6

LTC1257

DEFI ITIO S

LSB: The least significant bit or the ideal voltage difference

between two successive codes.

n

= The number of digital input bits

measured when all bits are set to 1

Resolution: The resolution is the number of DAC output

does not imply linearity.

INL: End-point integral nonlinearity is the maximum de-

viation from a straight line passing through the end-points

of the DAC transfer curve. Because the part operates from

a single supply and the output cannot go below ground,

the linearity is measured between full-scale and the first

code that guarantees a positive output. The INL error at a

given input code is calculated as follows:

INL

the given input code

DNL: Differential nonlinearity is the difference between

the measured change and the ideal 1LSB change between

any two adjacent codes. The DNL error between any two

codes is calculated as follows:

DNL

= (

two adjacent codes

Offset Error: The theoretical voltage at the output when

the DAC is loaded with all zeros. The output amplifier can

have a true negative offset, but because the part is oper-

ated from a single supply, the output cannot go below

ground. If the offset is negative, the output will remain near

0V resulting in the transfer curve shown in Figure 1.

Figure 1. Effect of Negative Offset

The offset of the part is measured at the first code that

produces an output voltage 0.5LSB greater than the pre-

vious code:

Full-Scale Error: Full-scale error is the difference be-

tween the ideal and measured DAC output voltages with all

bits set to one (Code = 4095). The full-scale error includes

the offset error and is calculated as follows:

FSE

external

Digital Feedthrough: The glitch that appears at the analog

output caused by AC coupling from the digital inputs when

they change state. The area of the glitch is specified in

(nV)(sec).

OUTPUT

VOLTAGE

NEGATIVE

DAC CODE

0V

1257 F01