Data Sheet

ADA4941-1

Rev. D | Page 17 of 23

Table 7, Table 8, and Table 9 show typical error budgets for the

circuits shown in Figure 49, Figure 50, and Figure 51.

RF = 1.0 kΩ, RG = 4.99 kΩ, RS_IN = 825 Ω, RS_REF = 0 Ω

Table 7. Output Voltage Error Budget for G = 2.4 Amplifier

Shown in Figure 49

Error

Source

Typical

Value

VOP_error

VON_error

VO_dm_error

VOS_A1

0.1 mV

+0.12 mV

−0.12 mV

+0.24 mV

IBP_A1

3 μA

+2.48 mV

−2.48 mV

−4.96 mV

IBN_A1

3 μA

−2.48 mV

+2.48 mV

+4.96 mV

VOS_A2

0.1 mV

0 mV

+0.2 mV

+0.2 mV

Total VO_error, dm = 0.44 mV

RF = 0 Ω, RG = ∞, RS_IN = 0 Ω, RS_REF = 0 Ω

Table 8. Output Voltage Error Budget for Amplifier Shown

in Figure 50

Error

Source

Typical

Value

VOP_error

VON_error

VO_dm_error

VOS_A1

0.1 mV

+0.1 mV

−0.1 mV

+0.2 mV

IBP_A1

3 μA

+2.48 mV

−2.48 mV

−4.96 mV

IBN_A1

3 μA

−2.48 mV

+2.48 mV

+4.96 mV

VOS_A2

0.1 mV

0 mV

+0.2 mV

+0.2 mV

Total VO_error, dm = 0.4 mV

RF = 1.02 kΩ, RG = 665 Ω, RS_IN = 402 Ω, RS_REF = 0 Ω

Table 9. Output Voltage Error Budget for G = 5 Amplifier

Shown in Figure 51

Error

Source

Typical

Value

VOP_error

VON_error

VO_dm_error

VOS_A1

0.1 mV

+0.25 mV

−0.25 mV

+0.5 mV

IBP_A1

3 μA

+1.21 mV

−1.21 mV

−2.4 mV

IBN_A1

3 μA

−1.21 mV

+1.21 mV

+2.4 mV

VOS_A2

0.1 mV

0 mV

+0.2 mV

+0.2 mV

Total VO_error, dm = 0.7 mV

OUTPUT VOLTAGE NOISE

1kΩ

1kΩ

RG

RF

RS

ip–A2

in–A2

vn–A1

500Ω

A2

A1

REF

IN

2

8

4

5

FB

OUT+

+

–

VOP

1

OUT–

+

–

VON

vn–A2

RS–REF

ip–A1

in–A1

√4kT (1kΩ)

√4kT (1kΩ)

√4kT (500Ω)

√4kT (RS–REF)

√4kTRS

√4kTRG

√4kTRF

Figure 53. Noise Sources

Figure 53 shows the major contributors to the ADA4941-1

differential output voltage noise. The differential output noise

mean-square voltage equals the sum of twice the noise mean-

square voltage contributions from the noninverting channel

(A1), plus the noise mean-square voltage terms associated with

the inverting channel (A2).





2

2

2

2

2

2

2

2

_

4

1

2

4

2

4

2

_

2

)

_

(

1

2

)

_

(

1

2

_

,

n

VON

kTR

R

R

R

R

kTR

kTR

R

A1

in

R

A1

ip

R

R

A1

vn

R

R

n

dm

V

S

G

F

G

F

G

F

F

S

G

F

G

F

O





































































































































(13)

where VON_n

2 is calculated as





 

)

(

16

(500)

16

(1000)

8

)

_

(

1000

)

_

500

)(

_

(

4

4

2

2

2

2

_REF

R

kT

kT

kT

A2

in

REF

R

A2

ip

vn_A2

VON_n

S

S















(14)

where:

vn_A1 and vn_A2 are the input voltage noises of A1 and A2,

each equal to 2.1 nV/√Hz.

in_A1, in_A2, ip_A1, and ip_A2 are amplifier input current

noise terms, each equal to 1 pA/√Hz.

RS, RF, and RG are the external source, feedback, and gain

resistors, respectively.

kT is Boltzmann’s constant times absolute temperature, equal to

4.2 x 10-21 W-s at room temperature.

RS_REF is any source resistance at the REF pin.

When A1 is used as a unity gain follower, the output voltage

noise spectral density is at its minimum, 10 nV/√Hz. Higher

voltage gains have higher output voltage noise.

Table 10, Table 11, and Table 12 show the noise contributions

and output voltage noise for the circuits in Figure 49, Figure 50,

and Figure 51.