DAC250Y BURR-BROWN [Burr-Brown Corporation], DAC250Y Datasheet - Page 9

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

DAC2902
APPLICATION INFORMATION
THEORY OF OPERATION
The architecture of the DAC2902 uses the current steering
technique to enable fast switching and a high update rate.
The core element within the monolithic DAC is an array of
segmented current sources that are designed to deliver a full-
scale output current of up to 20mA, as shown in Figure 1. An
internal decoder addresses the differential current switches
each time the DAC is updated and a corresponding output
current is formed by steering all currents to either output
summing node, I
deliver a differential output signal, which improves the
dynamic performance through reduction of even-order har-
monics, common-mode signals (noise), and double the peak-
to-peak output signal swing by a factor of two, compared to
single-ended operation.
The segmented architecture results in a significant reduction
of the glitch energy, improves the dynamic performance
(SFDR), and DNL. The current outputs maintain a very high
output impedance of greater than 200ký.
The full-scale output current is determined by the ratio of the
internal reference voltage (approx. +1.25V) and an external
resistor, R
factor of 32 to produce an effective DAC output current that
can range from 2mA to 20mA, depending on the value of R
The DAC2902 is split into a digital and an analog portion,
each of which is powered through its own supply pin. The
digital section includes edge-triggered input latches and the
decoder logic, while the analog section comprises the cur-
rent source array with its associated switches, and the
reference circuitry.
FIGURE 1. Block Diagram of the DAC2902.
SBAS167A
SET
. The resulting I
OUT
Data Input
Data Input
D[11:0]_1
D[11:0]_2
or I
WRT1
WRT2
Port 1
Port 2
CLK1
CLK2
OUT
REF
. The complementary outputs
is internally multiplied by a
Latch 1
Latch 2
DGND
Input
Input
+V
D
SET
Latch 1
Latch 2
DGND
+V
DAC
DAC
.
D
DAC2902
DAC TRANSFER FUNCTION
Each of the DACs in the DAC2902 has a complementary
current output, I
rent, I
output currents:
The individual output currents depend on the DAC code and
can be expressed as:
where ‘Code’ is the decimal representation of the DAC data
input word. Additionally, I
ence current I
voltage and the external setting resistor, R
In most cases the complementary outputs will drive resistive
loads or a terminated transformer. A signal voltage will
develop at each output according to:
OUTFS
Segmented Switches
Segmented Switches
Current Sources
Current Sources
I
Control Amplifier
, is the summation of the two complementary
OUTFS
DAC1
DAC2
Reference
I
REF
OUT
AGND
I
OUT
+V
OUT
, which is determined by the reference
= 32 • I
A
V
V
I
= I
OUTFS
1 and I
= I
OUT
OUT
OUTFS
OUTFS
= I
= I
= I
REF
OUT
OUTFS
OUT
OUT
• (4095 - Code)
OUT
• (Code/4096)
= 32 • V
2. The full-scale output cur-
• R
• R
+ I
is a function of the refer-
l
l
l
l
REF
FSA1
FSA2
GSET
PD
OUT
OUT
OUT
OUT
LOAD
LOAD
OUT
2
1
1
2
IN
REF
/R
SET
SET
.
(1)
(2)
(3)
(4)
(5)
(6)
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