AD780
NOISE PERFORMANCE
NOISE COMPARISON
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
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
specified performance of the LT1019.
NO AMPLIFIER
20 V
10ms
lower than the
COMPENSATION CAP, C2 – nF
100
90
10
10
1
0%
10Hz TO 10kHz
0.1
0.1
1
10
100
LOAD CAPACITOR, C1 – F
Figure 6. Reduced Noise Performance with C1 = 100
µ
F,
C2 = 100 nF
TEMPERATURE PERFORMANCE
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.
AMPLIFIER GAIN = 100
100 V
100
90
NO AMPLIFIER
1s
100
90
20 V
10ms
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
10
0%
10
0%
0.1 TO
10Hz
10Hz
TO 10kHz
1.6
1.2
ERROR – mV
Figure 4. Stand-Alone Noise Performance
0.8
0.4
+V
IN
NC
1 F
NC
V
OUT
0
–0.4
AD780
TRIM
TEMP
C2
O/P SELECT
2.5V – NC
3.0V – GND
C1
–0.8
–60
–40
–20
0
20
40
60
80
100
120
140
GND
TEMPERATURE – C
Figure 7. Typical AD780BN Temperature Drift
NC = NO CONNECT
Figure 5. Noise Reduction Circuit
REV. B
–5–
AD [ ANALOG DEVICES ]
