ADA4940-1ACPZ-R2 datasheet(20/32 Pages) AD

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ADA4940-1/ADA4940-2

Data Sheet

Rev. B | Page 20 of 32

TERMINOLOGY

DEFINITION OF TERMS

ADA4840-1/

ADA4940-2

RL, dm

VOUT, dm

+FB

+IN

+OUT

–OUT

–

+DIN

+VOCM

–DIN

–FB

–IN

Figure 61. Circuit Definitions

Differential Voltage

Differential voltage refers to the difference between two node

voltages. For example, the differential output voltage (or

equivalently, output differential mode voltage) is defined as

VOUT, dm = (V+OUT − V−OUT)

where V+OUT and V−OUT refer to the voltages at the +OUT and

−OUT terminals with respect to a common reference.

Similarly, the differential input voltage is defined as

VIN, dm = (+DIN − (−DIN))

Common-Mode Voltage (CMV)

CMV refers to the average of two node voltages. The output

common-mode voltage is defined as

VOUT, cm = (V+OUT + V−OUT)/2

Similarly, the input common-mode voltage is defined as

VIN, cm = (+DIN + (−DIN))/2

Common-Mode Offset Voltage

The common-mode offset voltage is defined as the difference

between the voltage applied to the VOCM terminal and the

common mode of the output voltage.

VOS, cm = VOUT, cm − VOCM

Differential VOS, Differential CMRR, and VOCM CMRR

The differential mode and common-mode voltages each have

their own error sources. The differential offset (VOS, dm) is the

voltage error between the +IN and −IN terminals of the amplifier.

Differential CMRR reflects the change of VOS,dm in response to

changes to the common-mode voltage at the input terminals

+DIN and −DIN.

OS,

IN,

DIFF

ΔV

CMRR

VOCM CMRR reflects the change of VOS, dm in response to

changes to the common-mode voltage at the output terminals.

OS,

OCM

ΔV

CMRR

OCM

Balance

Balance is a measure of how well the differential signals are

matched in amplitude; the differential signals are exactly 180°

apart in phase. By this definition, the output balance is the

magnitude of the output common-mode voltage divided by

the magnitude of the output differential mode voltage.

OUT

Error

Balance

Output

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