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LTC1456CS8

12-Bit Rail-to-Rail Micropower DAC with Clear Input

Linear Technology 

LTC1456

UU

DEFI ITIO S

Resolution (n): Resolution is defined as the number of

digital input bits, n. It defines the number of DAC output

states (2n) that divide the full-scale range. The resolution

does not imply linearity.

Full-Scale Voltage (VFS): This is the output of the DAC

when all bits are set to 1.

Voltage Offset Error (VOS): 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 operated from a single supply, the output cannot go

below zero. If the offset is negative, the output will remain

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

The offset of the part is measured at the code that corre-

sponds to the maximum offset specification:

VOS = VOUT – [(Code • VFS)/(2n – 1)]

Least Significant Bit (LSB): One LSB is the ideal voltage

difference between two successive codes.

LSB = (VFS – VOS)/(2n – 1) = (VFS – VOS)/4095

LSB = 4.095/4095 = 1mV

Integral Nonlinearity (INL): End-point INL is the maxi-

mum deviation 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 zero, the linearity is measured between full scale

and the code corresponding to the maximum offset speci-

fication. The INL error at a given input code is calculated

as follows:

INL = [VOUT – VOS – (VFS – VOS)(code/4095)]/LSB

VOUT = The output voltage of the DAC measured at

the given input code

Differential Nonlinearity (DNL): DNL 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 = (∆VOUT – LSB)/LSB

∆VOUT = The measured voltage difference between

two adjacent codes

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 0V

OFFSET

DAC CODE

1456 F01

Figure 1. Effect of Negative Offset

6

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