clc114 National Semiconductor Corporation, clc114 Datasheet - Page 7

• Manufacturer Part Number: clc114
• Description: Quad, Low-power Video Buffer
• Manufacturer: National Semiconductor Corporation

Typical Performance Characteristics
Equivalent Input Noise
2-Tone, 3rd Order Intermodulation Intercept
Application Division
Operation
The CLC114 is a quad, low power, high speed, unity gain
buffer. The closed loop topology provides accuracy not found
in open loop designs. The input stage incorporates a slew
enhancement circuit which allows low quiescent power with-
out sacrificing AC performance.
PC Board Layout and Crosstalk
High frequency devices demand a good printed circuit board
layout for optimum performance. The CLC114, with power
gain to 200 MHz, is no exception. A ground plane and power
supply bypassing with good high frequency ceramic capaci-
tors in close proximity to the supply pins is essential. Second
harmonic distortion can be improved by ensuring equal cur-
rent return paths for both the positive and negative supplies.
This can be accomplished by grounding the bypass capaci-
tors at the same point in the ground plane while keeping the
power supply side of the bypass capacitors within 0.1” of the
CLC114 supply pins.
Crosstalk (undesired signal coupling between buffer chan-
nels) is strongly dependent on board layout. Closely spaced
signal traces on the circuit board will degrade crosstalk due
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2nd and 3rd Harmonic Distortion
(Continued)
7
to interface capacitance. For this reason it is recommended
that unused package pins (2, 4, 6, 11) be connected to the
ground plane for better channel isolation at the device pins.
Similarly, crosstalk can be improved by using a grounded
guard trace between signal traces. This will reduce the dis-
tributed capacitance between signal lines.
Following are two graphs depicting the effects of crosstalk.
All-hostile crosstalk is measured by driving three of the four
buffers simultaneously while observing the fourth, undriven,
channel. Figure 2 , “All-hostile Crosstalk Isolation”, shows
this effect as a function of input signal frequency. R
resistive load for each driven channel. Figure 3 , “Most Sus-
ceptible Channel-to-Channel Pulse Coupling”, describes one
effect of crosstalk when one channel is driven with a 2V
step (tr = 5ns) while the output of the undriven channel is
measured. From Figure 2 it can be observed that crosstalk
decreases as the signal frequency is reduced. Similarly, the
pulse coupling crosstalk will decrease as the rise time in-
creases.
Evaluation Board
An evaluation board for the CLC114 is available. This board
maybe ordered as part CLC730023.
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