Datasheet

OPA2691
13
SBOS224D
www.ti.com
HIGH-SPEED ACTIVE FILTERS
Wideband current-feedback op amps make ideal elements
for implementing high-speed active filters where the amplifier
is used as a fixed gain block inside a passive RC circuit
network. Their relatively constant bandwidth versus gain,
provides low interaction between the actual filter poles and
the required gain for the amplifier. Figure 5 shows an ex-
ample single-supply buffered filter application. In this case,
one of the OPA2691 channels is used to setup the DC
operating point and provide impedance isolation from the
signal source into the 2nd-stage filter. That stage is set up to
implement a 20MHz maximally flat Butterworth frequency
response and provide an AC gain of +4.
FIGURE 5. Buffered Single-Supply Active Filter.
FIGURE 4. Two-Channel Video Multiplexer.
2kΩ
82.5Ω
75Ω Cable
RG-59
82.5Ω
75Ω
402Ω340Ω
Video 1
+5V
+5V
–5V
1/2
OPA2691
1/2
OPA2691
2kΩ
75Ω
402Ω340Ω
Video 2
–5V
+5V
V
DIS
DIS
DIS
Power-supply
decoupling not shown.
600Ω
20MHz, 2nd-Order Butterworth Low-Pass
1/2
OPA2691
+5V
Power-supply
decoupling not shown.
32.3Ω 105Ω
5kΩ
5kΩ51Ω
V
I
0.1µF
375Ω
1/2
OPA2691
4V
I
100pF
125Ω
0.1µF
150pF
12
8
4
0
–4
–8
–12
Frequency (MHz)
20MHz, 2ND-ORDER BUTTERWORTH
LOW-PASS FREQUENCY RESPONSE
0.1 100101
Gain (dB)