THS4031 datasheet(23/47 Pages) TI

23 / 47 page

eRg

eRf

eRs

IN+

Noiseless

IN−

eni

eno

ni +

) IN )

) IN–

F ø

) 4 kTRs ) 4 kT RF ø RG

Where:

k = Boltzmann’s constant = 1.380658

× 10−23

T = Temperature in degrees Kelvin (273 +

°C)

RF || RG = Parallel resistance of RF and RG

eno + eni AV + eni 1 )

(Noninverting Case)

THS4031

THS4032

www.ti.com

SLOS224G – JULY 1999 – REVISED MARCH 2010

NOISE CALCULATIONS AND NOISE FIGURE

Noise can cause errors on very small signals. This is especially true when amplifying small signals. The noise

model for the THS403x, shown in Figure 52, includes all of the noise sources as follows:

•

en = Amplifier internal voltage noise (nV/√Hz)

•

IN+ = Noninverting current noise (pA/

√Hz)

•

IN– = Inverting current noise (pA/

√Hz)

•

eRx = Thermal voltage noise associated with each resistor (eRx = 4 kTRx)

Figure 52. Noise Model

The total equivalent input noise density (eni) is calculated by using the following equation:

(1)

To get the equivalent output noise of the amplifier, just multiply the equivalent input noise density (eni) by the

overall amplifier gain (AV).

(2)

As the previous equations show, to keep noise at a minimum, small-value resistors should be used. As the

closed-loop gain is increased (by reducing RG), the input noise is reduced considerably because of the parallel

resistance term. This leads to the general conclusion that the most dominant noise sources are the source

resistor (RS) and the internal amplifier noise voltage (en). Because noise is summed in a root-mean-squares

method, noise sources smaller than 25% of the largest noise source can be effectively ignored. This advantage

can greatly simplify the formula and make noise calculations much easier to calculate.

For more information on noise analysis, refer to the application note, Noise Analysis for High-Speed Op Amps

(SBOA066).

Submit Documentation Feedback

Product Folder Link(s): THS4031 THS4032

THS4031 Datasheet(PDF) 23 Page - Texas Instruments

THS4031 Datasheet(HTML) 23 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 43 44 45 46 47

Datasheet Download

Link URL