LMP7702 datasheet(20/35 Pages) TI

20 / 35 page

eni =

en +

ei +

VOUT

VIN

LMP7701, LMP7702, LMP7704

SNOSAI9H – SEPTEMBER 2005 – REVISED MARCH 2013

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Figure 51. Noise Reduction Circuit

TOTAL NOISE CONTRIBUTION

The LMP7701/LMP7702/LMP7704 have 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 52 shows the typical input noise of the LMP7701/LMP7702/LMP7704 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:

The input current noise of the LMP7701/LMP7702/LMP7704 is so low that it will not become the dominant factor

in the total noise unless source resistance exceeds 300 M

Ω, which is an unrealistically high value.

As is evident in Figure 52, 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.

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Product Folder Links: LMP7701 LMP7702 LMP7704

LMP7702 Datasheet(PDF) 20 Page - Texas Instruments