DAC5674

SLWS148 − SEPTEMBER 2003

www.ti.com

16

Low-Pass/High-Pass 4x 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

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

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.

80 dB

80 dB

Input Spectrum

Output DUC

Fdata

0IF

2Fdata

3Fdata

4Fdata

First

2x Interpolation

Filter

Fdata

0IF

2Fdata

3Fdata

4Fdata

Spectrum After

2x Interpolation

Fdata

0IF

2Fdata

3Fdata

4Fdata

Second

2x Interpolation

Filter

Fdata

0IF

2Fdata

3Fdata

4

Fdata

Spectrum After

4x Interpolation

0IF

2Fdata

4Fdata

=

Fupdate

Fdata)IF

3Fdata*IF

Transition Band

+(Fdata*2IF) Fdata

Normalized Transition Band

+(1*2 0.4) 1+0.2

Transition Band

+(Fdata*IF) Fdata

Normalized Transition Band

+(1*0.4) 1+0.6

Fdata

3Fdata

Figure 17. Low-Pass 2x, High-Pass 2x Interpolation Filter Operation