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OP275_04 Datasheet, PDF (10/12 Pages) Analog Devices – Dual Bipolar/JFET, Audio Operational Amplifier | |||
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OP275
and dc offset errors. If the parallel combination of RF and RG is
larger than 2 kî, then an additional resistor, RS, should be used
in series with the noninverting input. The value of RS is deter-
mined by the parallel combination of RF and RG to maintain the
low distortion performance of the OP275.
Driving Capacitive Loads
The OP275 was designed to drive both resistive loads to 600 î
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 capaci-
tive loads from 10 pF to 1000 pF.
10
9
8
7
6
5
4
3
2
1
0
0
200
400
600
800
1000
CLOAD â pF
Figure 16. Bandwidth vs. CLOAD
High Speed, Low Noise Differential Line Driver
The circuit in 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 kî 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/îHz.
R3
2kî
2â
1
R9
50
3
A2
+
R1
2kî
VIN
3
1
2 A1
R4
2kî
R7
2kî
R2
2kî
R5
2kî R6
2kî
A1 = 1/2 OP275
6â
A3
5+
A2, A3 = 1/2 OP275
GAIN =
R3
R1
SET R2, R4, R5 = R1 AND R6, R7, R8 = R3
7
R8
2kî
R10
50î
VO1
R11
1kî
P1
10kî
VO2 â VO1 = VIN
R12
1kî
VO2
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 applications
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 ben-
efits of this filter topology over classical approaches are that the
op amp used in the FDNR is not in the signal path and that the
filterâs performance is relatively insensitive to component varia-
tions. Also, the configuration is such that large signal levels can
be handled without overloading any of the filterâs internal nodes.
As shown in Figure 19, the OP275âs symmetric slew rate and low
distortion produce a clean, well behaved transient response.
R1
95.3kî
C1
2â
2200pF
1
VIN
3
A1
+
R2
787î
R6
4.12kî
C2
2200pF
1
â2
A2
+
3
R3
1.82kî
C3
2200pF
C4
5
2200pF
6 A3 7
R7
100kî
5
7
6 A4
R9
1kî
R8
1kî
VOUT
R4
1.87kî
R5
1.82kî
A1, A4 = 1/2 OP275
A2, A3 = 1/2 OP275
Figure 18. A 3-Pole, 40 kHz Low-Pass Filter
100
90
VOUT
10V p-p
10kHz
10
0%
SCALE: VERTICALâ2V/ DIV
HORIZONTALâ10îs/ DIV
Figure 19. Low-Pass Filter Transient Response
â10â
REV. C
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