AD7262 Analog Devices, AD7262 Datasheet - Page 28

• Manufacturer Part Number: AD7262
• Description: 1 MSPS, 12-Bit, Simultaneous Sampling SAR ADC with PGA and Four Comparators
• Manufacturer: Analog Devices

Specifications of AD7262

• Resolution (bits): 12bit
• # Chan: 2
• Sample Rate: 1MSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p,5V p-p
• Adc Architecture: SAR
• Pkg Type: CSP,QFP

AD7262
ADJUSTING THE OFFSET CALIBRATION REGISTERS
The internal offset calibration register can be adjusted manually
to compensate for any signal path offset from the sensors to the
ADC. Here, no internal calibration is required, and the CAL pin
can remain at a low logic state. By changing the contents of the
offset register, different amounts of offset on the analog input
signal can be compensated for. To determine the digital code to
be written to the offset register
1.
2.
3.
4.
If a +10 mV offset is present in the analog input signal and the
gain of the PGA is 2, the code that needs to be written to the
offset register to compensate for the offset is
If a − 10 mV offset is present in the analog input signal and the
gain of the PGA is 2, the code that needs to be written to the
offset register to compensate for the offset is
Table 13. Decoding of Multiplication Factors for Gain Calibration
Analog Input
V
V
V
V
V
V
V
IN
IN
IN
IN
IN
IN
max
max – 244 μV
max − (63 × 244 μV)
max
max + 244 μV
max + (63 × 244 μV)
Configure the sensor to its offset state.
Perform a number of conversions using the AD7262/
AD7262-5.
Take the mean digital output code from both D
and D
is 12 bits; thus, the result can be stored directly in the
offset register.
Write the digital code to the offset registers to calibrate the
AD7262/AD7262-5.
. 1 (
(
305
−
+
22
10
10
μV/
mV
OUT
mV
mV
B. This is a 12-bit result and the offset register
) 2
2 /
= −16.39 = 1000 0001 0000
=
16
.
39
=
Digital Gain
Error
LSB
0 LSB
−2 LSB
−126 LSB
0 LSB
+2 LSB
+126 LSB
0000
0001
0000
Gain Register
Code
(Sign bit + 6 bits)
0 000000
0 000001
0 111111
1 000000
1 000001
1 111111
OUT
A
Rev. 0 | Page 28 of 32
Multiplier
Equation
(1 ± x/4096)
1 − 0/4096
1 − 1/4096
1 − 63/4096
1 + 0/4096
1 + 1/4096
1 + 63/4096
SYSTEM GAIN CALIBRATION
The AD7262/AD7262-5 also allow the user to write to an
external gain register, thus enabling the removal of any overall
system gain error. Both ADC A and ADC B have independent
external gain registers, allowing the user to calibrate
independently the gain on both ADC A and ADC B signal
paths. The gain calibration feature can be used to implement
accurate gain matching between ADC A and ADC B.
The system calibration function is used by setting the sensors to
which the AD7262/AD7262-5 are connected to a 0 gain state.
The AD7262/AD7262-5 convert this analog input to a digital
output code, which corresponds to the system gain and is avail-
able on the D
in the appropriate external register. For details on how to write to
a register, see the Writing to a Register section and Table 11.
The gain calibration register contains seven bits of data. By
changing the contents of the gain register, different amounts of
gain on the analog input signal can be compensated for. The
MSB is a sign bit, while the remaining six bits store the multiplica-
tion factor, which is used to adjust the analog input range. The
gain register value is effectively multiplied by the analog input
to scale the conversion result over the full range. Increasing the
gain register multiplication factor compensates for a larger
analog input range, and decreasing the gain register multiplier
compensates for a smaller analog input range. Each bit in the
gain calibration register has a resolution of 2.4 × 10
A maximum of 1.538% of the analog range can be calibrated for.
The multiplier factor stored in the gain register can be decoded
as outlined in Table 13.
The gain registers can be cleared by writing all 0s to each register,
as described in the Writing to a Register section. For accurate
gain calibration, both the positive and negative full-scale digital
output codes should be measured prior to determining the
multiplication factor that is written to the gain register.
Multiplier
Value
1
0.999755859
0.98461914
1
1.000244141
1.015380859
OUT
x pins. This digital output code can then be stored
Sign bit = 0, which implies negative sign
in multiplier equation
Sign bit = 0, which implies negative sign
in multiplier equation
Sign bit = 0, which implies negative sign
in multiplier equation
Sign bit = 1, which implies plus sign in
multiplier equation
Sign bit = 1, which implies plus sign in
multiplier equation
Sign bit = 1, which implies plus sign in
multiplier equation
Comments
−4
V (1/4096).