Datasheet

Data Sheet AD8671/AD8672/AD8674
Rev. F | Page 13 of 20
TOTAL HARMONIC DISTORTION (THD) AND NOISE
The AD8671/AD8672/AD8674 exhibit low total harmonic
distortion (THD) over the entire audio frequency range. This
makes them suitable for applications with high closed-loop
gains, including audio applications. Figure 33 shows
approximately 0.0006% of THD + N in a positive unity gain, the
worst-case configuration for distortion.
Hz
100 1k 10k
PERCENTAGE
LT1007
0.0001
0.0002
0.0005
0.0010
0.0020
0.0050
0.0100
0.0200
0.0500
0.1000
5020 500200
5k
2k
AD8671
20k
03718-B-035
V
S
= ±5V
V
IN
= 2.5V
R
L
= 600Ω
Figure 33. Total Harmonic Distortion and Noise
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 34 shows the output of the AD8671 with a capacitive
load of 1 nF. If heavier loads are used in low closed-loop gain or
unity-gain configurations, it is recommended to use external
compensation as shown in the circuit in Figure 35. 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 and 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 36.
03718-B-036
V
SY
=
±15V
R
L
= 2k
Ω
C
L
= 1nF
V
IN
= 100mV
A
V
= +1
CH2 +OVER
39.80%
CH2 –
OVER
39.80%
TIME (10µ
s/DIV)
VOLTAGE (500mV/DIV)
Figure 34. AD8671 Capacitive Load Drive
500Ω
R
F
V
CC
220pF
C
F
V
IN
V
EE
R
G
500Ω
10Ω
R
S
1nF
C
L
03718-B-037
2kΩ
R
L
Figure 35. Recommended Capacitive Load Circuit
03718-B-038
V
SY
= ±15V
R
L
= 2kΩ
C
L
= 1nF
C
F
= 220pF
V
IN
= 100mV
A
V
= +2
CH2 +OVER
5.051%
CH2 –OVER
6.061%
TIME (10µs/DIV)
VOLTAGE (100mV/DIV)
Figure 36. Compensated Load Drive