Microchip SY88353BL Handleiding

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SY88353BL Evaluation Board
3.3V, 3.2Gbps Limiting Post Amplifier with
Programmable Decision Threshold
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
May 2007
M9999-052207-B
hbwhelp@micrel.com or (408) 955-1690
General Description
The SY88353BL evaluation board enables fast and
thorough evaluation of the SY88353BL post amplifier.
It provides a unique pin (VTHP) at which a variable
DC signal can be applied to adjust the output signal
crossing from 20 to 80%. This feature eliminates input
DC offsets in DC-coupled applications, minimizes
jitter caused by duty cycle distortion, and ultimately
optimizes bit error rate (BER) performance. The
board is an easy-to-use, single-supply design,
designed to be driven by a high-speed, pattern
generator.
The SY88353BL evaluation board is intended to
terminate to a 50 scope and provides for simple
user adjustability of the LOS threshold through the
adjustment of an on-board potentiometer as well as
simple evaluation of the output signal crossings.
All data sheets and support documentation can be
found on Micrel’s web site at: www.micrel.com.
Features
• SY88353BL CML Low-Power Limiting Post Amplifier
with TTL LOS
• Single +3.3V power supply
• AC-coupled configuration for direct interface with
50 test equipment and easy evaluation of device.
• On-board LOS sensitivity adjustment
• On-board LOS-feedback variable resistor for higher
hysteresis adjustment.
• On-board output crossing adjustment
Related Documentation
SY88353BL: 3.3V, 3.2Gbps Limiting Post Amplifier with
Programmable Decision Threshold
____________________________________________________________________________________
Evaluation Board
Micrel, Inc.
SY88353BL Evaluation Board
May 2007
M9999-052207-B
hbwhelp@micrel.com or (408) 955-1690
2
Evaluation Board Description
The SY88353BL 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
The AC-Coupled inputs bias the input levels to a DC-
operating point that is either set to a fixed voltage,
which is a diode-drop below Vcc, to get 50% output
crossing or is varied by applying a DC voltage between
0V-2.5V at VTHP pin to adjust output crossings. Inputs
can be driven by a differential signal with amplitude
typically between 10mV
PP
-1800mVpp.
AC-Coupled Output
The SY88353BL is configured with AC-coupled outputs
allowing the board to interface directly with 50Ω
equipment. If only one output is being used, the unused
complimentary output should be terminated into 50Ω-to-
ground.
The following sections explain how to connect and
setup the SY88353BL evaluation board per Figure 1.
Ensure proper ESD precautionary measures are taken
before handling sensitive electronic equipment,
including the SY88353BL evaluation board.
Measurements
Evaluating DOUT & /DOUT
1. Set a DC power supply to +3.3V and turn it off.
Connect the positive lead to V
CC
post and the
negative lead to GND post.
2. Set the desired frequency on a pattern generator
with an amplitude between 10mV
PP
and 1800mV
PP
.
Typical data patterns are 2
7
-1 or 2
23
-1 PRBS
patterns depending upon the application. Since the
inputs to the board are AC-Coupled, the voltage
offset of the pattern generator is not significant so it
can be set between GND and V
CC
.
3. Connect the pattern generator with differential
outputs as a data source to the DIN and /DIN inputs
on the SY88353BL evaluation board. Use matched-
length differential cables.
4. For normal output (output crossing adjustment not
need), connect VTHN and VTHP to ground.
5. For crossing adjustment, place a jumper across
VTHN and VREF and apply a DC signal between 0-
2.5V at VTHP. Crossings can be varied from 20%
to 80%, reaching 50% when VTHP centers at
around 1.25V.
6. Place jumper across EN/ and GND to enable the
outputs.
7. Turn the power supply on.
8. Observe the DOUT and /DOUT outputs with a 50Ω
scope. The output rise and fall times should be less
than 100ps, with an amplitude around 400mV
(800mV
PP
differential).
Micrel, Inc.
SY88353BL Evaluation Board
May 2007
M9999-052207-B
hbwhelp@micrel.com or (408) 955-1690
3
LOS Hysteresis Measurements
The SY88353BL evaluation board provides a
potentiometer to allow for convenient adjustment of
LOS
LVL
without the need for an extra power supply.
LOS
LVL
taps off a potentiometer connected between V
CC
and V
CC
–1.3V. Hence, LOSLVL can be set to any
voltage between V
CC
and V
CC
–1.3, as specified in the
SY88353BL data sheet. The potentiometer R1 between
Vcc and LOSLVL creates a voltage divider. Thus,
V
( )
( )( )
⎥
⎦
⎤
⎢
⎣
⎡
+
×
−= 2.8kΩkΩR
kΩR1.3
LOS
LVL
Vcc
The steps below show how to measure the LOS
hysteresis as a function of the input voltage swing at the
DIN and /DIN inputs:
Minimum Input Swing Hysteresis Measurement
The minimum acceptable input swing for the
SY88353BL is around 10mV
PP
.
1. Set a DC power supply to +3.3V and turn it off.
Connect the positive lead to V
CC
post and the
negative lead to GND post.
2. Connect a DMM or similar voltage measurement
device between the LOS
LVL
pin and V
CC
.
3. Connect a second DMM or similar voltage
measurement device between the LOS output and
GND. For the remainder of this document, this
DMM will be referred to as the LOS DMM.
4. Connect the pattern generator with differential
outputs as a data source to the DIN and /DIN inputs
on the SY88353BL evaluation board. Use matched-
length differential cables.
5. Turn the power supply on.
6. Adjust the trimpot R1 so the voltage at the LOS
LVL
pin is around 1.3V below V
CC
. This sets the LOS for
maximum sensitivity. At this level the LOS output
should go HIGH or LOW (measured with the LOS
DMM set up in step 3) as the input voltage swing at
DIN and /DIN is varied around or below 10mV
PP
.
The input level at which the LOS output goes HIGH
or LOW is the LOS Assert voltage or LOS de-assert
voltage, respectively.
7. Now adjust the trimpot R1 to vary the voltage so it
is closer to V
CC
. Note that as the voltage at the
LOS
LVL
pin approaches V
CC
, a larger input voltage
swing is required to trigger assert and de-assert
levels. A smaller input voltage swing is required to
trigger assert and de-assert levels.
8. The hysteresis between the assert and de-assert
levels can be calculated with the following equation:
Hysteresis (dB) = 20log (LOS De-assert
voltage/LOS Assert voltage). This hysteresis should
be >2dB.
Using Squelching Function
To evaluate the squelching function, place a jumper
between LOS and EN/, and observe the outputs as
input signals are varied. This ensures output stability
under loss-of-signal condition. The EN/ de-asserts the
true output signals low without removing the inputs.
Need Higher Hysteresis?
The board provides an additional potentiometer R2
between LOS and LOSLVL. This feedback resistor can
be adjusted to increase the hysteresis needed,
especially for high-sensitivity LOS requirement. For
more details, refer to Applications Note 45.
Evaluation 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

Product specificaties

Merk: Microchip
Categorie: Niet gecategoriseerd
Model: SY88353BL

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