OPA692 datasheet(17/31 Pages) BURR-BROWN

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1/3

OPA3693

+5V

DIS

50W

300W

50W

-5V

1/3

OPA3693

Open

V /2

60.4W

100W

Source

604W

300W

6.8 F

0.1 F

DIS

1000pF

+5V

WIDEBAND UNITY-GAIN BUFFER WITH

-1

-2

-3

-4

-5

-6

100

1000

Frequency(MHz)

G=+1,Figure43

G=+1,Figure47

OPA3693

SBOS353 – DECEMBER 2006

While

the

circuit

Figure

shows

+5V

The input impedance is still set by RM as the

single-supply operation, this same circuit may be

apparent impedance looking into RG is very high. RM

used for single supplies ranging as high as +12V

may be increased to show a higher input impedance,

nominal. The noninverting input bias resistors are

but larger values begin to impact dc output offset

relatively low in Figure 45 to minimize output dc

voltage.

offset as a result of noninverting input bias current.

At higher signal-supply voltage, these resistors

should be increased to limit the added supply current

drawn through this path.

Figure 46 shows the AC-coupled, G = +1V/V,

single-supply specification and test circuit. In this

case, the gain setting resistor, RG, is simply left open

to get a gain of +1V for ac signals. Once again, the

noninverting input is dc biased at midsupply, putting

that same VS/2 at the output pin. The signal is

AC-coupled

into

this

midpoint

with

added

termination resistor on the source side of the

blocking capacitor.

Figure 47. Improved Unity-Gain Buffer

This circuit creates an additional input offset voltage

as the difference in the two input bias currents times

the impedance to ground at VI. Figure 48 shows a

comparison of small-signal frequency response for

the unity-gain buffer of Figure 43 compared to the

improved approach shown in Figure 47.

Figure 46. AC-Coupled, G = +1V/V, Single-Supply

Specification and Test Circuit

IMPROVED FLATNESS

As shown in the Typical Characteristic curves, the

unity-gain buffer configuration of Figure 43 illustrates

a peaking in the frequency response exceeding 2dB.

This

configuration

gives

the

slight

amount

Figure 48. Buffer Frequency Response

Comparison

overshoot and ringing apparent in the gain of +1V/V

pulse response curves. A similar circuit that holds a

flatter frequency response, giving improved pulse

fidelity, is shown in Figure 47. This circuit removes

the peaking by bootstrapping out any parasitic

effects on RG.

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