AD820AR-REEL Analog Devices Inc, AD820AR-REEL Datasheet - Page 16

• Manufacturer Part Number: AD820AR-REEL
• Description: IC,Operational Amplifier,SINGLE,BIPOLAR/JFET,SOP,8PIN,PLASTIC
• Manufacturer: Analog Devices Inc

Specifications of AD820AR-REEL

• Rohs Status: RoHS non-compliant
• Amplifier Type: J-FET
• Number Of Circuits: 1
• Output Type: Rail-to-Rail
• Slew Rate: 3 V/µs
• Gain Bandwidth Product: 1.8MHz
• -3db Bandwidth: 1.9MHz
• Current - Input Bias: 2pA
• Voltage - Input Offset: 400µV
• Current - Supply: 700µA
• Current - Output / Channel: 20mA
• Voltage - Supply, Single/dual (±): 5 V ~ 36 V, ±2.5 V ~ 18 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)

AD820
APPLICATIONS INFORMATION
INPUT CHARACTERISTICS
In the AD820, N-channel JFETs are used to provide a low offset,
low noise, high impedance input stage. Minimum input common-
mode voltage extends from 0.2 V below –V
+V
loss of amplifier bandwidth (as can be seen by comparing the
large signal responses shown in Figure 29 and Figure 32) and
increased common-mode voltage error, as illustrated in
Figure 20.
The AD820 does not exhibit phase reversal for input voltages
up to and including +V
AD820 voltage follower to a 0 V to 5 V (+V
The input and output are superimposed. The output polarity
tracks the input polarity up to +V
reduced bandwidth above a 4 V input causes the rounding of
the output waveform. For input voltages greater than +V
resistor in series with the AD820 positive input prevents phase
reversal, at the expense of greater input voltage noise. This is
illustrated in Figure 38b.
Because the input stage uses N-channel JFETs, input current
during normal operation is negative; the current flows out from
the input terminals. If the input voltage is driven more positive
than +V
device junctions become forward biased. This is illustrated in
Figure 7.
A current-limiting resistor should be used in series with the
input of the AD820 if there is a possibility of the input voltage
exceeding the positive supply by more than 300 mV, or if an
input voltage is applied to the AD820 when ±V
amplifier can be damaged if left in that condition for more than
10 seconds. A 1 kΩ resistor allows the amplifier to withstand up
to 10 V of continuous overvoltage, and increases the input
voltage noise by a negligible amount.
Input voltages less than −V
The amplifier can safely withstand input voltages 20 V below
the negative supply voltage as long as the total voltage from
the positive supply to the input terminal is less than 36 V. In
addition, the input stage typically maintains picoamp level
input currents across that input voltage range.
The AD820 is designed for 13 nV/√Hz wideband input voltage
noise and maintains low noise performance to low frequencies
(refer to Figure 14). This noise performance, along with the
AD820 low input current and current noise, means that the
AD820 contributes negligible noise for applications with source
resistances greater than 10 kΩ and signal bandwidths greater
than 1 kHz. This is illustrated in Figure 39.
S
. Driving the input voltage closer to the positive rail causes a
S
− 0.4 V, the input current reverses direction as internal
S
. Figure 38a shows the response of an
S
are a completely different story.
S
with no phase reversal. The
S
S
) square wave input.
to 1 V less than
S
= 0 V. The
S
, a
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GND
GND
+V
100k
10k
100
S
0.1
1k
10
Figure 38. (a) Response with R
1
10k
100
100
0%
0%
90
10
90
10
WHENEVER JOHNSON NOISE IS GREATER THAN
AMPLIFIER NOISE, AMPLIFIER NOISE CAN BE
CONSIDERED NEGLIGIBLE FOR APPLICATION.
Figure 39. Total Noise vs. Source Impedance
RESISTOR JOHNSON
100k
1V
1V
1V
1V
V
V
(b) V
NOISE
IN
OUT
+
–
= 0 V to +V
IN
SOURCE IMPEDANCE (Ω)
1M
= 0 V to +V
R
P
1V
AD820
S
10M
+
–
, R
(a)
(b)
P
= 0 Ω; V
S
P
5V
+ 200 mV,
= 49.9 kΩ
AMPLIFIER-GENERATED
100M
IN
from 0 V to +V
1kHz
NOISE
2µs
10µs
1G
V
+
–
OUT
10Hz
S
10G