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

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

PP

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.

Equivalent Input Noise

DS012738-16

2nd and 3rd Harmonic Distortion

DS012738-17

2-Tone, 3rd Order Intermodulation Intercept

DS012738-18

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