Application Division

Operation

the CLC111 is a low-power, very high speed unity gain buffer.

It uses a closed loop topology which allows for accuracy not

usually found in high speed open loop buffers. A slew

enhanced front end allows for low quiescent power while not

sacrificing AC performance.

Single Supply Operation

power supplies, there is no internal ground reference that

prevents operation from a single voltage power supply. For

single supply operation, the input signal should be biased at

a DC value of 1/2V

coupling and rebiasing, as shown in

Figure 1.

The

above

electrical

specifications

provide

typical

performance specifications for the CLC111 at 25˚ C while

operating from a single +3V or a single +5V power supply.

Printed Circuit Layout and Supply Bypassing

As with any high frequency device, a good PCB layout is

required for optimum performance. This is especially

important for a device as fast as the CLC111.

To minimize capacitive feedthrough, pins 2, 3, 6, and 7

should be connected to the ground plane, as shown in

Figure 1. Input and output traces should be laid out as

transmission lines with the appropriate termination resistors

very near the CLC111. On a 0.065 inch epoxy PCB material,

a 50 transmission line (commonly called stripline) can be

constructed by using a trace width of 0.01” over a complete

ground plane.

Figure 1 shows recommended power supply bypassing.

The ferrite beads are optional and are recommended only

where additional isolation is needed from high frequency

Parasitic or load capacitance directly on the output of the

CLC111 will introduce additional phase shift in the device.

This phase shift can decrease phase margin and increase

frequency response peaking. A small series resistor before

the capacitance effectively decouples this effect. The graphs

in this data sheet illustrate the required resistor value and the

resulting performance vs. capacitance.

Precision buffed resistors (PRP8351 series from Precision

Resistive Products), which have low parasitic reactances,

were used to develop the data sheet specifications.

Precision

carbon

composition

resistors

or

standard

spirally-trimmed RN55D metal file resistors will work, though

they will cause a slight degradation of AC performance due

to their reactive nature at high frequencies.

Evaluation Boards

Evaluation boards are available from National as part

numbers CLC730012 (DIP) and CLC730045 (SOIC). This

board was used in the characterization of the device and

provides optimal performance. Designers are encouraged to

copy these printed circuit board layouts for their applications.

DS012720-21

FIGURE 1. Recommended Circuit & Evaluation Board Schematic

www.national.com

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