OPA607 datasheet(28/50 Pages) TI1

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)

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4kTR

4kTR NG

BI F

4kTR

4kT

4kTR

4 kT

1.6E

20 J

at 290 K

Frequency (Hz)

-10

10k

100k

10M

100M

D806

RF = 200 :, RG = 50 :

RF = 10 k:, RG = 2.5 k:

RF = 1 M:, RG = 250 k:

Resistance (:)

0.1

100

1000

100

10k

100k

10M

D803

OPA810

SBOS799A – AUGUST 2019 – REVISED DECEMBER 2019

www.ti.com

Product Folder Links: OPA810

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Application Information (continued)

A lower phase margin results in peaking in the frequency response and lower bandwidth as Figure 69 shows,

which is synonymous with overshoot and ringing in the pulse response results. The OPA810 offers a flat-band

voltage noise density of 6.3 nV/

√Hz. TI recommends selecting an RF so the voltage noise contribution does not

exceed that of the amplifier. Figure 70 shows the voltage noise density variation with value of resistance at 25°C.

A 2-kΩ resistor exhibits a thermal noise density of 5.75 nV/√Hz which is comparable to the flatband noise of the

OPA810. Hence, TI recommends using an RF lower than 2 kΩ while being large enough to not dissipate

excessive power for the output voltage swing and supply current requirements of the application. The Noise

Analysis and the Effect of Resistor Elements on Total Noise section shows a detailed analysis of the various

contributors to noise.

Figure 69. Closed-Loop Gain vs. Frequency for Circuit of

Figure 66

Figure 70. Thermal Noise Density vs Resistance

9.1.3 Noise Analysis and the Effect of Resistor Elements on Total Noise

The OPA810 provides a low input-referred broadband noise voltage density of 6.3 nV/

√Hz while requiring a low

3.7-mA quiescent supply current. To take full advantage of this low input noise, careful attention to the other

possible noise contributors is required. Figure 71 shows the operational amplifier noise analysis model with all

the noise terms included. In this model, all the noise terms are taken to be noise voltage or current density terms

in nV/

√Hz or pA/√Hz.

Figure 71. Operational Amplifier Noise Analysis Model

The total output spot noise voltage is computed as the square root of the squared contributing terms to the

output noise voltage. This computation adds all the contributing noise powers at the output by superposition, then

calculates the square root to get back to a spot noise voltage. Figure 71 shows the general form for this output

noise voltage using the terms shown in Equation 7.

(7)

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