TLC5620C, TLC5620I

QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTERS

SLAS081E – NOVEMBER 1994 – REVISED NOVEMBER 2001

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

supply rail is ground, the output cannot drive below ground and clamps the output at 0 V.

The output voltage then remains at zero until the input code value produces a sufficient positive output voltage

to overcome the 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 this 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 zero-input code (all inputs 0) and full-scale code (all inputs 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

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.