clc409 National Semiconductor Corporation, clc409 Datasheet - Page 7

• Manufacturer Part Number: clc409
• Description: Very Wideband, Low Distortion Monolithic Op Amp
• Manufacturer: National Semiconductor Corporation

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 250Ω 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.
FIGURE 1. Recommended Non-Inverting Gain Circuit
FIGURE 2. Recommended Inverting Gain Circuit
7
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
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
ss
) shown across the supplies in Figure 1 and
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