f

=

-

3dB

1

2 R1C1

p

VI

VO

C1

+

−

RG

RF

R1

V

V

O

I

=(1+)

[

]

R

R

F

G

1

(1+sR1C1)

VI

C2

R2

R1

C1

RF

RG

_

+

f

=

-

3dB

1

2 RC

p

R1=R1=R

C1=C2=C

Q=PeakingFactor

(ButterworthQ=0.707)

R =

G

R

F

(2

)

-

1

Q

THS6032

SLOS233F – APRIL 1999 – REVISED AUGUST 2009....................................................................................................................................................... www.ti.com

GENERAL CONFIGURATIONS

A common error for the first-time CFB user is to create a unity-gain buffer amplifier by shorting the output directly

to the inverting input. A CFB amplifier in this configuration oscillates, so this is not recommended. The THS6032,

like all CFB amplifiers, must have a feedback resistor for stable operation. Additionally, placing capacitors directly

from the output to the inverting input is not recommended. This is because, at high frequencies, a capacitor has

a very low impedance. This results in an unstable amplifier, and should not be considered when using a

current-feedback amplifier. Because of this, simple low-pass filters, which are easily implemented on a VFB

amplifier, have to be designed slightly differently. If filtering is required, simply place an RC-filter at the

noninverting terminal of the operational-amplifier (see Figure 52).

Figure 52. Single-Pole Low-Pass Filter

If a multiple pole filter is required, the use of a Sallen-Key filter can work very well with CFB amplifiers. This is

because the filtering elements are not in the negative feedback loop and stability is not compromised. Because of

their high slew-rates and high bandwidths, CFB amplifiers can create very accurate signals and help minimize

distortion. One implementation of the Sallen-Key filter is shown in Figure 53. For more information on Sallen-Key

filters, refer to the Analysis of the Sallen-Key Architecture (SLOA024A).

Figure 53. 2-Pole Low-Pass Sallen-Key Filter

Another good use for the THS6032 amplifier is as a video distribution amplifier. One characteristic of distribution

amplifiers is the fact that the differential phase (DP) and the differential gain (DG) are compromised as the

number of lines increases and the closed-loop gain increases. Be sure to use termination resistors throughout

the distribution system to minimize reflections and capacitive loading.

24

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