usually placed at its input, which captures the instantaneous signal level and holds it for the entire time. Of conversation. A similar circuit can also be installed at the DAC output, suppressing the effect of transient processes within the DAC on the output signal parameters.
With time sampling, the spectrum of the pulse signal received in its lower part 0..Fa repeats the spectrum of the original signal, and above it contains a series of reflections (aliases, mirror spectra), which are located around the sampling frequency Fd and its harmonics (sidebands). In this case, the first reflection of the spectrum from the frequency Fd in the case of Fd = 2Fa is located directly behind the original signal band, and requires an analog filter (anti-alias filter) with a high cutoff slope to delete it. In the ADC, this filter is installed at the input to eliminate spectral overlap and its interference, and in the DAC, at the output, to suppress the supra-tone noise introduced by time sampling in the output signal.
