Datasheet

= -
S ( )+( )+a b - c
2
w d
P
2
( )
S ++
2
2
P
w
V
OUT
V
IN
sw
P
Q
P
sw
P
Q
P
=
where w
P
1
RC
£
,Q >1
P
w
P
2p
f
GBP
20Q
P
,Q 1
P
£
f
GBP
20
V
IN
V
OUT
50W
50W
1/3
OPA3690
25W
1/3
OPA3690
R
50W
1/3
OPA3690
75W
150W
C
V
IN
V
OUT
R/d
C
49.9W
R RR
R
C
Q R
P
Q R/c
P
Q R/b
P
R
ISO
1/3
OPA3690
1/3
OPA3690
aC
49.9W 49.9W
1/3
OPA3690
OPA3690
SBOS237G –MARCH 2002–REVISED MARCH 2010 www.ti.com
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
(2)
open-loop gain using two of the amplifiers and uses
the third to provide an input impedance buffering and
The desired filter frequency response is achieved by
low output impedance over broad frequencies
the correct selection of the feed-forward components
required for proper operation. The interstage
at the input.
attenuator (resistive divider into the last stage
noninverting input) is critical to maintaining stability; The resistor R
ISO
isolates the last op amp and the
see Figure 43. This circuit can deliver a 90° phase input driver from capacitive loading problems when a
shift over a five-decade frequency span. > 0. To ensure good performance, make sure that:
STATE VARIABLE FILTER
Figure 46 shows a state variable filter using the
OPA3690. This active filter is quite useful for high Q
(3)
filter responses, and will produce low-pass,
where f
GBP
is the OPA3690 gain bandwidth product
high-pass, bandpass, notch, and all-pass functions.
(300MHz).
The filter response is:
Figure 45. Wideband Integrator
Figure 46. State Variable Filter
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