THS6214IPWPR datasheet(24/41 Pages) TI

24 / 41 page

APPLICATION INFORMATION

WIDEBAND CURRENT-FEEDBACK

=1+

2 ´

(1)

1.24kW

-12V

+12V

1/2

THS6214

1/2

THS6214

274W

OUT

=1+

DIFF

´ F

OUT

THS6214

SBOS431 – MAY 2009 ....................................................................................................................................................................................................... www.ti.com

This approach allows the user to set a source

termination

impedance

the

input

that

OPERATION

independent of the signal gain. For instance, simple

The

THS6214

provides

the

exceptional

differential filters may be included in the signal path

performance of a wideband current-feedback op amp

right up to the noninverting inputs with no interaction

with

highly

linear,

high-power

output

stage.

with the gain setting. The differential signal gain for

Requiring only 21mA/port quiescent current, the

the circuit of Figure 81 is:

THS6214 swings to within 1.9V of either supply rail

on a 100

Ω load and delivers in excess of 416mA at

room

temperature.

This

low-output

headroom

requirement, along with supply voltage independent

Where AD = differential gain.

biasing, provides remarkable ±6V supply operation.

The

THS6214

delivers

greater

than

140MHz

Figure 81 shows a value of 274

Ω for the AD = +10V/V

bandwidth driving a 2VPP output into 100Ω on a ±6V

design. Because the THS6214 is a current feedback

supply. Previous boosted output stage amplifiers

(CFB) amplifier, its bandwidth is primarily controlled

typically suffer from very poor crossover distortion as

with the feedback resistor value; the differential gain,

the output current goes through zero. The THS6214

however, may be adjusted with considerable freedom

achieves a comparable power gain with much better

using just the RG resistor. In fact, RG may be reduced

linearity.

The

primary

advantage

by a reactive network that provides a very isolated

current-feedback op amp over a voltage-feedback op

shaping to the differential frequency response.

amp

that

performance

(bandwidth

and

Various combinations of single-supply or ac-coupled

distortion) is relatively independent of signal gain.

gain can also be delivered using the basic circuit of

Figure 81 shows the dc-coupled, gain of +10V/V, dual

Figure 81. Common-mode bias voltages on the two

power-supply circuit configuration used as the basis

noninverting inputs pass on to the output with a gain

of the ±12V Electrical and Typical Characteristics. For

of +1V/V because an equal dc voltage at each

test purposes, the input impedance is set to 50

Ω with

inverting node creates no current through RG. This

a resistor to ground and the output impedance is set

circuit does show a common-mode gain of +1V/V

to 50

Ω with a series output resistor. Voltage swings

from input to output. The source connection should

reported in the Electrical Characteristics are taken

either remove this common-mode signal if undesired

directly at the input and output pins, whereas load

(using an input transformer can provide this function),

powers (dBm) are defined at a matched 50

Ω load.

or the common-mode voltage at the inputs can be

For the circuit of Figure 81, the total effective load is

used to set the output common-mode bias. If the low

100

Ω || 1.24kΩ || 1.24kΩ = 86.1Ω.

common-mode rejection of this circuit is a problem,

the output interface can also be used to reject that

common-mode.

For

instance,

most

modern

differential input analog-to-digital converters (ADCs)

reject common-mode signals very well, while a line

driver

application

through

transformer

also

attenuates the common-mode signal through to the

line.

Figure 81. Noninverting Differential I/O Amplifier

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