Measurement Theory Principles

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5. SOURCES OF ERRORS. 5.4. Low-noise design
noise matching. 5.4.1. Optimum source resistance
5.4. Low-noise design noise matching
5.4.1. Optimum source resistance
The.
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5. SOURCES OF ERRORS. 5.4. Low-noise design
noise matching. 5.4.1. Optimum source resistance
Example Noise factor and SNR as a function
of Rs
en 2 nV/Hz0.5, in 20 pA /Hz0.5
vn in rms 4kTRs en rms2
(in rms Rs)20.5
in Rs
vn in rms, nV/Hz0.5
en
1
0.8
0.6
0.4
0.2
0
Rs, W
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5. SOURCES OF ERRORS. 5.4. Low-noise design
noise matching. 5.4.1. Optimum source resistance
A. Transformer matching with an 1 n turns
ratio
Measurement object
Measurement system

Rs
Vmsr
Vo
1 n
Vin
AV
RL
n2Rs nVin
Measurement object
Measurement system
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5. SOURCES OF ERRORS. 5.4. Low-noise design
noise matching. 5.4.1. Optimum source resistance
Example Optimum source resistance
Rs1 W, en 2 nV/Hz0.5, in 20 pA /Hz0.5
Rs
1 n
Vin
in Rs
vn in rms, nV/Hz0.5
en
Thermal noise in Rs
Rs n2 Vin n
Rs n2, W
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5. SOURCES OF ERRORS. 5.4. Low-noise design
noise matching. 5.4.1. Optimum source resistance
B. Transformer coupling with an n 1 turns
ratio
Measurement object
Measurement system

Rs
Vmsr
Vo
n 1
Vin
AV
RL
Rs /n2 Vin /n
Measurement object
Measurement system

Rs /n2
Vo
Vmsr
Vin /n
AV
RL
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5. SOURCES OF ERRORS. 5.4. Low-noise design
noise matching. 5.4.1. Optimum source resistance
Home exercise Optimize noise factor and SNR
Rs200 W, en 2 nV/Hz0.5, in 20 pA /Hz0.5
Rs
n 1
Vin
in Rs
vn in rms, nV/Hz0.5
Rs / n2 Vin / n
en
Thermal noise in Rs
?
SNR 0.5
F 0.5
Rs /n2, W
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5. SOURCES OF ERRORS. 5.4. Low-noise design
noise matching. 5.4.1. Optimum source resistance
C. Parallel connection of input stages
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