Datasheet

REV. B–10–
OP275
of the circuit and dc offset errors. If the parallel combination of
R
F
and R
G
is larger than 2 kW, then an additional resistor, R
S
,
should be used in series with the noninverting input. The value
of R
S
is determined by the parallel combination of R
F
and R
G
to
maintain the low distortion performance of the OP275.
Driving Capacitive Loads
The OP275 was designed to drive both resistive loads to 600 W
and capacitive loads of over 1000 pF and maintain stability.
While there is a degradation in bandwidth when driving capacitive
loads, the designer need not worry about device stability. The
graph in Figure 16 shows the 0 dB bandwidth of the OP275
with capacitive loads from 10 pF to 1000 pF.
10
9
8
7
6
5
4
3
2
1
0
0 200 400 600 800 1000
C
LOAD
– pF
BANDWIDTH – MHz
Figure 16. Bandwidth vs. C
LOAD
High Speed, Low Noise Differential Line Driver
The circuit of Figure 17 is a unique line driver widely used in
industrial applications. With ± 18 V supplies, the line driver can
deliver a differential signal of 30 V p-p into a 2.5 kW load. The
high slew rate and wide bandwidth of the OP275 combine to
yield a full power bandwidth of 130 kHz while the low noise
front end produces a referred-to-input noise voltage spectral
density of 10 nV/÷Hz.
1
2
3
A2
1
3
2
A1
5
6
7
A3
V
IN
V
O1
V
O2
R3
2k
⍀
R9
50
R11
1k
⍀
P1
10k
⍀
R12
1k
⍀
R10
50
⍀
R8
2k
⍀
R2
2k
⍀
R5
2k
⍀
R4
2k
⍀
R1
2k
⍀
R7
2k
⍀
V
O2
– V
O1
= V
IN
A1 = 1/2 OP275
A2, A3 = 1/2 OP275
GAIN =
SET R2, R4, R5 = R1 AND R6, R7, R8 = R3
R3
R1
R6
2k
⍀
–
+
–
+
–
+
Figure 17. High Speed, Low Noise Differential Line Driver
The design is a transformerless, balanced transmission system
where output common-mode rejection of noise is of paramount
importance. Like the transformer based design, either output
can be shorted to ground for unbalanced line driver applica-
tions without changing the circuit gain of 1. Other circuit gains
can be set according to the equation in the diagram. This
allows the design to be easily set to noninverting, inverting, or
differential operation.
A 3-Pole, 40 kHz Low-Pass Filter
The closely matched and uniform ac characteristics of the
OP275 make it ideal for use in GIC (Generalized Impedance
Converter) and FDNR (Frequency-Dependent Negative Resistor)
filter applications. The circuit in Figure 18 illustrates a linear-
phase, 3-pole, 40 kHz low-pass filter using an OP275 as an
inductance simulator (gyrator). The circuit uses one OP275
(A2 and A3) for the FDNR and one OP275 (A1 and A4) as
an input buffer and bias current source for A3. Amplifier A4
is configured in a gain of 2 to set the pass band magnitude
response to 0 dB. The benefits of this filter topology over classi-
cal approaches are that the op amp used in the FDNR is not in
the signal path and that the filter’s performance is relatively
insensitive to component variations. Also, the configuration is
such that large signal levels can be handled without overloading
any of the filter’s internal nodes. As shown in Figure 19, the
OP275’s symmetric slew rate and low distortion produce a
clean, well behaved transient response.
V
IN
3
2
1
A1
R1
95.3k⍀
R2
787⍀
C1
2200pF
C2
2200pF
R3
1.82k⍀
C3
2200pF
R4
1.87k⍀
R5
1.82k⍀
A2
1
2
3
5
6
7
A3
R6
4.12k⍀
C4
2200pF
R7
100k⍀
5
6
7
A4
R8
1k⍀
R9
1k⍀
V
OUT
A1, A4 = 1/2 OP275
A2, A3 = 1/2 OP275
–
+
–
+
–
+
–
+
Figure 18. A 3-Pole, 40 kHz Low-Pass Filter
V
OUT
10V p-p
10kHz
SCALE: VERTICAL–2V/ DIV
HORIZONTAL–10␮s/ DIV
10
0%
100
90
Figure 19. Low-Pass Filter Transient Response