CLC409ALC datasheet(7/10 Pages) NSC

7 / 10 page

Application Division

Feedback Resistor

The CLC409 achieves its excellent pulse and distortion per-

formance by using the current feedback topology pioneered

by Comlinear Corporation. The loop gain for a current feed-

back op amp, and hence the frequency response, is pre-

dominantly set by the feedback resistor value. The CLC409

is optimized for use with a 250

Ω feedback resistor. Using

lower values can lead to excessive ringing in the pulse

response while a higher value will limit the bandwidth. Appli-

cation Note OA-13 discusses this in detail along with the

occasions where a different R

f might be advantageous.

Harmonic Distortion

The CLC409 has been optimized for exceptionally low har-

monic distortion while driving very demanding resistive or

capacitive loads. Generally, when used as the input amplifier

to very high speed flash ADCs, the distortions introduced by

the converter will dominate over the low CLC409 distortions

shown on the plots on the previous page. The 0.01µF ca-

pacitor (C

ss) shown across the supplies in Figure 1 and

Figure 2 is critical to achieving the lowest 2nd harmonic

distortion.

The 2-tone, 3rd order spurious plot shows a relatively con-

stant difference between the test power level and the spuri-

ous level with that difference depending on frequency. The

01274812

FIGURE 1. Recommended Non-Inverting Gain Circuit

01274813

FIGURE 2. Recommended Inverting Gain Circuit

CLC409ALC Datenblatt(PDF) 7 Page - National Semiconductor (TI)