TLV5628C, TLV5628I

OCTAL 8-BIT DIGITAL-TO-ANALOG CONVERTERS

SLAS108A – JANUARY 1995 – REVISED NOVEMBER 1995

6

POST OFFICE BOX 655303

linearity, offset, and gain error

When an amplifier is operated from a single supply, the voltage offset can still be either positive or negative. With

a positive offset, the output voltage changes on the first code change. With a negative offset the output voltage

may not change with the first code depending on the magnitude of the offset voltage.

The output amplifier, with a negative voltage offset, attempts to drive the output to a negative voltage. However,

since the most negative supply rail is ground, the output cannot drive to a negative voltage.

So when the output offset voltage is negative, the output voltage remains at 0 volts until the input code value

produces a sufficient output voltage to overcome the inherent negative offset voltage resulting in the transfer

function shown in Figure 5.

DAC Code

Output

Voltage

0 V

Negative

Offset

Figure 5. Effect of Negative Offset (Single Supply)

The negative offset error produces a breakpoint, not a linearity error. The transfer function would follow the

dotted line if the output buffer could drive to a negative voltage.

For a DAC, linearity is measured between zero input code (all inputs 0) and full scale code (all inputs 1) after

offset and full scale is adjusted out or accounted for in some way. However, single supply operation does not

allow for adjustment when the offset is negative due to the breakpoint in the transfer function. The linearity in

the unipolar mode is measured between full scale code and the lowest code which produces a positive output

voltage.

The code is calculated from the maximum specification for the negative offset.

equivalent inputs and outputs

GND

Vref

Input

VDD

To DAC

Resistor

String

_

+

VDD

DAC

Voltage Output

ISINK

60

µA

Typical

84 k

Ω

84 k

Ω

× 1

× 2

Output

Range

Select

Input from

Decoded DAC

Register String

INPUT CIRCUIT

OUTPUT CIRCUIT

GND