TSH310 Datasheet, PDF (12/19 Pages) STMicroelectronics – 400A High-Speed Operational Amplifier

TSH310
5 Noise Measurements
The noise model is shown in Figure 28, where:
l eN: input voltage noise of the amplifier
l iNn: negative input current noise of the amplifier
l iNp: positive input current noise of the amplifier
Figure 28: Noise model
Noise Measurements
+
R3
iN+
_
N3 _{iN- eN}
output
HP3577
Input noise:
8nV/√Hz
N2
R2
R1
N1
The thermal noise of a resistance R is:
4kTR∆F
where ∆F is the specified bandwidth.
On a 1Hz bandwidth the thermal noise is reduced to
4kTR
where k is the Boltzmann's constant, equal to 1,374.10-23J/°K. T is the temperature (°K).
The output noise eNo is calculated using the Superposition Theorem. However eNo is not the simple sum
of all noise sources, but rather the square root of the sum of the square of each noise source, as shown
in Equation 1:
eNo = V12 + V22 + V32 + V42 + V52 + V62
Equation 1
eNo²
=
eN²
×
g²
+
i
Nn²
×
R
2
2
+
i
Np²
×
R
2
3
×
g²
+
R_-----2-- ²
R1
×
4k
T
R
1
+
4k
T
R
2
+
1
+
R_-----2--
R1
2
×
4
kT
R3
Equation 2
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