Ultra-Fast ECL-Output Comparator

with Latch Enable

_______________________________________________________________________________________

3

Note 1: Not tested, guaranteed by design.

PARAMETER

SYMBOL

UNITS

1.3

1.8

1.5

2.0

MAX9685M

MIN

TYP

MAX

1.3

1.8

CONDITIONS

MAX9685C/E

MIN

TYP

MAX

SWITCHING CHARACTERISTICS

__________Applications Information

Layout

Because of the MAX9685’s large gain-bandwidth char-

acteristic, 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 decou-

pling capacitors 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

120

Ω. For low-impedance applications, microstrip lay-

out at the input may also be helpful. Pay close atten-

tion to the bandwidth of the decoupling and terminating

components. Chip components can be used to mini-

mize lead inductance. An unused LE pin must be con-

nected to ground.

Input Slew-Rate Requirements

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

bandwidth product of these devices creates oscillation

problems when the input traverses through the linear

region. For clean switching without oscillation or steps

in the output 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 circuit employed. Poor layout and

larger source impedance will increase the minimum

slew-rate requirement.

Figure 1 shows a high-speed receiver application with

50

Ω input and output termination. With this configura-

tion, in which a ground plane and microstrip PC board

were used, the minimum slew rate for clean output

switching is 1.6V/µs. Sine-wave inputs imply a mini-

In many applications, the addition of regenerative feed-

back will assist the input signal through the linear

region, which will lower the minimum slew-rate require-

ment considerably. For example, with the addition of

10pF, the minimum slew-rate requirement can be

reduced by a factor of four.

ERMS =

Slew Rate

2 2nf

Input to Output High

(Notes 1, 2)

1.7

2.4

ns

1.3

1.8

1.3

1.8

1.5

2.0

Input to Output Low

(Notes 1, 2)

1.7

2.4

ns

1.2

1.7

1.2

1.7

1.4

2.0

Latch-Enable to Output

High (Notes 1, 2)

2.0

3.0

ns

1.2

1.7

1.2

1.7

1.4

2.0

Latch-Enable to Output

High (Notes 1, 2)

2.0

3.0

ns

Latch-Enable Pulse

Width (Note 2)

3.0

2.0

3.0

2.0

Minimum Setup Time

0.5

1.0

0.5

1.0

Minimum Hold Time

0.5

1.0

0.5

1.0

ns

ns

ns