ADA4945-1ACPZ-R2 datasheet(34/44 Pages) AD

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ADA4945-1

Data Sheet

Rev. 0 | Page 34 of 44

TERMINOLOGY

Differential Voltage

Differential voltage is 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 is 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

Common-mode offset voltage is 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 +DIN and −DIN (see

Figure 98).

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

+IN

–IN

+OUT

–OUT

+DIN

–FB

+FB

–DIN

VOCM

VOUT, dm

RL, dm

ADA4945-1

Figure 98. Circuit Definitions

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