DAC5686IPZP datasheet(34/53 Pages) TI1

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Digital Filters

f/fDATA

−160

−140

−120

−100

−80

−60

−40

−20

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

G023

f/fDATA

−160

−140

−120

−100

−80

−60

−40

−20

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

G024

DAC5686

SLWS147F – APRIL 2003 – REVISED JUNE 2009 ............................................................................................................................................................ www.ti.com

The PHSTR transition has a setup and hold time relative to the DAC output sample clock (ts_PHSTR and th_PHSTR)

equal to 50% of the DAC output sample clock period up to a maximum of 1 ns. At 500 MHz, the setup and hold

times are therefore 0.5 ns. The PHSTR signal can remain high after synchronization, or can return low. A new

low-to-high transition resynchronizes the input clock. Note that the PHSTR transition also resets the NCO

accumulator.

Figure 39 through Figure 42 show magnitude spectrum responses for 2×, 4×, 8×, and 16× FIR interpolation

filtering. The transition band is from 0.4 to 0.6 fDATA with < 0.002-dB pass-band ripple and > 80-dB stop-band

attenuation for all four configurations. The filters are linear phase. The sel field in register config_lsb selects the

interpolation filtering rate as 2×, 4×, 8×, or 16×; interpolation filtering can be completely bypassed by setting

fullbypass in register config_lsb.

Figure 43 shows the spectral correction of the DAC sinx/x rolloff achieved with use of inverse sinc filtering.

Pass-band ripple from 0 to 0.4 fDATA is < 0.03 dB. Inverse sinc filtering is enabled by sinc in register

config_msb.

MAGNITUDE

FREQUENCY

Figure 39. Magnitude Spectrum for

Figure 40. Magnitude Spectrum for

2× Interpolation (dB)

4× Interpolation (dB)

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