TLC5628C, TLC5628I

OCTAL 8-BIT DIGITAL-TO-ANALOG CONVERTERS

SLAS089E – NOVEMBER 1994 – REVISED APRIL 1997

5

POST OFFICE BOX 655303

linearity, offset, and gain error using single-end supplies

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

a positive offset voltage, 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, therefore, attempts to drive the output to a negative voltage. However, because the most

negative supply rail is ground, the output cannot drive below ground.

The output voltage remains at 0 V 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)

This offset error, not the linearity error, produces the breakpoint. The transfer function would have followed the

dotted line if the output buffer could drive below ground.

For a DAC, linearity is measured between the zero-input code (all inputs are 0) and the full-scale code (all inputs

are 1) after offset and full scale are 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. So the

linearity in the unipolar mode is measured between full-scale code and the lowest code that produces a positive

output voltage.

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