AD767

REV. A

–4–

THE AD767 OFFERS TRUE 12-BIT PERFORMANCE

OVER THE FULL TEMPERATURE RANGE

LINEARITY ERROR: Analog Devices defines linearity error as

the maximum deviation of the actual, adjusted DAC output

from the ideal analog output (a straight line drawn from 0 to

F.S. – 1 LSB) for any bit combination. This is also referred to as

relative accuracy. The AD767 is laser trimmed to typically

maintain linearity errors at less than

±1/8 LSB for the K and B

versions and

±1/2 LSB for the J, A and S versions. Linearity

over temperature is also held to

±1/2 LSB (K/B) or ±1 LSB

(J/A/S).

MONOTONICITY: A DAC is said to be monotonic if the

output either increases or remains constant for increasing digital

inputs such that the output will always be a nondecreasing

function of input. All versions of the AD767 are monotonic over

their full operating temperature range.

DIFFERENTIAL NONLINEARITY: Monotonic behavior

requires that the differential linearity error be less than 1 LSB

both at +25

°C as well as over the temperature range of interest.

Differential nonlinearity is the measure of the variation in analog

value, normalized to full scale, associated with a 1 LSB change

in digital input code. For example, for a 10 volt full-scale

output, a change of 1 LSB in digital input code should result in

a 2.44 mV change in the analog output (1 LSB = 10 V

1/4096 = 2.44 mV). If in actual use, however, a 1 LSB change

in the input code results in a change of only 0.61 mV (1/4 LSB)

in analog output, the differential nonlinearity error would be

–1.83 mV, or –3/4 LSB.

GAIN ERROR: DAC gain error is a measure of the difference

between an ideal DAC and the actual device’s output span. All

grades of the AD767 have a maximum gain error of 0.2% FS.

However, if this is not sufficient, the error can easily be adjusted

to zero (see Figures 2 and 3).

UNIPOLAR OFFSET ERROR: Unipolar offset error is a

combination of the offset errors of the voltage-mode DAC and

the output amplifier and is measured when the AD767 is

configured for unipolar outputs. It is present for all codes and is

measured with all “0s” in the DAC latches. This is easily

adjustable to zero when required.

BIPOLAR ZERO ERROR: Bipolar zero errors result from

errors produced by the DAC and output amplifier when the

AD767 is configured for bipolar output. Again, as with unipolar

offset and gain errors, this is easily adjusted to zero when

required.

ANALOG CIRCUIT CONNECTIONS

Internal scaling resistors provided in the AD767 may be connected

to produce bipolar output voltage ranges of

±10, ±5 or ±2.5 V

or unipolar output voltage ranges of 0 to +5 V or 0 to +10 V.

Gain and offset drift are minimized in the AD767 because of the

thermal tracking of the scaling resistors with other device

components. Connections for various output voltage ranges are

shown in Table I.

Figure 1. Output Amplifier Voltage Range Scaling Circuit

UNIPOLAR CONFIGURATION (Figure 2)

This configuration will provide a unipolar 0 to +10 volt output

range. In this mode, the bipolar offset terminal, Pin 4, should be

grounded if not used for trimming.

STEP I … ZERO ADJUST

Turn all bits OFF and adjust zero trimmer R1, until the output

reads 0.000 volts (1 LSB = 2.44 mV). In most cases this trim is

not needed, and Pin 4 should be connected to Pin 5.

STEP II … GAIN ADJUST

Turn all bits ON and adjust 100

Ω gain trimmer R2 until the

output is 9.9976 volts. (Full scale is adjusted to 1 LSB less than

nominal full scale of 10.000 volts.)

Figure 2. 0 to +10 V Unipolar Voltage Output

Table I. Output Voltage Range Connections

Output

Digital

Connect

Connect

Connect

Connect

Range

Input Codes

Pin 9 to

Pin 1 to

Pin 2 to

Pin 4 to

±10 V

Offset Binary

1

9

NC

6 (through 50

Ω fixed or 100 Ω trim resistor)

±5 V

Offset Binary

1 and 2

2 and 9

1 and 9

6 (through 50

Ω fixed or 100 Ω trim resistor)

±2.5 V

Offset Binary

2

3

9

6 (through 50

Ω fixed or 100 Ω trim resistor)

0 to +10 V

Straight Binary

1 and 2

2 and 9

1 and 9

5 (or optional trim – See Figure 2)

0 to +5 V

Straight Binary

2

3

9

5 (or optional trim – See Figure 2)