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AD526CD Datasheet(数据表) 14 Page - Analog Devices

部件型号  AD526CD
说明  Software Programmable Gain Amplifier
下载  15 Pages
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制造商  AD [Analog Devices]
网页  http://www.analog.com
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AD526CD Datasheet(HTML) 14 Page - Analog Devices

 
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AD526
REV. D
–13–
HIGH ACCURACY A/D CONVERTERS
Very high accuracy and high resolution floating-point A/D con-
verters can be achieved by the incorporation of offset and gain
calibration routines. There are two techniques commonly used
for calibration, a hardware circuit as shown in Figure 43 and/or
a software routine. In this application the microprocessor is
functioning as the autoranging circuit, requiring software over-
head; therefore, a hardware calibration technique was applied
which reduces the software burden. The software is used to set
the gain of the AD526. In operation the signal is converted, and
if the MSB of the AD574 is not equal to a Logical 1, the gain is
increased by binary steps, up to the maximum gain. This maxi-
mizes the full-scale range of the conversion process and insures
a wide dynamic range.
The calibration technique uses two point correction, offset and
gain. The hardware is simplified by the use of programmable
magnitude comparators, the 74ALS528s, which can be “burned”
for a particular code. In order to prevent under or over range
hunting during the calibration process, the reference offset and
gain codes should be different from the endpoint codes. A cali-
bration cycle consists of selecting whether gain or offset is to be
calibrated then selecting the appropriate multiplexer channel to
apply the reference voltage to the signal channel. Once the op-
eration has been initiated, the counter, a 74ALS869, drives the
D/A converter in a linear fashion providing a small correction
voltage to either the gain or offset trim point of the AD574. The
output of the A/D converter is then compared to the value pre-
set in the 74ALS528 to determine a match. Once a match is
detected, the 74ALS528 produces a low going pulse which stops
the counter. The code at the D/A converter is latched until the
next calibration cycle. Calibration cycles are under the control
of the microprocessor in this application and should be imple-
mented only during periods of converter inactivity.
A2
A1
A4
A3
AD588
NOISE
REDUCTION
R8
R1
R2
R3
R4
R5
R6
1 F
+VS
–VS
–5V
+5V
+15V
–15V
SYS
GND
0.1 F
0.1 F
AD7501
VIN1
VIN2
VIN3
VIN4
DECODED
ADDRESS
AD526
DECODED
ADDRESS
WR
WR
ADDRESS BUS
10k
–15V +15V
AD585
–15V +15V
200pF
F
S
21
7404
OP27
+15V
–15V
VREF
DE-
CODED
ADD
WR
+
+
+15V
–15V
+5V
10 F
10 F
MSB
LSB
+5V
50k
1k
AD574
DATA
BUS
12
12
MSB
LSB
74ALS
528
GAIN
P = Q
+5V
MSB
LSB
74ALS
528
OFFSET
P = Q
+5V
7475
7475
1/2
+5V
+5V
7475
1/2
7400
1
3
2
7400
6
4
5
PIN 28
AD574
ADG221
CONTROL
LOGIC
INPUT
BUFFER
LATCH
DAC A
LATCH
DAC B
AD7628
WR
A/B
VREF
VREF
WR
74ALS
869
MSB
LSB
CALIBRATION
PRESET
VALUE
+5V
+5V
5k
RFB A
RFB A
RFB A
RFB B
A1
C12
R21
OUT A
AD712
R72
10k
A2
AD712
R62
20k
PIN 15
AD588
R5
20k
R11
5k
A3
C22
R41
OUT B
AD712
AGND
AGND
R92
10k
R102
20k
PIN 15
AD588
A2
AD712
R8
20k
R12
5k
AGND
OFFSET
GAIN
NOTE: ALL BYPASS CAPACITORS ARE 0.1 F
Figure 43. High Accuracy A/D Converter




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