OPA2681 Datasheet, PDF (13/21 Pages) Burr-Brown (TI) – Dual Wideband, Current Feedback OPERATIONAL AMPLIFIER With Disable

+5V
V_DIS
2kΩ
Video 1
75Ω
+5V
Power supply
de-coupling not shown
1/2 ^DIS
OPA2681N
340Ω
340Ω
–5V
402Ω
402Ω
+5V
82.5Ω
75Ω Cable
RG-59
82.5Ω
Video 2
75Ω
2kΩ
1/2
OPA2681N
DIS
–5V
FIGURE 4. Two-Channel Video Multiplexer.
+5V
Power supply
de-coupling not shown
5kΩ
0.1µF
100pF
V_I
51Ω
5kΩ
1/2
OPA2681
32.3Ω
105Ω
150pF
1/2
OPA2681
4V_I
600Ω
375Ω
20MHz, 2nd Order Butterworth Low Pass
125Ω
0.1µF
FIGURE 5. Buffered, Single Supply Active Filter.
HIGH SPEED ACTIVE FILTERS
Wideband current feedback op amps make ideal elements
for implementing high speed active filters where the ampli-
fier is used as fixed gain block inside a passive RC circuit
network. Their relatively constant bandwidth vs gain, pro-
vides low interaction between the actual filter poles and the
required gain for the amplifier. Figure 5 shows an example
single-supply buffered filter application. In this case, one of
the OPA2681 channels is used to set-up 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.
The 51Ω input matching resistor is optional in this case. The
input signal is AC coupled to the 2.5V DC reference voltage
developed through the resistor divider from the +5V power
supply. This first stage acts as a gain of +1 voltage buffer for
the signal where the 600Ω feedback resistor is required for
®
13
OPA2681