Mixed-Signal Digital to Analog Reconstruction Filter Criteria

DAC discrete-sample creation will produce images of the base-band signal at integer multiples of the sampling frequency, f_s.  The DAC sampling process is typically zero-order hold, which means that the sample value is held constant until the next sample value.  The zero-order hold is a rectangular pulse, which has a Fourier transform given by the sinc (sin(пf/f_s)/пf/f_s) function. Thus, the zero-order hold process attenuates the sample spectrum amplitude by the sinc function. This sinc attenuation is very mild, with a 1/f roll-off.  Often, the image filtration must be supplemented by additional analog filtration, called a "reconstruction filter" to meet out-of-band requirements for interference concerns or to meet regulatory compliance limits.  The reconstruction filter is often multi-order and must also not degrade the pass-band response (amplitude, phase, delay).  Inverse-sinc correction can be added to correct much of the in-band sinc attenuation due to the zero-order hold.  Design of the reconstruction filter can be quite involved.  Over-sampling DACs can reduce the cost and complexity of the reconstruction filter in appropriate applications.

The analog experts at Analog Advice can assist you with mixed-signal requirements and design, including DAC and reconstruction filter.