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參數(shù)資料
| 型號： | AD1672 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Complete 12-Bit, 3 MSPS Monolithic A/D Converter(完備的12位單片A/D轉(zhuǎn)換器) |
| 中文描述： | 完整的12位，3 MSPS的單片機的A / D轉(zhuǎn)換器（完備的12位單片的A / D轉(zhuǎn)換器） |
| 文件頁數(shù)： | 14/20頁 |
| 文件大?。?/td> | 480K |
| 代理商： | AD1672 |
AD1672
REV. 0
–14–
GAIN AND OFFSET ADJUSTMENT
The AD1672 is factory trimmed to minimize gain, offset and
linearity errors. In some applications, the gain and offset errors
need to be externally trimmed to zero. Since the gain and offset
errors of the AD1672 are interdependent, an iterative process is
required to trim both errors. The OTR pin can be monitored to
trim the offset and gain errors to within 1/2 LSB of negative and
positive full-scale (i.e., –FS and +FS) respectively. In this case,
the calibration procedure would be to iterate between –FS and
+FS voltage levels which are applied to the input of the AD1672
and adjust the offset and gain until OTR toggles at both –FS
and +FS.
Both gain and offset errors may be trimmed with external cali-
bration circuits based on a potentiometer or a DAC. Digital
calibration circuits using a DAC offers greater flexibility and
can be programmed for various operating conditions. The fol-
lowing digital calibration circuits are based on the DAC08
which is a low cost, 8-bit current output DAC with 85 ns set-
tling time performance. Different adjustment spans and resolu-
tion may be achieved by judicious selection of the resistors in
the circuit.
Figure 28 shows an offset correction circuit for the unipolar
input ranges of 0 V to 2.5 V and 0 V to 5.0 V. The complemen-
tary current outputs of the DAC08 provide a bipolar adjustment
range at the output of the op amp if R
S
is made equal to R
F
/G.
G is the noninverting gain of the op amp and is equal to
1 + R
F
/R
A
. REFOUT divided by R
IN
sets the full-scale current
output, I
FS
, for the DAC08 Note, R
P
is a pull-up resistor used
to source additional current if I
FS
is greater than 500
μ
A. The
bipolar voltage adjustment span at the output of the op amp is
equal to I
FS
×
R
F
. R
I
isolates the op amp from the DAC08
output capacitance. Note, that the values of these resistors can
be optimized for any circuit requirement or adjustment span
since they are not uniquely defined for any given voltage span.
R
F
R
A
R
I
R
I
V
REF(+)
V
REF(–)
DAC08
I
O
I
O
R
IN
R
IN
1μF
R
P
AD1672
AIN
REFOUT
+V
CC
Figure 28. Unipolar Offset Correction Using the DAC08
Figure 29 shows an offset correction circuit for the bipolar input
range of –2.5 to +2.5 V. This circuit is similar to the circuit
shown in Figure 28 except that the op amp is configured in an
inverting topology so that the voltage compliance of the DAC08
is not exceeded.
R
F
R
A
R
I
R
I
V
REF(+)
V
REF(–)
DAC08
I
O
I
O
R
IN
R
IN
1μF
R
P
+V
CC
R
S
AD1672
AIN
REFOUT
Figure 29. Bipolar Offset Correction Using the DAC08
Figure 30 shows a gain correction circuit which is also similar to
the circuit shown in Figure 28. The circuit consists of a unity
gain amplifier in which R
S
and R
F
are equal to 158
. In this
case, the full-scale output current of the DAC08, I
FS
, is set at
500
μ
A to minimize the load to the AD1672 REFOUT. The
output of the op amp can be varied over a
±
78 mV range
around the midscale voltage of REFOUT. Also, R
S
and R
F
are
selected such that 1 LSB of the DAC08 corresponds to 1 LSB
of the AD1672.
500
5k
5k
1μF
4.7k
+V
CC
AD1672
REFIN
REFOUT
2.5V
V
REF(+)
V
REF(–)
DAC08
I
O
I
O
500
158
158
2.5
±
0.078V
Figure 30. Gain Correction Using the DAC08
OUTPUT LATCHES
The AD1672/EB evaluation board schematic in Figure 31
shows the AD1672 connected to the 74HC541 octal/buffer line
drivers with three-state outputs. The latch can drive highly ca-
pacitive loads (i.e., bus lines, I/O ports) while maintaining the
data signal integrity.
AD1672 EVALUATION BOARD GENERAL DESCRIPTION
The AD1672/EB is an evaluation board for the AD1672 12-bit
3 MSPS analog-to-digital converter (ADC). Figure 31 shows the
schematic for the AD1672/EB evaluation board. Careful attention
to layout and circuit design combined with analog and digital proto-
typing areas allows the user to easily and effectively evaluate the
AD1672 in any application requiring high resolution, high speed
conversion.
The analog input to the AD1672/EB may be driven directly or
via an onboard buffer amplifier. The AD1672/EB contains an
8-bit DAC which can be easily configured for input offset ad-
justment or for reconstruction of the digital output. An optional
external voltage reference is included for greater dc precision
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