Micrel, Inc.
SY87725L Evaluation Board
July 2008
2
M9999-071108-B
or (408) 955-1690
Evaluation Board Description
AC-Coupled Evaluation Board
The SY87725L is 64-pin EPAD-TQFP package. The
evaluation board is designed to operate with a single 3.3V
±10% power supply and is configured with AC-coupled
inputs and outputs. The high-speed input and output
channels are brought out to SMA connectors through
matched-length AC-coupled differential strip-line traces.
AC-Coupled Input
For ease of use, the AC-coupled inputs are biased on-
board. The user need only supply the appropriate input
swing to the board.
AC-Coupled Output
The SY87725L is configured with AC-coupled outputs
allowing the board to interface directly with 50
Ω
equipment. AC-coupling allows the board to use a single
power supply.
Unused Output
Single-Ended to Scope
Unused complimentary outputs should be terminated into
50
Ω
-to-ground to prevent unwanted reflections.
AC-Coupled Evaluation Board Setup
Setting up the SY87725L AC-Coupled Evaluation
Board
1. Set the voltage on a DC supply to +3.3V and
turn off the supply. Connect the GND terminal to
the negative side of a DC power supply.
Connect the V
CC
terminal to the positive side of
a DC power supply.
2. For a LVPECL input signal, set V
T
to V
CC
–2.0V.
3.
Signal Generator: Using a differential signal
source, set the amplitude of each side of the
differential pair to 400mV (800mV measured
differentially). Set the offset to a positive value,
the value of the offset is not critical, since the
AC-coupled inputs will be automatically biased.
Turn off the outputs of the signal source.
4. I/O Cable Interface: Using equal length 50
Ω
impedance coaxial cables connect the signal
source to the inputs on the evaluation board.
Using equal length 50
Ω
impedance coaxial
cables connect the outputs of the evaluation
board to the oscilloscope of another
measurement device that has an internal 50
Ω
termination. Unequal length cables are not
recommended since they introduce duty cycle
distortion and unwanted signal delays.
5. Connect the trigger input of the scope to the
trigger output of the signal generator.
6. Set the evaluation board dipswitch to the
appropriate input selection.
7.
Enable the signal source, turn on the DC source,
and monitor the outputs.
Evaluation Board Layout
PC Board Layout
The evaluation boards are constructed with Rogers 4003
material and are coplanar in design fabricated to minimize
noise, achieve high bandwidth and minimize crosstalk.
L1
GND and Signal
L2
GND
L3
VCC
L4
GND
Table 1. Layer Stack
