OPA690 datasheet(13/30 Pages) TI1

13 / 30 page

OPA2691

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.

Ω

82.5

Ω

Ω Cable

RG-59

82.5

Ω

402

Ω

340

Ω

Video 1

+5V

–5V

1/2

OPA2691

1/2

OPA2691

Ω

402

Ω

340

Ω

Video 2

–5V

+5V

DIS

Power-supply

decoupling not shown.

600

Ω

20MHz, 2nd-Order Butterworth Low-Pass

1/2

OPA2691

+5V

Power-supply

decoupling not shown.

32.3

Ω

105

Ω

0.1

µF

375

Ω

1/2

OPA2691

100pF

125

Ω

0.1

µF

150pF

–4

–8

–12

Frequency (MHz)

20MHz, 2ND-ORDER BUTTERWORTH

LOW-PASS FREQUENCY RESPONSE

0.1

100

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