Datasheet OP275 (Analog Devices) - 10

OP275 OP275
and dc offset errors. If the parallel combination of RF and RG is The design is a transformerless, balanced transmission system larger than 2 k, then an additional resistor, RS, should be used where output common-mode rejection of noise is of paramount in series with the noninverting input. The value of RS is deter- importance. Like the transformer based design, either output can mined by the parallel combination of RF and RG to maintain the be shorted to ground for unbalanced line driver applications low distortion performance of the OP275. without changing the circuit gain of 1. Other circuit gains can be
Driving Capacitive Loads
set according to the equation in the diagram. This allows the The OP275 was designed to drive both resistive loads to 600 design to be easily set to noninverting, inverting, or differential  and capacitive loads of over 1000 pF and maintain stability. While operation. there is a degradation in bandwidth when driving capacitive loads,
A 3-Pole, 40 kHz Low-Pass Filter
the designer need not worry about device stability. The graph in The closely matched and uniform ac characteristics of the OP275 Figure 16 shows the 0 dB bandwidth of the OP275 with capaci- make it ideal for use in GIC (Generalized Impedance Converter) tive loads from 10 pF to 1000 pF. and FDNR (Frequency-Dependent Negative Resistor) filter applications. The circuit in Figure 18 illustrates a linear-phase,
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3-pole, 40 kHz low-pass filter using an OP275 as an inductance
9
simulator (gyrator). The circuit uses one OP275 (A2 and A3) for
8
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
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of 2 to set the pass band magnitude response to 0 dB. The ben-
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efits of this filter topology over classical approaches are that the
5
op amp used in the FDNR is not in the signal path and that the filter’s performance is relatively insensitive to component varia-
4
tions. Also, the configuration is such that large signal levels can
BANDWIDTH – MHz 3
be handled without overloading any of the filter’s internal nodes.
2
As shown in Figure 19, the OP275’s symmetric slew rate and low distortion produce a clean, well behaved transient response.
1 0 R1 0 200 400 600 800 1000 95.3k

C – pF LOAD C1 2 – 2200pF
Figure 16. Bandwidth vs. C
1
LOAD
A1 V 3 IN + High Speed, Low Noise Differential Line Driver R2 787 R6
 The circuit in Figure 17 is a unique line driver widely used in
4.12k

5 + 7
industrial applications. With ±18 V supplies, the line driver can
C2 C4 6 A4 VOUT – 2200pF R7
deliver a differential signal of 30 V p-p into a 2.5 k
2200pF 5 +
 load. The
7 100k

A3
high slew rate and wide bandwidth of the OP275 combine to
6 – R3 R8
yield a full power bandwidth of 130 kHz while the low noise
1.82k

R9 1k

2 1k
 front end produces a referred-to-input noise voltage spectral
1 – A2 C3
density of 10 nV/Hz.
3 + 2200pF R3 2k R4

1.87k

R9 A1, A4 = 1/2 OP275 2 – 50 1 A2, A3 = 1/2 OP275 V R5 3 A2 O1 + 1.82k

R11 1k

R1 2k

R7 R4 2k
 Figure 18. A 3-Pole, 40 kHz Low-Pass Filter
3 2k

+ V V O2 – VO1 = VIN IN 1 P1 2 A1 – 10k

R5 2k

R6 100 R2 2k

90 2k

R12 1k

6 R10 VOUT – 7 50

10V p-p A3 V 5 O2 10kHz A1 = 1/2 OP275 + R8 2k

A2, A3 = 1/2 OP275 10 GAIN = R3 R1 0% SET R2, R4, R5 = R1 AND R6, R7, R8 = R3
Figure 17. High Speed, Low Noise Differential Line Driver
SCALE: VERTICAL–2V/ DIV HORIZONTAL–10

s/ DIV
Figure 19. Low-Pass Filter Transient Response –10– REV. C REV. C –11– Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION PIN CONNECTIONS SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ORDERING GUIDE Typical Performance Characteristics APPLICATIONS Circuit Protection Total Harmonic Distortion Noise Noise Testing Input Overcurrent Protection Output Voltage Phase Reversal Overload or Overdrive Recovery Measuring Settling Time Driving Capacitive Loads High Speed, Low Noise Differential Line Driver A 3-Pole, 40 kHz Low-Pass Filter OP275 SPICE Model OUTLINE DIMENSIONS Revision History