PLMP7704HBHSLASHEM datasheet(23/31 Pages) TI

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8.1.2 Total Noise Contribution

The LMP7704-SP have very low input bias current, very low input current noise, and very low input voltage

noise. As a result, these amplifiers are excellent choices for circuits with high impedance sensor applications.

Figure 8-2 shows the typical input noise of the LMP7704-SP 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 =

en +

ei +

The input current noise of the LMP7704-SP is so low that this noise does not become the dominant factor in the

total noise unless the source resistance exceeds 300 MΩ, which is an unrealistically high value.

As is evident in Figure 8-2, at lower RS values, total noise is dominated by the amplifier input voltage noise. After

RS is larger than a few kilo-ohms, then the dominant noise factor becomes the thermal noise of RS. As

mentioned previously, the current noise will not be the dominant noise factor for any practical application.

100k

10M

RS (:)

0.1

1000

10k

100

eni

Figure 8-2. Total Input Noise

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LMP7704-SP

SNOSDB6A – DECEMBER 2020 – REVISED JANUARY 2021

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PLMP7704HBH/EM Datasheet(PDF) 23 Page - Texas Instruments