AD8390AACPZ-R7 datasheet(9/12 Pages) AD

9 / 12 page

Data Sheet

AD8390A

Rev. B | Page 9 of 12

THEORY OF OPERATION

56kΩ

VCC

VCOM

OUTP

AD8390A

OUTN

INP

INN

VEE

56kΩ

Figure 15. Functional Block Diagram

The AD8390A is a true differential amplifier with common-

mode feedback. The AD8390A is functionally equivalent to three

amplifiers, as shown in Figure 15. Amplifier A and Amplifier B

form a standard dual amplifier in an inverting configuration.

Amplifier C maintains the common-mode voltage VCOM at

the output.

With VCOM left unconnected, the outputs are internally biased

to midsupply. VCOM can be driven externally to set the dc

output common-mode voltage.

OUTN

OUTP

INP

INN

VCOM

RL, DM VOUT, DM

–

VIN, DM

–

Figure 16. Basic Application Circuit

The high open-loop gain of the AD8390A and the negative

feedback minimize the differential and common-mode error

voltages.

With the differential and common-mode error voltages assumed

to be 0, the differential-mode gain and input impedance of the

basic application circuit shown in Figure 16 are as follows:

OUT





 2

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