DAC39RFS10 datasheet(49/178 Pages) TI

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8.3.1.1 NRZ Mode

Non-return-to-zero (NRZ) mode is the standard zero-order hold mode. The timing diagram for NRZ mode is

given in Figure 8-3. The sample is output from the DAC on the DACCLK rising edge and held until the rising

edge. This output waveform can be thought of as a rectangular filter in time domain resulting in a sinc response

in the frequency domain. The result is a frequency response that has significant power loss in the 2nd and 3rd

Nyquist zones and a null at the sampling rate and is meant for 1st Nyquist zone operation only. A plot of the

frequency response of NRZ mode is shown in Figure 8-4.

DACCLK+

DACCLKt

DAC Output

(Sine Wave)

+IFS

-IFS

tpd

TS = 1/FDACCLK

Figure 8-3. NRZ Mode Timing Diagram

FOUT/FDAC

0.5

1.5

-50

-40

-30

-20

-10

NRZm

Figure 8-4. NRZ Mode Output Frequency Response

8.3.1.2 RTZ Mode

Return-to-zero (RTZ) mode is similar to the standard zero-order hold mode used by DACs, however the

response adds a return-to-zero pulse for the second half of the sample period. The timing diagram for RTZ

mode is given in Figure 8-5. This output waveform can be thought of as a rectangular filter in time domain that

is half the length of that which is used in NRZ mode, resulting in a sinc response that is expanded by two times

in the frequency domain. The result is a frequency response with less power loss in the 2nd Nyquist zone and

a null at twice the sampling rate. It can be used for 1st and 2nd Nyquist zone applications. The return-to-zero

pulse provides flatter response through the first Nyquist zone at a tradeoff of 6-dB lower peak power. A plot of

the frequency response of RTZ mode is shown in Figure 8-6.

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DAC39RF10

SBASAC8 – MAY 2023

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