DA converters(D/A), digital-to- analog converters or digital-to-analog converters (DAU), are electronic circuits for converting a digitally coded quantity into an analog current or voltage waveform. The ideal DA converter generates the analog output voltage from the binary input code, with a linear relationship between the two quantities.
The structure of digital-to-analog converters
The entire conversion of a digital word into an analog signal takes place in several stages. First, the digital word is converted into individual analog voltage values in the actual DA converter. R-2R converters, pulse width modulation( PWM) converters or others are used for this conversion. The voltage at the output has a staircase shape. In the following stage, the staircase-shaped signal is smoothed. This can be done by a sample and hold (S/H) circuit or with filters.
Resampling in a sample and hold circuit reduces the pulse width. Then the stepped signal is reconstructed and smoothed in a low-pass filter, which must have a cutoff frequency equal to half the sampling frequency. Filtering cuts off the higher frequencies and harmonics, as well as the frequencies that are present around the sampling rate.
Important parameters of DA-converters
Important parameters of D/A converters include accuracy, which depends on the data word length of the digital input signal, conversion speed and conversion time, and noise margin and distortion. As with the AD converter, the signal-to-noise ratio of the D/A converter depends on the word length of the digital word, while the distortion factor depends on the converter linearity. The resolution of DA converters on the market is between 8 bits and 24 bits; in exceptional cases, 32 bits can also be achieved.