OPA698 datasheet(20/27 Pages) TI

20 / 27 page

OPA698

SBOS258B

www.ti.com

OPA698

Open

OUT

402

Ω

OPA698

Ω

402

Ω

–0.2V

FIGURE 19. Sync Stripper Circuit.

BOARD

LITERATURE

PRODUCT

PACKAGE

PART NO.

REQUEST NO.

OPA698ID

SO-8

DEM-OPA68xU

SBOU009

TABLE I. Demo Board Summary Information.

DC RESTORER

Figure 18 shows a DC restore circuit using the OPA698 and

OPA660. The buffer element of the OPA660 is used to buffer

the input signal while the transconductance element is used

to restore the DC level after the decoupling capacitor C1. The

DC level is set using R1 and R2. The OPA698 is configured

at a gain of 2 to compensate for the 75

Ω series into a 75Ω

load. The OPA698 also limits the output to ground.

VIDEO SYNC STRIPPER

Figure 19 shows a sync stripper using two OPA698 output-

limiting op amps. One OPA698 is configured as a limiting

inverting comparator. Referred to the input, the negative

excursions lower than –0.2V are clipped to ground, and all

excursions greater than –0.2V generate an output voltage

set by the default limiting value (–3.5V). The second OPA698

is using this waveform to effectively remove the sync pulse

from the video signal.

DESIGN-IN TOOLS

APPLICATIONS SUPPORT

The Texas Instruments Applications Department is available

for design assistance at 1-972-644-5580. The Texas Instru-

ments web site (www.ti.com) has the latest product data

sheets and other design aids.

DEMONSTRATION BOARDS

A PC board is available to assist in the initial evaluation of

circuit performance of the OPA698ID. It is available as an

unpopulated PCB with descriptive documentation. See the

demonstration board literature for more information. The

summary information for this board is shown in Table I.

FIGURE 18. DC Restore to Ground.

This board can be requested through the TI web site.

OPERATING SUGGESTIONS

THEORY OF OPERATION

The OPA698 is a voltage-feedback op amp that is unity-gain

stable. The output voltage is limited to a range set by the

voltage on the limiter pins (5 and 8). When the input tries to

overdrive the output, the limiters take control of the output

buffer. This action from the limiters avoids saturating any part

of the signal path, giving quick overdrive recovery and

OPA698

Ω

Load

H = Open

402

Ω

200

Ω

402

Ω

200

Ω

250

Ω

19.6k

Ω

µF

CCII

U1 = OPA660

Q = 250Ω (sets IQ for U1)

1, D2 = 1N4148

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