AD5763CSUZ datasheet(23/31 Pages) AD

23 / 31 page

Preliminary Technical Data

AD5763

Rev. PrA | Page 23 of 31

OFFSET AND GAIN ADJUSTMENT WORKED

EXAMPLE

Using the information provided in the previous section, the

following worked example demonstrates how the AD5763

functions can be used to eliminate both offset and gain errors.

As the AD5763 is factory calibrated, offset and gain errors

should be negligible. However, errors can be introduced by the

system that the AD5763 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 is assumed.

Removing Offset Error

The AD5763 can eliminate an offset error in the range of −2 mV to

+1.98 mV with a step size of ⅛ of a 16-bit LSB.

Calculate the step size of the offset adjustment.

625

192

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

Size

Step

Offset

Value

Offset

Measured

Steps

Number

625

614

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

Convert adjustment value to binary: 00101000.

Convert this 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

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 AD5763 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.

Calculate the step size of the gain adjustment.

192

Size

Step

Adjust

Gain

Measure the gain error by programming 0x8000 to the data

error is the difference between this value and −4.096 V; for this

example, the gain error is −0.8 mV.

Calculate how many gain adjustment steps this value represents.

Steps

Size

Step

Gain

Value

Gain

Measured

Steps

Number

The gain error measured is negative (in terms of magnitude);

therefore, a positive adjustment of 13 steps is required. The gain

required gain register value can be determined as follows:

Convert adjustment value to binary: 001101.

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

binary number.

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