AD561 Low Cost 10-Bit Monolithic D/A Converter
REV. A
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reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
a
AD561
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
World Wide Web Site: http://www.analog.com
Fax: 617/326-8703
Analog Devices, Inc., 1997
Low Cost 10-Bit
Monolithic D/A Converter
FUNCTIONAL BLOCK DIAGRAM
TO-116
PRODUCT DESCRIPTION
The AD561 is an integrated circuit 10-bit digital-to-analog
converter combined with a high stability voltage reference
fabricated on a single monolithic chip. Using ten precision high-
speed current-steering switches, a control amplifier, voltage
reference, and laser-trimmed thin-film SiCr resistor network,
the device produces a fast, accurate analog output current.
Laser trimmed output application resistors are also included to
facilitate accurate, stable current-to-voltage conversion; they are
trimmed to 0.1% accuracy, thus eliminating external trimmers
in many situations.
Several important technologies combine to make the AD561 the
most accurate and most stable 10-bit DAC available. The low
temperature coefficient, high stability thin-film network is
trimmed at the wafer level by a fine resolution laser system to
0.01% typical linearity. This results in an accuracy specification
of
1/4 LSB max for the K and T versions, and 1/2 LSB max
for the J and S versions.
The AD561 also incorporates a low noise, high stability
subsurface zener diode to produce a reference voltage with
excellent long term stability and temperature cycle characteris-
tics, which challenge the best discrete Zener references. A
temperature compensation circuit is laser-trimmed to allow
custom correction of the temperature coefficient of each device.
This results in a typical full-scale temperature coefficient of
15 ppm/
C; the TC is tested and guaranteed to 30 ppm/
C max
for the K and T versions, 60 ppm/
C max for the S, and
80 ppm/
C for the J.
The AD561 is available in four performance grades. The
AD561J and K are specified for use over the 0
C to +70
C
temperature range and are available in either a 16-pin
FEATURES
Complete Current Output Converter
High Stability Buried Zener Reference
Laser Trimmed to High Accuracy (1/4 LSB Max Error,
AD561K, T)
Trimmed Output Application Resistors for 0 V to +10 V,
5 V Ranges
Fast Settling 250 ns to 1/2 LSB
Guaranteed Monotonicity Over Full Operating
Temperature Range
TTL/DTL and CMOS Compatible (Positive True Logic)
Single Chip Monolithic Construction
Available in Chip Form
MlL-STD-883-Compliant Versions Available
hermetically-sealed ceramic DIP or a 16-pin molded plastic
DIP. The AD561S and T grades are specified for the 55
C to
+125
C range and are available in the ceramic package.
PRODUCT HIGHLIGHTS
1. Advanced monolithic processing and laser trimming at the
wafer level have made the AD561 the most accurate 10-bit
converter available, while keeping costs consistent with large
volume integrated circuit production. The AD561K and T
have 1/4 LSB max relative accuracy and 1/2 LSB max
differential nonlinearity. The low TC R-2R ladder guaran-
tees that all AD561 units will be monotonic over the entire
operating temperature range.
2. Digital system interfacing is simplified by the use of a
positive true straight binary code. The digital input voltage
threshold is a function of the positive supply level; connect-
ing V
CC
to the digital logic supply automatically sets the
threshold to the proper level for the logic family being used.
Logic sink current requirement is only 25
A.
3. The high speed current steering switches are designed to settle
in less than 250 ns for the worst case digital code transition.
This allows construction of successive-approximation A/D
converters in the 3
s to 5
s range.
4. The AD561 has an output voltage compliance range from
2 V to +10 V, allowing direct current-to-voltage conversion
with just an output resistor, omitting the op amp. The 40 M
open collector output impedance results in negligible errors
due to output leakage currents.
5. The AD561 is available in versions compliant with MIL-
STD-883. Refer to the Analog Devices Military Products
Databook or current AD561/883B data sheet for detailed
specifications.
2
REV. A
AD561SPECIFICATIONS
AD561J
AD561K
Model
Min
Typ
Max
Min
Typ
Max
Units
RESOLUTION
10 Bits
10 Bits
ACCURACY (Error Relative
1/4
1/2
1/8
1/4
LSB
to Full Scale)
(0.025)
(0.05)
(0.012)
(0.025)
% of FS
DIFFERENTIAL NONLINEARITY
1/2
1/4
1/2
LSB
DATA INPUTS
TTL, V
CC
= +5 V
Bit ON Logic "1"
+2.0
*
V
Bit OFF Logic "0"
+0.8
*
V
CMOS, 10 V
V
CC
16.5 V
Bit ON Logic " 1 "
70% V
CC
*
V
Bit OFF Logic "0"
30% V
CC
*
V
Logic Current (Each Bit) (T
MIN
to T
MAX
)
Bit ON Logic "1"
+5
+100
*
*
nA
Bit OFF Logic "0"
5
25
*
*
A
OUTPUT
Current
Unipolar
1.5
2.0
2.4
*
*
*
mA
Bipolar
0.75
1.0
1.2
*
*
*
mA
Resistance (Exclusive of
Application Resistors)
40 M
*
Unipolar Zero (All Bits OFF)
0.01
0.05
*
*
% of FS
Capacitance
25
*
pF
Compliance Voltage
2
3
+10
*
*
*
V
SETTLING TIME TO 1/2 LSB
All Bits ON-to-OFF or OFF-to-ON
250
*
ns
POWER REQUIREMENTS
V
CC
, +4.5 V dc to +16.5 V dc
8
10
*
*
mA
V
EE
, 10.8 V dc to 16.5 V dc
12
16
*
*
mA
POWER SUPPLY GAIN SENSITIVITY
V
CC
, +4.5 V dc to +16.5 V dc
2
10
*
*
ppm of FS/%
V
EE
, 10.8 V dc to 16.5 V dc
4
25
*
*
ppm of FS/%
TEMPERATURE RANGE
Operating
0 to +70
*
*
C
Storage ("D" Package)
65 to +150
*
*
C
("N" Package)
25 to +85
*
*
C
TEMPERATURE COEFFICIENTS
With Internal Reference
Unipolar Zero
1
10
1
5
ppm of FS/
C
Bipolar Zero
2
20
2
10
ppm of FS/
C
Full Scale
15
80
15
30
ppm of FS/
C
Differential Nonlinearity
2.5
2.5
ppm of FS/
C
MONOTONICITY
Guaranteed Over Full Operating
Guaranteed Over Full Operating
Temperature Range
Temperature Range
PROGRAMMABLE OUTPUT
0 to +10
*
V
RANGES
5 to +5
*
V
CALIBRATION ACCURACY
Full-Scale Error with Fixed 25
`
Resistor
0.1
*
% of FS
Bipolar Zero Error with Fixed 10
Resistor
0.1
*
% of FS
CALIBRATION ADJUSTMENT
RANGE
Full Scale (With 50
Trimmer)
0.5
*
% of FS
Bipolar Zero (With 50
Trimmer)
0.5
*
% of FS
NOTES
*Specifications same as AD561J specifications.
Specifications subject to change without notice.
(T
A
= +25 C, V
CC
= 15 V, unless otherwise noted.)
3
REV. A
AD561
AD561S
AD561T
Model
Min
Typ
Max
Min
Typ
Max
Units
RESOLUTION
10 Bits
10 Bits
ACCURACY (Error Relative
1/4
1/2
1/8
1/4
LSB
to Full Scale)
(0.025)
(0.05)
(0.012)
(0.025)
% of FS
DIFFERENTIAL NONLINEARITY
1/2
1/4
1/2
LSB
DATA INPUTS
TTL, V
CC
= +5 V
Bit ON Logic "1"
+2.0
**
V
Bit OFF Logic "0"
+0.8
**
V
CMOS, 10 V
V
CC
16.5 V
Bit ON Logic " 1 "
70% V
CC
**
V
Bit OFF Logic "0"
30% V
CC
**
V
Logic Current (Each Bit) (T
MIN
to T
MAX
)
Bit ON Logic "1"
+20
+100
**
**
nA
Bit OFF Logic "0"
25
100
**
**
A
OUTPUT
Current
Unipolar
1.5
2.0
2.4
**
**
**
mA
Bipolar
0.75
1.0
1.2
**
**
**
mA
Resistance (Exclusive of
Application Resistors)
40 M
**
Unipolar Zero (All Bits OFF)
0.01
0.05
**
**
% of FS
Capacitance
25
**
pF
Compliance Voltage
2
3
+10
**
**
**
V
SETTLING TIME TO 1/2 LSB
All Bits ON-to-OFF or OFF-to-ON
250
**
ns
POWER REQUIREMENTS
V
CC
, +4.5 V dc to +16.5 V dc
6
10
**
**
mA
V
EE
, 10.8 V dc to 16.5 V dc
11
16
**
**
mA
POWER SUPPLY GAIN SENSITIVITY
V
CC
, +4.5 V dc to +16.5 V dc
2
10
**
**
ppm of FS/%
V
EE
, 10.8 V dc to 16.5 V dc
4
25
**
**
ppm of FS/%
TEMPERATURE RANGE
Operating
55 to +125
**
**
C
Storage
65 to +150
**
**
C
TEMPERATURE COEFFICIENTS
With Internal Reference
Unipolar Zero
1
10
1
5
ppm of FS/
C
Bipolar Zero
2
20
2
10
ppm of FS/
C
Full Scale
15
60
15
30
ppm of FS/
C
Differential Nonlinearity
2.5
2.5
ppm of FS/
C
MONOTONICITY
Guaranteed Over Full Operating
Guaranteed Over Full Operating
Temperature Range
Temperature Range
PROGRAMMABLE OUTPUT
0 to +10
**
V
RANGES
5 to +5
**
V
CALIBRATION ACCURACY
Full-Scale Error with Fixed 25
Resistor
0.1
**
% of FS
Bipolar Zero Error with Fixed 10
Resistor
0.1
**
% of FS
CALIBRATION ADJUSTMENT
RANGE
Full Scale (With 50
Trimmer)
0.5
**
% of FS
Bipolar Zero (With 50
Trimmer)
0.5
**
% of FS
NOTES
**Specifications same as AD561S specifications.
Specifications subject to change without notice.
AD561
4
REV. A
THE AD561 OFFERS TRUE 10-BIT RESOLUTION OVER
FULL TEMPERATURE RANGE
Accuracy: Analog Devices defines accuracy as the maximum
deviation of the actual, adjusted DAC output (see page 5) from
the ideal analog output (a straight line drawn from 0 to FS l
LSB) for any bit combination. The AD561 is laser trimmed to
1/4 LSB (0.025% of FS) maximum error at +25
C for the K
and T versions 1/2 LSB for the J and S.
Monotonicity: A DAC is said to be monotonic if the output
either increases or remains constant for increasing digital inputs
such that the output will always be a single-valued function of the
input. All versions of the AD561 are monotonic over their full
operating temperature range.
Differential Nonlinearity: Monotonic behavior requires that
the differential nonlinearity error be less than
1 LSB both at +25
C and over the temperature range of
interest. Differential nonlinearity is the measure of the variation
in analog value, normalized to full scale, associated with a
1 LSB change in digital input code. For example, for a 10 volt
full scale output, a change of 1 LSB in digital input code should
result in a 9.8 mV change in the analog output (1 LSB = 10 V
1/1024 = 9.8 mV). If in actual use, however, a 1 LSB change
in the input code results in a change of only 2.45 mV (1/4 LSB)
in analog output, the differential nonlinearity error would be
7.35 mV, or 3/4 LSB The AD561K and T have a max differen-
tial linearity error of 1/2 LSB.
The differential nonlinearity temperature coefficient must also
be considered if the device is to remain monotonic over its full
operating temperature range. A differential nonlinearity tempera-
ture coefficient of 2.5 ppm/
C could, under worst case condi-
tions for a temperature change of +25
C to +125
C, add 0.025%
(100 2.5 ppm/
C of error). The resulting error could then be
as much as 0.025% + 0.025% = 0.05% of FS (1/2 LSB represents
0.05% of FS). To be sure of accurate performance all versions of
the AD561 are therefore 100% tested to be monotonic over the
full operating temperature range.
Figure 1. Chip Bonding Diagram
CONNECTING THE AD561 FOR BUFFERED VOLTAGE
OUTPUT
The standard current-to-voltage conversion connections using
an operational amplifier are shown here with the preferred
trimming techniques. If a low offset operational amplifier
(AD510, AD741L, AD301AL) is used, excellent performance
can be obtained in many situations without trimming. (A 5 mV
op amp offset is equivalent to 1/2 LSB on a 10 volt scale.) If a
25
fixed resistor is substituted for the 50
trimmer, unipolar
zero will typically be within
1/10 LSB (plus op amp offset),
and full scale accuracy will be within
1 LSB. Substituting a
25
resistor for the 50
bipolar offset trimmer will give a
bipolar zero error typically within
1 LSB.
The AD509 is recommended for buffered voltage-output
applications that require a settling time to
1/2 LSB of one
microsecond. The feedback capacitor is shown with the
optimum value for each application; this capacitor is required to
compensate for the 25 picofarad DAC output capacitance.
ORDERING GUIDE
ACCURACY
GAIN T C
PACKAGE
MODEL
1
TEMP RANGE
@ +25 C
(of FS/ C)
OPTION
2
AD561JD
0
C to +70
C
1/2 LSB max
80 ppm max
D-16
AD561JN
0
C to +70
C
1/2 LSB max
80 ppm max
N-16
AD561KD
0
C to +70
C
1/4 LSB max
30 ppm max
D-16
AD561KN
0
C to +70
C
1/4 LSB max
30 ppm max
N-16
AD561SD
55
C to +125
C
1/2 LSB max
60 ppm max
D-16
AD561TD
55
C to +125
C
1/4 LSB max
30 ppm max
D-16
AD561/883B
55
C to +125
C *
*
*
NOTES
1
For details on grade and package offerings screened in accordance with MIL-STD-883, refer to the
Analog Devices Military Products Databook or current AD561/883B data sheet.
2
D = Ceramic DIP; N = Plastic DIP.
*Refer to AD561/883B military data sheet.
PIN CONFIGURATION
TOP VIEW
AD561
5
REV. A
UNIPOLAR CONFIGURATION
This configuration, shown in Figure 2, will provide a unipolar
0 V to +10 V output range.
STEP I . . . ZERO ADJUST
Turn all bits OFF and adjust op amp trimmer, R
1
, until the
output reads 0.000 volts (1 LSB = 9.76 mV).
STEP 11. . . GAIN ADJUST
Turn all bits ON and adjust 50
gain trimmer, R
2
, until the
output is 9.990 volts. (Full scale is adjusted to 1 LSB less than
nominal full scale of 10.000 volts.) If a 10.23 V full scale is desired
(exactly 10 mV/bit), insert a 120
resistor in series with R
2
.
BIPOLAR CONFIGURATION
This configuration, shown in Figure 3, will provide a bipolar
output voltage from 5.000 to +4.990 volts, with positive full
scale occurring with all bits ON (all 1s).
STEP 1. . . ZERO ADJUST
Turn ON MSB only, turn OFF all other bits. Adjust 50
trimmer R
3
, to give 0.000 output volts. For maximum resolution
a 120
resistor may be placed in parallel with R
3
.
STEP 11. . . GAIN ADJUST
Turn OFF all bits, adjust 50
gain trimmer to give a reading of
5.000 volts.
Please note that it is not necessary to trim the op amp to obtain
full accuracy at room temperature. In most bipolar situations,
the op amp trimmer is unnecessary unless the untrimmed offset
drift of the op amp is excessive.
10 VOLT BUFFERED BIPOLAR OUTPUT
The AD561 can also be connected for a
10 volt bipolar range
with an additional external resistor as shown in Figure 4. A
larger value trimmer is required to compensate for tolerance in
the thin film resistors, which are trimmed to match the full-scale
current. For best full scale temperature coefficient performance,
the external resistors should have a TC of 50 ppm/
C.
CIRCUIT DESCRIPTION
A simplified schematic with the essential circuit features of the
AD561 is shown in Figure 5. The voltage reference, CR1, is a
buried Zener (or subsurface breakdown diode). This device
exhibits far better all-around performance than the NPN base-
emitter reverse-breakdown diode (surface Zener), which is in
nearly universal use in integrated circuits as a voltage reference.
Greatly improved long-term stability and lower noise are the
major benefits the buried Zener derives from isolating the
breakdown point from surface stress and mobile oxide charge
effects. The nominal 7.5 volt device (including temperature
compensation circuitry) is driven by a current source to the
negative supply so the positive supply can be allowed to drop as
low as 4.5 volts. The temperature coefficient of each diode is
individually determined; this data is then used to laser trim a
compensating circuit to balance the overall TC to zero. The
typical resulting TC is 0 to
15 ppm/
C. The negative reference
level is inverted and scaled by A
1
to give a +2.5 volt reference,
which can be driven by the low positive supply. The AD561,
packaged in the 16-pin DIP, has the +2.5 volt reference (REF
OUT) connected directly to the input of the control amplifier
(REF IN). The buffered reference is not directly available
externally except through the 2.5 k
bipolar offset resistor.
The 2.5 k
scaling resistor and control amplifier A
2
then force a
1 mA reference current to flow through reference transistor Q
1
,
which has a relative emitter area of 8A. This is accomplished by
forcing the bottom of the ladder to the proper voltage. Since Q
1
and Q
2
have equal emitter areas and equal 5 k
emitter resistors,
Q
2
also carries 1 mA. The ladder voltage drop constrains Q
7
(with area 4A) to carry only 0.5 mA; Q
8
carries 0.25 mA, etc.
The first four significant bit cells are exactly scaled in emitter
area to match Q
1
for optimum V
BE
and V
BE
drift match, as well
as for beta match. These effects are insignificant for the lower
order bits, which account for a total of only 1/16 of full scale.
However, the 18 mV V
BE
difference between two matched
transistors carrying emitter currents in a ratio of 2:1 must be
corrected. This is achieved by forcing 120
A through the
150
interbase resistors. These resistors, and the R-2R ladder
resistors, are actively laser-trimmed at the wafer level to bring
total device accuracy to better than 1/4 LSB. Sufficient ratio
accuracy in the last two bits is obtained by simple emitter area
Figure 2. 0 V to +10 V Unipolar Voltage Output
Figure 3.
5 V Buffered Bipolar Voltage Output
Figure 4.
10 V Buffered Voltage Output
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