Datasheet
OPA835
V
IN+
V
IN-
V
CM
V
CM
R
G
R
G
R
F
R
F
V
REF
V
SIG-
V
SIG+
G[(V )-(
SIG
+
V )]
SIG-
V
OUT
V
REF
F
G
R
G =
R
( )
-
æ ö
- ´
ç ÷
è ø
F
OUT IN+ IN REF
G
R
V = V V + V
R
1k
V
OUT+
49.9
+
V
OUT-
2k2k
OPA835
+
V
REF
V
IN
V
SIG
V
REF
-V
SIG
V
REF
V
REF
V
SIG
OPA835
49.9
OPA835
OPA2835
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SLOS713E –JANUARY 2011–REVISED JULY 2013
Figure 56. CAT 5 Line Driver with Gain = 2 V/V (6 dB)
Differential to Signal Ended Amplifier
Figure 57 shows a differential amplifier that is used to convert differential signals to single-ended and provides
gain (or attenuation) and level shifting. This circuit can be used in applications like a line receiver for converting a
differential signal from a CAT 5 cable to single-ended.
If we set V
IN+
= V
CM
+ V
SIG+
and V
IN-
= V
CM
+ V
SIG-
, then
(4)
The signal gain of the circuit is set by: , V
CM
is rejected, and V
REF
provides a level shift around which
the output signal swings. The single ended output signal is in-phase with the differential input signal.
Figure 57. Differential to Single Ended Amplifier
Line termination can be accomplished with a resistor shunt across the input. The impedance seen differential
from the line will be the resistor value in parallel with the amplifier circuit. For low gain and low line impedance
the resistor value to add is approximately the impedance of the line. For example, if 100 Ω CAT5 cable is used
with a gain of 1 amplifier and R
F
= R
G
= 2 kΩ, adding a 100 Ω shunt across the input will give a differential
impedance of 99 Ω; this should be adequate for most applications.
For best CMRR performance, resistors must be matched. Assuming CMRR ≈ the resistor tolerance; so 0.1%
tolerance will provide about 60 dB CMRR.
Differential to Differential Amplifier
Figure 58 shows a differential amplifier that is used to amplify differential signals. This circuit has high input
impedance and is often used in differential line driver applications where the signal source is a high impedance
driver like a differential DAC that needs to drive a line.
If we set V
IN±
= V
CM
+ V
SIG±
then
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