ADA4075-2ACPZ-R7 datasheet(20/25 Pages) AD

20 / 25 page

Data Sheet

ADA4075-2

Rev. C | Page 19 of 24

BALANCED LINE RECEIVER

Figure 68 depicts a unity-gain balanced line receiver capable of

a high degree of hum rejection. The CMRR is approximately

given by

)

(

log

−

Therefore, R1 to R4 should be close tolerance components to

obtain the best possible CMRR without adjustment. The presence

of A2 ensures that the impedances are symmetric at the two inputs

(unlike many other designs), and, as a bonus, A2 also provides

a complementary output. A3 raises the common-mode input

impedance from approximately 7.5 kΩ to approximately 70 kΩ,

reducing the degradation of CMRR due to mismatches in source

impedance.

Note that A3 is not in the signal path, and almost any op amp

works well here. Although it may seem as though the inverting

output should be noisier than the noninverting one, they are in

fact symmetric at about −111 dBV (20 kHz bandwidth).

Sometimes an overall gain of ½ is desired to provide an extra

6 dB of differential input headroom. This can be attained by

reducing R3 and R4 to 5 kΩ and increasing R9 to 22 kΩ.

Ω

OUT–

OUT+

IN–

*A3 REDUCES THE DEGRADATION OF CMRR

(SEE THE BALANCED LINE RECEIVER SECTION FOR MORE DETAILS).

22µF

(NON-POLAR)

IN+

10k

Ω

1/2

ADA4075-2

10k

Ω

50pF

11k

Ω

A3*

5.6k

Ω

5.6k

Ω

1/2

ADA4075-2

50pF

R10

11k

Ω

Figure 68. Balanced Line Receiver

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