MAX9691 Maxim, MAX9691 Datasheet - Page 6

• Manufacturer Part Number: MAX9691
• Description: The MAX9691/MAX9692/MAX9693 are ultra-fast ECL comparators capable of very short propagation delays
• Manufacturer: Maxim

Single/Dual, Ultra-Fast, ECL-Output
Comparators with Latch Enable
__________ Applications Information
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 50Ω to 200Ω (for
V
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.
As with all high-speed comparators, the high gain-
bandwidth product of these devices creates oscillation
Figure 1. Regenerative Feedback—High-Speed Receiver with
50 Ω Input and Output Termination
6
T
= -2V). For low-impedance applications, microstrip
_______________________________________________________________________________________
V
IN
50Ω
50Ω
Input Slew-Rate Requirements
R
f
LE
Q
Q
C
f
50Ω
50Ω
-2V
Layout
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
50Ω 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
feedback components, R
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
input signal level of 14mV
Figure 2. Signal Processed at 100MHz with Input Signal Level
of 14mV
500mV/div
20mV/div
OUTPUT
INPUT
RMS
RMS
2ns/div
f
= 1kΩ and C
.
f
= 10pF, the
-1.7V
0V
-0.9V