CLC412 datasheet(5/12 Pages) NSC

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½CLC412

Vin

Vout

Rin

-Vcc

+Vcc

Application Introduction

Offered in an 8-pin package for reduced space and cost,

the wideband CLC412 dual current-feedback op amp

provides closely matched DC & AC electrical performance

characteristics making the part an ideal choice for

wideband signal processing. Applications such as

broadcast-quality video systems, IQ amplifiers, filter

blocks, high-speed peak detectors, integrators and

transimpedance amplifiers will all find superior

performance in the CLC412 dual op amp.

Feedback Resistor Selection

The loop gain and frequency response for a current-

feedback operational amplifier is determined largely by

the feedback resistor, Rf. The Electrical Characteristics

and Typical Performance plots specify an Rf of 634

Ω, a

gain of +2V/V and operation with

±5V power supplies

(unless otherwise stated). Generally, lowering Rf from its

recommended value will peak the frequency response

and extend the bandwidth while increasing its value will

roll off the response. Reducing the value of Rf too far

below its recommended value will cause overshoot,

ringing and eventually oscillation.

The plot above labeled "Frequency Response vs. Rf"

shows the CLC412’s frequency and phase response as

Rf is varied while the gain remains constant at +2V/V

(RL=100

Ω). This plot shows that one particular value of

Rf will optimize the frequency and phase response at the

specified gain setting, i.e. 634

Ω at a gain of +2V/V.

Current-feedback op amps, unlike voltage-feedback op

amps, have a direct relationship between their frequency

and phase response to the value of the feedback resistor,

Rf. For more information see Application Note OA-13

which describes the relationship between Rf and closed-

loop frequency response.

When configuring the CLC412 for other inverting or non-

inverting gains, it is necessary to adjust the value of the

feedback resistor in order to optimize the device’s

frequency and phase response. The two plots below

provide the means of selecting the recommended

feedback-resistor value for both inverting and non-

inverting gain selections. Both plots show the value of Rf

approaching a non-zero minimum (dashed line) at high

gains, which is characteristic of current-feedback op

amps, while the linear portion of the two (solid) curves

(i.e. -5>Av>+6) results from the limitation placed on Rg

(i.e. Rg

≥50Ω). This limitation is due to the desire to keep

Rg greater in value than that of the inverting input

resistance. Therefore, the resulting small-signal

Vin

Vout

-Vcc

+Vcc

½CLC412

Figure 1

Figure 2

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