Datasheet

DAC5681Z
www.ti.com SLLS865F –AUGUST 2007–REVISED AUGUST 2012
Table 5. FIR0 and FIR1 Digital Filter Taps
TAP# COEFF TAP# COEFF
1, 47 –5 2, 46 0
3, 45 18 4, 44 0
5, 43 –42 6, 42 0
7, 41 85 8, 40 0
9, 39 –158 10, 38 0
11, 37 272 12, 36 0
13, 35 –444 14, 34 0
15, 33 704 16, 32 0
17, 31 –1106 18, 30 0
19, 29 1795 20, 28 0
21, 27 –3295 22, 26 0
23, 25 10368 — —
24 16384 — —
DUAL-CHANNEL REAL UPCONVERSION
Each DAC5681Z digital filter has a normal Low Pass (LP) characteristic, but can be configured to perform a High
Pass (HP) function by mixing a 1 –1....sequence at the output of the FIR to invert the spectrum. The mixing
mode for each filter is controlled by FIR0_HP and FIR1_HP bits in register CONFIG2. With 1X4 interpolation and
cascaded combinations of HP and LP filter modes, the output frequency response will be digitally shifted or
upconverted. The wide bandwidths of both FIR0 and FIR1 (40% bandpass) provide options for setting six
different frequency ranges, listed in Table 6. With the High Pass (1X2 HP mode), High Pass/Low Pass (1X4
HP/LP mode) and Low Pass/High Pass (1X4 LP/HP mode) settings, the upconverted signal is spectrally inverted.
Table 6. Dual-Channel Real Upconversion Options
FIR0, FIR1,
INTERP. INPUT SIGNAL SPECTRUM
MODE NAME CMIX0 CMIX1 OUTPUT FREQUENCY
FACTOR FREQUENCY BANDWIDTH INVERTED?
MODE MODE
1X2 X2 -- LP 0.0 to 0.4 × f
DATA
0.0 to 0.4 × f
DATA
0.4 × f
DATA
No
1X2 HP X2 -- HP 0.0 to 0.4 × f
DATA
0.6 to 1.0 × f
DATA
0.4 × f
DATA
Yes
1X4 X4 LP LP 0.0 to 0.4 × f
DATA
0.0 to 0.4 × f
DATA
0.4 × f
DATA
No
1X4 HP/LP X4 HP LP 0.2 to 0.4 × f
DATA
0.6 to 0.8 × f
DATA
0.2 × f
DATA
Yes
1X4 HP/HP X4 HP HP 0.2 to 0.4 × f
DATA
1.2 to 1.4 × f
DATA
0.2 × f
DATA
No
1X4 LP/HP X4 LP HP 0.0 to 0.4 × f
DATA
1.6 to 2.0 × f
DATA
0.4 × f
DATA
Yes
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