AD8045(RevB) View Datasheet(PDF) - Analog Devices

Part Name

Description

MFG CO.

AD8045
(Rev.:RevB)

3 nV/√Hz, Ultralow Distortion, High Speed Op Amp

Analog Devices 

AD8045

OUTPUT NOISE

Figure 66 shows the contributors to the noise at the output of a

noninverting configuration.

VRS RS

VEN

IEN+

+ VOUT –

IEN–

VRF

RF

RG

VRG

Figure 66. Amplifier DC Errors

Ven , IN+, and IN− are due to the amplifier. VRF , VRG , and

VRS are due to the feedback network resistors, RG and RF, and

the source resistor, RS. The total output voltage noise, VOUT _ EN ,

is the rms sum of all the contributions.

Data Sheet

VOUT _ EN =

( ) ( ) ( ) Gn ×Ven 2 + IN + × RS × Gn 2 + IN − × RF||RG × Gn 2 + 4kTR f + 4kTRG (Gn )2 + 4kTRS (Gn )2

where:

Gn

is the

noise

gain





RF + RG

RG





.

Ven is the op amp input voltage noise.

IN is the op amp input current noise.

Table 6 lists the expected output voltage noise spectral density

for several gain configurations.

Table 6. Noise and Bandwidth for Various Gains

Gain RF RG RS

−3 dB

Bandwidth1

Output Noise

(nV/√Hz)

+1 0 − 100 1 GHz

3.3

+2 499 499 0

400 MHz

7.4

+5 499 124 0

90 MHz

16.4

+10 499 56 0

40 MHz

31

−1 499 499 N/A2 300 MHz

7.4

1 RL = 1 kΩ.

2 N/A means not applicable.

Rev. B | Page 18 of 24

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