AD7846APZ datasheet(10/24 Pages) AD

10 / 24 page

AD7846

Rev. G | Page 10 of 24

TERMINOLOGY

Least Significant Bit

This is the analog weighting of 1 bit of the digital word in a

DAC. For the AD7846, 1 LSB = (VREF+ − VREF−)/216.

Relative Accuracy

Relative accuracy or endpoint nonlinearity 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 both endpoints (that is, offset and gain errors are

adjusted out) and is normally expressed in least significant bits

or as a percentage of full-scale range.

Differential Nonlinearity

Differential nonlinearity is the difference between the measured

change and the ideal change between any two adjacent codes. A

specified differential nonlinearity of ±1 LSB over the operating

temperature range ensures monotonicity.

Gain Error

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

DAC and the actual device output with all 1s loaded after offset

error has been adjusted out. Gain error is adjustable to zero

with an external potentiometer.

Offset Error

This is the error present at the device output with all 0s loaded

in the DAC. It is due to op amp input offset voltage and bias

current and the DAC leakage current.

Bipolar Zero Error

When the AD7846 is connected for bipolar output and 10…000

is loaded to the DAC, the deviation of the analog output from

the ideal midscale of 0 V is called the bipolar zero error.

Digital-to-Analog Glitch Impulse

This is the amount of charge injected from the digital inputs to

the analog output when the inputs change state. This is normally

specified as the area of the glitch in either pA-sec or nV-sec

depending upon whether the glitch is measured as a current or

a voltage.

Multiplying Feedthrough Error

This is an ac error due to capacitive feedthrough from either of

the VREF terminals to VOUT when the DAC is loaded with all 0s.

Digital Feedthrough

When the DAC is not selected (that is, CS is held high), high

frequency logic activity on the digital inputs is capacitively

coupled through the device to show up as noise on the VOUT pin.

This noise is digital feedthrough.

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