CLC1002 Datasheet, PDF (13/17 Pages) Cadeka Microcircuits LLC. – Ultra-Low Noise Amplifier

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.
+Vs
6.8μF
Input
+
0.1μF
-
0.1μF
Rg
6.8μF
-Vs
Output
RL
Rf
G = 1 + (Rf/Rg)
Figure 1. Typical Non-Inverting Gain Circuit
+Vs
6.8μF
Input
R1
+
Rg
-
0.1μF
0.1μF
Rf
Output
RL
6.8μF
-Vs
G = - (Rf/Rg)
For optimum input offset
voltage set R1 = Rf || Rg
Figure 2. Typical Inverting Gain Circuit
Achieving Low Noise in an Application
Making full use of the low noise of the CLC1002 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 25Ω, at
which point the noise from R_f and R_g is about equal to the
noise from the CLC1002. Lower value resistors could be
used at the expense of more distortion.
Figure 3 shows 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.
3
2.75
2.5
2.25
2
1.75
1.5
1.25
1
0.75
0.5
100
G = +5
G = +11
G = +21
Rf (Ohms)
1000
Figure 3: Input Referred Voltage Noise vs. R_f and R_g
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:
i_R =
4kT
R
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.
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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