DAC16 Analog Devices, DAC16 Datasheet - Page 4

• Manufacturer Part Number: DAC16
• Description: 16-Bit High Speed Current-Output DAC
• Manufacturer: Analog Devices

DAC16
OPERATION
Novel DAC Architecture
The DAC16 was designed with a compound DAC architecture
to achieve high accuracy, excellent linearity, and low transition
errors. As shown in Figure 3, the DAC’s five most-significant
bits utilize 31 identical segmented current sources to obtain
optimal high speed settling at major code transitions. The lower
nine bits utilize an inverted R-2R ladder network which is laser-
trimmed to ensure excellent differential nonlinearity. The middle
two bits (DB9 and DB10) arc binary-weighted and scaled from
the MSB segments. Note that the flow of output current is into
the DAC16—there is no signal inversion. As shown, the switches
for each current source are essentially diodes. It is for this rea-
son that the output voltage compliance of the DAC16 is limited
to a few millivolts. The DAC16 was designed to operate with an
operational amplifier configured as an I–V converter; therefore,
the DAC16’s output must be connected to the sum node of an
operational amplifier for proper operation. Exceeding the output
voltage compliance of the DAC16 will introduce linearity errors.
The reference current buffer assures full accuracy and fast set-
tling by controlling the MSB reference node. The 16-bit paral-
lel digital input is TTL/CMOS compatible and unbuffered,
I
REF
+5V
18k
10k
C
Figure 2. Burn-In Diagram
COMP
10
11
12
1
2
3
4
5
6
7
8
9
SW
31 CURRENT SOURCES
SW
DB11 – DB15
125 A EACH
24
23
22
21
20
19
18
17
16
15
14
13
NC
SW
–15V
SW
Figure 3. DAC16 Architecture
62.5 A 31.25 A
DB10
SW10
SW9
DB9
–4–
I
SW8
OUT
minimizing the deleterious effects of digital feedthrough
while allowing the user to tailor the digital interface to
the speed requirements and bus configuration of the
application.
Equivalent Circuit Analysis
An equivalent circuit for static operation of the DAC16 is
illustrated in Figure 4. I
DAC16 and is set externally to the device by V
R
mately 10 pF and is code independent. Its output resis-
tance R
where
DB9 = State of Data Bit 9 = 0 or 1;
DB10 = State of Data Bit 10 = 0 or 1; and
X = Decimal representation of the 5 MSBs (DB11–DB15)
= 0 to 31.
Table I provides the relationship between the input digital
code and the output resistance of the DAC16.
Hex Digital Code
FFFF
BFFF
7FFF
3FFF
0
4k
REF
Table I. DAC16 Output Resistance vs. Digital Code
I
SW7
DAC
. The output capacitance of the DAC16 is approxi-
9 CURRENT SOURCES
Figure 4. Equivalent Circuit for the DAC16
8k
O
15.63 A EACH
4k
R
is code dependent and is given by:
1
O
SW6
8k
4k
8 k
DB0 – DB8
R
1
O
4k
Scale
Zero
1/4
1/2
3/4
Full – 1 LSB
288 k
REF
DB9
SW0
4k
is the current applied to the
C
O
144 k
AGND
SWITCH DETAIL
DB10
I
I
R
C
OUT
OUT
DB0 – DB15
O
O
= SEE TEXT
= 10pF
= 8 • I
Output Resistance
8 k
4.2 k
2.9 k
2.2 k
1.8 k
REF
72 k
+5V
REF
X
65,535 Digital Code
and
FROM
SWITCH
DECODER
65,536
REV. B