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LINEARITY, OFFSET, AND GAIN ERROR USING SINGLE ENDED SUPPLIES

DAC Code

Output

Voltage

0 V

Negative

Offset

TLV5637

SLAS224C – JUNE 1999 – REVISED JUNE 2007

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 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 0V.

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

to overcome the negative offset voltage, resulting in the transfer function shown in Figure 14 .

Figure 14. 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 the ground rail.

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.

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