AD9154 datasheet(76/124 Pages) AD

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AD9154

Data Sheet

Rev. C | Page 76 of 124

NORMAL AND MIX MODES OF OPERATION

INPUT

DATA

DACCLK

TWO-SWITCH

DAC OUTPUT

QUAD-SWITCH

DAC OUTPUT

(NORMAL MODE)

D9 D10

Figure 81. Two-Switch and Quad-Switch DAC Waveforms

The DAC cores have a quad-switch architecture. During each

DACCLK cycle, one input sample is presented twice. Figure 81

shows the time domain DAC core output when operating in

normal mode (default). In normal mode, the same output signal

is presented twice during each DAC clock cycle. The DAC

output mode is selected using Bit 0 of Register 0x04A.

Figure 82 depicts a time domain DAC output signal in mix mode.

During each DACCLK cycle, the input sample is presented at

the output on the rising edge and the inverse of the input sample is

presented at the output on the falling edge of DACCLK.

INPUT

DATA

DACCLK

QUAD-SWITCH

DAC OUTPUT

(

fS MIX MODE)

–D6

–D7

–D8

–D9

–D10

D10

–D1

–D2

–D3

–D4

–D5

D9 D10

Figure 82. Mix Mode Waveform

Figure 83 is a depiction of the uncompensated DAC SINC roll-off

for normal (or baseband) mode and for mix mode. In normal

mode, the first Nyquist zone copy of the output signal has the

highest amplitude. The output sampling images in the second

and third Nyquist zones are attenuated. In MIX mode, the

second and third Nyquist zone sampling images are emphasized,

and the first Nyquist zone signal is attenuated.

This ability to change modes provides the user the flexibility to

place a carrier anywhere in the first three Nyquist zones, depending

on the operating mode selected. Switching between baseband

and mix mode reshapes the sinc roll-off inherent at the DAC

output.

NORMALIZED FREQUENCY RELATIVE TO

fDACCLK (Hz)

1.50

1.25

1.00

0.75

0.50

0.25

–35

–30

–25

–20

–15

–10

–5

FIRST

NYQUIST ZONE

SECOND

NYQUIST ZONE

THIRD

NYQUIST ZONE

MIX MODE

BASEBAND

MODE

Figure 83. Sinc Roll-Off for Normal Mode and Mix-Mode Operation

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