AD9961 Datasheet, PDF (54/60 Pages) Analog Devices – 10-/12-Bit, Low Power, Broadband MxFE

AD9961/AD9963
The curves in Figure 89 represent four of the possible DAC
transfer functions with the full-scale voltage of 3.0 V and spans
of 0.5 V, 1.0 V, 1.5 V, and 2.0 V. The curves in Figure 90
represent four of the possible DAC transfer functions with the
full-scale voltage of 1.5 V and spans of 0.5 V, 1.0 V, 1.5 V, and
2.0 V. Note that the 2.0 V span results in clamping at the lower
end of the scale at 0 V where the equation resultsin negative
output voltages.
3.5
3.0
2.5
2.0
RNG00
RNG01
RNG10
1.5
RNG11
1.0
0.5
0
128 256 384 512 640 768 896 1024
CODE
Figure 89. AUXDAC10 Voltage Output vs. Digital Code, V_TOP = 3.0 V
(R_TOP = 3.2 kΩ)
2.00
1.75
1.50
1.25
1.00
0.75
RNG00
RNG01
0.50
RNG10
RNG11
0.25
0
0
128 256 384 512 640 768 896 1024
CODE
Figure 90. AUXDAC10 Voltage Output vs. Digital Code, V_TOP = 1.5 V
(R_TOP = 8.0 kΩ)
12-Bit Auxiliary DACs
The two 12-bit DACs have similar transfer functions and are
output on the DAC12A and DAC12B pins. The two DACs can
be independently enabled and configured. Figure 91 shows a
simplified schematic of the 12-bit auxiliary DAC.
AUX33V
2.3Ω
R
REFIO
AUXDACREF
1
0
DACCODE
VREF 0 TO VREF
DAC12
R
R_TOP
DAC12TOP: 0 = R_TOP = 0.8R
1 = R_TOP = 2.3R
Figure 91. Simplified Schematic of the 12-Bit Auxiliary DAC
Note that VREF can be derived from a 1.0 V bandgap reference
or be ratiometric with the AUX33V supply. An additional gain
stage follows the DAC that sets the final full-scale output
voltage . The following equation describes the no load output
voltage:
V_OUT
= V_FS
× _ ^DACCODE _{}
 1024 
where V_FS is set with the combination of bits shown in Table 29.
Table 29. 12-Bit Auxiliary DAC Full-Scale Voltage Selection
AUXDAC_REF
0
DAC10x_RNG¹
0
V_FS
AUX33V
0
1
0.54 × AUX33V
1
0
3.3 V
1
1
1.8 V
1 _{x = A or B.}
The curves in Figure 92 show the two transfer functions when
using the internal 1.0 V bandgap reference.
3.5
3.0
2.5
V_FS = 3.3V
2.0
1.5
V_FS = 1.8V
1.0
0.5
0
0
128 256 384 512 640 768 896 1024
CODE
Figure 92. AUXDAC12 Voltage Output vs. Digital Code
Rev. 0 | Page 54 of 60