MAX5894
The programmable interpolation filters multiply the
MAX5894 input data rate by a factor of 2x, 4x, or 8x to
separate the reconstructed waveform spectrum and the
DAC image. The original spectral images, appearing at
around multiples of the input data rate, are attenuated
by the internal digital filters. This feature provides three
benefits:
1) Image separation reduces complexity of analog
reconstruction filters.
2) Lower input data rates eliminate board-level high-
speed data transmission.
3) Sin(x)/x rolloff is reduced over the effective bandwidth.
Figure 9 illustrates a practical example of the benefits
when using the MAX5894 in 2x, 4x, and 8x interpolation
modes with the third filter configured as a lowpass filter.
With no interpolation filter, the first image signal appears
in the second Nyquist zone between f
S
/2 and f
S
. The first
interpolating filter removes this image. In fact, all of the
14-Bit, 500Msps, Interpolating and Modulating
Dual DAC with CMOS Inputs
20 ______________________________________________________________________________________
Figure 9. Spectral Representation of Interpolating Filter Responses (Output Frequencies are Relative to the Data Input Frequency, f
S
)
