Single/Dual, Ultra-Fast, ECL-Output

Comparators with Latch Enable

6

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__________ Applications Information

Layout

Because of the MAX9691/MAX9692/MAX9693s’ large

gain-bandwidth characteristic, special precautions

must be taken to use them. A PC board with a ground

plane is mandatory. Mount 0.01µF ceramic decoupling

capacitors as close to the power-supply pins as possi-

ble, and process the ECL outputs in microstrip fashion,

consistent with the load termination of 50

Ω to 200Ω (for

layout and terminations at the input may also be help-

ful. Pay close attention to the bandwidth of the decou-

pling and terminating components. Chip components

can be used to minimize lead inductance. Connect

GND1 and GND2 together to a solid copper ground

plane for the MAX9691/MAX9692. GND1 biases the

input gain stages, while GND2 biases the ECL output

stage. If the LE function is not used, connect the LE pin

to GND (MAX9692/MAX9693) and the complementary

LE to ECL logic high level (MAX9693 only). Do not

leave the inputs of an unused comparator floating for

the MAX9693.

Input Slew-Rate Requirements

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

bandwidth product of these devices creates oscillation

problems when the input goes 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

are used, the minimum slew rate for clean output

switching is 1V/µs.

In many applications, adding regenerative feedback

will assist the input signal through the linear region,

which will lower the minimum slew-rate requirement

considerably. For example, with the addition of positive

minimum slew-rate requirement can be reduced by a

factor of four.

As high-speed receivers, the MAX9691/MAX9692/

MAX9693 are capable of processing signals in excess

of 600MHz. Figure 2 is a 100MHz example with an

-2V

50

Ω

50

Ω

50

Ω

50

Ω

Q

Q

LE

Figure 1. Regenerative Feedback—High-Speed Receiver with

50

Ω Input and Output Termination

0V

-0.9V

-1.7V

OUTPUT

500mV/div

INPUT

20mV/div

2ns/div

Figure 2. Signal Processed at 100MHz with Input Signal Level