AD7740

REV. A

–5–

TERMINOLOGY

INTEGRAL NONLINEARITY

For the VFC, Integral Nonlinearity (INL) is a measure of the maxi-

mum deviation from a straight line passing through the actual

endpoints of the VFC transfer function. The error is expressed in

% of the actual frequency span:

Frequency Span = FOUT(max) – FOUT(min)

OFFSET ERROR

Ideally, the output frequency for 0 V input voltage is 10% of

to the input is the offset error at BUF = 0. In buffered mode the

minimum output frequency (corresponding to 0.10 V minimum

from this value referred to the input is the offset error at BUF = 1.

Offset error is expressed in mV.

GAIN ERROR

This is a measure of the span error of the VFC. The gain is the

scale factor that relates the input VIN to the output FOUT.

The gain error is the deviation in slope of the actual VFC transfer

characteristic from the ideal expressed as a percentage of the full-

scale span. See Figure 2.

OFFSET ERROR DRIFT

This is a measure of the change in Offset Error with changes in

temperature. It is expressed in

µV/°C.

GAIN ERROR DRIFT

This is a measure of the change in Gain Error with changes in

temperature. It is expressed in (ppm of span)/

°C.

POWER SUPPLY REJECTION RATIO (PSRR)

This indicates how the apparent input voltage of the VFC is

affected by changes in the supply voltage. The input voltage is

10% at 3.3 V and

±5% at 5 V. The ratio of the apparent change

in input voltage to the change in VDD is measured in dBs.

0

REFIN

WITH OFFSET

ERROR ONLY

IDEAL

GAIN ERROR

OUTPUT

FREQUENCY

FOUT

OFFSET

ERROR

WITH OFFSET

ERROR AND

GAIN ERROR

INPUT

VOLTAGE

VIN

0.1

Figure 2. Offset and Gain