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| SM72501 Datasheet, PDF (18/28 Pages) National Semiconductor (TI) – SolarMagic Precision, CMOS Input, RRIO, Wide Supply Range Amplifier | |||
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SM72501
SNIS157C â JANUARY 2011 â REVISED APRIL 2013
www.ti.com
V+
VIN
+
-
RG
V-
RO
VOUT
RF
V+
+
-
RO
RG
V-
RF
V+
+
-
RG
V-
RO
RF
V+
+
-
RG
V-
RO
RF
Figure 47. Noise Reduction Circuit
TOTAL NOISE CONTRIBUTION
The SM72501 has very low input bias current, very low input current noise, and very low input voltage noise. As
a result, these amplifiers are ideal choices for circuits with high impedance sensor applications.
Figure 48 shows the typical input noise of the SM72501 as a function of source resistance where:
en denotes the input referred voltage noise
ei is the voltage drop across source resistance due to input referred current noise or ei = RS * in
et shows the thermal noise of the source resistance
eni shows the total noise on the input.
Where:
eni = en2 + e2i + et2
(7)
The input current noise of the SM72501 is so low that it will not become the dominant factor in the total noise
unless source resistance exceeds 300 Mâ¦, which is an unrealistically high value.
As is evident in Figure 48, at lower RS values, total noise is dominated by the amplifier's input voltage noise.
Once RS is larger than a few kilo-Ohms, then the dominant noise factor becomes the thermal noise of RS. As
mentioned before, the current noise will not be the dominant noise factor for any practical application.
18
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