AD8061/AD8062/AD8063
3.6
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
3.7
3.5
3.3
3.1
2.9
2.7
2.5
2.3
2.1
VOLTAGE STEP
FROM 2.4V TO 3.4V
2V TO 3V STEP
2.1V TO 3.1V STEP
VOLTAGE STEP
FROM 2.4V TO 3.6V
2.2V TO 3.2V STEP
2.3V TO 3.3V STEP
VOLTAGE STEP
FROM 2.4V TO 3.8V,
4V AND 5V
2.4V TO 3.4V STEP
0
100
200
300
400
500
600
0
4
8
12
16
20
24
28
32
TIME (ns)
TIME (ns)
Figure 48. Pulse Response for G = 1 Follower,
Input Step Overloading the Input Stage
Figure 47. Output Rising Edge for 1 V Step at
Input Headroom Limits, G = 1, VS = 5 V, 0 V
Output
As the saturation point of the output stage is approached, the
output signal shows increasing amounts of compression and
clipping. As in the input headroom case, the higher frequency
signals require a bit more headroom than lower frequency
signals. Figure 16, Figure 17, and Figure 18 illustrate this point,
plotting typical distortion vs. output amplitude and bias for
gains of 2 and 5.
Output overload recovery is typically within 40 ns after the
amplifier’s input is brought to a nonoverloading value. Figure 49
shows output recovery transients for the amplifier recovering
from a saturated output from the top and bottom supplies to a
point at midsupply.
5.0
4.6
OVERLOAD BEHAVIOR AND RECOVERY
Input
OUTPUT VOLTAGE
4.2
5V TO 2.5V
3.8
OUTPUT VOLTAGE
3.4
The specified input common-mode voltage of the AD806x
is −200 mV below the negative supply to within 1.8 V of
the positive supply. Exceeding the top limit results in lower
bandwidth and increased settling time as seen in Figure 46
and Figure 47. Pushing the input voltage of a unity-gain
follower beyond 1.6 V within the positive supply leads to the
behavior shown in Figure 48—an increasing amount of output
error and much increased settling time. Recovery time from
input voltages 1.6 V or closer to the positive supply is approxi-
mately 35 ns, which is limited by the settling artifacts caused by
transistors in the input stage coming out of saturation.
0V TO 2.5V
3.0
2.6
2.2
1.8
1.4
1.0
INPUT VOLTAGE
EDGES
R
5V
R
V
–
IN
2.5V
V
O
–
0.6
0.2
–0.2
0
10
20
30
40
TIME (ns)
50
60
70
Figure 49. Overload Recovery, G = −1, VS = 5 V
The AD806x family does not exhibit phase reversal, even for
input voltages beyond the voltage supply rails. Going more
than 0.6 V beyond the power supplies will turn on protection
diodes at the input stage, which will greatly increase the device’s
current draw.
CAPACITIVE LOAD DRIVE
The AD806x family is optimized for bandwidth and speed, not
for driving capacitive loads. Output capacitance creates a pole
in the amplifier’s feedback path, leading to excessive peaking
and potential oscillation. If dealing with load capacitance is a
requirement of the application, the two strategies to consider
are as follows:
1. Use a small resistor in series with the amplifier’s output and
the load capacitance.
2. Reduce the bandwidth of the amplifier’s feedback loop by
increasing the overall noise gain.
Rev. D | Page 15 of 20
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