OP285 Analog Devices, OP285 Datasheet - Page 11

• Manufacturer Part Number: OP285
• Description: Dual, 9 MHz Precision Operational Amplifier
• Manufacturer: Analog Devices

Specifications of OP285

• -3db Bandwidth: 9MHz
• Slew Rate: 22V/µs
• Vos: 35µV
• Ib: 100nA
• # Opamps Per Pkg: 2
• Input Noise (nv/rthz): 6nV/rtHz
• Vcc-vee: 9V to 44V
• Isy Per Amplifier: 2.5mA
• Packages: SOIC

A 3-Pole, 40 kHz Low-Pass Filter
The closely matched and uniform ac characteristics of the OP285
make it ideal for use in GIC (Generalized Impedance Converter)
and FDNR (Frequency Dependent Negative Resistor) filter appli-
cations. The circuit in Figure 16 illustrates a linear-phase,
3-pole, 40 kHz low-pass filter using an OP285 as an inductance
simulator (gyrator). The circuit uses one OP285 (A2 and A3)
for the FDNR and one OP285 (Al 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 classical 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 compo-
nent 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 17, the OP285’s symmetric
slew rate and low distortion produce a clean, well-behaved
transient response.
10V p-p
10kHz
V
OUT
100
90
10
0%
V
SCALE: VERTICAL – 2V/ DIV
IN
HORIZONTAL – 10 S/ DIV
2
3
A1
1
1
A2
95.3k
2200pF
R1
C1
2
3
2200pF
2200pF
787
1.82k
1.87k
1.82k
R2
C2
C3
R3
R4
R5
5
6
4.12k
A3
R6
Driving Capacitive Loads
The OP285 was designed to drive both resistive loads to 600 Ω
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 18 shows the 0 dB bandwidth of the OP285 with capacitive
loads from 10 pF to 1000 pF.
7
A1, A4 = 1/2 OP285
A2, A3 = 1/2 OP285
2200pF
C4
10
9
8
7
6
5
4
3
2
1
0
0
100k
R7
1k
200
R9
5
6
A4
1k
R8
400
C
7
LOAD
– pF
V
OUT
600
800
OP285
1000