AD8610ARM Analog Devices, AD8610ARM Datasheet - Page 12

• Manufacturer Part Number: AD8610ARM
• Description: Precision Very Low Noise Low Input Bias Current Wide Bandwith JFET Operational Amplifier
• Manufacturer: Analog Devices

AD8610
Input Overvoltage Protection
When the input of an amplifier is driven below V
V
substrate through the negative supply (V–) or the positive supply
(V+), respectively, to the input pins, which can destroy the de-
vice. If the input source can deliver larger currents than the
maximum forward current of the diode (>5 mA), a series resis-
tor can be added to protect the inputs. With its very low input
bias and offset current, a large series resistor can be placed in front
of the AD8610 inputs to limit current to below damaging levels.
Series resistance of 10 kΩ will generate less than 25 µV of offset.
This 10 kΩ will allow input voltages more than 5 V beyond either
power supply. Thermal noise generated by the resistor will add
7.5 nV/√Hz to the noise of the AD8610. For the AD8610, differ-
ential voltages equal to the supply voltage will not cause any
problem (see Figure 15). In this context it should also be noted
that the high breakdown voltage of the input FETs eliminates the
need to include clamp diodes between the inputs of the amplifier, a
practice that is mandatory on many precision op amps. Unfortu-
nately, clamp diodes greatly interfere with many application
circuits such as precision rectifiers and comparators. The
AD8610 is free from these limitations.
No Phase Reversal
Many amplifiers misbehave when one or both of the inputs are
forced beyond the input common-mode voltage range. Phase
reversal is typified by the transfer function of the amplifier,
effectively reversing its transfer polarity. In some cases this can
cause lockup and even equipment damage in servo systems, and
may cause permanent damage or nonrecoverable parameter
shifts to the amplifier itself. Many amplifiers feature compensation
circuitry to combat these effects, but some are only effective for
the inverting input. The AD8610 is designed to prevent phase
reversal when one or both inputs are forced beyond their input
common-mode voltage range.
CC
by more than one V
0V
0V
CH
CH
1
2
14V
= 20.8V/DIV
= 19.4V/DIV
V1
0
BE
, large currents will flow from the
TIME – 400ns/DIV
3
2
+13V
–13V
7
4
AD8610
6
EE
or above
THD Readings vs. Common-Mode Voltage
Total Harmonic Distortion of the AD8610 is well below 0.0006%
with any load down to 600 Ω. The AD8610 outperforms the
OPA627 for distortion, especially at frequencies above 20 kHz.
0.0001
0.001
0.001
0.01
0.01
0.1
0.1
10
0
10
V
R
SY
L
= 600
=
4V rms
13V
100
100
6V rms
FREQUENCY – Hz
2V rms
TIME – 400 s/DIV
FREQUENCY – Hz
1k
1k
V
IN
10k
V
V
BW = 80kHz
SY
IN
OPA627
AD8610
= 5V rms
=
V
10k
13V
OUT
80k
20k