DAC250Y BURR-BROWN [Burr-Brown Corporation], DAC250Y Datasheet - Page 13

• Manufacturer Part Number: DAC250Y
• Description: Dual, 12-Bit, 125MSPS DIGITAL-TO-ANALOG CONVERTER
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

DAC2902
Figure 8 shows an example of a DC-coupled interface with
DC level-shifting, using a precision resistor network. An ac-
coupled interface, as shown in Figure 9, has the advantage
that the common-mode levels at the input of the modulator
can be set independently of those at the output of the DAC.
Furthermore, no voltage loss is obtained in this setup.
INTERNAL REFERENCE OPERATION
The DAC2902 has an on-chip reference circuit that com-
prises a 1.25V bandgap reference and two control amplifi-
ers, one for each DAC. The full-scale output current, I
of the DAC2902 is determined by the reference voltage,
V
lated by:
The external resistor R
Scale Adjust), see Figure 10. The reference control amplifier
operates as a V-to-I converter producing a reference current,
I
shown in Equation 10). The full-scale output current, I
results from multiplying I
FIGURE 9. AC-Coupled Interface to Quadrature Modulator Applying Level Shifting.
REF
REF
SBAS167A
, which is determined by the ratio of V
, and the value of resistor R
I
OUTFS
= 32 • I
DAC2902
SET
REF
REF
connects to the FSA pin (Full-
= 32 • V
by a fixed factor of 32.
I
I
OUT
OUT
SET
1
1
. I
REF
OUTFS
I
I
OUT
OUT
/ R
REF
1
1
can be calcu-
SET
and R
50
SET
OUTFS
OUTFS
(10)
(as
R
LOAD
,
,
FIGURE 8. DC-Coupled Interface to Quadrature Modulator
50
DAC2902
0.01 F
0.01 F
Applying Level Shifting.
I
I
OUT
OUT
1
1
V
R
R
DC
I
I
1
2
OUT
OUT
1
1
V
V
OUT
OUT
V
1
1
R
R
R
DC
3
4
5
V
V
OUT
OUT
1
1
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