AD797BRZ-REEL Analog Devices Inc, AD797BRZ-REEL Datasheet - Page 12

• Manufacturer Part Number: AD797BRZ-REEL
• Description: IC,Operational Amplifier,SINGLE,BIPOLAR,SOP,8PIN,PLASTIC
• Manufacturer: Analog Devices Inc

Specifications of AD797BRZ-REEL

• Amplifier Type: General Purpose
• Number Of Circuits: 1
• Slew Rate: 20 V/µs
• Gain Bandwidth Product: 110MHz
• -3db Bandwidth: 8MHz
• Current - Input Bias: 250nA
• Voltage - Input Offset: 10µV
• Current - Supply: 8.2mA
• Current - Output / Channel: 50mA
• Voltage - Supply, Single/dual (±): ±5 V ~ 15 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD797
NOISE AND SOURCE IMPEDANCE CONSIDERATIONS
The AD797 ultralow voltage noise of 0.9 nV/√Hz is achieved
with special input transistors running at nearly 1 mA of collector
current. Therefore, it is important to consider the total input-
referred noise (e
noise (e
where R
This equation is plotted for the AD797 in Figure 33. Because
optimum dc performance is obtained with matched source
resistances, this case is considered even though it is clear from
Equation 1 that eliminating the balancing source resistance
lowers the total noise by reducing the total R
At very low source resistance (R
amplifier dominates. As source resistance increases, the Johnson
noise of R
achieved; the current noise component is larger than the
resistor noise.
The AD797 is the optimum choice for low noise performance if
the source resistance is kept <1 kΩ. At higher values of source
resistance, optimum performance with respect to only noise is
obtained with other amplifiers from Analog Devices (Table 5).
For up to date information, see AN-940 at www.analog.com
Table 5. Recommended Amplifiers for Different Source
Impedances
R
0 to <1
1 to <10
10 to <100
>100
S
(kΩ)
e
100
0.1
10
N
1
N
total
10
S
), current noise (i
is the total input source resistance.
S
dominates until a higher resistance of R
=
[
N
e
total), which includes contributions from voltage
Figure 33. Noise vs. Source Resistance
N
Recommended Amplifier
AD8597/AD8599, AD797, ADA4004-
1/ADA4004-2/ADA4004-4, AD8671/AD8672/
AD8674
AD8675/AD8676,
ADA4004-2/ADA4004-4, OP1177, OP27/OP37,
OP184
AD8677, OP1177, OP2177, OP4177,
AD8610/AD8620, AD8605/AD8606/AD8608,
ADA4627-1, OP97, AD548, AD549,
2
+
4
SOURCE RESISTANCE (Ω)
100
kTR
N
), and resistor noise (√4 kTR
S
+
S
RESISTOR
NOISE
ONLY
< 50 Ω), the voltage noise of the
(
i
N
ADA4075-2, ADA4004-1/
TOTAL NOISE
×
R
1000
S
)
2
]
1
2 /
S
by a factor of 2.
S
AD745
> 2 kΩ is
OP471
10000
S
).
Rev. H | Page 12 of 20
(1)
LOW FREQUENCY NOISE
Analog Devices specifies low frequency noise as a peak-to-peak
quantity in a 0.1 Hz to 10 Hz bandwidth. Several techniques can
be used to make this measurement. The usual technique involves
amplifying, filtering, and measuring the amplifier noise for a
predetermined test time. The noise bandwidth of the filter is
corrected for, and the test time is carefully controlled because
the measurement time acts as an additional low frequency roll-off.
The plot in Figure 6 uses a slightly different technique: an FFT-
based instrument (Figure 34) is used to generate a 10 Hz brickwall
filter. A low frequency pole at 0.1 Hz is generated with an external
ac coupling capacitor, which is also the instrument being dc coupled.
Several precautions are necessary to attain optimum low
frequency noise performance:
•
•
•
•
WIDEBAND NOISE
Due to its single-stage design, the noise of the AD797 is flat
over frequencies from less than 10 Hz to beyond 1 MHz. This
is not true of most dc precision amplifiers, where second-stage
noise contributes to input-referred noise beyond the audio
frequency range. The AD797 offers new levels of performance in
wideband imaging applications. In sampled data systems, where
aliasing of out-of-band noise into the signal band is a problem,
the AD797 outperforms all previously available IC op amps.
1 Ω
Care must be used to account for the effects of R
a 10 Ω resistor has 0.4 nV/√Hz of noise (an error of 9%
when root sum squared with 0.9 nV/√Hz).
The test setup must be fully warmed up to prevent e
from erroneously contributing to input noise.
Circuitry must be shielded from air currents. Heat flow out
of the package through its leads creates the opportunity for
a thermoelectric potential at every junction of different metals.
Selective heating and cooling of these by random air currents
appears as 1/f noise and obscures the true device noise.
The results must be interpreted using valid statistical
techniques.
*USE THE POWER SUPPLY BYPASSING SHOWN IN FIGURE 35.
Figure 34. Test Setup for Measuring 0.1 Hz to 10 Hz Noise
2
3
AD797
100k Ω
+V
–V
7
4
S
S
*
*
6
V
OUT
1.5µF
HP 3465
DYNAMIC SIGNAL
ANALYZER
(10Hz)
S
. Even
OS
drift