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AD7568BS

LC2MOS Octal 12-Bit DAC

Analog Devices 

AD7568

TERMINOLOGY

Relative Accuracy

Relative Accuracy or endpoint linearity is a measure of the

maximum deviation from a straight line passing through the

endpoints of the DAC transfer function. It is measured after

adjusting for zero error and full-scale error and is normally ex-

pressed in Least Significant Bits or as a percentage or full-scale

reading.

Differential Nonlinearity

Differential nonlinearity is the difference between the measured

change and the ideal 1 LSB change between any two adjacent

codes. A specified differential nonlinearity of 1 LSB maximum

ensures monotonicity.

Gain Error

Gain Error is a measure of the output error between an ideal

DAC and the actual device output. It is measured with all 1s in

the DAC after offset error has been adjusted out and is

expressed in Least Significant Bits. Gain error is adjustable to

zero with an external potentiometer.

Output Leakage Current

Output leakage current is current which flows in the DAC lad-

der switches when these are turned off. For the IOUT1 terminal,

it can be measured by loading all 0s to the DAC and measuring

the IOUT1 current. Minimum current will flow in the IOUT2 line

when the DAC is loaded with all 1s. This is a combination of

the switch leakage current and the ladder termination resistor

current. The IOUT2 leakage current is typically equal to that in

IOUT1.

Output Capacitance

This is the capacitance from the IOUT1 pin to AGND.

Output Voltage Settling Time

This is the amount of time it takes for the output to settle to a

specified level for a full-scale input change. For the AD7568, it

is specified with the AD843 as the output op amp.

Digital to Analog Glitch Impulse

This is the amount of charge injected into the analog output

when the inputs change state. It is normally specified as the area

of the glitch in either pA-secs or nV-secs, depending upon

whether the glitch is measured as a current or voltage signal. It

is measured with the reference input connected to AGND and

the digital inputs toggled between all 1s and all 0s.

AC Feedthrough Error

This is the error due to capacitive feedthrough from the DAC

reference input to the DAC IOUT terminal, when all 0s are

loaded in the DAC.

Channel-to-Channel Isolation

Channel-to-channel isolation refers to the proportion of input

signal from one DAC’s reference input which appears at the

output of any other DAC in the device and is expressed in dBs.

Digital Crosstalk

The glitch impulse transferred to the output of one converter

due to a change in digital input code to the other converter is

defined as the Digital Crosstalk and is specified in nV-secs.

Digital Feedthrough

When the device is not selected, high frequency logic activity on

the device digital inputs is capacitively coupled through the de-

vice to show up as noise on the IOUT pin and subsequently on

the op amp output. This noise is digital feedthrough.

Table I. AD7568 Loading Sequence

DB15

DB0

DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 A0 DS2 DS1 DS0

Table II. DAC Selection

DS2

DS1

DS0

Function

0

0

0

DAC A Selected

0

0

1

DAC B Selected

0

1

0

DAC C Selected

0

1

1

DAC D Selected

1

0

0

DAC E Sclected

1

0

1

DAC F Selected

1

1

0

DAC G Sclected

1

1

1

DAC H Selected

REV. B

–5–

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