ADA4841-1YRZ Analog Devices, ADA4841-1YRZ Datasheet - Page 14

• Manufacturer Part Number: ADA4841-1YRZ
• Manufacturer: Analog Devices

ADA4841-1
The output noise spectral density can be calculated by
where:
k is Boltzmann’s Constant.
T is the absolute temperature, degrees Kelvin.
ien is the amplifier input current noise spectral density, pA/√Hz.
ven is the amplifier input voltage spectral density, nV/√Hz.
R
R
Figure 38.
Source resistance noise, amplifier voltage noise ( ven ), and the
voltage noise from the amplifier’s current noise ( ien × R
all subject to the noise gain term (1 + R
2 nV/√Hz input voltage noise and 1 pA/√Hz input current, the
noise contributions of the amplifier are relatively small for
source resistances between approximately 200 Ω and 30 kΩ.
Figure 39 shows the total RTI noise due to the amplifier vs. the
source resistance. In addition, the value of the feedback resistors
used impacts the noise. It is recommended to keep the value of
feedback resistors between 250 Ω and 1 kΩ to keep the total
noise low.
HEADROOM CONSIDERATIONS
The ADA4841-1 is designed to provide maximum input and
output signal ranges with 16-bit to 18-bit dc linearity. As the
input or output headroom limits are reached, the signal’s
linearity degrades.
vout
S
F
4
is the source resistance as shown in Figure 38.
and R
kTRf
1000
_
100
0.1
en
10
1
10
+
G
=
⎛
⎜
⎜
⎝
are the feedback network resistances, as shown in
1
+
SOURCE RESISTANCE NOISE
R
R
Figure 39. RTI Noise vs. Source Resistance
G
F
⎞
⎟
⎟
⎠
2
[
4
100
kTRs
SOURCE RESISTANCE (Ω)
AMPLIFIER + RESISTOR NOISE
+
ien
2
R
S
1k
2
+
ven
TOTAL AMPLIFIER NOISE
F
2
/R
]
+
G
⎛
⎜
⎜
⎝
). Note that with a
R
R
10k
G
F
⎞
⎟
⎟
⎠
2
4
kTRg
S
) are
+
100k
ien
Rev. A | Page 14 of 20
(6)
2
R
F
2
The input stage positive limit is almost exactly a volt below the
positive supply at room temperature. Input voltages above that
start to show clipping behavior. The positive input voltage limit
increases with temperature with a coefficient of about 2 mV/°C.
The lower supply limit is nominally below the minus supply;
therefore, in a standard gain configuration, the output stage
limits the signal headroom on the negative supply side. Figure 40
and Figure 41 show the nominal CMRR behavior at the limits of
the input headroom for three temperatures—this is generated
using the subtractor topology shown in Figure 42, which avoids
the output stage limitation.
–100
–140
–180
–220
–260
–300
300
260
220
180
140
100
–20
–60
60
20
–100
–150
–200
–250
–300
–350
–400
–450
–500
–550
–600
–650
–700
–750
–800
–50
3.00
–6.00
0
+125°C
–40°C
+25°C
3.20
–5.80 –5.60 –5.40 –5.20 –5.00 –4.80 –4.60 –4.40 –4.20
Figure 40. V
Figure 41. V
– V
Figure 42. Common-Range Subtractor
3.40
CM
+
COMMON-MODE VOLTAGE (V)
3.60
OS
COMMON-MODE VOLTAGE (V)
OS
vs. +CMP vs. Common-Mode Error
vs. −CMP vs. Common-Mode Error
3.80
4.00
4.20
+ V
4.40
OUT
–
4.60
+125°C
–40°C
+25°C
4.80
–4.00
5.00