AD8671 AD8672 AD8674 Analog Devices, AD8671 AD8672 AD8674 Datasheet - Page 12

• Manufacturer Part Number: AD8671 AD8672 AD8674
• Description: Precision, Very Low Noise, Low Input Bias Current Operational Amplifiers
• Manufacturer: Analog Devices

AD8671/AD8672/AD8674
THD + NOISE
The AD8671/AD8672/AD8674 exhibit low total harmonic
distortion over the entire audio frequency range. This makes
them suitable for applications with high closed-loop gains
including audio applications. Figure 35 shows approximately
0.0006% of THD + N in a positive unity gain, the worst-case
configuration for distortion.
DRIVING CAPACITIVE LOADS
The AD8671/AD8672/AD8674 can drive large capacitive loads
without causing instability. However, when configured in unity
gain, driving very large loads can cause unwanted ringing or
instability.
Figure 36 shows the output of the AD8671 with a capacitive
load of 1 nF. If heavier loads are to be used in low closed-loop
gain or unity gain configurations, it is recommended to use
external compensation as shown in the circuit in Figure 37. This
technique reduces the overshoot and prevents the op amp from
oscillation. The trade-off of this circuit is a reduction in output
swing. However, a great added benefit stems from the fact that
the input signal as well as the op amp’s noise are filtered, and
thus the overall output noise is kept to a minimum.
The output response of the circuit is shown in Figure 38.
0.1000
0.0500
0.0200
0.0100
0.0050
0.0020
0.0010
0.0005
0.0002
0.0001
20
Figure 35. Total Harmonic Noise and Distortion
50
100
200
Hz
500
1k
LT1007
2k
AD8671
5k
V
V
R
S
IN
L
= ±5V
= 600Ω
03726-0-014
= 2.5V
10k
20k
Rev. A | Page 12 of 16
Figure 37. Recommended Capacitive Load Circuit
500Ω
R
G
Figure 38. Compensated Load Drive
Figure 36. Capacitive Load Drive
V
C
680pF
IN
F
V
V
EE
CC
500Ω
V
R
C
V
A
V
R
C
C
V
A
R
SY
IN
SY
L
L
F
IN
V
L
L
V
F
= 2kΩ
= 1nF
= +1
= 2kΩ
= 1nF
= 220pF
= +1
= 100mV
= 100mV
= ±15V
= ±15V
10Ω
R
S
03726-0-023
03726-0-024
03726-0-017
CH2 +OVER
39.80%
CH2 –OVER
39.80%
C
1nF
CH2 +OVER
5.051%
CH2 –O V E R
6.061%
L