AD5764R Datasheet, PDF (26/32 Pages) Analog Devices – Complete Quad, 16-Bit, High Accuracy, Serial Input, Bipolar Voltage Output DAC

AD5764R
OFFSET AND GAIN ADJUSTMENT WORKED
EXAMPLE
Using the information provided in the previous section, the
following worked example demonstrates how the AD5764R
functions can be used to eliminate both offset and gain errors.
As the AD5764R is factory calibrated, offset and gain errors
should be negligible. However, errors can be introduced by the
system that the AD5764R is operating within, for example, a
voltage reference value that is not equal to +5 V introduces a
gain error. An output range of ±10 V and twos complement
data coding is assumed.
Removing Offset Error
The AD5764R can eliminate an offset error in the range of −4.88
mV to +4.84 mV with a step size of ⅛ of a 16-bit LSB.
Calculate the step size of the offset adjustment,
Offset
Adjust
Step Size
=
20
2¹⁶ ×
8
=
38.14
μV
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.
How many offset adjustment steps does this value represent?
Numberof Steps = ^{Measured Offset Value} = ^{614 µV} = 16 Steps
Offset Step Size
38.14 µV
The offset error measured is positive, therefore, a negative
adjustment of 16 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:
Convert adjustment value to binary; 00010000.
Convert this to a negative twos complement number by
inverting all bits and adding 1; 11110000.
11110000 is the value that should be programmed to the offset
register.
Note: 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.
Preliminary Technical Data
Removing Gain Error
The AD5764R can eliminate a gain error at negative full-scale
output in the range of −9.77 mV to +9.46 mV with a step size of
½ of a 16-bit LSB.
Calculate the step size of the gain adjustment
Gain Adjust Step Size = ²⁰ = 152.59 µV
2¹⁶ × 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 −10 V, for this
example, the gain error is −1.2 mV.
How many gain adjustment steps does this value represent?
Number of Steps = ^{Measured Gain Value} = ^{1.2 mV} = 8 Steps
Gain Step Size 152.59 µV
The gain error measured is negative (in terms of magnitude);
therefore, a positive adjustment of eight steps is required. The
gain register is 6 bits wide and the coding is twos complement,
the required gain register value can be determined as follows:
Convert adjustment value to binary; 001000.
The value to be programmed to the gain register is simply this
binary number.
Rev. PrA | Page 26 of 32