OP285 Analog Devices, OP285 Datasheet - Page 9

• 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

In inverting and noninverting applications, the feedback resis-
tance forms a pole with the source resistance and capacitance
(R
shown in Figure 10. With R
pole can create excess phase shift and even oscillation. A small
capacitor, C
setting R
is completely removed.
High-Speed, Low-Noise Differential Line Driver
The circuit of Figure 11 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 kΩ load. The
high slew rate and wide bandwidth of the OP285 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. 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.
S
and C
S
(C
S
) and the OP285’s input capacitance (C
FB
R
S
S
, in parallel with R
+ C
V
IN
IN
4.99k
2.49k
) = R
C
S
FB
S
C
2
3
and R
FB
OP285
+
–
4.99k
10pF
–15V
, the effect of the feedback pole
+15V
1/2
FB
C
C
R
8
4
IN
FB
FB
0.1 F
0.1 F
10 F
10 F
+
F
eliminates this problem. By
in the kilohm range, this
+
1
2k
V
OUT
V
OUT
IN
), as
Low Phase Error Amplifier
The simple amplifier configuration of Figure 12 uses the OP285
and resistors to reduce phase error substantially over a wide
frequency range when compared to conventional amplifier designs.
This technique relies on the matched frequency characteristics
of the two amplifiers in the OP285. Each amplifier in the circuit
has the same feedback network which produces a circuit gain of
10. Since the two amplifiers are set to the same gain and are
matched due to the monolithic construction of the OP285, they
will exhibit identical frequency response. Recall from feedback
theory that a pole of a feedback network becomes a zero in the
loop gain response. By using this technique, the dominant pole
of the amplifier in the feedback loop compensates for the domi-
nant pole of the main amplifier,
V
IN
3
2
A1
1
2k
2k
V
R1
R2
A1 = 1/2OP285
A2, A3 = 1/2 OP285
GAIN = SET R2, R4, R5 = R1 AND R, R7, R8 = R2
IN
549
R1
499
R3
5
6
2
3 A2
R4
2k
R5
2k
2k
A3
R3
6
5
3
2
2k
R6
4.99k
A2
A1
7
R2
1
2k
2k
R7
R8
A1, A2 = 1/2 OP285
7
1
50
R10
50
R9
R4
4.99
549
R5
10k
1k
1k
R11
R12
P1
V
OUT
OP285
V
O2
V
– V
V
O2
O1
O1
= V
IN