OPA653IDBVR datasheet(9/19 Pages) TI

9 / 19 page

APPLICATION INFORMATION

Wideband, Noninverting, and Inverting

OPA653

OUT

IN-

IN+

160 W

49.9 W

160 W

72.3 W

49.9 W

0.1

+6V

-6V

50-W

Load

50-W

Source

S+

S-

OPA653

OUT

IN-

IN+

160 W

49.9 W

160 W

49.9 W

0.1

+6V

-6V

50-W

Load

50-W

Source

S+

S-

OPA653

www.ti.com........................................................................................................................................................................................... SBOS348 – DECEMBER 2008

Figure 22 shows the OPA653 in a noninverting gain

of –1 V/V configuration in a 50-

Ω test environment as

Operation

was used for testing the Typical Characteristics. The

circuit operation is essentially the same as Figure 21

The OPA653 is a very broadband, voltage-feedback

except that a 72.3-

Ω termination resistor is now used

amplifier with internal gain-setting resistors that set a

between the VIN– input and ground, so that together

fixed gain of +2 V/V or -1 V/V and a high-impedance

with the gain-setting resistor (RG = 160 Ω), the input

JFET-input stage. Its very high bandwidth of 500 MHz

impedance is approximately 50

Ω. The VIN+ input is

can be used to either deliver high signal bandwidths

terminated to ground using a 49.9-

Ω resistor as a

at a gain of +2 V/V or, if driven from a low-impedance

precaution to avoid single transistor oscillations at the

source, a gain of –1 V/V . The OPA653 is designed to

input; the value is not critical, but attention should be

provide very low noise and accurate pulse response

paid to avoid large values because of the noise

with low overshoot and ringing. To achieve the full

contribution as noted below.

performance of the OPA653, careful attention to

printed circuit board (PCB) layout and component

selection is required as discussed in the remaining

sections of this data sheet.

Figure 21 shows the noninverting gain of +2-V/V

circuit that is used as the basis for the Typical

Characteristics.

Most

the

curves

were

characterized using signal sources with 50-

Ω driving

impedance, and with measurement equipment that

presents a 50-

Ω load impedance. In Figure 21, the

49.9-

Ω shunt resistor to ground at the VIN+ input is

used to match the source impedance of the test

generator and cable, while the 49.9-

Ω series output

resistor VOUT provides matching impedance for the

measurement equipment load and cable. Data sheet

voltage

swing

specifications

are

taken

the

Figure 22. Noninverting Gain of –1 V/V in 50-

Ω

noninverting input pin, VIN+, or the output pin, VOUT,

Test Environment

unless otherwise noted.

Note that the 72.3-

Ω input termination resistor and

the 50-

Ω source impedance of the test equipment

modify the noise gain to +1.84 V/V and the amplifier

is compensated for optimal performance with a noise

gain of +2 V/V. This compensation reduces the phase

margin and results in more peaking in the frequency

response and more overshoot/ringing in the pulse

response. This effect can be seen by comparing the

inverting

and

noninverting

frequency

and

pulse

response graphs in the characteristic data. The

amplifier phase margin can be restored in an

application that uses an inverting configuration if it is

driven from a very low impedance source such as an

op amp.

Figure 21. Noninverting Gain of +2 V/V in 50-

Ω

Test Environment

space

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