Datasheet

Digital Filters
f/f
DATA
−160
−140
−120
−100
−80
−60
−40
−20
0
20
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Magnitude – dB
G023
f/f
DATA
−160
−140
−120
−100
−80
−60
−40
−20
0
20
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Magnitude – dB
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 (t
s_PHSTR
and t
h_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 f
DATA
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 f
DATA
is < 0.03 dB. Inverse sinc filtering is enabled by sinc in register
config_msb.
MAGNITUDE MAGNITUDE
vs vs
FREQUENCY FREQUENCY
Figure 39. Magnitude Spectrum for Figure 40. Magnitude Spectrum for
2 × Interpolation (dB) 4 × Interpolation (dB)
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