AD5764CSUZ datasheet(23/28 Pages) AD

23 / 28 page

Data Sheet

AD5764

Rev. F | Page 23 of 28

OFFSET AND GAIN ADJUSTMENT WORKED

EXAMPLE

Using the information provided in the Fine Gain Register and

Offset Register sections, the following worked example demon-

strates how the AD5764 functions can be used to eliminate both

offset and gain errors. Because the AD5764 is factory calibrated,

offset and gain errors should be negligible. However, errors can

be introduced by the system that the AD5764 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 AD5764 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.

μV

Size

Step

Adjust

Offset

Measure the offset error by programming 0x0000 to the data

example, the measured value is 614 μV.

Calculate the number of offset adjustment steps that this value

represents.

Steps

μV

614

Size

Step

Offset

Value

Offset

Measured

Steps

Number

The offset error measured is positive, therefore, a negative

adjustment of 16 steps is required. The offset register is eight

bits wide and the coding is twos complement. The required

offset register value can be calculated as follows:

Convert the adjustment value to binary: 00010000.

Convert this to a negative twos complement number by inverting

all bits and adding 1 to obtain 11110000, 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 AD5764 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.

μV

152

Size

Step

Adjust

Gain

Measure the gain error by programming 0x8000 to the data

error is the difference between this value and −10 V. For this

example, the gain error is −1.2 mV.

Calculate how many gain adjustment steps this value represents.

Steps

μV

152

Size

Step

Gain

Value

Gain

Measured

Steps

Number

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 the adjustment value to binary: 001000.

The value to be programmed to the gain register is simply this

binary number.

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