OPA694 datasheet(11/28 Pages) TI1

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OPA2694

SBOS320D − SEPTEMBER 2004 − REVISED APRIL 2013

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APPLICATION INFORMATION

WIDEBAND CURRENT FEEDBACK OPERATION

The OPA2694 provides exceptional AC performance for a

wideband, low-power, current-feedback operational

amplifier. Requiring only 5.8mA/ch quiescent current, the

OPA2694 offers a 690MHz bandwidth at a gain of +2,

along with a 1700V/μs slew rate. An improved output stage

provides ±70mA output drive, along with < 1.5V output

voltage headroom. This combination of low power and

high bandwidth can benefit high-resolution video

applications.

Figure 1 shows the DC-coupled, gain of +2, dual power-

supply circuit configuration used as the basis of the ±5V

Electrical Characteristic tables and Typical Characteristic

curves. For test purposes, the input impedance is set to

50Ω with a resistor to ground and the output impedance is

set to 50Ω with a series output resistor. Voltage swings

reported in the Electrical Charateristics are taken directly

at the input and output pins, while load powers (dBm) are

defined at a matched 50Ω load. For the circuit of Figure 1,

the total effective load will be 100Ω || 804Ω = 89Ω. One

optional component is included in Figure 1. In addition to

the usual power-supply decoupling capacitors to ground,

a 0.01μF capacitor is included between the two

power-supply pins. In practical PCB layouts, this optional

added capacitor will typically improve the 2nd-harmonic

distortion performance by 3dB to 6dB.

+5V

−5V

−VS

+VS

ΩLoad

ΩSource

402

6.8

μF

0.1

μF

Optional

0.01

μF

1/2

OPA2694

6.8

μF

0.1

μF

Figure 1. DC-Coupled, G = +2, Bipolar-Supply

Specification and Test Circuit

Figure 2 shows the DC-coupled, gain of −2V/V, dual

power-supply circuit used as the basis of the inverting

Typical Characteristic curves. Inverting operation offers

several performance benefits. Since there is no

common-mode signal across the input stage, the slew rate

for inverting operation is higher and the distortion

performance is slightly improved. An additional input

resistor, RT, is included in Figure 2 to set the input

impedance equal to 50Ω. The parallel combination of RT

and RG sets the input impedance. Both the noninverting

and inverting applications of Figure 1 and Figure 2 will

benefit from optimizing the feedback resistor (RF) value for

bandwidth (see the discussion in Setting Resistor Values

to Optimize Bandwidth). The typical design sequence is to

select the RF value for best bandwidth, set RG for the gain,

then set RT for the desired input impedance. As the gain

increases for the inverting configuration, a point will be

reached where RG will equal 50Ω, where RT is removed

and the input match is set by RG only. With RG fixed to

achieve an input match to 50Ω, RF is simply increased, to

increase gain. This will, however, quickly reduce the

achievable bandwidth, as shown by the inverting gain of

–10 frequency response in the Typical Characteristic

curves. For gains > 10V/V (14dB at the matched load),

noninverting operation is recommended to maintain

broader bandwidth.

1/2

OPA2694

+5V

+VS

−VS

−5V

ΩLoad

66.5

200

6.8

μF

0.1

μF

6.8

μF

0.1

μF

Optional

0.01

μF

ΩSource

402

Figure 2. DC-Coupled, G = −2V/V, Bipolar-Supply

Specification and Test Circuit

OPA694 Datasheet(PDF) 11 Page - Texas Instruments

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