AD669
REV. A
–5–
DEFINITIONS OF SPECIFICATIONS
INTEGRAL NONLINEARITY: Analog Devices defines inte-
gral nonlinearity as the maximum deviation of the actual, ad-
justed DAC output from the ideal analog output (a straight line
drawn from 0 to FS–1 LSB) for any bit combination. This is
also referred to as relative accuracy.
DIFFERENTIAL NONLINEARITY: Differential nonlinearity
is the measure of the change in the analog output, normalized to
full scale, associated with a 1 LSB change in the digital input
code. Monotonic behavior requires that the differential linearity
error be within ±1 LSB over the temperature range of interest.
MONOTONICITY: A DAC is monotonic if the output either
increases or remains constant for increasing digital inputs with
the result that the output will always be a single-valued function
of the input.
GAIN ERROR: Gain error is a measure of the output error be-
tween an ideal DAC and the actual device output with all 1s
loaded after offset error has been adjusted out.
OFFSET ERROR: Offset error is a combination of the offset
errors of the voltage-mode DAC and the output amplifier and is
measured with all 0s loaded in the DAC.
BIPOLAR ZERO ERROR: When the AD669 is connected for
bipolar output and 10 . . . 000 is loaded in the DAC, the devia-
tion of the analog output from the ideal midscale value of 0 V is
called the bipolar zero error.
DRIFT: Drift is the change in a parameter (such as gain, offset
and bipolar zero) over a specified temperature range. The drift
temperature coefficient, specified in ppm/°C, is calculated by
measuring the parameter at T
MIN
, 25°C and T
MAX
and dividing
the change in the parameter by the corresponding temperature
change.
TOTAL HARMONIC DISTORTION + NOISE: Total har-
monic distortion + noise (THD+N) is defined as the ratio of the
square root of the sum of the squares of the values of the har-
monics and noise to the value of the fundamental input fre-
quency. It is usually expressed in percent (%).
THD+N is a measure of the magnitude and distribution of lin-
earity error, differential linearity error, quantization error and
noise. The distribution of these errors may be different, depend-
ing upon the amplitude of the output signal. Therefore, to be
the most useful, THD+N should be specified for both large and
small signal amplitudes.
SIGNAL-TO-NOISE RATIO: The signal-to-noise ratio is de-
fined as the ratio of the amplitude of the output when a full-
scale signal is present to the output with no signal present. This
is measured in dB.
DIGITAL-TO-ANALOG GLITCH IMPULSE: This is the
amount of charge injected from the digital inputs to the analog
output when the inputs change state. This is measured at half
scale when the DAC switches around the MSB and as many
as possible switches change state, i.e., from 011 . . . 111 to
100 . . . 000.
DIGITAL FEEDTHROUGH: When the DAC is not selected
(i.e.,
CS is held high), high frequency logic activity on the digi-
tal inputs is capacitively coupled through the device to show up
as noise on the V
OUT
pin. This noise is digital feedthrough.
THEORY OF OPERATION
The AD669 uses an array of bipolar current sources with MOS
current steering switches to develop a current proportional to
the applied digital word, ranging from 0 mA to 2 mA. A seg-
mented architecture is used, where the most significant four
data bits are thermometer decoded to drive 15 equal current
sources. The lesser bits are scaled using a R-2R ladder, then ap-
plied together with the segmented sources to the summing node
of the output amplifier. The internal span/bipolar offset resistor
can be connected to the DAC output to provide a 0 V to +10 V
span, or it can be connected to the reference input to provide a
–10 V to +10 V span.
SPAN/
BIP OFF
AGND
DGND
REF IN
REF OUT
V
OUT
LDAC
DB15
(MSB)
(LSB)
DB0
CS
L1
–V
EE
+V
CC
+V
LL
16-BIT LATCH
10k
AMP
AD669
22
7
6
5
23
27
28
10V REF
2143
26
24
10k
10.05k
16-BIT LATCH
16-BIT DAC
25
Figure 2. AD669 Functional Block Diagram
ANALOG CIRCUIT CONNECTIONS
Internal scaling resistors provided in the AD669 may be con-
nected to produce a unipolar output range of 0 V to +10 V or a
bipolar output range of –10 V to +10 V. Gain and offset drift
are minimized in the AD669 because of the thermal tracking of
the scaling resistors with other device components.
UNIPOLAR CONFIGURATION
The configuration shown in Figure 3a will provide a unipolar
0 V to +10 V output range. In this mode, 50 Ω resistors are tied
between the span/bipolar offset terminal (Pin 26) and V
OUT
(Pin
25), and between REF OUT (Pin 28) and REF IN (Pin 27). It
is possible to use the AD669 without any external components
by tying Pin 28 directly to Pin 27 and Pin 26 directly to Pin 25.
Eliminating these resistors will increase the gain error by 0.25%
of FSR.
OUTPUT
GND
LDAC
DB15
(MSB)
(LSB)
DB0
CS
L1
–V
EE
+V
CC
+V
LL
16-BIT LATCH
10k
AMP
AD669
22
7
6
5
23
27
28
10V REF
2
1
43
10k
10.05k
16-BIT LATCH
16-BIT DAC
26
25
24
R1
50Ω
R2
50Ω
Figure 3a. 0 V to +10 V Unipolar Voltage Output
