Figure 22 shows a simplified block diagram of the AD9774. The
AD9774 is a complete, 4′ oversampling, 14-bit DAC that includes
two cascaded 2′ interpolation filters, a phase-locked loop
(PLL) clock multiplier, and a 1.20 Volt bandgap voltage reference.
The 14-bit DAC provides two complementary current
outputs whose full-scale current is determined by an external
resistor. Input data that is latched into the edge-triggered input
latches is first interpolated by a factor of four by the interpolation
filters before updating the 14-bit DAC. A PLL clock multiplier
produces the necessary internally synchronized 1′, 2′ and 4′
clocks from an external reference. The AD9774 can support
input data rates as high as 32 MSPS, corresponding to a DAC
update rate of 128 MSPS.