Data Sheet
Application Information
Basic Operation
Figures 1 and 2 illustrate typical circuit configurations for
non-inverting, inverting, and unity gain topologies for dual
supply applications. They show the recommended bypass
capacitor values and overall closed loop gain equations.
+V
s
6.8μF
total input voltage noise (amp+resistors) versus R
f
and
R
g
. As the value of R
f
increases, the total input referred
noise also increases.
2.75
2.5
C
omlinear
CLC1001
Ultra-Low Noise Amplifier
Input Referred Noise (nV/rtHz)
2.25
2
1.75
1.5
1.25
1
0.75
0.5
100
G = +41
G = +21
G = +11
Input
+
-
0.1μF
Output
0.1μF
R
L
R
f
G = 1 + (R
f
/R
g
)
1000
Rf (Ohms)
R
g
-V
s
6.8μF
Figure 3: Input Referred Voltage Noise vs. R
f
and R
g
Figure 1. Typical Non-Inverting Gain Circuit
+V
s
6.8μF
The noise caused by a resistor is modeled with either a
voltage source in series with the resistance:
4kTR
Or a current source in parallel with it:
R
1
Input
R
g
+
-
0.1μF
Output
0.1μF
6.8μF
-V
s
R
L
R
f
G = - (R
f
/R
g
)
For optimum input offset
voltage set R
1
= R
f
|| R
g
Rev 1D
i
R
=
4kT
R
Figure 2. Typical Inverting Gain Circuit
Op amp noise is modeled with three noise sources, e
n
, i
n
and i
i
. These three sources are analogous to the DC input
voltage and current errors V
os
, I
bn
and I
bi
.
Achieving Low Noise in an Application
Making full use of the low noise of the CLC1001 requires
careful consideration of resistor values. The feedback and
gain set resistors (R
f
and R
g
) and the non-inverting source
impedance (R
source
) all contribute noise to the circuit and
can easily dominate the overall noise if their values are
too high. The datasheet is specified with an R
g
of 22.1Ω,
at which point the noise from R
f
and R
g
is about equal to
the noise from the CLC1001. Lower value resistors could
be used at the expense of more distortion. Figure 3 shows
The noise models must be analyzed in-circuit to deter-
mine the effect on the op amp output noise.
Since noise is statistical in nature rather than a continuous
signal, the set of noise sources in circuit add in an RMS
(root mean square) fashion rather than in a linear fashion.
For uncorrelated noise sources, this means you add the
squares of the noise voltages. A typical non-inverting ap-
plication (see figure 1) results in the following noise at the
output of the op amp:
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www.cadeka.com
13
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