SC70, 5ns, Low-Power, Single-Supply,

Precision TTL Comparators

8

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tional factor in resolution is the comparator’s stability in

its linear region. Many high-speed comparators are

useless in their linear region because they oscillate.

This makes the differential input voltage region around

zero unusable. Hysteresis helps to cure the problem

but reduces resolution (Figure 2). The devices do not

oscillate in the linear region and require no hysteresis,

which greatly enhances their resolution.

Applications Information

Power Supplies, Bypassing, and

Board Layout

These products operate over a supply voltage range of

mount ceramic capacitor. Mount the ceramic capacitor

as close as possible to the supply pin to minimize lead

inductance.

As with all high-speed components, careful attention to

board layout is essential for best performance. Use a

PC board with an unbroken ground plane. Pay close

attention to the bandwidth of bypass components and

place them as close as possible to the device.

Minimize the trace length and area at the comparator

inputs. If the source impedance is high, take the utmost

care in minimizing its susceptibility to pickup of unwant-

ed signals.

Input Slew Rate

Most high-speed comparators have a minimum input

slew-rate requirement. If the input signal does not

transverse the region of instability within a propagation

delay of the comparator, the output can oscillate. This

makes many high-speed comparators unsuitable for

processing either slow-moving signals or fast-moving

signals with low overdrive. The design of these devices

eliminates the minimum input slew-rate requirement.

They are excellent for circuits from DC up to 200MHz,

even with very low overdrive, where small signals need

to be resolved.

Figure 1. Timing Diagram

(DIFFERENTIAL)

LATCH

ENABLE (LE)

OUT

Figure 2. Effect of Hysteresis on Input Resolution

HYSTERESIS

BAND*

WITH HYSTERESIS

IDEAL (WITHOUT HYSTERESIS)

* WHEN HYSTERESIS IS ADDED, A COMPARATOR CANNOT RESOLVE ANY INPUT SIGNAL WITHIN THE HYSTERESIS BAND.

OUT

IN-

IN+