EVAL-AD5765EBZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD5765EBZ' PDF : 28 Pages View PDF
AD5765
OFFSET AND GAIN ADJUSTMENT WORKED
EXAMPLE
Using the information provided in the Theory of Operation
section, the following worked example demonstrates how the
AD5765 functions can be used to eliminate both offset and gain
errors. Because the AD5765 is factory calibrated, offset and gain
errors should be negligible. However, errors can be introduced
by the system that the AD5765 is operating within; for example,
a voltage reference value that is not equal to 2.048 V introduces
a gain error. An output range of ±4.096 V and twos complement
data coding are assumed.
Removing Offset Error
The AD5765 can eliminate an offset error in the range of −2 mV to
+1.98 mV with a step size of â…› of a 16-bit LSB.
1. Calculate the step size of the offset adjustment.
Offset
Adjust
Step Size
=
8.192
216 × 8
= 15.625
μV
2. Measure the offset error by programming 0x0000 to the
data register and measuring the resulting output voltage;
for this example, the measured value is 614 µV.
3. Calculate the number of offset adjustment steps that this
value represents.
Number of Steps = Measured Offset Value = 614 μV = 13 Steps
Offset Step Size 15.625 μV
The offset error measured is positive; therefore, a negative
adjustment of 40 steps is required. The offset register is 8-bits
wide and the coding is twos complement.
The required offset register value can be calculated as follows:
1. Convert the adjustment value to binary: 00101000.
Data Sheet
2. Convert the binary number to a negative twos complement
number by inverting all bits and adding 1: 11011000.
11011000 is the value that should be programmed to the
offset register.
Note that this twos complement conversion is not
necessary in the case of a positive offset adjustment. The
value to be programmed to the offset register is simply the
binary representation of the adjustment value.
Removing Gain Error
The AD5765 can eliminate a gain error at negative full-scale
output in the range of −2 mV to +1.94 mV with a step size of ½
of a 16-bit LSB.
1. Calculate the step size of the gain adjustment.
Gain
Adjust
Step Size
=
8.192
216 × 2
=
62.5
μV
2. Measure the gain error by programming 0x8000 to the data
register and measuring the resulting output voltage. The
gain error is the difference between this value and −4.096 V;
for this example, the gain error is −0.8 mV.
3. Calculate how many gain adjustment steps this value
represents.
Number of Steps = Measured Gain Value = 0.8 mV = 13 Steps
Gain Step Size
62.5 μV
The gain error measured is negative (in terms of magnitude);
therefore, a positive adjustment of 13 steps is required. The gain
register is six bits wide and the coding is twos complement.
The required gain register value can be determined as follows:
1. Convert the adjustment value to binary: 001101.
The value to be programmed to the gain register is simply
this binary number.
Rev. C | Page 22 of 28
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