OPA682 datasheet(13/22 Pages) TI1

13 / 22 page

OPA2681

SBOS091A

FIGURE 4. Two-Channel Video Multiplexer.

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 51

Ω 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 600

Ω feedback resistor is required for

Ω

82.5

Ω

Ω Cable

RG-59

82.5

Ω

402

Ω

340

Ω

Video 1

+5V

–5V

1/2

OPA2681N

1/2

OPA2681N

Ω

402

Ω

340

Ω

Video 2

–5V

+5V

DIS

Power supply

de-coupling not shown

600

Ω

20MHz, 2nd Order Butterworth Low Pass

1/2

OPA2681

+5V

Power supply

de-coupling not shown

32.3

Ω

105

Ω

0.1

µF

375

Ω

1/2

OPA2681

100pF

125

Ω

0.1

µF

150pF

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