Ultra-Fast ECL-Output Comparator

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3

__________Applications Information

Layout

Because of the MAX9690’s large gain-bandwidth charac-

teristic, special precautions need to be taken if its high-

speed capabilities are to be used. A PC board with a

ground plane is mandatory. Mount all decoupling capac-

itors as close to the power-supply pins as possible, and

process the ECL outputs in microstrip fashion, consistent

with the load termination of 50

Ω to 120Ω. For low-imped-

ance applications, microstrip layout at the input may also

be helpful. Pay close attention to the bandwidth of the

decoupling and terminating components. Chip compo-

nents can be used to minimize lead inductance.

Input Slew-Rate Requirements

As with all high-speed comparators, the high gain-band-

width product of these devices creates oscillation prob-

lems when the input traverses through the linear region.

For clean switching without oscillation or steps in the out-

put waveform, the input must meet certain minimum slew-

rate requirements. The tendency of the part to oscillate is

a function of the layout and source impedance of the cir-

cuit employed. Both poor layout and larger source imped-

ance increase the minimum slew-rate requirement.

____________________Timing Diagram

The timing diagram illustrates the series of events that

completes the compare function, under worst-case

conditions. The leading edge of the input signal (illus-

trated as a large-amplitude, small-overdrive pulse)

switches the comparator. Outputs

–

Q

–

and Q are similar

in timing.

Definition of Terms

Input Offset Voltage—The voltage required

between the input terminals to obtain 0V differ-

ential at the output.

Input Voltage Pulse Amplitude

Input Voltage Overdrive

Input to Output High Delay—The propagation

delay measured from the time the input signal

crosses the input offset voltage to the 50% point

of an output low-to-high transition.

Input to Output Low Delay—The propagation

delay measured from the time the input signal

crosses the input offset voltage to the 50% point

of an output high-to-low transition.

SWITCHING CHARACTERISTICS

Note 1: Not tested, guaranteed by design.

PARAMETER

SYMBOL

MAX9690C/E

MIN

TYP

MAX

MAX9690M

MIN

TYP

MAX

UNITS

1.3

1.8

1.3

1.8

1.5

2.0

Input to Output High

(Notes 1, 2)

1.7

2.4

ns

1.3

1.8

1.3

1.8

1.5

2.0

CONDITIONS

Input to Output Low

(Notes 1, 2)

1.7

2.4

ns