OPA2613 datasheet(21/36 Pages) TI2

21 / 36 page

OPA2614

SBOS305D − JUNE 2004 − REVISED AUGUST 2008

www.ti.com

For the ADSL CPE upstream driver design of Figure 10,

the peak current is 150mA for a signal that requires a crest

factor of 5.33 with a target line power of 13dBm into 100

Ω

(20mW). With a typical quiescent current of 12mA and a

nominal supply voltage of +12V, the total internal power

dissipation for the solution of Figure 10 will be:

TOT + 12mA(12V) )

150mA

5.33

(12V)

* 2(20mW) + 400mW

DESIGN-IN TOOLS

DEMONSTRATION FIXTURE

A printed circuit board (PCB) is available to assist in the

initial

evaluation of circuit performance using the

OPA2614. The fixture is offered free of charge as an

unpopulated PCB, delivered with user’s guide. The

summary information for this fixture is shown in Table 2.

Table 2. Demonstration Fixture

PRODUCT

PACKAGE

ORDERING

NUMBER

LITERATURE

NUMBER

OPA2614ID

SO-8

DEM

-OPA-SO−2A

SBOU003

The demonstration fixture can be requested at the Texas

Instruments web site (www.ti.com) through the OPA2614

product folder.

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 OPA2614 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 OPA2614 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

OPA2614.

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

OPA2614

453

Ω

113

Ω

+6V

−6V

Ω

Ω Load

Power−supply

decoupling not

shown.

Ω

Source

Ω

110

Ω

0.01

µF

−

−4

Figure 14. Inverting Gain of −4 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 PCB 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 14, the RM

value combines in parallel with the external 50

Ω source

impedance, yielding an effective driving impedance of

Ω || 89Ω = 32Ω. This impedance is added in series with

RG for calculating the noise gainwhich gives NG = 4.12.

Note that the noninverting input in this bipolar supply

inverting application is connected to ground through a

110

Ω resistor. It is often suggested that an additional

resistor be connected to ground on the noninverting input

to achieve bias current error cancellation at the output.

(15)

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