OPA690IDBVT datasheet(16/37 Pages) TI1

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OPA690

High-Speed

DAC

V =I R

50W

2 R C

p F F

GBP

4 R C

p F D

-3dB

GBP

2 R C

OPA690

2kW

0.1 F

400W

50W

+12V

5pF

50W

Source

50W

Load

2kW

OPA690

SBOS223F – DECEMBER 2001 – REVISED FEBRUARY 2010

www.ti.com

HIGH-PERFORMANCE DAC

The 5pF capacitor in the feedback loop provides

TRANSIMPEDANCE AMPLIFIER

added bandwidth control for the signal path.

High-frequency,

direct

digital

synthesis

(DDS)

Digital-to-Analog Converters (DACs) require a low

distortion output amplifier to retain their SFDR

performance into real-world loads. See Figure 40 for

a single-ended output drive implementation. In this

circuit, only one side of the complementary output

drive signal is used. The diagram shows the signal

output current connected into the virtual ground

summing junction of the OPA690, which is set up as

a transimpedance stage or I-V converter. The unused

current output of the DAC is connected to ground. 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 OPA690. The dc gain for this

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

output capacitance will produce a zero in the noise

gain for the OPA690 that may cause peaking in the

closed-loop frequency response. CF is added across

RF to compensate for this noise gain peaking. To

Figure 40. DAC Transimpedance Amplifier

achieve a flat transimpedance frequency response,

the pole in the feedback network should be set to:

(1)

which

will

give

closed-loop

transimpedance

bandwidth, f−3dB, of approximately:

(2)

Where GBP = gain bandwidth product (Hz) for the

OPA690.

HIGH-POWER LINE DRIVER

The large output swing capability of the OPA690 and

its high current capability allow it to drive a 50

Ω line

Figure 41. High-Power Coax Line Driver

with a peak-to-peak signal up to 4VPP at the load, or

8VPP at the output of the amplifier using a single 12V

supply. Figure 41 shows such a circuit set for a gain

of 8 to the output or 4 to the load.

Product Folder Link(s): OPA690

OPA690IDBVT Datasheet(PDF) 16 Page - Texas Instruments

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