Output Voltage Filtering in Pulse Width Modulation Based D/A Converters

Filtering of the output voltage in pulse width modulated digital to analog converters is analyzed in the paper. Filter design is approached using methods of power electronics: linear ripple approximation and sinusoidal approximation. Filters of the first and the second order are analyzed, and the rules for their design are stated in algorithmic fashion. A table that relates the number of bits to the pole natural frequency is provided for filters of the first and the second order. Output voltage setting time is provided by another table, depending on the number of bits. Effects of the second order filter Q-factor on the setting time are discussed. It is shown that filters of the second order provide much faster transients.