OPA3690ID Datasheet, PDF (18/39 Pages) Texas Instruments – Triple, Wideband, Voltage-Feedback OPERATIONAL AMPLIFIER with Disable

OPA3690
SBOS237G – MARCH 2002 – REVISED MARCH 2010
WIDEBAND INTEGRATOR
The three unity-gain stable, voltage-feedback
amplifiers in the OPA3690 may be used to develop
an exceptional integrator function, as shown in
Figure 45. This circuit effectively multiplies the
open-loop gain using two of the amplifiers and uses
the third to provide an input impedance buffering and
low output impedance over broad frequencies
required for proper operation. The interstage
attenuator (resistive divider into the last stage
noninverting input) is critical to maintaining stability;
see Figure 43. This circuit can deliver a 90° phase
shift over a five-decade frequency span.
STATE VARIABLE FILTER
Figure 46 shows a state variable filter using the
OPA3690. This active filter is quite useful for high Q
filter responses, and will produce low-pass,
high-pass, bandpass, notch, and all-pass functions.
The filter response is:
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V_OUT
V_IN
=
-
S²(a)
+
sw_P
Q_P
(b
-
c)
+
w_P²(d)
S²
+
sw_P
Q_P
+
w_P²
where w_P =
1
RC
(2)
The desired filter frequency response is achieved by
the correct selection of the feed-forward components
at the input.
The resistor R_ISO isolates the last op amp and the
input driver from capacitive loading problems when a
> 0. To ensure good performance, make sure that:
f
w_P
£
GBP
20Q_P
,
Q_P
>
1
2p
f
GBP
20
,
Q_P
£
1
(3)
where f_GBP is the OPA3690 gain bandwidth product
(300MHz).
C
50W
V_IN
1/3
R
1/3
50W
OPA3690
1/3
OPA3690
150W
OPA3690
25W
75W
50W
V_OUT
Figure 45. Wideband Integrator
R
R/d
V_IN
C
R
Q_PR
R
R
C
V_OUT
49.9W
1/3
OPA3690
1/3
OPA3690
1/3
OPA3690
Q_PR/c
aC
Q_PR/b
R_ISO
49.9W
49.9W
Figure 46. State Variable Filter
18
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