OPA690 datasheet(20/27 Pages) TI

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OPA2613

SBOS249D − JUNE 2003− REVISED APRIL 2004

www.ti.com

DESIGN-IN TOOLS

DEMONSTRATION BOARDS

A PC board is available to assist in the initial evaluation of

circuit performance using the OPA2613 in its two package

styles. It is available, free, as an unpopulated PC board

delivered with descriptive documentation. The summary

information for this unit is shown in Table 2.

Check the TI web site (www.ti.com) to request this board.

Table 2. Demonstration Board Ordering

Information

PRODUCT

PACKAGE

DEMO BOARD

NUMBER

ORDERING

NUMBER

OPA2613ID

SO-8

DEM

-OPA268XU

SBOU003

MACROMODELS AND APPLICATIONS

SUPPORT

Computer simulation of circuit performance using SPICE

is often useful when analyzing the performance of analog

circuits and systems. This is particularly true for video and

RF amplifier circuits where parasitic capacitance and

inductance can have a major effect on circuit performance.

A SPICE model for the OPA2613 is available through the

TI web site (www.ti.com). This model does a good job of

predicting small-signal AC and transient performance

under a wide variety of operating conditions, but does not

do as well in predicting the harmonic distortion or video

dG/dP characteristics. This model does not attempt to

distinguish between the package types in small-signal AC

performance, nor does it attempt to simulate channel-to-

channel coupling.

INVERTING AMPLIFIER OPERATION

As the OPA2613 is a general-purpose, wideband

voltage-feedback op amp, most of the familiar op amp

application

circuits are available to the designer.

Wideband inverting operation is particularly suited to the

OPA2613.

Figure

shows

typical

inverting

configuration where the I/O impedances and signal gain

from Figure 1 are retained in an inverting circuit

configuration.

1/2

OP A2613

402

Ω

200

Ω

+6V

−6V

Ω

Ω Load

Power−supply

decoupling not

shown.

Ω

Source

66.7

Ω

−

−2

Figure 10. Inverting Gain of −1 with Impedance

Matching

the

inverting

configuration,

two

key

design

considerations must be noted. The first is that the gain

resistor (RG) becomes part of the input impedance. If input

impedance matching is desired (which is beneficial

whenever the signal is coupled through a cable, twisted-

pair, long PC board trace, or other transmission line

conductor), it is normally necessary to add an additional

matching resistor to ground. RG, by itself, is not normally

set to the required input impedance since its value, along

with the desired gain, will determine an RF, which may be

non-optimal from a frequency response standpoint. The

total input impedance for the source becomes the parallel

combination of RG and RM.

The second major consideration, touched on in the

previous paragraph, is that the signal source impedance

becomes part of the noise gain equation and has an effect

on the bandwidth. In the example of Figure 10, the RM

value combines in parallel with the external 50

Ω source

impedance, yielding an effective driving impedance of

Ω || 66.7Ω = 28.6Ω. This impedance is added in series

with RG for calculating the noise gainwhich gives

NG = 2.76. Note that the noninverting input in this bipolar

supply inverting application is connected to ground

through a 146

Ω resistor. It is often suggested that an

additional resistor be connected to ground on the

noninverting

input

achieve

bias

current

error

cancellation at the output.

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