OPA690 datasheet(18/35 Pages) TI

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HIGH-PERFORMANCE DAC

WIDEBAND VIDEO MULTIPLEXING

2 R C

p F F

GBP

4 R C

p F D

(1)

-3dB

GBP

2 R C

p F D

1/2

OPA2890

1/2

OPA2890

High-Speed

DAC

V =I R

V = I R

GBP

GainBandwidth

Product(Hz)fortheOPA2890

-IO

50W

305W

2kW

82.5W

Cable

Load

RG-59

82.5W

75W

750W

634W

Video1

+5V

-5V

1/2

OPA2890

1/2

OPA2890

305W

2kW

75W

750W

634W

Video2

-5V

+5V

DIS

DISA

DISB

OPA2890

SBOS364A – DECEMBER 2007 – REVISED DECEMBER 2007

TRANSIMPEDANCE AMPLIFIER

One common application for video speed amplifiers

High-frequency

DDS

digital-to-analog

converters

that include a disable pin is to wire multiple amplifier

(DACs) require a low distortion output amplifier to

outputs together, then select one of several possible

retain SFDR performance into real-world loads.

video inputs to source onto a single line. This simple

Figure

shows

single-ended

output

drive

wired-OR

video

multiplexer

can

easily

implementation. The diagram shows the signal output

implemented using the OP2890IDGS (MSOP-10

current(s) connected into the virtual ground summing

package only), as shown in Figure 54.

junction(s) of the OPA2890, which is set up as a

transimpedance stage or I-V converter. If the DAC

requires that its outputs terminate to a compliance

voltage

other

than

ground

for

operation,

the

appropriate voltage level may be applied to the

noninverting input of the OPA2890. The dc gain for

this circuit is equal to RF. At high frequencies, the

DAC output capacitance (CD in Figure 53) produces a

zero in the noise gain for the OPA2890 that may

cause

peaking

the

closed-loop

frequency

response. CF is added across RF to compensate for

this

noise

gain

peaking.

achieve

flat

transimpedance frequency response, the pole in each

feedback network should be set to:

which gives a cutoff frequency f–3dB of approximately:

Figure 53. DAC Transimpedance Amplifier

Figure 54. 2-Channel Video Multiplexer (MSOP-10 package only)

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