AD815ARB-24Z-REEL Analog Devices Inc, AD815ARB-24Z-REEL Datasheet - Page 13

• Manufacturer Part Number: AD815ARB-24Z-REEL
• Manufacturer: Analog Devices Inc

Specifications of AD815ARB-24Z-REEL

• Power Supply Requirement: Dual
• Slew Rate: 900V/us
• Pin Count: 24
• Lead Free Status / RoHS Status: Compliant

REV. C
Another means for creating a differential signal from a single-
ended signal is to use a transformer with a center-tapped
secondary. The center tap of the transformer is grounded and
the two secondary windings are connected to obtain opposite
polarity signals to the two inputs of the AD815 amplifiers. The
bias currents for the AD815 inputs are provided by the center
tap ground connection through the transformer windings.
One advantage of using a transformer is its ability to provide
isolation between circuit sections and to provide good common-
mode rejection. The disadvantages are that transformers have
no dc response and can sometimes be large, heavy, and expensive.
This circuit is shown in Figure 53.
Direct Single-Ended-to-Differential Conversion
Two types of circuits can create a differential output signal from
a single-ended input without the use of any other components
than resistors. The first of these is illustrated in Figure 54.
Figure 53. Differential Driver with Transformer Input
Figure 52. Differential Driver with Single-Ended
Differential Converter
1k
1k
50
6
3
5
2
1/2
AD826
1/2
AD826
–15V
+15V
4
8
1k
1k
0.1 F
0.1 F
1
7
50
200
100
100
10
11
4
5
1/2
AD815
1/2
AD815
100
100
100
R
–15V
+15V
G
8
7
1k
1k
10
11
4
5
6
9
0.1 F
0.1 F
1/2
AD815
1/2
AD815
+15V
–15V
8
7
10 F
10 F
499
499
6
R
R
9
0.1 F
0.1 F
F
F
R
L
10 F
10 F
R
L
–13–
Amp 1 has its + input driven with the input signal, while the
+ input of Amp 2 is grounded. Thus the – input of Amp 2 is
driven to virtual ground potential by its output. Therefore
Amp 1 is configured for a noninverting gain of five, (1 + R
because R
When the + input of Amp 1 is driven with a signal, the same
signal appears at the – input of Amp 1. This signal serves as an
input to Amp 2 configured for a gain of –5, (–R
two outputs move in opposite directions with the same gain and
create a balanced differential signal.
This circuit can work at various gains with proper resistor
selection. But in general, in order to change the gain of the
circuit, at least two resistor values will have to be changed. In
addition, the noise gain of the two op amps in this configuration
will always be different by one, so the bandwidths will not match.
A second circuit that has none of the disadvantages mentioned
in the above circuit creates a differential output voltage feedback
op amp out of the pair of current feedback op amps in the AD815.
This circuit, drawn in Figure 55, can be used as a high power
differential line driver, such as required for ADSL (asymmetrical
digital subscriber loop) line driving.
Each of the AD815’s op amps is configured as a unity gain
follower by the feedback resistors (R
also drives the other as a unity gain inverter via the two R
creating a totally symmetrical circuit.
If the + input to Amp 2 is grounded and a small positive signal
is applied to the + input of Amp 1, the output of Amp 1 will be
driven to saturation in the positive direction and the output of
Amp 2 driven to saturation in the negative direction. This is
similar to the way a conventional op amp behaves without any
feedback.
Figure 54. Direct Single-Ended-to-Differential Conversion
G
V
is connected to the virtual ground of Amp 2’s – input.
IN
100
AMP 1
AMP 2
R
G
10
11
4
5
1/2
AD815
1/2
AD815
+15V
–15V
8
7
499
402
R
R
6
9
F2
F1
A
). Each op amp output
R
L
F2
V
/R
AD815
OUT
G
). Thus the
F1
B
/R
s,
G
),