AD8045ACPZ-R2 View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

AD8045ACPZ-R2

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

IEN+

IEN–

VEN

+ VOUT –

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

source resistor, RS. Total output voltage noise, VOUT _ EN , is the

rms sum of all the contributions.

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 7 lists the expected output voltage noise spectral density

for several gain configurations.

Table 7. Noise and Bandwidth for Various Gains

Output

−3 dB

Noise

Gain RF

RG

RS

Bandwidth1 (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/A 300 MHz

7.4

1 RL = 1 kΩ.

Rev. A | Page 18 of 24

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