Texas Instruments OPA3695EVM Evaluation Module OPA3695EVM OPA3695EVM 데이터 시트
제품 코드
OPA3695EVM
1/3
OPA3695
+5V
-5V
50W
50W
22pF
226W
100W
0W
Source
R
G
604W
R
F
604W
22pF
V
I
V
O
1/3
OPA3695
+5V
+V
S
DIS
V /2
S
604W
100W
V
O
V
I
604W
R
G
499W
R
F
499W
0.1 F
m
0.1 F
m
+
6.8 F
m
0.1 F
m
50
Source
W
60.4W
HIGH-FREQUENCY ACTIVE FILTERS
9
6
3
0
-3
-6
-9
-12
-15
-18
-21
-24
Gain(dB)
1
10
100
1000
Frequency (MHz)
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SBOS355A – APRIL 2008 – REVISED SEPTEMBER 2008
shows the ac-coupled, G = +2V/V,
single-supply specification and test circuit. Once
again,
again,
the
noninverting
input
is
dc-biased
at
midsupply to put that same V
S
/2 at the output pin.
Figure 39. Line Driver with 40MHz Low-Pass
Active Filter
This type of filter depends on a low output impedance
from the amplifier through very high frequencies to
continue to provide an increasing attenuation with
frequency. As the amplifier output impedance rises
from the amplifier through very high frequencies to
continue to provide an increasing attenuation with
frequency. As the amplifier output impedance rises
Figure 38. AC-Coupled, G = +2V/V, Single-Supply
with frequency, any input signal or noise starts to
Specification and Test Circuit
feed directly through to the output via the feedback
capacitor. Because the OPA3695 used in
capacitor. Because the OPA3695 used in
has a 900MHz bandwidth, the active filter continues
to roll-off through frequencies that exceed 200MHz.
to roll-off through frequencies that exceed 200MHz.
The extremely wide bandwidth of the OPA3695
shows the frequency response for the filter
allows an extensive range of active filter topologies to
of
, where the desired 40MHz cutoff is
be implemented with minimal amplifier bandwidth
achieved and a 40dB/dec roll-off is held through very
interaction in the filter shape. While Sallen-Key filters
high frequencies.
work very well with current-feedback amplifiers, the
use
use
of
multiple
feedback
(MFB)
filters
is
not
recommended because an MFB filter places a
capacitor
capacitor
in
the
feedback
path
which
in
turn
eliminates compensation and results in an oscillator.
In general, given a desired filter
In general, given a desired filter
ω
O
, the amplifier
should have a minimum of 10X
ω
O
to minimize filter
interaction with the amplifier frequency response.
illustrates an example gain of +2 line driver
using the OPA3695 that incorporates a 40MHz
low-pass Butterworth response with only a few
external components. The filter resistor values have
been adjusted slightly here from an ideal filter
analysis to account for parasitic effects.
low-pass Butterworth response with only a few
external components. The filter resistor values have
been adjusted slightly here from an ideal filter
analysis to account for parasitic effects.
Figure 40. 40MHz Low-Pass Active Filter
Response
Copyright © 2008, Texas Instruments Incorporated
15
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