AD780

REV. B

–5–

NOISE PERFORMANCE

The impressive noise performance of the AD780 can be further

improved if desired by the addition of two capacitors: a load ca-

pacitor C1 between the output and ground, and a compensation

capacitor C2 between the TEMP pin and ground. Suitable val-

ues are shown in Figure 3.

100

1

0.1

0.1

1

100

10

10

LOAD CAPACITOR, C1 –

F

Figure 3. Compensation and Load Capacitor Combinations

C1 and C2 also improve the settling performance of the AD780

when subjected to load transients. The improvement in noise

performance is shown in Figures 4, 5 and 6 following.

10

90

100

0%

100 V1s

AMPLIFIER GAIN = 100

10

90

100

0%

20 V

10ms

NO AMPLIFIER

Figure 4. Stand-Alone Noise Performance

NC

TEMP

TRIM

GND

O/P SELECT

2.5V – NC

3.0V – GND

NC

AD780

NC = NO CONNECT

C2

1 F

C1

Figure 5. Noise Reduction Circuit

NOISE COMPARISON

The wideband noise performance of the AD780 can also be ex-

pressed in ppm. The typical performance with C1, C2 is

0.6 ppm and without external capacitors is 1.2 ppm.

This performance is respectively 7

and 3

lower than the

specified performance of the LT1019.

10

90

100

0%

20 V

10ms

10Hz TO 10kHz

NO AMPLIFIER

Figure 6. Reduced Noise Performance with C1 = 100

µF,

C2 = 100 nF

TEMPERATURE PERFORMANCE

The AD780 provides superior performance over temperature by

means of a combination of patented circuit design techniques,

precision thin film resistors and drift trimming. Temperature

performance is specified in terms of ppm/

°C, but because of

nonlinearity in the temperature characteristic, the Box-Test

method is used to test and specify the part. The nonlinearity

takes the form of the characteristic S-shaped curve shown in

Figure 7. The Box-Test method forms a rectangular box around

this curve, enclosing the maximum and minimum output volt-

ages over the specified temperature range. The specified drift is

equal to the slope of the diagonal of this box.

2.0

–0.8

140

0.4

–0.4

–40

0

–60

1.6

0.8

1.2

120

100

80

60

40

20

0

–20

TEMPERATURE – C

Figure 7. Typical AD780BN Temperature Drift