Analog and Digital Conversion/DAC Converters
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DAC Converter Steps 
An Digital to Analog converter (DAC) takes a digital signal and converts it, through a mathematical function, into an analog signal. Again, the DAC may be implemented in a number of ways, but conceptually it contains two steps:
- Convert each time step of the digital signal into an "impulse" with the appropriate energy. In a real system, this could be accomplished by creating short pulses that have the same voltage, but whose total power is modified by changing the pulse length. This pulse train produces a signal whose frequency response is periodic (and theoretically extends to infinity).
- Apply a low-pass filter or an appropriate holding circuit to the time sequence of impulses. This removes all of the high-frequency periodicities, leaving only the reconstructed signal.