OPA1655DBVT datasheet(19/42 Pages) TI

19 / 42 page

8 Application and Implementation

Note

Information in the following applications sections is not part of the TI component specification,

and TI does not warrant its accuracy or completeness. TI’s customers are responsible for

determining suitability of components for their purposes, as well as validating and testing their design

implementation to confirm system functionality.

8.1 Application Information

8.1.1 Basic Noise Calculations

Low-noise circuit design requires careful analysis of all noise sources. External noise sources can dominate in

many cases; consider the effect of source resistance on overall op amp noise performance. Total noise of the

circuit is the root-sum-square combination of all noise components.

Figure 8-1 shows noninverting (A) and inverting (B) op amp circuit configurations with gain. In circuit

configurations with gain, the feedback network resistors contribute noise. In general, the current noise of the

op amp reacts with the feedback resistors to create additional noise components.

The selected feedback resistor values make these noise sources negligible. Low impedance feedback resistors

load the output of the amplifier. The equations for total noise are shown for both configurations.

(A) Noise in Noninverting Gain Configuration

GND

Source

GND

Source

(B) Noise in Inverting Gain Configuration

:1; '

1 =

l1+42

p„¨:A

;2 +:A

;2 +

41æ42

o2+:E

„ 45

;2 +

„

d41„42

41 + 42

hp2 >8

4/5

:2; A

5 =

¥4„G$„6(-)„45 d 8

¾*V

:3; A

41æ42 =

¨4„G

„ 6(-) „

d41„42

41 + 42

h d 8

¾*V

:4; G

$ = 1.38065

„ 10

F23

d ,

:5; 6(-) = 237.15+6(°%) >-?

Noise at the output is given as EO, where

:6; '

1 =

l1+ 42

45 + 41

p„¨:A

;2 +

41+45 æ42

o2+FE

„

H:45 +41;„42

45 + 41 + 42 IG

4/5

:7; A

41+45 æ42 =

¨4„G

„ 6(-) „

H:45 +41;„42

45 + 41 + 42 I

d 8

¾*V

:8; G

$ = 1.38065

„ 10

F23

d ,

:9; 6(-) = 237.15+6(°%) >-?

Thermal noise of RS

Thermal noise of R1 || R2

Boltzmann Constant

Temperature in kelvins

Boltzmann Constant

Temperature in kelvins

Thermal noise of (R1 + RS) || R2

where

• eN is the voltage noise of the amplifier. For the OPA165x, eN = 4.3 nV/√Hz at 1 kHz.

• iN is the current noise of the amplifier. For the OPA165x, iN = 6 fA/√Hz at 1 kHz.

Note: For additional resources on noise calculations, see TI's Precision Labs Series.

Figure 8-1. Noise Calculation in Gain Configurations

www.ti.com

OPA1655, OPA1656

SBOS901C – MARCH 2019 – REVISED SEPTEMBER 2022

Submit Document Feedback

Product Folder Links: OPA1655 OPA1656

OPA1655DBVT Datasheet(PDF) 19 Page - Texas Instruments

OPA1655DBVT Datasheet(HTML) 19 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

Datasheet Download

Link URL