OPA692 datasheet(19/31 Pages) BURR-BROWN

19 / 31 page

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HIGH-SPEED INSTRUMENTATION

MULTIPLEXED CONVERTER DRIVER

LOW-PASS FILTER

1/3

OPA3693

1/3

OPA3693

1/3

OPA3693

300W

150W

300W

OUT

-3

-6

-9

-12

-15

Frequency(Hz)

10M

100M

20log

VOUT

OPA3693

SBOS353 – DECEMBER 2006

AMPLIFIER

The converter driver in Figure 53 multiplexes among

Figure 51 shows an instrumentation amplifier based

the three input signals. The OPA3693 enable and

on the OPA3693. The offset matching between

disable times support multiplexing among video

inputs makes this configuration an attractive input

signals.

The

make-before-break

disable

stage

for

this

application.

The

characteristic of the OPA3693 ensures that the

differential-to-single-ended gain for this circuit is

output is always under control. To avoid large

2V/V. The inputs are high-impedance, with only

switching glitches, switch during the sync or retrace

1.2pF to ground at each input. The loads on the

portions of the video signal—the two inputs should

OPA3693 outputs are equal for the best harmonic

be almost equal at these times. The output is always

distortion possible.

under control, so the switching glitches for two 0V

inputs are < 20mV. With standard video signals

levels at the inputs, the maximum differential voltage

across the disabled inputs does not exceed the

±1.2V maximum allowed.

The output resistors isolate the outputs from each

other

when

switching

between

channels.

The

feedback network of the disabled channels forms

part of the load seen by the enabled amplifier,

attenuating the signal slightly.

The

circuit

Figure

realizes

7th-order

Butterworth low-pass filter with a –3dB bandwidth of

20MHz. This filter is based on the KRC active filter

Figure 51. High-Speed Instrumentation Amplifier

topology that uses an amplifier with the fixed gain

≥

1. The OPA3693 makes a good amplifier for this type

of filter. The component values have been adjusted

As shown in Figure 52, the OPA3693 used as an

to compensate for the parasitic effects of the op

instrumentation amplifier has a

420MHz,

–3dB

amp.

bandwidth. This plot has been made for a 1VPP

output signal using a low-impedance differential input

source.

Figure 52. High-Speed Instrumentation Amplifier

Response

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