DAC5674 Datasheet, PDF (16/39 Pages) Texas Instruments – 14BIT 400 MSPS, 2 X/ 4X INTERPOLATING COMMS DAC DIGITAL TO ANALOG CONVERTER

DAC5674
SLWS148A − SEPTEMBER 2003 − REVISED OCTOBER 2005
www.ti.com
Low-Pass/High-Pass 4y Interpolation Filter Operation
By configuring the low-pass filters as high-pass filters, the user can select one of the images present at multiples
of the clock. Figure 17 shows the low-pass/high-pass filter response. After digital filtering, the DAC transmits
at 2F_data − IF and 2F_data + IF. This configuration is equivalent to sub-sampling receiver systems where a
high-speed analog-to-digital converter samples high IF frequencies with relatively low sample rates, resulting
in low (output) data rates.
The placement of the IF in the first Nyquist zone combined with the DAC5674 input data determines the final
output signal frequency. For F_data = 100 MSPS and a fundamental IF of 0.4 × F_data = 40 MHz, this would translate
into images located at 160 MHz and 240 MHz. Note that this is the equivalent of mixing a 40-MHz analog IF
signal with a 200-MHz sine wave. By doing this, the first mixer in the total transmission chain is eliminated.
Input Spectrum
Output of DUC
1st 2x
interpolation
filter
Fdata
80 dB of
Attenuation
Fdata
Fdata
Fdata
Spectrum after
2x interpolation
2nd 2x
interpolation
filter
HPF filters out
unwanted
image
Spectrum after
4x interpolation
Fdata
Fdata
Fdata
Fdata
Fdata
Fdata
Fdata
Fdata
Fdata
Figure 17. Low-Pass/High-Pass 4y Interpolation Filter Operation
Fdata
HPF filters out
unwanted
image
Fdata
Fdata
=
Fdac
16