Datasheet

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
)(2
2
log
20
32
4
1
324341
10
RRRR
RR
RR
R
R
−
+
+
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.
R5
5k
Ω
OUT–
OUT+
IN–
*A3 REDUCES THE DEGRADA
TION OF CMRR
(SEE THE BALANCED LINE RECEIVER SECTION FOR MORE DE
TAILS).
C1
22µF
(NON-POLAR)
IN+
07642-071
R4
10kΩ
1/2
ADA4075-2
R3
10k
Ω
R6
5k
Ω
R1
5kΩ
R2
5k
Ω
C2
50pF
R9
11kΩ
A3*
R8
5.6k
Ω
R7
5.6kΩ
1/2
A1
A2
ADA4075-2
C3
50pF
R10
11kΩ
Figure 68. Balanced Line Receiver